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6.1 External masonry walls

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6.1 - Appendix 6.1A
   Suitable wall constructions for use with full cavity insulation
   Map showing categories of exposure to wind driven rain
6.1 - Appendix 6.1B
   Areas of severe exposure to frost attack
6.1 - Appendix 6.1C
   Mortar mixes
6.1 - Appendix 6.1D
   Dpcs and cavity trays
6.1 - Appendix 6.1E
   Durability classification of bricks

Appendix 6.1-A

Suitable wall constructions for use with full cavity insulation
Minimum
insulation thickness (mm)
Exposure
category		 Suitable wall construction Built-in
insulation		 Retro-fill
(other than
UF foam)		 UF
foam
Very Severe Any wall with impervious cladding 50 50 50

Fairfaced masonry with impervious cladding to all walls above ground storey 100 100 N/A

Any wall fully rendered2 75 75 N/A

Fairfaced masonry1 N/A N/A N/A
Severe Any wall with impervious cladding or render2 50 50 50

Fairfaced masonry with impervious cladding or render2 to all walls above ground storey 50 75 50

Fairfaced masonry 75 75 N/A
Moderate Any wall with impervious cladding or render 50 50 50

Fairfaced masonry with impervious cladding or render to all walls above ground storey 50 50 50

Fairfaced masonry 50 75 75
Sheltered Any wall with impervious cladding or render 50 50 50

Fairfaced masonry with impervious cladding or render to all walls above ground storey 50 50 50

Fairfaced masonry 50 50 50

 
N/A - not applicable

Notes

  1. In Very Severe exposure locations fairfaced masonry with full cavity insulation is not permitted.
  2. Render on an external leaf of clay bricks (F2,S1 or F1,S1 designation bricks to BS EN 771) in Severe or Very Severe exposures is not permitted where the cavity is to be fully filled with insulation.
  3. This table covers walls where the external leaf does not exceed 12m in height.
  4. The exposure category of the dwelling is determined by its location on the map showing categories of exposure to wind driven rain.
  5. Fairfaced masonry includes clay, calcium silicate and concrete bricks and blocks and dressed natural stone laid in an appropriate mortar (see Appendix 6.1-C) preferably with struck or weathered or bucket handle joints. Cavity walls of random rubble or random natural stone should not be fully filled.
  6. Recessed mortar joints should not be used.
  7. In Scotland, it is not permissible to fill the full width of the cavity with any thermal insulation at the time of construction.
  8. In Northern Ireland and the Isle of Man it is not permissible to fill the cavity with pumped thermal insulants (for example, UF foam) at the time of construction.

MAP SHOWING CATEGORIES OF EXPOSURE TO WIND DRIVEN RAIN

Map showing categories of exposure to wind driven rain

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Appendix 6.1-B

Areas of severe exposure to frost attack

The tinted areas have a frost incidence over 60 days a year, rainfall over 1000mm per year and an elevation over 90m above sea level.

Areas of severe exposure to frost attack

Map reproduced by permission of Hanson.


The following list identifies the postal areas within which the three criteria for severe exposure to frost attack are met.

Only in a few instances is the whole of the post code district within the area of severe frost exposure.

                   54 
                   40 
                   28 
                   27 
                   26 
                   25 
                   24 
    23              23 
    22        47     22 
    20        2184    19 
 12  1948   14  552083    18 
 11  1747   13  481982    17 
 10  1646   12  471881    1626
 9  1345   11  461777    1519
 8  1244   10  451676    1418
 724 1143   8  441575    1317
 62391042   7  431474    1216
 5228941   6  281372    76
 4217840   4 132712658  765
 3202739   3 122611647 5644
52151637 962 11238634 3433
311305878418814162332211
AABBBDBLCACFCHDDDEDGDHDLEHFKGHDHGHRHXIVKA

 

    57                
    55      21         
    54      20         
    41    16 1941        
    40    15 1840        
    33    14411739        
    32    13401638        
    28    12381537 48      
14   27    11371136 44  25   
13 23 26 12  10361035 40  24   
12 22 25 11 44935934 3917 23   
11 21824 10 8834833 3316 22   
10 20723 9717733732 3215 21   
9 12622 8666632631 2014 2071  
8 10521 7495527530 1913 1911  
7 9420 6484426426301312 188 22
6 8316 3473325325111111 175 21
5 6215 246222422310101013162 18
31321112411911231226961010196
KWKYLALDLLMMLNENPOLPAPHSSASKSTSYTDTSYO

 partly within
 wholly within

Reproduced by permission of the London Brick Company Ltd.

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Appendix 6.1-C

Mortar mixes

Unless recommended otherwise by the brick manufacturer, the mixes in the table below should be used for clay bricks.

