Building Regulations: Technical Standards Part J: page 4

Building Regulations: Technical Standards

J3 Buildings in purpose groups 2 to 7

STANDARDS FOR BUILDINGS IN PURPOSE GROUPS 2 TO 7

J3.1 A building in purpose groups 2 to 7 must have provision for conservation of fuel and power in accordance with J3.2 or J3.3 or J3.4.

ELEMENTAL STANDARDS FOR BUILDINGS IN PURPOSE GROUPS 2 TO 7 [Note 1]

J3.2 The specified elements of a building in purpose groups 2 to 7 must have U-values and areas of glazing and doors not exceeding those prescribed in the tables to this standard.

Table 1 to J3.2: U-values of elements [Note 2]

	U-values (W/m²K)
	1	2	3	4	5	6	7
*Purpose* *group* [Note 3]	*exposed* walls and basement walls	*exposed* floors, ground floors and basement floors [Note 3]	*semi-* *exposed* walls and floors	pitched roofs with a roof space [Note 4]	roofs other than those in col. 4	windows, personnel doors and rooflights [Note 5]	vehicle access and similar large doors
2	0.45	0.45	0.6	0.25	0.35	3.3	0.7
3,4,5,6,7	0.45	0.45	0.6	0.25	0.45	3.3	0.7

Notes:

1. For guidance on meeting elemental requirements see Appendix D.
2. For information on meeting elemental U-values in the absence of manufacturer's information certified by an independent test house, see Appendix E.
3. For calculating U-values for basement walls and floors see BRE Information Paper IP 14/94.
4. A roof space here refers to a clear volume not having an attic room or similar accommodation which would impede the free ventilation of the space.
5. 3.3 W/m² is an indicative value for double glazing and doors from which the areas in Table 2 to this standard have been derived. Where those elements have better U-values which have been certified by an independent test house or are as those given in Table 3 to this standard then the maximum areas in Table 2 may be amended in accordance with Table 4 to this standard. Single glazing with secondary glazing may be used provided that it has a comparable performance.

Table 2 to J3.2: Percentage areas of windows, doors and rooflights for buildings in purpose groups 2 to 7 [Note 1]

*purpose group*	windows and doors as % of exposed wall area	rooflights as % of roof area
2 3,4,5 [Note 2] 6,7 [Note 2]	30 40 15	20 20 20

Notes:

1. For information on meeting areas of glazing and doors see Appendix E.
2. Larger areas of windows, doors (both personnel and vehicle access) and rooflights are permitted
provided there is a compensating improvement in the average U-value. Table 4 to J3.2 indicates
the variation in the area of openings which may be achieved within this constraint.

Table 3 to J3.2: Indicative U-values (W/m²K) for windows, doors and rooflights for a building in purpose groups 2 to 7

Frame Type	wood		metal		thermal break		pvc-u
Air gap in sealed unit in mm	6	12	6	12	6	12	6	12
Windows
double glazed	3.3	3.0	4.2	3.8	3.6	3.3	3.3	3.0
double glazed, low E	2.9	2.4	3.7	3.2	3.1	2.6	2.9	2.4
double glazed, argon fill	3.1	2.9	4.0	3.7	3.4	3.2	3.1	2.9
double glazed, low E, argon fill	2.6	2.2	3.4	2.9	2.8	2.4	2.6	2.2
triple glazed	2.6	2.4	3.4	3.2	2.9	2.6	2.6	2.4
single glazed	4.7	5.8	5.3	4.7
Rooflights
double glazed and at less than 70° from the horizontal [Note 1]	3.6	3.4	4.6	4.4	4.0	3.8	3.6	3.4
Doors [Note 2]
half double glazed	3.1	3.0	3.6	3.4	3.3	3.2	3.1	3.0
fully double glazed	3.3	3.0	4.2	3.8	3.6	3.3	3.3	3.0
single glazed	4.7		5.8		5.3		4.7
half single glazed	3.7
solid timber panel	3.0

Notes:

1. At 70° or more to the horizontal, rooflights are treated as windows.
2. Exposed doors with single-glazed panels are acceptable provided that they do not increase the average U-value for windows, doors and rooflights beyond 3.3 W/m². Doors and windows with single-glazed panels protected by enclosed draught-proofed spaces (which may be unheated) can be assumed to have a U-value of 3.3 W/m²K.

