DW 144

Other Ductwork-Related PublicationsCopies of the above publications are available from: Publications Unit Heating and Ventilating Contractors Association Old Mansion House Eamont Bridge

Specification for Sheet Metal Ductwork

Low, medium and high pressure/velocity air systems

1998

Copyright © 1998 by the Heating and Ventilating Contractors’ Association All rights reserved

ISBN 0-903783-27-4

Further copies of this publication are available from:

Publications Unit

Heating and Ventilating Contractors Association

Old Mansion House Eamont Bridge

Penrith Cumbria CA10 2BX Tel: 01768 864771 Fax 01768 867138

THE INDUSTRY

STANDARD

Ken Parslow

Chairman Executive Committee Ductwork Group 1996-98

For more than a decade-and-a-half, the DW/142 Specification for Sheet Metal

Ductwork published by the Heating and Ventilating Contractors’ Association

has gained national and international recognition as the industry standardagainst which the quality of ductwork manufacture and installation can be judged

In recent years, however, it has become increasingly evident to the members ofthe HVCA Ductwork Group that the developments in technology and workingpractices which have taken place since the drafting of DW/142 have renderedobsolete significant parts of the document

It was an acknowledgement of this state of affairs which led the Technical Committee of the Ductwork Group, ably chaired by Edgar Poppleton, to undertakethe task of producing a radically revised specification which would promote bestpractice and quality standards well into the next Millennium

Sub-This new publication — designated DW/144 — represents the direct result ofthat initiative

The new specification recognises the computer age — with special reference toCAD/CAM procedures and techniques — and the international performance stan-dards established by the Committee for European Normalisation (CEN), as well asthe need to update and consolidate much of the information contained in the origi-

nal DW/142 publication and its Addendum A companion volume.

During the drafting process, the Technical Sub-Committee has consulted widelywith individuals and organisations throughout the building services and construc-tion sectors in order to ensure that the new specification fully reflected the currentthe “state-of-the-art” in terms both of technical expertise and industry best practice

I firmly believe that this process has resulted in a publication which clearlydemonstrates the high level of professionalism which exists within the ductworkcommunity — and I take this opportunity of thanking all those who have con-tributed to its production

In particular, my thanks go to Edgar Poppleton and his colleagues on theTechnical Sub-Committee, to Keith Elphick for the provision of invaluable techni-cal consultancy, and to Ductwork Group secretary Gareth Keller for overseeing theproject as a whole

MAINTAINING QUALITY

Like most industries, the ductwork sectormust be prepared continually to innovate in

order to survive and prosper

A key element in that innovation process is the

timely review and updating of quality standards to

ensure that they continue to offer realistic

bench-marks to which all professional individuals and

organisations can perform

The development of this new Specification for

Sheet Metal Ductwork — designated DW/144 —

has been carried out with that objective in mind

In the 16 years since the publication of its

predecessor, DW/142 — and in the ten years since

the supplementary volume Addendum A appeared

— many technical advances, changes in working

practices and regulatory introductions and

amend-ments have taken place

The common performance standards for

duct-work being developed by the Committee for

European Normalisation (CEN), for example, had

to be taken fully into account during the drafting

process Similarly, notice had to be given to the

provisions of the Control of Substances Hazardous

to Health (COSHH) and Construction (Design and

Management) Regulations, neither of which had

been issued when DW/142 was published

It is not possible — nor, I think, desirable — to

include in this foreword an exhaustive catalogue of

the points of difference between this specification

and its predecessor These will clearly emerge

from a detailed reading of the text

I should, however, like to take the opportunity

to highlight a few topics which I believe to be of

particular significance They are:

•to conform to European practice);

•by the designer;

•

•ducts;

•

•to DW/TM1 no longer illustrated in detail;

•of hangers and supports;

•cleaning considerations;

•

Edgar Poppleton

Chairman Technical Sub-Committee Ductwork Group

transport, handling, storage and interface with

DW/TM2 Guide to Good Practice — Internal Cleanliness of New Ductwork Installations;

an overview of fire-rated ductwork;

a new appendix on inspection, servicing andcleaning access openings (the default inclusion

of Level 1 should be noted);

a new section on standard component drawings

— incorporating a framework of nomenclature,and a description of drawing symbols, abbrevia-tions and rules — which is intended to reduceambiguity and promote common understanding;

a rewritten description of all forms of dampers,for which I am indebted to Bill Clark and JohnMawdsley of the HEVAC Association

I take this opportunity to acknowledge the mission granted by the Sheet Metal and AirConditioning Contractors’ National Association(SMACNA) of the USA for the use of its tie rodspecification (designer approval required)

per-And I also include a plea on behalf of ductworkconstructors to be allowed to make the final choice

of components and techniques within the ters set by the designer, and allowed within thisspecification to satisfy performance characteristics

parame-It will, of course, be clear to anyone who hasever taken on such a task that the production of thisspecification has involved a colossal input in terms

of industry consultation and from a wide variety ofindividuals, a number of whom I should like toidentify for special mention

They are: former Technical Sub-Committeemembers Keith Waldron and the late Keith Angood;current members Chris Collins, Stuart Howard,Brian James and — last but by no means least —Jim Murray; technical consultant Keith Elphick; andDuctwork Group secretary Gareth Keller

Finally, may I remind readers of the crucialimportance of ensuring that all ductwork is manu-factured and installed in a manner which is safe,efficient, effective and free of risk

The publication of DW/144 is intended to assistsignificantly in the achievement of this objective

the omission of high-pressure Class D (in order

the highlighting of information to be provided

the end-sealing of ducts and explosion risks;

the removal of standard sizes of rectangular

the omission of cleated joints;

the acceptance of proprietary flanges certificated

the consolidation into the document of coverage

the addition of a note on linings, along with their

the consolidated graphical representation of

Technical Consultant:

Keith Elphick

Ductwork Group Secretary:

Gareth Keller

Other Ductwork-Related Publications

Copies of the above publications are available from:

Publications Unit

Heating and Ventilating Contractors Association Old Mansion House Eamont Bridge Penrith Cumbria CA10 2BX Tel: 01768 864771 Fax 01768 867138 e-mail: hvcapublications@hvwelfare.co.uk

Previous Sheet Metal Ductwork Specifications

Ductwork Specification for High-Velocity Air Systems (Circular) 1963 Standard Range of Rectangular Ducting 1967 Sheet Metal Ductwork Specification for High-Velocity Air

