NATIONAL ANNEX NA to BS EN 1991 1 3 2003 UK National Annex to Eurocode 1 Actions on structures — Part 1 3 General actions — Snow loads ICS 91 010 30; 91 080 01 ����������������������������������������[.]
NATIONAL ANNEX NA to BS EN to NA+A1:2015 BS EN 1991-1-3: 1991-1-3:2003 Incorporating 2003+A1:2015 corrigendum Incorporatingno corrigendum no UK National Annex to Eurocode 1: Actions on structures — Part 1-3: General actions — Snow loads ICS 91.010.30; 91.080.01 NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 Committees responsible for this National Annex The preparation of this National Annex was entrusted by Technical Committee B/525, Building and civil engineering structures, to Subcommittee B/525/1, Actions (loadings) and basis of design, upon which the following bodies were represented: Association of Consulting Engineers British Constructional Steelwork Association British Masonry Society Building Research Establishment Concrete Society Health and Safety Executive Highways Agency Institution of Civil Engineers Institution of Structural Engineers National House Building Council Office of the Deputy Prime Minister Steel Construction Institute This National Annex was published under the authority of the Standards Policy and Strategy Committee on 23 December 2005 © The British Standards Institution 2015 Published by BSI Standards Limited 2015 First edition 23 December 2005 ISBN 978 580 91564 Amendments/corrigenda issued since publication Amd No Date Comments 17170 29 June 2007 NA.2.8 equation NA.1 A + 100 changed to A – 100 Figure NA.1 legend for Zone 1 changed from 0,25 to 0,30 Corrigendum No 31 December 2015 See Introduction NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 Contents Page Committees responsible Inside front cover Introduction NA.1 Scope NA.2 Nationally Determined Parameters NA.3 Decisions on the status of informative annexes NA.4 References to non-contradictory complementary information 1 8 Bibliography Figure NA.1 — Characteristic ground snow load map Figure NA.2 — Snow load shape coefficients for relative load arrangements for roofs no longer than 10m in the UK Figure NA.3 — Drifted snow load arrangement for a duo-pitched roof in the UK Figure NA.4 — Drifted snow load arrangements for a cylindrical roof in the UK Table NA.1 — Snow load shapes for coefficients for monopitched roofs in the UK Table NA.2 — Drifted snow load shape coefficient for a duo-pitched roof in the UK Table NA.3 — Drifted snow load shape coefficients for a cylindrical roof in the UK © The British Standards Institution 2015 i blank NA to BS EN 1991-1-3:2003 NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 National Annex (informative) to BS EN 1991-1-3:2003, EurocodeEurocode 1: Actions 1991-1-3:2003+A1:2015, 1:on Actions on structures — Part 1-3: General actions — Snow loads structures — Part 1-3: General actions — Snow loads Introduction This National Annex has been prepared by BSI Subcommittee B/525/1, Actions (loadings) and basis of design In the UK it is to be used in conjunction with BS EN 1991-1-3:2003+A1:2015 1991-1-3:2003 The start and finish of text introduced or altered by National Amendment No.1 is indicated in the text by NA.1 Scope tags Minor editorial changes are not tagged This National Annex gives: National Amendment No.1 was made to reflect CEN amendment A1 to BS EN 1991-1-3:2003 a) the UK decisions for the Nationally Determined Parameters described in the following subclauses of NA.1 Scope BS EN 1991-1-3:2003: This — National 1.1 (2) Annex gives: — 4.2 (1) — 5.3.5 (1) —the 1.1UK (3) decisions — — 5.3.5 (3) Parameters described in the following subclauses of a) for4.3 the(1) Nationally Determined BS EN 1991-1-3:2003+A1:2015: — 1.1 (4) — 5.2 (2) — 5.3.6 (1) — 1.1 (2) — 4.2 (1) — 5.3.4 — (3) 5.2 (5) 5.3.6 (3) — (3) — 1.1 (4) — — 1.1 3.3 (4) (1) — 4.3 5.2 (1) (6) — 5.2 5.2 (2) (7) — 5.3.5 6.2 (2)(1) — 5.3.5 6.3 (1)(3) — (3) (3) — 23.3 — (4) (1) — 24.1 — 5.2 5.2 (5) (8) — 5.2 (6) 5.3.3 (4) — 5.3.6 6.3 (2)(1) — 5.3.6 Annex(3)A (1) — — 5.2 (7) — 6.2 (2) — 3.3 4.1 (1) (2) 5.3.4 (3) — 3.3 (3) — 5.2 (8) — 6.3 (1) b) the UK decisions on the status of BS EN 1991-1-3:2003 informative annexes; — 4.1 (1) — 