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. 1
corrigendum no. 1

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 0 580 91564 2

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. 1

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
1
1
8
8

Bibliography

9

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

3
4

5
7
4
5
6

i


1

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
— 2 (3)
5.2 (5)
5.3.6 (3)
—
(3)
— 1.1
2 (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 1 500
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 1 500 m. For altitudes greater than
NA.2scope
Nationally
Determined
Parameters
1 500 m specialist advice should be sought from the Meteorological Office on the snow loads likely to occur
NA.2.1
Altitudes greater than 1 500 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
1 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,
2 (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,
2 (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, 2 (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, 2 (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
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
­­­­­­­­­­­­­­­­­­­
=
[
0
,
15
+
(
0
,
1Z
+
0
,
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
1 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.
1 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
2
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
2


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)

1

0,30


2

0,40

3

0,50

4

0,60

5

0,70

6,5

0,85

NA

NB

NF

NG

NL


NM

5

IN

IR

NE

NH

NJ

NK

10

9

8

NO NP

7

NT

NU


NY

NZ

HT

SE

TA    

6

5

IO

IS

IW

1

ND

SC

SH

SD
SJ


SMSN

SO

SK TF

3

TL

SP

TM

IX

2

4

HT

IT

1

0

NC


11

IJ

2

0

HZ

NX

IH

IM

IV

HY

NS

3

IQ

HT

12


IC

IG

IL

HU

NN

4

IF

HT

NR

IB

7

HP

3

SR

TQ


SU

SS

TR

2

ST

1

SW
SY

TW

TV

SZ

1

SX
0

1

2


7
3

4

5

6

0

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

3

© The British Standards Institution 2015

3


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)]
2

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 )
2

Case (ii)
ls2

P 1,(D )
1

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

5 < 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
<)/30
µ1 < 60º

0,8(601,6– µ)/30
1,2(60

α ≥ 60
µ10U 60º

0,0



NA.2.18 Drifted snow load arrangement for multi-span roofs [BS EN 1991-1-3:2003, 5.3.4 (3)]
BS EN 1991-1-3:2003, Annex B should be used in place of the drift load arrangement given in
BS EN 1991-1-3:2003, 5.3.4 (3).
NA.2.19 Snow load shape coefficient for cylindrical roofs [BS EN 1991-1-3:2003, 5.3.5 (1)]
The roof shape coefficient È3 should take an upper value of 2,0 as recommended in BS EN 1991-1-3.

4

© The British Standards Institution 2015


NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015
NA.2.15 Exposure coefficient used for determining snow load on a roof
[BS EN 1991-1-3:2003, 5.2 (7)]
NA.2.15 Exposure coefficient used for determining snow load on a roof
The
value5.2
for (7)]
exposure coefficient Ce in the UK is 1,0 for all topographies.
[BS recommended

EN 1991-1-3:2003,
NA.2.16
Thermal value
coefficient
used to
accountCfor
the reduction of snow load on roofs with high
The recommended
for exposure
coefficient
e in the UK is 1,0 for all topographies.
thermal transmittance [BS EN 1991-1-3:2003, 5.2 (8)]
NA.2.16
Thermal
coefficient
used to account
for the roofs
reduction of snow load on roofs with high
NA.2.18
Drifted snow
arrangement
forCpitched
The
recommended
valueload
for
thermal
coefficient
in the
t 5.2

thermal
transmittance
[BS
EN5.3.3
1991-1-3:2003,
(8)]UK is 1,0 for all roofing materials.
[BS EN 1991-1-3:2003+A1:2015,
(4)]
NA.2.17
Drifted snow
load
arrangement
forCpitched
roofs
[BS
EN
5.3.3 (4)]
The
recommended
value
for thermal
coefficient
the UK
is 1,0
for
all 1991-1-3:2003,
roofing
t inTable
The load
arrangement

given
in Figure
NA.3 and
NA.2
should
be usedmaterials.
in place of
BS EN
1991-1-3:2003+A1:2015,
5.3.3 (4)
to determine
the
drifted
snow used
load on
a duo-pitched
in
The
load
arrangement
Figure
NA.2
and
NA.1
should
in place
of 5.3.3roof
NA.2.17
Drifted
snowgiven

loadin
arrangement
for Table
pitched
roofs
[BSbe
EN 1991-1-3:2003,
(4)]
the UK.
BS
EN 1991-1-3:2003, 5.3.3 (4) to determine the drifted snow load on a duo-pitched roof in the UK.
The load arrangement given in Figure NA.2 and Table NA.1 should be used in place of
BS EN 1991-1-3:2003, 5.3.3 (4) to determine the drifted snow load on a duo-pitched roof in the UK.
P 1,(D )
2