In the case of concrete or calcium silicate bricks, particular attention should be paid to manufacturers' recommendations.

Mortar mixes using ordinary Portland or sulfate-resisting cements where required (see also Design clauses 6.1- D5(b) and (d)).




Location
Recommended
cement: lime: sand mix		 Recommended
cement: sand mix with air-entraining
plasticiser		 Recommended
masonry cement:
sand mix		 Mortar
designation
to BS5628-3
General wall area above dpc
 in areas of Severe or Very Severe exposure - high durability 1 : ½ : 4½ 1 : 3½ 1 : 3 (ii)
other exposure categories - general use 1 : 1 : 5½ 1 : 5½ 1 : 4½ (iii)
Below dpc level and in chimney stacks - high durability 1 : ½ : 4½ 1 : 3½ 1 : 3 (ii)
Cappings, copings and sills - low permeability 1 : 0 to ¼ : 3 - - (i)

Air-entraining plasticiser can be incorporated in the following general use and high durability mortars:

1 : 1 : 5½, cement : lime : sand, or

1 : 1 : 4½, cement : lime : sand.

Retarded mortar

Retarded mortar and most pre-mixed mortars can be used over a longer period of time than site mixed, cement : lime : sand mortars. The timescale of use is defined by the manufacturer, whose advice should be followed:

  • protect retarded mortar against freezing prior to use
  • do not use retarded mortar beyond the time for which it is effective
  • because of delayed setting, temporary bracing of larger walls, for example gable peaks and long walls, may be necessary.

Admixtures and additives

Where air-entraining plasticisers or other additives are to be used, follow manufacturers' instructions:

  • do not overdose, 'more is not better'
  • an air entraining agent can help reduce frost damage but it is not an anti-freeze
  • do not use unauthorised additives.
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Appendix 6.1-D

Dpcs and cavity trays

Some positions where dpcs and cavity trays should be provided:

LocationProvision of dpcs and cavity trays
Base of walls, piers, etcA dpc should be provided a minimum 150mm above adjoining surfaces and linked with the dpm in solid floors.
dpc should be provided a minimum 150mm above adjoining surfaces
Base of partitions built off oversite where there is no integral dpmDpc should be full width of partition.
Base of wall built off beam, slab, etcDetail to prevent entry of damp by driving rain.
Parapet

(1) Beneath coping, and
(2) 150mm above adjoining roof surface to link with the roof upstand.
In cavity walls over openings, air bricks and the like
 A cavity tray should be provided to direct to the outside any water that enters the cavity. The cavity tray should fully protect the opening.
At the horizontal abutment of all roofs over enclosed areas
and balconies to walls
A cavity tray should be provided 150mm above the adjoining roof or balcony surface. The tray should be lapped over any roof upstand or flashing to ensure water penetrating into the cavity does not enter the enclosed area.
At sloping abutments of all roofs over enclosed areas to cavity walls
A stepped cavity tray should be provided above the roof surface and linked to any roof upstand or flashing to ensure any water penetrating into the cavity does not enter the enclosed area.
DoorstepsA dpc should be provided behind a doorstep where it is higher than a wall dpc.

A dpc should be provided behind a doorstep where higher than a wall dpc

SillsWhere precast concrete or similar sills incorporate joints or are of a permeable material, a dpc should be provided beneath them for the full length and be turned up at the back and the end of the sill.
Jambs in cavity
The reveal should be protected throughout its width by a continuous dpc. The width of the dpc should be sufficient to be fixed to, or overlap, the frame and fully protect the reveal.

For Severe and Very Severe exposure conditions: rebated reveal construction, with or without closed cavity and dpc.



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Appendix 6.1-E

Durability classification of bricks

BS EN 771-1 classifies clay bricks according to their freeze/thaw resistance and active soluble salts content as follows:

DurabilityFreeze/thaw resistance
Active soluble salts content
F2,S2
Freeze/thaw resistant (F2), durable in all building situations
Low (S2)
F2,S1
Freeze/thaw resistant (F2), durable in all building situations
Normal (S1)
F1,S2
Moderately freeze/thaw resistant (F1), durable except when saturated and subject to repeated freezing and thawing
Low (S2)
F1,S1
Moderately freeze/thaw resistant (F1), durable except when saturated and subject to repeated freezing and thawing
Normal (S1)
F0,S2
Not freeze/thaw resistant (F0), liable to be damaged by freezing and thawing
Low (S2)
F0,S1
Not freeze/thaw resistant (F0), liable to be damaged by freezing and thawing
Normal (S1)

 
Calcium silicate and concrete bricks contain no significant active soluble salts. Information on their durability is given in Materials clause 6.1 - M2(b).

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