5.3.2 (3) — 6.3 (2) c) references to non-contradictory complementary information — 4.1 (2) — 5.3.3 (4) — Annex A (1) NA.2 Nationally Determined Parameters b) the UK decisions on the status of BS EN 1991-1-3:2003+A1:2015 informative annexes; NA.2.1 Altitudes greater than 500 m [BS EN 1991-1-3:2003, c) references to non-contradictory complementary information 1.1 (2)] The of BS EN 1991-1-3 does not include sites at altitudes above 500 m For altitudes greater than NA.2scope Nationally Determined Parameters 500 m specialist advice should be sought from the Meteorological Office on the snow loads likely to occur NA.2.1 Altitudes greater than 500 m [BS EN 1991-1-3:2003+A1:2015, 1.1 (2)] at the site The scope of BS situations EN 1991-1-3and doesload not include sites at altitudes above 500 m Forlocations altitudes greater than NA.2.2 Design arrangements to be used for1different 500EN m specialist advice1.1 should [BS 1991-1-3:2003, (3)] be sought from the Meteorological Office on the snow loads likely to occur at the site The scope of BS EN 1991-1-3 states that information on design situations and load arrangements to be used NA.2.2 Design situations and arrangements be used for different locations is given in load BS EN 1991-1-3:2003,toAnnex A for different locations [BS EN 1991-1-3:2003+A1:2015, 1.1 (3)] The design situations summarized as case B2 in BS EN 1991-1-3:2003, Table A.1 should be the only The scope ofcondition BS EN 1991-1-3 states for that informationimposed on design situations andinload to be exceptional to be checked determining roof snow loads the arrangements UK used for different locations is given in BS EN 1991-1-3:2003+A1:2015, Annex A NA.2.3 Snow load shape coefficients for exceptional snow drifts [BS EN 1991-1-3:2003, 1.1 (4)] The design situations summarized as case B2 in BS EN 1991-1-3:2003+A1:2015, Table A.1 should be the The of BS EN 1991-1-3 states that for information on snow loadroof shape coefficients for UK exceptional snow only scope exceptional condition to be checked determining imposed snow loads in the drifts is given in BS EN 1991-1-3:2003, Annex B NA.2.3 Snow load shape coefficients for exceptional snow drifts BS Annex B should be used in the UK in order to determine exceptional snow drift loads [BSEN EN1991-1-3:2003, 1991-1-3:2003+A1:2015, 1.1 (4)] NA.2.4 Exceptional snow load onthat theinformation ground [BSonEN 1991-1-3:2003, (3)] The scope of BS EN 1991-1-3 states snow load shape coefficients for exceptional snow drifts is given in BS ENon1991-1-3:2003+A1:2015, Annexas B accidental actions Exceptional snow load the ground should be treated BS EN 1991-1-3:2003+A1:2015, Annex B should be used in the UK in order to determine exceptional NA.2.5 Load due to exceptional snow drift [BS EN 1991-1-3:2003, (4)] snow drift loads Drift loads determined using the guidance given in BS EN 1991-1-3:2003, Annex B should be treated as NA.2.4 Exceptional snow load on the ground [BS EN 1991-1-3:2003+A1:2015, (3)] accidental actions Exceptional snow load onexceptional the ground should treated asground accidental NA.2.6 Locations with snow be load on the butactions with no load due to exceptional snow [BS EN 3.3 (1)] NA.2.5drift Load due to1991-1-3:2003, exceptional snow drift [BS EN 1991-1-3:2003+A1:2015, (4)] Locations experience these are not to occur in the UK Annex B should be Drift loadsthat determined using theconditions guidance given inconsidered BS EN 1991-1-3:2003+A1:2015, treated as accidental actions © BSI 2007 © The British Standards Institution 2015 1 NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 NA to BS EN 1991-1-3:2003 NA to BS EN 1991-1-3:2003 NA to BS EN 1991-1-3:2003 NA to BS EN 1991-1-3:2003 NA.2.6 Locations with exceptional snow load on the ground but with no load due to exceptional snow drift [BS EN 1991-1-3:2003+A1:2015, 3.3 (1)] Locations that experience these conditions are not considered to occur in the UK NA.2.7 Locations with exceptional snow load on the ground and and with with load load due due to to exceptional exceptional NA.2.7 Locations exceptional on the ground and with load due to exceptional snow drift [BS ENwith 1991-1-3:2003, 3.3snow (3)] load 1991-1-3:2003+A1:2015, 3.3 (3)] NA.2.7 Locations exceptional snow drift [BS ENwith 1991-1-3:2003, 3.3snow (3)] load on the ground and with load due to exceptional BS EN 1991-1-3:2003, Annex B should be used inbe place ofinBS EN of 1991-1-3:2003, 6.2due in order to determine 1991-1-3:2003+A1:2015, Annex B(3)] should used place BS EN 1991-1-3:2003+A1:2015, 6.2 in NA.2.7 Locations exceptional load on the ground and with load to exceptional snow drift [BS ENwith 1991-1-3:2003, 3.3snow BS EN 1991-1-3:2003, Annex Bthe should be used in place of BS EN 1991-1-3:2003, 6.2 in order to determine the load case due to drifting in UK order to determine the load case due to drifting in the UK snow drift [BS EN 1991-1-3:2003, 3.3 (3)] BS EN AnnexinBthe should the load1991-1-3:2003, case due to drifting UK.be used in place of BS EN 1991-1-3:2003, 6.2 in order to determine NA.2.8 EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 4.1 (1)] Characteristic value of snow ground [BS EN 4.1 (1)] BS EN Annex should usedon in the place of BS EN 1991-1-3:2003, 6.2 in order to determine the load1991-1-3:2003, case due to drifting inBthe UK.beload NA.2.8 Characteristic value of snow load on the ground [BS EN 1991-1-3:2003, 4.1 (1)] the load case due to drifting in the UK The characteristic ground snow loads sk to be used in the UK should be obtained from the map shown in NA.2.8 Characteristic value of snow load on the ground [BS EN 1991-1-3:2003, 4.1 (1)] The characteristic ground snow loads s to be used in the UK should be obtained from the map shown in Figure and Equation (NA.1) NA.2.8 NA.1 Characteristic value of snowk load on the ground [BS EN 1991-1-3:2003, 4.1 (1)] The characteristic ground snow loads sk to be used in the UK should be obtained from the map shown in Figure NA.1 and Equation (NA.1) – 100 ⎞ ⎛A (NA.1) used in the UK should be obtained from the map shown in Thes kcharacteristic ground snow sk to be = NA.1 [ 0, 15and + ( 0Equation , 1Z + 0, 05 ) ] +loads (NA.1) Figure (NA.1) – 100 ⎝A ⎠ 525 ⎛ [ 0, 15and + ( 0Equation , 1Z + 0, 05 ) ] + ⎞ (NA.1) s k = NA.1 Figure (NA.1) – 100 ⎞⎠ ⎝A 525 where (NA.1) s k = [ 0, 15 + ( 0, 1Z + 0, 05 ) ] + ⎛ ⎝⎛A – 100 ⎠⎞ 525 where = [ , 15 + ( , 1Z + , 05 ) ] + (NA.1) s k sk is the characteristic ground⎝snow ⎠ (kN/m2); 525load where sk is the characteristic ground snow load (kN/m2); where Z is the zone number obtained from the map in Figure NA.1; sk is the characteristic ground snow load (kN/m2); Z is the zone number obtained from the map in Figure NA.1; sAk isisthe thesite characteristic ground snow load (kN/m2); altitude (m) Z is the zone number obtained from the map in Figure NA.1; A is the site altitude (m) Z is thelocal zoneeffects number obtained from the map in Figure NA.1; Unusual may not have been accounted for in the analysis undertaken to produce the ground A is the site altitude (m) Unusual local effects may not have been accounted for in shelter the analysis to produce the ground snow load map given in Figure NA.1 These include local from undertaken the wind, which can result in A is the site altitude (m) Unusual may not been accounted for in shelter the analysis undertaken to funnel produce thesnow ground snow loadlocal mapeffects givenloads in Figure NA.1 These includein local from the which wind, may which can result in and increased local snow andhave local configurations mountainous areas, the Unusual may not been accounted for in shelter the analysis undertaken to funnel produce thesnow ground snow loadlocal mapeffects givenloading in Figure NA.1 These includein local from the which wind, which can result in and increased local snow loads and local configurations mountainous areas, the give increased local Ifhave the designer suspects that there are unusual localmay conditions that need to snow loadinto map givenloading in Figure NA.1 These include shelter from the wind, which can result in and increased local snow loads and local configurations inlocal mountainous areas, which may funnel the give increased local If coastal the designer suspects that there unusual local conditions that need to be taken account, then for sites below 100 m the mapare value should be used without thesnow altitude increased local snowloading loads local configurations in mountainous areas, which may funnel the and give increased local If coastal the suspects that there unusual local that need to be taken into account, thenand for sites below 100 m the mapare value should be used without thesnow altitude modification Alternatively, and in designer other cases, the Meteorological Office should beconditions consulted give increased local loading If coastal the suspects that there unusual local to be taken into account, then for sites below 100 m the mapare value should be used withoutthat the need altitude modification Alternatively, and in designer other cases, the Meteorological Office should beconditions consulted characteristic of snow load ground NA.2.9 ground [BS EN 1991-1-3:2003, (2)] be takenRefined into account, then for coastal sites below 100 mon thethe map value should be used without the4.1 altitude modification Alternatively, and invalue other cases, the Meteorological Office should be consulted [BS ENRefined 1991-1-3:2003+A1:2015, 4.1 (2)] NA.2.9 characteristic of snow load on the ground EN 1991-1-3:2003, 4.1 (2)] modification and invalue other cases, Meteorological Office[BS should be consulted.Office Where a moreAlternatively, refined characteristic ground snowthe load value sk is required, the Meteorological should NA.2.9 Refined characteristic value of snow load on the ground [BS EN 1991-1-3:2003, 4.1 (2)] Where a more refined characteristic ground snow load value sk is required, the Meteorological Office should be consulted NA.2.9 Refined characteristic value of snow load on the ground [BS EN 1991-1-3:2003, 4.1 (2)] Where a more refined characteristic ground snow load value sk is required, the Meteorological Office should be consulted NA.2.10 Other representative values for snow load onsthe ground [BS EN 1991-1-3:2003, 4.2 (1)] Where a more refined characteristic ground snow load value be consulted k is required, the Meteorological Office should NA.2.10 ground [BS EN 1991-1-3:2003, 4.2 (1)] Other representative values for snow load on the ground be Theconsulted UK National Annex to BS EN 1990 gives values that should be used in the UK for the NA.2.10 Other representative values [BS EN 1991-1-3:2003+A1:2015, 4.2 (1)]for snow load on the ground [BS EN 1991-1-3:2003, 4.2 (1)] The UK National 1990 gives values that should be used in the UK for the coefficients Ò0, Òrepresentative and Ò2.to BS ENvalues Annex NA.2.10 Other for snow load on the ground [BS EN 1991-1-3:2003, 4.2 (1)] The UK National coefficients Ò0, Ò1 Annex and Ò2.to BS EN 1990 gives values that should be used in the UK for the NA.2.11 Treatment of exceptional snow on that the ground EN The UK National values should be[BS used in1991-1-3:2003, the UK for the 4.3 (1)] coefficients Ò0, Ò1 Annex and Ò2.to BS EN 1990 givesload NA.2.11 Treatment of exceptional snow load on the ground [BS EN 1991-1-3:2003, 4.3 (1)] coefficients Ò0, Ò Ò2 and The coefficient for exceptional snow loads C should take a value of 2,0 as recommended in NA.2.11 Treatment of exceptional snowesl [BS EN 1991-1-3:2003, 4.3 (1)] load on the ground TheEN coefficient for exceptional snow loads Cesl should take a value of 2,0 as recommended in BS 1991-1-3 NA.2.11 Treatment of exceptional snow load on the ground [BS EN 1991-1-3:2003, 4.3 (1)] [BS coefficient EN 1991-1-3:2003+A1:2015, 4.3loads (1)] The for exceptional snow Cesl should take a value of 2,0 as recommended in BS EN 1991-1-3 NA.2.12 Determining load arrangements snow loads on roofs [BS EN 1991-1-3:2003, 5.2 (2)] TheEN coefficient for exceptional snow loads Cesl for should take a value of 2,0 as recommended in BS 1991-1-3 NA.2.12 Determining load arrangements for snow loads on roofs [BS EN 1991-1-3:2003, 5.2 (2)] BS EN 1991-1-3 BS EN 1991-1-3:2003, Annex B should be used to determine the imposed roof loads due to drifted snow for: NA.2.12 Determining load arrangements for snow loads on roofs [BS EN 1991-1-3:2003, 5.2 (2)] BS EN 1991-1-3:2003, Annex B should be used to determine the imposed roof loads due to drifted snow for: Determining for snow 5.3.4 loads(3)]; on roofs NA.2.12 roofs [BS EN 1991-1-3:2003, 5.2 (2)] a) multi-span roofs [inload placearrangements of BS EN 1991-1-3:2003, BS EN 1991-1-3:2003, Annex B should be used to determine the imposed roof loads due to drifted snow for: [BS 1991-1-3:2003+A1:2015, 5.2EN (2)]1991-1-3:2003, 5.3.4 (3)]; a) EN multi-span roofs [in place of BS BSb)EN 1991-1-3:2003, B should be used to[in determine imposed roof loads due drifted snow for: roofs abutting andAnnex close to taller structures place of the BS EN 1991-1-3:2003, 5.3.6to(3)]; a) multi-span roofs [in place of BS EN 1991-1-3:2003, 5.3.4 (3)]; roofs abutting and close to taller [in used placetoofdetermine BS EN 1991-1-3:2003, 5.3.6loads (3)]; due to BSb)EN 1991-1-3:2003+A1:2015, Annexstructures B should be the imposed roof a) drifting multi-span roofs [in place BS EN 1991-1-3:2003, 5.3.4 c) at projections and of obstructions [in place of BS EN(3)]; 1991-1-3:2003, 6.2 (2)] b) roofs abutting drifted snow for: and close to taller structures [in place of BS EN 1991-1-3:2003, 5.3.6 (3)]; c) drifting at projections and obstructions [in place of BS EN 1991-1-3:2003, 6.2 (2)] b) roofsLoad abutting and close to taller structures [in place BS EN 1991-1-3:2003, 5.3.6 (3)]; NA.2.13 for orofredistribution on a roof c) drifting at arrangements projections and of obstructions [inremoval place of BS EN 1991-1-3:2003, 6.2 (2)] a) multi-span roofs [in place BSartificial EN 1991-1-3:2003+A1:2015, 5.3.4 (3)]; of snow NA.2.13 Load arrangements for artificial removal or redistribution of snow on a roof [BS EN 1991-1-3:2003, 5.2 (5)] c) drifting at projections and obstructions [in place of BS EN 1991-1-3:2003, 6.2 (2)] b) EN roofs1991-1-3:2003, abutting and close to for taller structures [in place BS EN 1991-1-3:2003+A1:2015, 5.3.6 (3)]; NA.2.13 Load arrangements artificial removal orofredistribution of snow on a roof [BS 5.2 (5)] In certainLoad cases,arrangements snow may be artificially removed from ororredistributed on a of roof, e.g due toroof excessive heat NA.2.13 for artificial removal redistribution snow on a [BS EN 1991-1-3:2003, 5.2 (5)] c) drifting atsmall projections obstructions [into place ofor BS EN 1991-1-3:2003+A1:2015, 6.2 (2)] in more In certain cases, snow may and be artificially removed from redistributed on a roof, e.g duecan to excessive heat loss a section roof or manually maintain access to a service door This result [BS through EN 1991-1-3:2003, 5.2 of (5)] In certain cases, snow may be removed fromfrom or redistributed on a roof, e.g due to excessive heat loss through a small section of artificially roofthan or manually to maintain access to1991-1-3:2003, a service door This can resultBin more severe load imbalances occurring those resulting BS EN 5.3 and Annex (which NA.2.13 Load arrangements for artificial removal or redistribution of snow on a roof In certain cases, snow may be artificially removed from or redistributed on a roof, e.g due to excessive heat loss through a small section ofdeposition roofthan or manually to maintain access to1991-1-3:2003, a service door This can result in more severe load imbalances occurring those resulting from BS EN 5.3 and Annex B (which have been derived for natural patterns) To provide for these situations, if they are likely to occur [BS EN 1991-1-3:2003+A1:2015, 5.2 (5)] loss through a small roofthan or manually to maintain to1991-1-3:2003, a service door.if5.3 This can result in more severe loadinformation imbalances those from BS EN and Annex (which have been derived forsection natural deposition To provide for these situations, they are likelyBimposed to occur and other isoccurring notof available, a patterns) loadresulting case should beaccess considered comprising the minimum In certain cases, snow may be artificially removed from orbe redistributed on aroof roof, e.g due tolikely excessive severe loadinformation imbalances occurring those resulting from BS EN 1991-1-3:2003, and Annex Bimposed have been derived for natural deposition To provide for these situations, if5.3 they are to(which occur and other is not available, a patterns) load case should considered comprising the minimum uniformly distributed load (BS ENthan 1991-1-3:2003, 5.3) on any portion of the area zero load on the heatother loss afor small section roofa patterns) or manually maintain access to aroof service door This canimposed have beenthrough derived natural deposition Toto provide for these situations, if the they are likely toresult occur and information is not available, load case should be considered comprising minimum uniformly distributed load (BS ENof1991-1-3:2003, 5.3) on any portion of the area and zero load on the remainder of the area in more severe load imbalances occurring than those from BS EN 5.3 and other information is not available, a load case should considered theand minimum imposed uniformly distributed load (BS EN 1991-1-3:2003, 5.3)resulting on be any portion ofcomprising the 1991-1-3:2003+A1:2015, roof area zero load on the remainder of the area NA.2.14 Load arrangements for1991-1-3:2003, situations arising rainfallofon onfor roofs and Annex B (which have derived for natural deposition patterns) Tosnow provide these uniformly distributed loadbeen (BS EN 5.3) onfrom any portion the roof area and zerosituations, load on the remainder of the area NA.2.14 Load arrangements for situations from rainfall onberoofs [BS ENare 1991-1-3:2003, if they likely to occur5.2 and(6)] other informationarising is not available, a load on casesnow should considered remainder of the area NA.2.14 Load arrangements situations arising from rainfall on snow on roofs [BS EN 1991-1-3:2003, 5.2 (6)]foruniformly comprising the minimum imposed distributed load (BS EN 1991-1-3:2003+A1:2015, 5.3) for on any The UK National Annex to BS EN 1991-1-1 specifies minimum imposedon loads on on roofs with access NA.2.14 Load arrangements situations arising from rainfall snow roofs [BS EN 1991-1-3:2003, 5.2 zero (6)]for portion the only roof area and load onfor thea specifies remainder of theof area The UKof National Annex to BS EN 1991-1-1 minimum imposed loads onnot roofs with access for of maintenance These values allows certain build-up water but it does allow for the effect [BS EN 1991-1-3:2003, 5.2 (6)] The UKbecoming National Annex BStoEN 1991-1-1 minimum imposed onwhere roofs with access for of maintenance only These to values allows forice a specifies certain build-up ofshould water but it does not allow the effect drains blocked due debris or Specialist advice be loads sought the for consecutive The UKbecoming National Annex to BSto EN 1991-1-1 specifies minimum imposed loads onwhere roofs with access for of maintenance only These values allows forice apossible certain build-up water it does not allow the effect drains blocked due debris or Specialist advice should beoccur sought the consecutive melting and freezing of snow together with rainfall isoflikely tobut and block rooffor drainage maintenance only These values allowswith forice apossible certain build-up watertobut it does not allow the effect of drains becoming blocked due to debris or Specialist advice should beoccur sought the consecutive melting and freezing of snow together rainfall isoflikely andwhere block rooffor drainage © Theand British Standards Institution 2015 drains becoming blocked due together to debris with or ice Specialist advice shouldtobeoccur sought where the melting and freezing of snow possible rainfall is likely block roofconsecutive drainage melting and freezing of snow together with possible rainfall is likely to occur and block roof drainage © BSI 2007 NA to BS EN 1991-1-3:2003 NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 Zone numbers Ground snow load at 100m a.m.s.l (kN/m2) 0,30 0,40 0,50 0,60 0,70 6,5 0,85 NA NB NF NG NL NM IN IR NE NH NJ NK 10 NO NP NT NU NY NZ HT SE TA IO IS IW ND SC SH SD SJ SMSN SO SK TF TL SP TM IX HT IT NC 11 IJ HZ NX IH IM IV HY NS IQ HT 12 IC IG IL HU NN IF HT NR IB HP SR TQ SU SS TR ST SW SY TW TV SZ SX Jersey - Zone 3, 0,50 kN/m2 at 100m a.m.s.l, Guernsey - Zone 2, 0,40 kN/M2 at 100m a.m.s.l Figure NA.1 — Characteristic ground snow load map © BSI 2007 © The British Standards Institution 2015 NA.2.13 Load arrangements for artificial removal or redistribution of snow on a roof [BS EN 1991-1-3:2003, 5.2 (5)] NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 In certain cases, snow may be