Case (ii)

P 1,(D )
2

ls2

Case (ii)
Case (iii)

P 1,(D )
1

Case (iii)


P 1,(D )
1

ls2
ls1
ls1

lsi = bi

D1

D2

D1

D2

lsi = bi
b1

b2

b1

b2

Figure NA.2
— Drifted
snow

load
arrangement
forfor
a duo-pitched
roof
in the
UKUK
Figure
NA.3
— Drifted
snow
load
arrangement
a duo-pitched
roof
in the
Figure NA.2 — Drifted snow load arrangement for a duo-pitched roof in the UK
Table NA.1
— Drifted
snow
load
shape
coefficient
for for
a duo-pitched
roof
in the
UKUK
Table
NA.2

— Drifted
snow
load
shape
coefficient
a duo-pitched
roof
in the

È1

Snow
load shape
Table
NA.1
coefficent
Snow load shape
coefficent

of pitch for
of roof
(µi, i =1,2)
— Drifted snow load shape Angle
coefficient
a duo-pitched
roof in the UK
0º k µ1 k 15º

0,80º k µ k 15º
1


15º
< µ1 k
< µ1 < 60º
Angle
of30º
pitch of roof (µi,30º
i =1,2)

0,8 + 0,4(µ
– 15)/15
15º < µ k 30º
1

1,2(60
– µ)/30
30º < µ < 60º
1

µ1 U 60º

0,0

µ1 U 60º

È1
0,8
0,8 + 0,4(µ – 15)/15
1,2(60 – µ)/30
0,0

NA.2.19 Drifted snow load arrangement for multi-span roofs
NA.2.18
roofs [BS EN 1991-1-3:2003, 5.3.4 (3)]
[BS EN 1991-1-3:2003+A1:2015, 5.3.4 (3)]
BS
EN 1991-1-3:2003,
B should be used
place of the roofs
drift load
given in
NA.2.18
Drifted snowAnnex
load arrangement
forinmulti-span
[BSarrangement
EN 1991-1-3:2003,
5.3.4 (3)]
BS EN 1991-1-3:2003+A1:2015,
1991-1-3:2003, 5.3.4 (3). Annex B should be used in place of the drift load arrangement given in
BS EN 1991-1-3:2003+A1:2015,
5.3.4
(3).
1991-1-3:2003, Annex B should be used in place of the drift load arrangement given in
NA.2.19
Snow load shape
coefficient for cylindrical roofs [BS EN 1991-1-3:2003, 5.3.5 (1)]
BS EN 1991-1-3:2003,
5.3.4 (3).
NA.2.20 Snow load shape coefficient for cylindrical roofs
The

shape
È3 coefficient
should
take(1)]
an upper
value ofroofs
2,0 as[BS
recommended
in BS EN
1991-1-3.
[BS roof
EN 1991-1-3:2003+A1:2015,
5.3.5
NA.2.19
Snow coefficient
load shape
for
cylindrical
EN 1991-1-3:2003,
5.3.5
(1)]
The roof shape coefficient È3 should take an upper value of 2,0 as recommended in BS EN 1991-1-3.

4

© BSI 2007

4

© BSI 2007


© The British Standards Institution 2015

5


NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015

NA to BS EN 1991-1-3:2003

NA.2.21 Drifted snow load arrangement for cylindrical roofs
[BS EN 1991-1-3:2003+A1:2015,
5.3.5 (3)] for cylindrical roofs [BS EN 1991-1-3:2003, 5.3.5 (3)]
NA.2.20
Drifted snow load arrangement

NA.4
Table
NA.3
bein
used
in of
place of
The load arrangement given in Figure
Figure NA.3
andand
Table
NA.2
shouldshould
be used

place
BS EN 1991-1-3:2003+A1:2015,
1991-1-3:2003, 5.3.5 (3). 5.3.5 (3).
NA.2.20 Drifted snow load ar
NA.4
are defined
as follows:
The angles shown in Figure
Figure NA.3
are defined
as follows:
¸ is the angle between the horizontal and the tangent to the roof at the eaves.

