6.1 External masonry walls

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

MAP SHOWING CATEGORIES OF EXPOSURE TO WIND DRIVEN RAIN

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.

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									21	84					19
	12			19	48				14			55	20	83					18
	11			17	47				13			48	19	82					17
	10			16	46				12			47	18	81					16	26
	9			13	45				11			46	17	77					15	19
	8			12	44				10			45	16	76					14	18
	7	24		11	43				8			44	15	75					13	17
	6	23	9	10	42				7			43	14	74					12	16
	5	22	8	9	41				6			28	13	72					7	6
	4	21	7	8	40				4		13	27	12	65	8			7	6	5
	3	20	2	7	39				3		12	26	11	64	7		5	6	4	4
5	2	15	1	6	37		9	6	2		11	23	8	63	4		3	4	3	3
3	1	13	0	5	8	7	8	4	1	8	8	14	1	62	3	3	2	2	1	1
AA	BB	BD	BL	CA	CF	CH	DD	DE	DG	DH	DL	EH	FK	G	HD	HG	HR	HX	IV	KA

 

				57
				55							21
				54							20
				41					16		19	41
				40					15		18	40
				33					14	41	17	39
				32					13	40	16	38
				28					12	38	15	37		48
14				27					11	37	11	36		44			25
13		23		26		12			10	36	10	35		40			24
12		22		25		11		44	9	35	9	34		39	17		23
11		21	8	24		10		8	8	34	8	33		33	16		22
10		20	7	23		9	71	7	7	33	7	32		32	15		21
9		12	6	22		8	66	6	6	32	6	31		20	14		20	71
8		10	5	21		7	49	5	5	27	5	30		19	13		19	11
7		9	4	20		6	48	4	4	26	4	26	30	13	12		18	8		22
6		8	3	16		3	47	3	3	25	3	25	11	11	11		17	5		21
5		6	2	15		2	46	2	2	24	2	23	10	10	10	13	16	2		18
3	13	2	1	11	24	1	19	1	1	23	1	22	6	9	6	10	10	1	9	6
KW	KY	LA	LD	LL	M	ML	NE	NP	OL	PA	PH		S	SA	SK	ST	SY	TD	TS	YO

partly within

wholly within

Reproduced by permission of the London Brick Company Ltd.

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)).

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.

Appendix 6.1-D

Dpcs and cavity trays

Some positions where dpcs and cavity trays should be provided:

Location	Provision of dpcs and cavity trays
Base of walls, piers, etc	A dpc should be provided a minimum 150mm above adjoining surfaces and linked with the dpm in solid floors.
Base of partitions built off oversite where there is no integral dpm	Dpc should be full width of partition.
Base of wall built off beam, slab, etc	Detail 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.
Doorsteps	A dpc should be provided behind a doorstep where it is higher than a wall dpc.
Sills	Where 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.

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:

Durability	Freeze/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).