artificially removed from or redistributed on a roof, e.g due to excessive heat loss through a small section of roof or manually to maintain access to a service door This can result in more severe load imbalances occurring than those resulting from BS EN 1991-1-3:2003, 5.3 and Annex B (which have been derived for natural deposition patterns) To provide for these situations, if they are likely to occur and other information is not available, a load case should be considered comprising the minimum imposed uniformly distributed load (BS EN 1991-1-3:2003, 5.3) on any portion of the roof area and zero load on the remainder of the area NA to BS EN 1991-1-3:2003 NA.2.14 Load arrangements for situations arising from rainfall rainfall on on snow snow on on roofs roofs [BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 5.2 (6)] 5.2 (6)] The UK National Annex to BS EN 1991-1-1 specifies minimum imposed loads on roofs with access for maintenance only These values allows for a certain build-up of water but it does not allow for the effect of drains becoming blocked due to debris or ice Specialist advice should be sought where the consecutive melting and freezing of snow together with possible rainfall is likely to occur and block roof drainage NA.2.15 Exposure coefficient used for determining snow load load on on aa roof roof [BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 5.2 (7)] 5.2 (7)] The recommended value for exposure coefficient C in the UK is 1,0 for all topographies © BSI 2007 e NA.2.16 Thermal coefficient used to account for the reduction of snow load on roofs with high high thermal transmittance [BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 5.2 (8)] 5.2 (8)] The recommended value for thermal coefficient Ct in the UK is 1,0 for all roofing materials roofs [BS EN 1991-1-3:2003+A1:2015, 5.3.2(3)] NA.2.17 Monopitch Drifted snow load arrangement for pitched roofs [BS EN 1991-1-3:2003, 5.3.3 (4)] Use the recommendations forNA.2 drifting arrangement forberoofs a dimension greater The loadfollowing arrangement given in Figure andload Table NA.1 should usedwith in place of than 10m in length For roofs(4)with dimensions less than snow 10m in length EN 1991-1-3 BS EN 1991-1-3:2003, 5.3.3 to determine the drifted load on a the duo-pitched roof recommendation in the UK should be used P 1,(D ) Case (ii) ls2 P 1,(D ) Case (iii) ls1 D1 D2 lsi = bi b1 b2 Figure NA.2 — Snow load shape coefficients for relative load arrangements roofs no longer than in the UK Figure NA.2 — Drifted snowfor load arrangement for a10m duo-pitched roof in the UK Table NA.1 load shapes coefficients forfor monopitched roofs in in the UKUK Table NA.1 — Snow Drifted snow load for shape coefficient a duo-pitched roof the Angle of pitch Snow load shape of roof α coefficent µ1 È1 µ2 0≤α≤5 0º k µ11k 15º 0,8 0,8+0,8α/30 < α ≤ 30 30 < α ≤ 60 Angle of pitch of roof (µi, i =1,2) 15º 0,8 < µ1 k 30º 0,8+0,8 α/30 0,8 + 0,4(µ – 15)/15 30º α 60° is the angle between the horizontal and a line drawn from the crown to the point theangle roof between the horiz The load arrangements shown in Figure NA.3 need only beonly considered for roofs is greater than 15° Figure NA.4 need be considered forwhere roofs µ where is forgreater > 60 is the angle betwee The valueThe for the snow shapeload coefficient for one side theside roofofshould be should zero, while thewhere valuesthe for tangent the than 15° value for load the snow shape coefficient forofone the roof be zero, while the to the surface valuesside for the other shouldfrom be obtained from and Figure NA.4 and NA.3 The values for the other should beside obtained Figure NA.3 Table NA.2 TheTable values for the snow load shape The load arrangements shown in snow load shape coefficients areconstant assumedintothe be direction constant in the direction parallel to the eaves coefficients are assumed to be parallel to the eaves The value for the snow load shap Table NA.3 — Drifted snow load shape coefficients a cylindrical roof in the UKshould be obtained fro Table NA.2 snow load shape coefficients forfor a cylindrical roof in the UK — Drifted other side coefficients are assumed to be co Snow load shape coefficient Equivalent slope for curved roof µ 0° k µ k 15° 15° < µ k 30° Table NA.2 — Drifted s 30° < µ < 60° È1 0,4 0,4 È2 0,8 + 0,4[(µ – 15)/15] 1,2(60 – µ)/30 µ U 60° Snow load shape coefficient È1 È2 NA.2.22 Snow load shape coefficient for a roof abutting abutting and NA.2.21 and close close to to taller taller construction construction works works È3 [BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 5.3.6 (1)] 5.3.6 (1)] È3 È2(60 á)/30 ẩ2(60 á)/30 k k 0 BS EN 1991-1-3:2003, Annex B should be used to determine the drifted snow load case ThisNA.2.21 methodSnow does load shape coe not include the snow load shape coefficient Èw, therefore, no range of values is specified for this [BScoefficient EN 1991-1-3:2003, 5.3.6 (1 for use in the UK BS EN 1991-1-3:2003, Annex B not include the snow load shape NA.2.22 roof abutting abutting and and close close to to taller taller construction construction NA.2.23 Drifted snow load arrangement for a roof for use in the UK works [BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 5.3.6 (3)] 5.3.6 (3)] BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, Annex B should beshould used tobedetermine the drifted snow loadsnow case.loadNA.2.22 Annex B used to determine the drifted case Drifted snow load ar works [BS EN 1991-1-3:2003, NA.2.24 Drifting at projections and obstructions [BS NA.2.23 [BS EN EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 6.2 (2)] 6.2 (2)] BS EN 1991-1-3:2003, Annex B Annex B used to determine the drifted BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, Annex B should beshould used tobedetermine the drifted snow loadsnow case.load case NA.2.23 Drifting at projection NA.2.25 Altitude at which to consider the effects of snow overhanging NA.2.24 overhanging the the edge edge of of aa roof roof BS EN 1991-1-3:2003, Annex B [BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 6.3 (1)] 6.3 (1)] besites usedat foraltitudes sites at altitudes greater 800 sea mNA.2.24 above BS EN 1991-1-3:2003+A1:2015, 1991-1-3:2003, 6.3 should6.3 beshould used for greater than 800 than m above level Altitude at which to sea level [BS EN 1991-1-3:2003, 6.3 (1)] NA.2.25 Calculating the loads caused by snow overhanging the edge of a roof BS EN 1991-1-3:2003, 6.3 shoul NA.2.26 Calculating the [BS EN 1991-1-3:2003, 6.3loads (2)] caused by snow overhanging the edge of a roof [BS EN 1991-1-3:2003+A1:2015, 6.3 (2)] When calculating the load caused by snow overhanging the edge of a roof, the coefficient forNA.2.25 the irregular Calculating the load When calculating load caused by snow in overhanging edge a roof, theEN coefficient for[BS the EN irregular shape of the snow the k should be determined accordancethe with theofNote to BS 1991-1-3:2003, 6.3 1991-1-3:2003, (2) 6.3 (2)] shape of the snow k should be determined in accordance with the Note to BS EN 1991-1-3:2003+A1:2015, When calculating the load cause NA.2.26 6.3 (2) Design situations and load arrangements to be used for different locations shape of the snow k should be de [BS EN 1991-1-3:2003, Annex A] NA.2.27 Design situations and load arrangements to be used for different locations The drifts given in BS EN 1991-1-3:2003, Annex B have been classified as exceptional driftsDesign due NA.2.26 situations an [BS localized EN 1991-1-3:2003+A1:2015, Annex A] to the maritime climate of the UK [BS EN 1991-1-3:2003, Annex The localized drifts given in BS EN 1991-1-3:2003+A1:2015, Annex B have been classified as exceptional Load B2the described in BS EN 1991-1-3:2003, Annex A should be used in place of The localized drifts given in BS drifts case due to maritime climate of the UK BS EN 1991-1-3:2003, 6.2 for local drifting at projections and obstructions to the maritime climate of the U Load case B2 described in BS EN 1991-1-3:2003, Annex A should be used in place of Load case B2 described in BS EN BS EN 1991-1-3:2003+A1:2015, 6.2 for local drifting at projections and obstructions BS EN 1991-1-3:2003, 6.2 for loc © BSI 2007 © The British Standards Institution 2015 NA to BS EN 1991-1-3:2003 en t NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015 Tan Ta ng en t ng Ta G G b P2 30˚ D t gen D D b P1 P3 b/2 P2 P1 b/2 G