The load arrangement given in F
BS EN 1991-1-3:2003, 5.3.5 (3).

where the tangent to the surface makes an angle of 60 with the horizontal.

à for á k 60 is the angle betwee

The angles shown in Figure NA.
à for á k 60° is the angle between the horizontal and a line drawn from the crown to the eaves.
á isofthe
à for ¸ > 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 à
where
à is
forgreater
á > 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

0,4

0,4

0

È2

0

0,8 + 0,4[(µ – 15)/15]

1,2(60 – µ)/30

0

µ U 60°
Snow load shape
coefficient

0 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)]
ẩ3

0

ẩ2(60 á)/30

ẩ2(60 á)/30

0 k à k 1

0
0
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


6
© BSI 2007

© The British Standards Institution 2015

5


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 <_ 60˚


G < 30˚

Tan

gen

t

G

t

gen

Tan

30˚

Ta

ng
en
t

D

60˚

b


P2
P1

G < 60˚

Figure NA.3
— Drifted
snow
load
arrangements
forfor
a cylindrical
roof
in in
the
UK
Figure
NA.4
— Drifted
snow
load
arrangement
a cylindrical
roof
the
UK

© The British Standards Institution 2015
6


© BSI 2007
7


NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015

NA to BS EN 1991-1-3:2003

NA.3
status of
of informative
informative annexes
annexes
NA.3 Decisions
Decisions on
on the
the status
NA.3.1
snow load
load maps
maps [BS
[BS EN
EN 1991-1-3:2003+A1:2015,
1991-1-3:2003, Annex C]Annex C]
NA.3.1 European
European ground
ground snow
BS
Annex C should

be used
tobe
determine
ground snow
loadssnow
in the
UK.in
The
BS EN
EN 1991-1-3:2003,
1991-1-3:2003+A1:2015,
Annex not
C should
not
used to determine
ground
loads
theground
UK.
snow
load map
given
Figure
NA.1
shouldNA.1
be used.
The ground
snow
loadinmap
given

in Figure
should be used.
NA.3.2 Adjustment of the ground snow load according to return period
[BS EN 1991-1-3:2003,
Annex D]Annex D]
1991-1-3:2003+A1:2015,
BS EN 1991-1-3:2003,
Annex D Annex
may only
be used
UKinfor
annual probabilities
of
1991-1-3:2003+A1:2015,
D may
onlyinbethe
used
thedetermining
UK for determining
annual probabilities
exceedance
smaller
than
0,2.
of exceedance
smaller
than
0,2.
NA.3.3 Bulk weight density of snow [BS EN 1991-1-3:2003+A1:2015,
1991-1-3:2003, Annex E]Annex E]

BS EN 1991-1-3:2003,
Annex E may
be Eused
UK.
1991-1-3:2003+A1:2015,
Annex
mayinbethe
used
in the UK.
NA.4 References to non-contradictory complementary information
information
NA.4.1 Specialist aspects of snow loading [BS EN 1991-1-3:2003+A1:2015,
1991-1-3:2003, 1.1 (8)] 1.1 (8)]
NA.4.1.1 Snow loading on bridges
Snow loads should be considered in accordance with local conditions. For those local conditions prevailing
in the United Kingdom, this loading may generally be ignored. However, there are circumstances, e.g. for
opening bridges, covered bridges including roofed footbridges, or where stability due to permanent loads is
critical, when snow loading should be taken into account in the design.
On ordinary bridges the accumulation of any material quantity of snow will effectively reduce the traffic
loads, probably by amounts greater than the snow loads, but certainly to such an extent that the combined
mass of snow and traffic loading will not exceed the nominal live load. On opening bridges, however, snow
load can be significant. These bridges are likely to be designed to move under permanent loads only and
the added weight could have serious adverse effects on machinery and moving parts. On swing bridges too,
where snow might have been cleared from one wing of the rotating structure but not the other, the stability
against overturning could be impaired.
NA.4.1.2 Combination of actions on bridges
The combination of snow and wind loads, and the value of Ò,, for the design of bridges is given in
1)
1990:2002+A1:2005,
A2.

BS EN 1990:2002,
Annex A2Annex
.
NA.4.2 Snow load shape coefficients for exceptional snow
snow loads
loads
1991-1-3:2003+A1:2015,
Additional information
information concerning
concerningthe
thesnow
snowload
loadshape
shapecoefficients
coefficientsgiven
givenininBS
BSEN
EN
1991-1-3:2003,
Annex B is given
given in
in BRE
BRE Digest
Digest439,
439,Roof
Roofloads
loadsdue
duetotolocal
localdrifting
driftingofofsnow

snow[1].
[1].
NA.4.3 Snow load shape coefficients for roofs intersecting at right angles
Shape coefficients and drift lengths for roofs intersecting at 90º are given in BRE Digest 439, Roof loads
due to local drifting of snow [1].