Systems (Rectangular) 1968 Specification for Sheet Metal Ductwork (Low-Velocity

Low-Pressure Air Systems) (Rectangular and Circular) — Metric 1969 Specification for Sheet Metal Ductwork (Low-Velocity

Low-Pressure Air Systems (Rectangular and Circular) — British 1969 Standard Range of Rectangular Ducts and Fittings — Metric and

British Units 1970 Specification for Sheet Metal Ductwork (High-Velocity

High-Pressure Air Systems) (Rectangular, Circular and Flat Oval) — Metric 1970 Specification for Sheet Metal Ductwork (Low and High-Velocity/

Pressure Air Systems) (Rectangular, Circular and Flat Oval)

— Metric 1977 Specification for Sheet Metal Ductwork (Low, Medium and High Pressure/Velocity Air Systems) 1982 Specification for Sheet Metal Ductwork Addendum A (Low,

Medium and High Pressure/Velocity Air Systems) 1988

Page

Notes

Part One - Technical Information to be

provided by the designer

8 Ductwork Construction and Joint Sealing

Part Three - Rectangular Ducts

9 Rectangular Duct Sizes

Part Five - Flat Oval Ducts

15 Standard Sizes and Sheet Thicknesses

16 Construction (Spirally wound)

13131314

151515151515151616161616161616

1 61717

27272727272929292929

3535353535

16.4 Fastenings 3516.5 Stiffening 35

17 Construction (Straight Seamed) 35

18 Fittings 3518.1 General Construction Requirements 3518.2 Standardisation of fittings 35

Part Six - Hangers and Supports

28 Connections to Building Openings

29 Internal Duct Linings

30 Thermal Insulation

31 Kitchen Ventilation

32 Fire Rated Ductwork

33 Standard Component Drawingsand Abbreviations

4748495051515253535454545454

Part Eight - Appendices

Hot Dip Galvanizing afterManufacture

Stainless Steel for DuctworkPre-Coated Steel

Aluminium DuctworkEurovent

Summary of BS.EN10142:

1991 Continuously Hot-DipZinc Coated Mild Steel Stripand Sheet for Cold Forming

‘Design Notes for Ductwork’(CIBSE Technical

Memorandum No 8)

7580

82Appendix D

92Appendix L

93Appendix M

Appendix N

Appendix P

Guidance Notes For Inspection,Servicing and Cleaning AccessOpenings 94Bibliography 95Conversion Tables 97

List of Tables

Part Two - Standards

1 Ductwork Classification and Air

Part Four - Circular Ducts

10 Fittings Sheet Thicknesses

2929

Part Five - Flat Oval Ducts

11 Standard sizes and sheet thicknesses

Part Six - Hangers and Supports

15 Supports for horizontal ducts - rectangular,

flat oval and circular 44

Part Seven - General

16 Standard Abbreviations 72-73

Part Eight - Appendices

17 Air Leakage Rates

18 Recommended duct identification colours

19 Examples of further identification symbols

20 Ductwork galvanized after manufacture

-rectangular

21 Compositions of the commonly used

Stainless Steel grades

22 Rectangular aluminium ducts

-low pressure constructional requirements

23 Circular aluminium ducts

-low pressure constructional requirements

24 Zinc coating mass (weight)

25 Access requirements for inspection,

servicing and cleaning

768081858890919394

List of Illustrations

Figs Pages

Part Three - Rectangular Ducts

1-8 Longitudinal Seams 20

9 Illustrations of panel stiffening 20

10-12 Flanged cross joints 21

13-1718-2425-282930

3132-3839-45

53-5859-63

64-7576-77

78-798081-124

Socket and spigot cross jointsStiffeners

Tie rod assemblyHard and Easy bendsTurning Vanes

Part Four - Circular Ducts

Spiral and straight seamsCross joints spirally wound ductsCross joints straight seamed ducts

Part Five - Flat Oval Ducts

Cross joints spirally wound ductsCross joints straight seamed ducts

Part Six - Hangers and Supports

Horizontal ductsbearers and hangersVertical ducts supports

Part Seven - General

Fire barrier/fire damper expansionFlexible joint connectionsStandard component drawings -Rectangular

178179

2223242525

2930-3132-33

39-4041-42

45-4646

505255-61Circular 62-67153-167 Standard component drawings -

Flat Oval 68-70168-177 Plant/equipment/miscellaneous 71

Part Eight - Appendices

Permitted leakage at variouspressures 78Example of duct identification symbol 81

The technical information to be provided by the designer is fore set out in detail on page 11.

relationship of the Pascal to other units of pressure is: 500 pascals

= 500 Newtons per square metre = 5 millibars = approximately 2 (9)

inches water gauge.

Duct pressure classification

As the static pressure in a duct system progressively changes from the fan,economic advantage can be obtained by changing the duct pressureclassification to match more closely the duct distribution static pressure.For example, some large systems could well be classified for leakagelimits as follows:

Plant rooms and risers Class CMain floor distribution Class BLow-pressure outlets Class A

Even where a ductwork job specification calls for the system to be

All dimensions quoted in this specification refer to the nominal

Manufacturing techniques are continually subject to change and

The expressions ‘low-pressure,’ ‘medium-pressure’ and

‘high-‘Mean air velocity’ means the design volume flow rate related to

Reference to the air distribution system pressure relate to the

stat-The symbol for litres is ‘L’: 1000 litres per second is equivalent to The Pascal (Pa) is the internationally agreed unit of pressure The

Part One – Technical information to be

provided by the designer to the ductwork contractor

1 INTRODUCTION

The selection of constructional methods is the

decision of the Manufacturer to conform with the

performance requirements of the specified

ductwork classification Sections 2-4 below

define the information that is to be provided by

the Designer

2 STANDARDS

2.1 Pressure classification (Table 1)

2.2 Leakage classification (Table 1)

2.3 Positive and Negative pressures (Table 1)

2.4 Materials (Section 7)

2.5 Any special system requirements

3 COMPONENTS

3.1 Inspection/servicing access openings

(Section 20 and Appendix M)

Number and location of all panels and covers

for inspection and/or servicing access other than

those covered in Section 20 and summarised as

Level 1 requirements in table 25 of Appendix

M Number and location of test holes,

instrument connections and hinged doors as

defined in Section 20

3.2 Cleaning access

(Section 20.8 and Appendix M)

Designers shall stipulate their requirements for

periodic internal cleaning of ductwork and for

the consequent need for adequate access for

specialist cleaning equipment

3.3 Regulating dampers (Section 21)

Specification, location and mode of operation of

all regulating dampers

3.4 Fire dampers (Section 22)

Specification and location of all fire dampers to

meet the requirements of the Authority directly

concerned with fire protection

3.5 Smoke dampers (Section 23)/Combination

smoke and fire dampers (Section 24)

Specification and location of all smoke dampers

to meet the requirements of the Authority

directly concerned with fire protection

3.6 Flexible ducts (Section 25)

Specification and location of any flexible

ductwork

3.7 Flexible joint connections (Section 26)

Specification and location of any flexible

con-nections eg plant or building expansion joints

4 PARTICULAR REQUIREMENTS

4.1 Air leakage testing (Section 6 and Appendix A)

The extent of any air leakage testing While it

shall be mandatory for high-pressure ductwork

(as defined in this specification) to be tested for

air leakage in accordance with the procedure set

out in DW/143, A practical guide to Ductwork

Leakage Testing, no such testing of low- or

4.2 Protective finishes (Section 27)

Details and specification of any protectivefinishes

4.3 Fire rated and smoke extract ductwork

A detailed specification of materials and method

of application is required The practical aspects

of cleaning or maintenance must be addressed bythe designer before deciding to internally lineductwork

4.5 External thermal/acoustic insulation

(Section 30)

The extent and thickness of insulation to beprovided by others should be stated

4.6 Special supports (Section 19)

Details of any spanning steel or special supportrequirements not covered by Section 19

4.7 Attachment to building structure (Section 28)

Specific requirements for the junction ofductwork and associated components toopenings should be detailed and specified andthe limits of responsibility defined

The provision of penetrations and associatedframings are outside the scope of thisspecification

4.8 Air terminal units

Detail and specifications of all Air TerminalUnits It is expected that all Air Terminal Unitsand their Plenums (See Figures 120 to 124) will

be supported by the Ceiling Grids unless thedesigner indicates an independent method ofsupport

4.9 Ductwork layout drawings

Details of any special requirements relating toCAD, scales, etc It is common practice and costeffective for ductwork manufacturers to utilisetheir approved ductwork layout drawings as abasis of their manufacturing/installationinformation by adding the necessary details tothe same drawing Scales of 1:50 or smaller maypreclude this practice, therefore, larger scalesmight be more appropriate The final choice ofmanufacturing/installation scales shall be left tothe ductwork contractor

4.10 Other requirements

Details of any requirements for the ductworknot in accordance with the provisions of thisspecification, including any modified con-struction required to conform with anyrequirements concerning external ductwork(See 5.3) or to meet the regulations of a localauthority or other controlling body

4.11 Reference to the designer

In consideration of the foregoing, reference is alsomade to the designer in the following clauses:-Clause Page5.3 137.4, 7.5, 7.6 1410.5.2 16

14.1 2916.3.1 3519.1, 19.4 4319.6, 19.7 4420.1, 20.1.1.1, 20.6, 20.8 4720.9 4821.1, 21.3.1 4821.3.4 4922.3, 22.7 5024.3 5125.1 5126.1 52

27, 27.3.4 5329.1, 29.4, 30.2, 30.3, 33.2 54Fig 176 71Appendix A 75-79Appendix B 80, 81Appendix C 82Appendix D 83, 84Appendix E 85

Appendix L 93Appendix M 94

Part Two - Standards

5 APPLICATION

5.1 This specification sets out minimum

require-ments for the manufacture and installation of

duct-work for commercial and industrial air

distribu-tion systems, made from any of the materials listed

in Section 7 and being within the limits of size

and/or metal thicknesses specified in the relevant

tables Normal operating temperatures are

assumed within the pressure/velocity limits and

the limits of air leakage for the various pressure

classes prescribed in Table 1

5.2 This specification is not intended to apply to

ductwork handling air which is polluted or is

other-wise exceptional in respect of temperature or

humidity (including saturated air); nor is it suitable

for ductwork exposed to a hostile environment,

e.g contaminated air, off-shore oil rigs, etc The

design, construction, installation, supports and

finishes in such cases should be given special

con-sideration in relation to the circumstances of each

case

5.3 This specification is not suitable for ductwork

exposed to external atmosphere and the Designer

will need to give specific details of any special

finishes/construction (See Section 27)

6 DUCTWORK CLASSIFICATION AND

AIR LEAKAGE

6.1 Classification and air leakage limits

Ductwork classification and air leakage limits are

set out in Table 1

6.2 Compatibility with CEN

The leakage factors used in Table 1 for Classes A,

B and C are the same as those for the classes

similarly designated in the CEN Document

Pr EN12237/Pr EN1507

6.3 Leakage at various pressures; and other relationships

Applying the limits specified in Table 1, Appendix

A (Table 17) sets out the permitted leakage at each

of a series of pressures up to a maximum for eachclass Included in that appendix is a graphical pre-sentation of the pressure/leakage relationship.DW/143 A practical guide to Ductwork LeakageTesting, also gives details of the basis for theleakage limits specified in Table 1

6.4 Air leakage testing

Air leakage testing of low and medium pressureductwork is not mandatory under this specifica-tion

Air leakage testing of high pressure ductwork ismandatory under the specification and for details

of testing procedure refer to DW/143 A practicalguide to Ductwork Leakage Testing

7 M A T E R I A L S 7.1 Application

This specification applies to ductwork constructedfrom materials as defined below, or equal.Minimum steel thickness is to be taken as a nom-inal thickness within the tolerances toBS.EN10143:1993 (See Appendix K)

7.2 Zinc-coated steel

Ductwork will normally be constructed fromhot-dip galvanized steel to BS.EN10142:1991,Grade DX51D+Z, coating type Z275

T a b l e 1 D u c t w o r k C l a s s i f i c a t i o n a n d A i r L e a k a g e L i m i t s

Static pressure limit

Maximum air Duct pressure class

velocity Positive Negative

Where p is the differential, pressure in pascals.

Air leakage limits litres per second per square metre of duct surface area

5

0.027 x p0.650.009 x p0.650.003 x p0.65

7.3 Mild steel

Where mild steel is specified, it shall be

cold-reduced steel to BS.EN10130:1991, Grade FEP

01A

7.4 Stainless steel

Where stainless steel is specified it will be the

responsibility of the designer to indicate the type

most suitable for the conditions to which the

duct-work will be exposed In doing so, it is

recom-mended that the factors set out in Appendix F

should be taken into account In this connection,

reference must be made to BS 1449: Part 2, which

includes stainless steel

7.5 Pre-coated steel

Pre-coated steel may be specified for aesthetic or

other reasons The designer must then consider

the availability of suitable materials and the

restriction on fabrication methods Guidance

notes are available in Appendix G

7 6 A l u m i n i u m

Where aluminium is specified, it will be the

responsibility of the designer to define the type

most suitable for the conditions to which the

duct-work will be exposed Reference must be made to

BS.EN485, BS.EN515 and BS.EN573 for

aluminium sheet and BS.EN755 Parts 3-6 for

aluminium section (Constructional requirements

for ductwork made from aluminium sheet and

general notes on the material are set out in

Appendix H.)

8 DUCTWORK CONSTRUCTION AND

JOINT SEALING

8.1 Ductwork construction

The selection of longitudinal, cross joint and

stiff-ener types within the criteria laid down in the

tables should be the responsibility of the

manu-facturer

8.2 Joint sealing and sealants

8.2.1 General

The integrity of the ductwork depends on the

successful application of the correct sealant,

gaskets or tape The materials used should be

suitable for the purpose intended and satisfy the

specified pressure classification

Illustrations indicating sealant locations will be

found in the following sections dealing with the

construction of rectangular, circular and flat

oval duct sections

IN ALL CASES, SEALANT MATERIALS

MUST BE APPLIED STRICTLY IN

ACCORDANCE WITH THE

MANU-FACTURER’S INSTRUCTIONS AND

COSHH ASSESSMENT

8.2.2 Liquid and mastic sealants

These are typically applied to a longitudinalseam formed between two sheets of metal, asocket and spigot, cleated or flanged cross joints.Particular care is needed when sealing of “corner

pieces” on the proprietary ‘slide-on’ type flange

and reference should be made to the turer’s assembly and sealing instructions

manufac-8.2.3 Gaskets

These can be of various materials in the form of

a preformed roll, sheet or strip, applied betweenopposing faces of flanged cross joints In the

case of proprietary ‘slide-on’ type flanges, it is

advisable to use the gasket strip recommended

by the manufacturer

Factory-fitted proprietary synthetic rubber ring type gaskets are also acceptable for socketand spigot joints on circular duct systems

‘O’-8.2.4 Tapes 8.2.4.1 The application of tapes – Bestsuited, but not limited, to cross joints oncircular or flat oval ductwork Where chemi-cal reaction tape, heat shrinkable tape or otherapproved material is used on flat oval duct-work care should be taken to maintain closecontact between the material and the flat sides

of the duct until the joint is completed

8.2.4.2 Chemical reaction tape – Animpregnated woven fibre tape and a resin typeactivator/adhesive On application of theactivator/adhesive the tape becomes pliableand can then be applied to any surface shape.The liquid reacts with the tape, causing the 2-part system to ‘set’

8.2.4.3 Heat shrinkable band/tape – A

ther-moplastic material, coated on the inside withhot metal adhesive The band (or an appropri-ate length of tape) is cut from the roll andwrapped around the joint When heated thetape shrinks tightly around the joint thus pro-viding a seal

8.2.4.4 Self adhesive tape – Manufactured

from various materials including cloth based,PVC and aluminium foil Typically appliedexternally to socket and spigot cross joints.However, it is difficult to provide the dry, dustand grease free surface that is required for asuccessful application and this method istherefore not recommended as a primarysource of sealant

NB! Risk of explosions

Where ductwork is blanked off prior to leakagetesting or to prevent the ingress of contamination,care should be taken to ensure that all joint sealingsolvent vapours are dispersed from the ductworksystems

Part Three - Rectangular Ducts

9 RECTANGULAR DUCT SIZES

This specification covers duct sizes up to a

maxi-mum longer side of 3,000 mm Duct sizes with an

aspect ratio greater than 4:1 are not

recommend-ed Although they offer no problems of

construc-tion, they increase frictional resistance and the

possibility of noise

10 CONSTRUCTION

10.1 General

The minimum constructional requirements for

rectangular ductwork depend upon the pressure

classification as set out in Tables 2 to 4 The

duct-work construction and joint sealing standards are

set out in section 8

10.2 Steel thicknesses

Minimum steel thicknesses related to duct longer

side to pressure classification are given in

Tables 2 to 4

10.3 Longitudinal Seams

Longitudinal seams are illustrated in Figs 1 to 8

The limits of use, if any, are given with the

indi-vidual illustrations

10.3.1 Sealing of Longitudinal Seams

Sealant will be applied using one of the

c) Internal to the joint seam itself

The most appropriate method will be

deter-mined by the manufacturer relative to their

product and will be associated with either

tradi-tional fabrication/assembly methods, factory or

site based, and/or proprietary methods The

ulti-mate proof of a seal is that the ductwork system

meets the pressure classification specified For

details of sealant see section 8

10.3.2 Welded seams

A welded seam is acceptable without sealant,

provided that the welding is continuous

10.4 Cross joints

10.4.1 Cross joint ratings

For cross joints, a system of rating has been

used to define the limits of use The rating for

each cross joint is given with its drawing, and

the limits applying to that rating, in terms of

duct size longer side and maximum spacing, aregiven in Tables 2 to 4 Other limits on use aregiven with the individual drawings

Note: Proprietary products used in the tion of cross joints should be approved by anindependent test house following tests defined

construc-in DW/TM1 “Acceptance scheme for new ucts – Rectangular cross joint classification.”Figures Nos 10 and 13 to 17 illustrate non pro-prietary joints that have an established rating

prod-10.4.2 Sealant in cross joints

Sealant shall be used between sheet and section

in all cross joint assemblies (see section 8) With socket and spigot joints made on site,

sealant shall be applied during or after assembly

of the joint It is permissible to use reaction tape or heat-shrink strip as alternativemethods of sealing, provided that close contact

chemical-is maintained over the whole perimeter of thejoint until the joint is completed

With all flanged joints, the sealant between

sheet and section should preferably be

incorpo-r a t e d d u incorpo-r i n g c o n s t incorpo-r u c t i o n a t w o incorpo-r k s , b u t s i t eapplied sealant is acceptable The joint betweensections of ductwork is then made, usingapproved type of sealant or gasket Withproprietary flanging systems particular attentionshould be paid to the sealing of corner piecesand flanges, reference should be made to themanufacturer’s assembly and sealing instruc-tions

10.4.3 Adjustable/slip joints

In order to accommodate ing tolerances, site modifications etc, it isaccepted practice to use an adjustable joint asillustrated in Fig 14

manufacturing/build-10.5 Stiffeners 10.5.1 External stiffeners

The sections (including proprietary flanges)

suitable for use as single stiffeners have been

given a rating from S1 to S6 in terms of ductsize longer side and maximum spacing The rat-ings are specified with the illustrations of thestiffeners, Figs 18 to 23, and the limits of useare given in Tables 2 to 4 The stiffeners forsocket and spigot joints covered in Figs 15, 16and 17 are also applicable to stiffeners in general

10.52 Internal stiffeners

Tie bars connecting the flanges of cross joints

illustrated in Figs 11 and 12, are the only form

of internal stiffening for rectangular ductwork

recognised by this specification and reference

should be made to HVCA publication

D W / T M 1

Alternative methods for the attachment of tie

bars are shown in Figs 25 to 28

The use of tie bars or other forms of internal

s t i f f e n i n g o r b r a c i n g s h a l l b e a c c e p t a b l e i f

proved to the designer to be equally satisfactory

S M A C N A (Sheet Metal and Air Conditioning

Contractors’ National Association), which is the

American equivalent to the HVCA Ductwork

G r o u p , h a v e p r o d u c e d a n A d d e n d u m N o 1

(November 1997) to their publication “HVAC

Duct Construction Standards, Second Edition

-1995” The addendum contains the extensive

technical information and data on the subject of

mid panel tie rods and SMACNA have given

their kind permission for this specification to

make reference to this fact Designers and

man-ufacturers who wish to incorporate this form of

internal stiffening into a ductwork system

should contact SMACNA direct to obtain copies

of their publications (See Appendix N,

Bibliography)

10.6 Ductwork galvanized after manufacture

A p p e n d i x E s e t s o u t t h e r e c o m m e n d e d s h e e t

thicknesses and stiffening for ductwork

galva-nized after manufacture

10.7 Fastenings

10.7.1 Permitted types and maximum centres

Table 5 sets out the permitted fastenings and the

maximum spacings for all ductwork

classifica-tions All duct penetrations shall be sealed

10.7.2 Rivets

Manufacturers’ recommendations as to use,

size and drill size are to be followed Rivets

re-sulting in an unsealed aperture shall not be used

10.7.3 Set screws, nuts and lock bolts

Materials shall be of mild steel, protected by

electro-galvanizing, sherardizing, zinc-plating,

or other equal and approved corrosion resistant

finish

10.7.4 Self tapping and piercing screws

Providing an adequate seal can be achieved, and

the protrusions into the ductwork are unlikely to

cause injury, then self-tapping or piercing

screws may be used

10.7.5 Welding of sheet

The suitability of welding for sheet-to-sheet

fastening will be governed by the sheet

thick-ness, the size and shape of the duct or fitting and

the need to ensure airtighteness Welded joints

a minimum

Areas where the galvanizing has been damaged ordestroyed by welding or brazing shall be suitablyprepared and painted internally and externally withzinc-rich or aluminium paint as defined in Section27.3.2

11 FITTINGS 11.1 Standardisation of fittings

The terminology and descriptions of rectangularduct fittings as set out in Section 33 are recom-mended for adoption as standard practice to pro-vide common terms of reference for designers,quantity surveyors and ductwork contractors, and

of those using computers in ductwork design andfabrication

Bends are designated as ‘hard’ or ‘easy’, and theseterms as used herein have the following meanings:

‘Hard’ signifies rotation in the plane of the

longer side of the cross section.

‘Easy’ signifies rotation in the plane of the

shorter side of the cross section.

An example illustrating these terms is given inFig 29

11.2 Stiffeners

The flat sides of fittings shall be stiffened in dance with the construction Tables 2 to 4 On theflat sides of bends, stiffeners shall be arranged in

accor-a raccor-adiaccor-al paccor-attern, with the spaccor-acing meaccor-asured accor-alongthe centre of the bend

11.3 Splitters

If the leading edge of the splitters exceeds 1250

mm fit central tie bars at both ends to support thesplitters Leading and trailing edges of splittersmust be edge folded and flattened and be parallel

to the duct axis

Splitters shall be attached to the duct by bolts ormechanically-closed rivets at 100 mm maximumspacing (or by such other fixing as can be shown

to be equally satisfactory e.g proprietary sealedsplitter pins)

11.4 Turning vanes

Where specified, or shown on drawings, squarethroat bends with either duct dimension greaterthan 200 mm shall be fitted with turning vaneswhich are illustrated in Figures 30a and 30b.Turning vanes at 60 mm maximum centres shall

be fixed at both ends either to the duct or ible mounting tracks in accordance with manufac-turer’s instructions, the whole bank being fixedinside the duct with bolts or mechanically closedrivets at 150 mm maximum spacing

compat-The maximum length of turning vane betweenduct walls or intermediate support shall be 615

mm for single skin vanes and 1250 mm for doubleskin vanes

Typical examples of fitting turning vanes when

11.5 Branches

When fitting branch ducts to a main duct, care

should be taken to ensure that the rigidity of the

duct panel is maintained in terms of the stiffening

criteria

11.6 Change shapes

Where a change shape is necessary to

accommo-date the duct and the cross-sectional area is to be

maintained, the slope shall not exceed 22½° on

any side (See Figs 99 to 103) Where a change in

shape includes a local reduction in duct

cross-sectional area, the slope should not exceed 15° on

any side and the reduction in area should not

exceed 20 per cent

11.7 Expansions and contractions

Where these are required, an expansion shall bemade upstream of a branch connection and a con-traction downstream of a branch connection Theslope of either an expansion or a contractionshould not exceed 22½° on any side Where thisangle is not practicable, the slope may be increas-

ed, providing that splitters are positioned to bisectthe angle between any side and the centre line ofthe duct (See Figs 99 to 101)

11.8 Sealant

Sealant shall be used in all longitudinal seams andcross joints of fittings Sealant shall be to theoptions listed in Section 8

Constructional Requirements – Rectangular Ducts

Table 2 LOW PRESSURE (limited to 500 Pa positive and 500 Pa negative)

Maximum duct size

Dimensions in mm

Notes (applicable to Tables 2 to 4)

(1) The joints and stiffeners have been rated in terms of duct longer side and maximum spacing – see 10.4for joints and 10.5 for stiffeners

(2) In Col 3:

‘PS’ = plain sheet

‘SS’ = stiffened sheet, by means of

(a) beading at 400 mm maximum centres: or (b) cross-breaking within the frame formed by joints and/or stiffeners: or (c) pleating at 150 mm maximum centres.

(3) Stiffened panels may limit the choice of insulation materials

(4) For ductwork galvanized after manufacture, see 10.6 and Appendix E

(5) For aluminium ductwork, see Appendix H

(6) For constructional constraints of stainless steel ductwork see Appendix F

(7) Although not covered in this specification, due to their relatively infrequent use, cleated cross joints are

an accepted constructional practice and the HVCA Ductwork Group should be contacted if details oftheir ratings and limitations are required

(8) Intermediate stiffeners using rolled sheet angle profiles, illustrated in Figs 19 to 23 of the appropriaterating may also be utilised ensuring that rigid corners are achieved

Constructional Requirements – Rectangular Ducts

Table 3 MEDIUM PRESSURE (limited to 1000 Pa positive and 750 Pa negative

Constructional Requirements – Rectangular Ducts

Table 4 HIGH PRESSURE (limited to 2000 Pa positive and 750 Pa negative)

Dimensions in mm

Longitudinal seams

For permitted fastenings (types and spacing), see Table 5

Fig 1 Grooved seam Fig 5 Returned standing seam (internal or

sealant

locations

Alternativesealant locations

Fig 4 Button punch snap lock seam Fig 8 Lap seam

Alternative Fasteningsealant locations

Fig 9 Illustrations of panel stiffening

Cross breaking betweenjoints or stiffeners

Pleating (may also

be along the duct)

Beading (may also

be along the

duct)

Examples of Cross sections

Flanged cross joints

Minimum

Fig 10 Rolled steel

angle-flanged joint, with welded

corners

Fixing Bolt

25 x 3 J3

Low

3 0 x 4 J4

4 0 x 4 J5 Medium

Gasket or Sealant if 5 0 x 5 J6 High

sealant turn up not

Angle flanged joint does NOTrequire DW/TM1 certification

A turn up as illustrated is NOTmandatory If not used, the toe

of the angle is to be sealed

Fig 11 Examples of typical rollformed sheet metal profiles

Sealant, clamps/cleats and fixings omitted for clarity

Fig 12 Examples of typical cross joint flanges formed from the duct wall

NOTE: The above illustrations are typical examples of cross joint profiles that are in common use for connecting rectangular sheet metal ducts.

There are no set dimensions for these profiles shown in Figs 11 and 12 provided they are certified under the HVCA testing scheme DW/TM1 “Acceptance Scheme for new products – Rectangular cross joint classification” and are appropriate to the duct application The manufacturer’s technical data should be followed with respect to:

Connections to duct wall Corner treatment Addition of cleats Application of sealants Strength ratings Application of tie bars

A list of manufacturers and profiles that are covered by current DW/TM1 certificate is available from the Ductwork Group Secretary at HVCA.

mm

Socket and spigot cross joints

Note – Particular care must be taken in the sealing of these joints The ratings stated for cross joints

in Figs 13 to 17 inclusive do not require DW/TM1 certification

For permitted fastenings (types and spacing), see Table 5

Fig 13 Plain

Alternative sealant locations Fastening

–

A1

L o wMediumHigh

adjacent stiffener with arating appropriate to theduct size

Fig 15 Angle reinforced (Ducts with

shorter side 400 mm and less)

Fig 16 Back to back stiffeners (Ducts with

both sides greater than 400 mm) 25 x 3 A2 Low

Corners can be mitred

Fig 17 Full girth welded stiffeners

(Ducts with both sides greater

Single stiffeners

Dimensions and ratings

For permitted fastenings (types and spacings), see Table 5

S2S3S1

S4S5

S1S2S3

For permitted fastenings (types and

spacings) see Table 5

Illustrations show rolled steel angle

stiffeners Stiffeners shown in Figs 19 to

23 are permitted If used as full girth

stiffeners rigid corners are required

Full girth stiffener withwelded corners

Longest side stiffener

Back to back stiffener with

Ductwork with short side 400 mm and less

bolted corners

H

40

Tie rod assembly – alternative arrangement

Fig 26 With tubing or

conduit and Fig 25 With internal and threaded inserts

external nuts

Fig 27 With spacers

Fig 28 With shouldered rod

Sheet to sheet Sheet to section (1)

L a p & Capped &

–

150 –

–

75–

300 150

(1) A minimum of 2 fixings per side, with a maximum distance from the corner to the first fixing of 50 mm(2) Except when pierced dimpling is used, one of the other types of fastening must be used at each end inaddition to dimpling

(3) In addition to dimpling, one of the other types of fastening must be used at 450 mm centres, and in allcases not less than 1 per side

(4) Where manufacturers have specific recommendations, then these shall take precedence over the centres

in the Table above

Fig 29 Bends - examples of ‘hard’

Fig 30a and 30b

Maximum distance between

centres of turning vanes should

not exceed 60 mm pitch.

Example of bracing when vane length exceeds max permitted.

Alternatively use two banks of vanes fixing the centre rails together at

150 mm centres.

Max vane length Single skin – 615 mm Double skin – 1250 mm

Part Four – Circular Ducts

12 STANDARD SIZES

The duct sizes in Table 6 have been selected from

the ISO and CEN Standard Ranges

Table 6 Circular Ducts – Standard

Sizes

ISO standard sizes (nominal diameter)

Duct Surface Duct Surface

Other sizes may be available from individual

manufacturers including larger diameters up to

2000 mm.

*May be phased out of future CEN Standards

†Are neither ISO nor CEN Standards

13 CONSTRUCTION

Spirally-wound ducts and straight seamed

ducts

The minimum constructional requirements set out

in Table 7 and 8 are common to the full range of

pressures covered in this specification

The ductwork construction and joint sealing

stan-dards are set out in section 8

Spirally wound duct with thinner than traditional

wall thickness and with one or more corrugations

(ribs) formed between the lock seams are now

available As design and installation experience

with these are gained and more functional

perfor-mance criteria are identified it is anticipated that

such forms may be added to later updates

Design-ers and contractors in the meantime are invited toevaluate them based on information currentlyavailable

13.1 Longitudinal seams 13.1.1 Spirally-wound ducts

The seam used in spirally-wound circular ducts,provided it is tightly formed to produce a rigidduct, is accepted as airtight to the requirements

of all the pressure classifications covered in thisspecification, without sealant in the seam

13.1.2 Straight-seamed ducts

The longitudinal seam for straight-seamed cular ducts shall be either the grooved seamcontinued to the extreme end of the duct andsealed, or a continuous butt lap weld orspot/stitch weld and sealed lap joint (at 30 mmcentres) provided this gives a smooth internalfinish (see Fig 31)

cir-13.2 Cross joints 13.2.1 General

Cross joints for circular ducts, both wound and straight-seamed, are illustrated inFigs.32 to 45 They include several proprietarytypes and the limits of use in terms of diameterand pressure classes are noted against each

heat-13.2.3 Welded joints

The limitations for welded joints are given in 13.3.5

13.3 Fastenings 13.3.1 Permitted types and maximum centres

Table 9 sets out the permitted fastenings andmaximum spacings for low-, medium- and high-pressure ducts All duct penetrations shall be sealed

13.3.2 Rivets

Manufacturers’ recommendations as to use, sizeand drill size are to be followed Rivetsresulting in an unsealed aperature shall not be used

13.3.3 Set screws, nuts and lock bolts

Materials shall be of mild steel, protected byelectro-galvanizing, sherardizing, zinc plating

or other equal and approved finish

13.3.4 Self tapping and piercing screws

Providing an adequate seal can be achieved, andthe protrusions into the ductwork are unlikely tocause injury, then self-tapping or piercingscrews may be used

13.3.5 Welding of sheet

The suitability of continuous welding or spot

welding for sheet to sheet fastening will be

gov-erned by the sheet thickness, the size and shape

of the duct or fitting and the need to ensure

air-tightness Welded joints shall provide a smooth

internal surface and shall be free from porosity.Distortion shall be kept to a minimum

Areas where the galvanizing has been damaged

or destroyed by welding or brazing shall be ably prepared and painted internally and exter-nally with zinc-rich or aluminium paint

suit-Table 7 SPIRALLY-WOUND DUCTS (ALL PRESSURE CLASSIFICATIONS)

None if helically beaded If not helically beaded use

1000 1.0 Fig 35 (angle reinforced) or Fig 36, 37 or 38

(angle flanged) – all at 3000 mm maximum spacing

1500 1.2 Figs 36, 37 or 38 at 3000 mm maximum spacing

Table 8 STRAIGHT-SEAMED DUCTS

High-2 3

mm mm0.6 0.8

4

None

S w a g e d at spigot end as Figs 39 and 40

Swaged at socket and spigot end as Figs 39 and 4 0

Figs 42 to 45 at 1500 mm maximum spacing

Figs 42 to 45 at 1500 mm maximum spacing

1 4 F I T T I N G S

14.1 Standardisation of fittings

The terminology and descriptions of circular duct

fittings as set out in Section 33 are recommended

for adoption as standard practice, to provide

com-mon terms of reference for designers, quantity

surveyors and ductwork contractors, and those

using computers in ductwork design and

fabrica-tion

The requirements for circular duct fittings apply

throughout the pressure ranges covered in this

specification

14.2 Nominal diameters

The nominal diameter (see Table 6) is the size

used for design and ordering With socket and

spigot joints, care should be taken to ensure that

the dimensions of the ducts and fittings are

cor-rectly related, so that the joint can be effectively

sealed

14.3 Sheet thickness

Sheet thickness for circular duct fittings

(deter-mined by the largest diameter) shall be not less

than those quoted in Table 10

Sheet to section

Type ofFastening

Sheet to sheet flanges and(jointing

intermediatestiffeners)Lap Cross Spirally Straight

J o i n t s J o i n t s w o u n d s e a m e d

1 2 3 *

mm mmMechanically

Closed Rivets 60 150Self piercing

screws 60 150Set screws

Lock Bolts 60 –Spot Welds 30 30

* Minimum of three fixings

Circular duct cross joints

Note – All duct penetrations shall be sealed

Limits of use

Spirally-wound ducts Angle Maximum Pressure

size diameter classes

Fig 33 Socket and spigot (duct to duct) with

connector

sealant locations

– 1000

LowMediumHigh

Fig 3 4 Socket and spigot with synthetic rubber

To be used strictly inaccordance withmanufacturers instructions

Fastenings

and size limitations

Not suitable for helically beaded

Fig 35 Angle reinforced socket and

spigot

Fastening

Alternative sealant locations

*25 x 3

*30 x 3

40 x 4

80010001500

Alternative

Fastening

gasket

Alternative

Spirally-wound ducts

Fig 36 Example of typical roll formed

sheet metal profile

Fastenings and sealant

in accordance with manufacturer’s instructions

Fig 37 Angle flanged (external)

Fixing Bolts Fastening Fastening

Limits of useMaximum Pressurediameter classesmm

To be used strictly in accordance withmanufacturer’s recommendations

*25 x 3

*30 x 3

40 x 4

80010001500

LowMediumHigh

*Where flanged joints are specified.Note: A turn up as illustrated is notmandatory If not used the toe ofthe angle is to be sealed

Limits of use

Straight-seamed ducts Angle Maximum Pressure

size diameter classes

Fig 42 Socket and spigot – angle reinforced

Fig 39 Socket and spigot – plain

Fastening

Alternative sealant locations

Gasket

LowMediumhigh

LowMediumHigh

Fastening

Swage only required if

Fastening

LowMediumHigh

80010001500

Sealant if turn up not used

Fastening

or Gasket

Fig 45 Flat

Anglesizemm

Maximumdiametermm

Pressureclasses

To be used strictly in accordance withmanufacturer’s recommendations

Also acceptable with flange setinternally similar to Fig 38

25 x 3

30 x 3

40 x 4

80010001500

LowMedium

Turn up minimum

of 8 mm Sealant

Fastening

Sealant or Gasket Turn up of

8 mm

8 mmBolt size

LowMediumHigh

80010001500

ring flanged

Part Five – Flat Oval Ducts

15 STANDARD SIZES AND SHEET

THICKNESSES

15.1 Table 11 sets out the standard sizes of

spirally-wound oval ducts offered by the manufacturers of

ducts of this section

1 6 C O N S T R U C T I O N ( S P I R A L L Y - W O U N D

DUCTS)

16.1 General

‘Flat oval’ is the term used to describe a duct of

cross-section with flat opposed sides and

semi-circular ends The duct is formed from a

spirally-wound circular duct, using a special former

Apart from stiffening (see Tables 12 and 13), flat

oval ducts have the same constructional

require-ments throughout the pressure ranges covered in

this specification

The ductwork construction and joint sealing

stan-dards are set out in Section 8

16.2 Longitudinal seams

Spirally-wound flat oval duct is accepted as airtight

to the requirements of this specification without

sealant in the seams, provided the grooved seam is

tightly formed to produce a rigid duct

16.3 Cross joints

16.3.1 General

Cross joints shall be as Figs 53 to 58 inclusive

or such other joint as can be demonstrated to the

designer to be equally satisfactory

16.4.1 Permitted types and maximum centres

Table 14 sets out the permitted fastenings and

maximum spacings for low-, medium- and

high-pressure ducts All duct penetrations shall be

sealed

16.4.2 Rivets

Manufacturers’ recommendations as to use, size

and drill size are to be followed Rivets resulting

in an unsealed aperature shall not be used

16.4.3 Set screws, nuts and lock bolts

S e t s c r e w s a n d n u t s s h a l l b e o f m i l d s t e e l ,

protected by electro-galvanizing, sherardizing,

zinc plating or other equal and approved finish

16.4.4 Self tapping and piercing screws

Providing an adequate seal can be achieved, and

the protrusions into the ductwork are unlikely to

cause injury, then self-tapping or piercing

screws may be used

16.4.5 Welding of sheet

The suitability of continuous welding or spot

welding for sheet to sheet fastening will be

governed by the sheet thickness, the size andshape of the duct or fitting and the need toensure air-tightness Welded joints shall provide

a smooth internal surface and shall be freefrom porosity Distortion shall be kept to aminimum

Areas where the galvanizing has been damaged

or destroyed by welding or brazing shall besuitably prepared and painted internally andexternally with zinc-rich or aluminium paint

16.5 Stiffening

The larger sizes of flat oval duct are stiffened byswages, as indicated in Table 11 Additionally, tierods (see Figs 25 to 28) are required, positioned

as indicated in the respective tables and illustrations

In special situations as an alternative to tie rods,stiffening in the form of external angles may beused to meet the requirements of the correspondingrectangular duct sizes

17 CONSTRUCTION (STRAIGHT-SEAMED)

Flat oval ducts with opposed sides andsemi-circular ends may also be formed usingplain sheet and straight seams Ducts so formedshould follow the metal thicknesses and stif-fening requirements specified for the corres-ponding sizes of rectangular ducts, except thatstiffening is necessary on the flat sides only.Seams and cross joints (see Figs 59 to 63) shall besealed to ensure the necessary degree of airtight-ness throughout the pressure ranges covered in thisspecification

18 FITTINGS 18.1 General constructional requirements

Sheet thicknesses for flat oval fittings (determined

by the periphery of the larger end) shall be not lessthan those given in Table 11 for the ducts them-selves

With socket and spigot joints, care should be taken

to ensure that the dimensions of ducts and fittingsare correctly related

All the seams and joints integral to a fitting shall besealed to the same standard as the duct (See Sec-tion 8)

18.2 Standardisation of fittings

The terminology and descriptions of flat oval ductfittings as set out in Section 33 are recommendedfor adoption as standard practice, to provide com-mon terms of reference for designers, quantity sur-veyors and ductwork contractors, and those usingcomputers in ductwork design and fabrication.The requirements for flat oval duct fittings applythroughout the pressure ranges covered in this

Table 11 Flat oval ducts – Standard sizes and sheet thicknesses

2

sq metres

0.7180.7980.8780.9581.0371.1171.197

1.2771.4361.5961.7561.915

2.0752.2382.3942.5532.8733.1923.5113.830

Depth of duct (minor axis — ‘D’) — nominal

75 100 125 150 200 250 300 350 400 450 500

3

mm mm mm mm mm mm mm mm mm mm mm320

Table 12 – Flat oval ducts – low- and medium-pressure – stiffening requirements

Depth of duct (minor axis — ‘D’) – nominalTie rods

1 2

mm mm mm mm mm mm mm mm mm mm mm320

360 350 330 320Not required

Table 13 – Flat oval ducts – high-pressure – stiffening requirements

Depth of duct (minor axis — ‘D’) – nominalTie rods

75 100 125 150 200 250 300 350 400 450 500

1 2

mm mm mm mm mm mm mm mm mm mm mm320

360 350 330 320

400 390 370 360

440 430 410 400Not required

Flat oval duct cross joints

Note – All duct penetrations shall be sealed

Limits of use

mm mm

Fig 53 Plain socket and spigot (duct of fitting)

Low– 1785 Medium

High

Fig 54 Socket and spigot (duct of duct) with

connector

sealant locations

Low– 1785 Medium

High

Fig 55 Alternative socket and spigot (duct to

duct) with connector and tie rod

Alternative sealant loacations

The tie rod pattern to be in accordance with Tables 12 and 13.

Low

High

Fig 56 Example of typical roll formed

sheet metal profile

Fastenings and sealant

in accordance with manufacturer’s instructions

To be used strictly in accordance withmanufacturer’s recommendations

Fastening

sealant locations

Fastening

Alternative

Fastening Alternative

Limits of use

size width classes

mm mm

Fig 57 Angle flanged (external)

Sealant

Turn up minimum

A turn up as illustrated is notmandatory If not used, the toe of the

*Where flanged jointsare specified

Fig 58 Angle flanged Angle flanged

(internal) Alternativesealant

3 4* 5 6* 2

60

1 Mechanically close rivets Self piercing screws Set screws and nuts Lock bolts Spot welds

150 60

– 300 60

30 75

*Minimum of two fixings.

Roll formed flanges shall be fitted strictly in accordance with manufacturers instructions.

30

150 150 150 150 150

300 30

150 150

– –

75

Cross joints Flat Semi- Flat Semi- sides circular sides circular ends ends

Straight-seamed ducts

Limits of useAngle Maximum Pressuresize width classes

Socket swage not reqauired onducts 500 wide and below

Fig 60 Socket and spigot with connector

Alternative sealant

Sealant Turn up

or minimum Gasket of 8 mm

A turn up as illustrated is notmandatory If not used, the toe ofthe angle is to be sealed.Also acceptable with flange setinternally similar to fig 58

Alternative sealant locations