Table 4 to J3.2: Permitted variation in windows, rooflights and personnel doors for buildings in purpose groups 2 to 7 [Note 1]

Average U-value (W/m²K)	*Purpose groups*			Rooflights *(all purpose groups)*
	2	3, 4 & 5	6 & 7	Rooflights *(all purpose groups)*
	% of wall area			% of roof area
2.0 2.1 2.2 2.3 2.4	55 52 49 46 44	74 69 65 62 58	28 26 24 23 22	37 35 33 31 29
2.5 2.6 2.7 2.8 2.9	42 40 38 36 35	56 53 51 49 47	21 20 19 18 17	28 27 25 24 23
3.0 3.1 3.2 3.3 3.4	34 32 31 30 29	45 43 41 40 39	17 16 16 15 14	22 22 21 20 19
3.5 3.6 3.7 3.8 3.9	28 27 26 26 25	37 36 35 34 33	14 14 13 13 12	19 18 18 17 17
4.0 4.1 4.2 4.3 4.4	24 23 23 22 22	32 31 30 30 29	12 12 11 11 11	16 16 15 15 14
4.5 4.6 4.7 4.8 4.9 5.0	21 21 20 20 19 19	28 27 27 26 26 25	11 10 10 10 10 9	14 14 13 13 13 13

Note:

1. The data in this table have been derived assuming a constant heat loss through the walls and roofs. The constant heat loss amounts to the loss through the wall or roof component plus the loss through the basic area allowance of windows, personnel doors or rooflights respectively as calculated using the U-values in Table 1 to J3.2 and the percentage areas in Table 2 to J3.2.

CALCULATION STANDARD [Note 1]

J3.3 Under this method the individual values in Tables 1 and 2 to J3.2 may be exceeded if the total rate of heat loss through the fabric elements of a proposed building would not exceed the total rate of heat loss through the fabric elements of a notional building complying with the values in Tables 1 and 2 to J3.2.

In using this method the following rules apply in addition to those in J1.3 -

a. If the U-value of a floor next to the ground without insulation in the proposed building is less than 0.45 W/m²K then that lower value must be used in the notional building.

b. If the total area of windows, doors and rooflights in the proposed building is less than the total area obtained by applying Table 2 to J3.2 then the smaller area must be used in the notional building.

Procedure

c. Calculate the total rate of heat loss for the proposed building in accordance with the table to this standard.

d. Repeat the calculation for a notional building in accordance with the table to this standard but using the values given in Tables 1 and 2 to J3.2.

e. The proposed building would meet the relevant standard if the total rate of heat loss is less than that for the notional building.

Table to J3.3

Calculated total rate of heat loss through the enclosing fabric

Element	Gross Area in m2	Openings in m2	Net Area in m2	U-value in W/m2K(W/K)	AxU
exposed walls & basement walls	_________—________		= ________x________		= ________
exposed floors, ground floors & basement floors	_________—________		= ________x________		= ________
semi-exposed walls & floors	_________—________		= ________x________		= ________
pitched roofs with a roof space	_________—________		= ________x________		= ________
other roofs	_________—________		= ________x________		= ________
TOTAL A					= ________
windows			________x________		= ________
personnel doors			________x________		= ________
rooflights			________x________		= ________
vehicle & similar large access doors			________x________		= ________
TOTAL B					= ________
TOTAL RATE OF HEAT LOSS = TOTAL A + TOTAL B					= ________

Note:

For example calculations see Appendix H.

ENERGY USE STANDARDS

J3.4* Under this method the annual energy consumption of the proposed building must be shown by calculation not to exceed that of a notional building complying with the elemental standards in J3.2. Any recognised energy use method acceptable to the local authority may be used, including those taking into account heat and solar gains.