1)

In preparation.

©
8 BSI 2007

7
© The British Standards Institution 2015


NA to BS EN 1991-1-3:2003

NA+A1:2015 to BS EN 1991-1-3:2003+A1:2015

Bibliography
Standards publications
—structural
Basis of structural
BS EN 1990:2002+A1:2005,
1990:2002, Eurocode Eurocode
— Basis of
design. design.
UK National

AnnexAnnex
for Eurocode
— Basis
structural
design. design.
NA to BS EN 1990,
1990:2002,
UK National
for Eurocode
0 —ofBasis
of structural
NA to BS EN 1991-1-1, UK National Annex to Eurocode 1: Actions on structures — Part 1-1: General
actions — Densities, self-weight, imposed loads for buildings.
Other publications
[1] BRE Digest 439, Roof loads due to local drifting of snow, Watford: BRE, 1999.

© The British Standards Institution 2015
8

© BSI 2007
9


NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW

British Standards Institution (BSI)
BSI is the national body responsible for preparing British Standards and other
standards-related publications, information and services.
BSI is incorporated by Royal Charter. British Standards and other standardization
products are published by BSI Standards Limited.


About us

Revisions

We bring together business, industry, government, consumers, innovators
and others to shape their combined experience and expertise into standards
-based solutions.

Our British Standards and other publications are updated by amendment or revision.

The knowledge embodied in our standards has been carefully assembled in
a dependable format and refined through our open consultation process.
Organizations of all sizes and across all sectors choose standards to help
them achieve their goals.

Information on standards
We can provide you with the knowledge that your organization needs
to succeed. Find out more about British Standards by visiting our website at
bsigroup.com/standards or contacting our Customer Services team or
Knowledge Centre.

Buying standards
You can buy and download PDF versions of BSI publications, including British
and adopted European and international standards, through our website at
bsigroup.com/shop, where hard copies can also be purchased.
If you need international and foreign standards from other Standards Development
Organizations, hard copies can be ordered from our Customer Services team.

Subscriptions

Our range of subscription services are designed to make using standards
easier for you. For further information on our subscription products go to
bsigroup.com/subscriptions.
With British Standards Online (BSOL) you’ll have instant access to over 55,000
British and adopted European and international standards from your desktop.
It’s available 24/7 and is refreshed daily so you’ll always be up to date.
You can keep in touch with standards developments and receive substantial
discounts on the purchase price of standards, both in single copy and subscription
format, by becoming a BSI Subscribing Member.
PLUS is an updating service exclusive to BSI Subscribing Members. You will
automatically receive the latest hard copy of your standards when they’re
revised or replaced.
To find out more about becoming a BSI Subscribing Member and the benefits
of membership, please visit bsigroup.com/shop.
With a Multi-User Network Licence (MUNL) you are able to host standards
publications on your intranet. Licences can cover as few or as many users as you
wish. With updates supplied as soon as they’re available, you can be sure your
documentation is current. For further information, email

BSI Group Headquarters
389 Chiswick High Road London W4 4AL UK

We continually improve the quality of our products and services to benefit your
business. If you find an inaccuracy or ambiguity within a British Standard or other
BSI publication please inform the Knowledge Centre.

Copyright
All the data, software and documentation set out in all British Standards and
other BSI publications are the property of and copyrighted by BSI, or some person
or entity that owns copyright in the information used (such as the international

standardization bodies) and has formally licensed such information to BSI for
commercial publication and use. Except as permitted under the Copyright, Designs
and Patents Act 1988 no extract may be reproduced, stored in a retrieval system
or transmitted in any form or by any means – electronic, photocopying, recording
or otherwise – without prior written permission from BSI. Details and advice can
be obtained from the Copyright & Licensing Department.

Useful Contacts:
Customer Services
Tel: +44 845 086 9001
Email (orders):
Email (enquiries):
Subscriptions
Tel: +44 845 086 9001
Email:
Knowledge Centre
Tel: +44 20 8996 7004
Email:
Copyright & Licensing
Tel: +44 20 8996 7070
Email: