SCOTTISH EXECUTIVE

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Building Regulations: Technical Standards

The standards

J1 Application of Part J

J1.1 This Part sets out the required standards for Regulation 22.

J1.2 The standards apply to all buildings as follows -

Purpose group 1: J1, J2, J4 & J5

Purpose groups 2 to 7: J1, J3, J4, J5 & J6

except -

a. the standards do not apply to a building or part of a building specified in regulation 22(2). (Note that Regulation 22 does apply even if the intended level of provision of heating cannot be established because the use of the building is not known at the construction stage, e.g. speculative development.);

b. J5.2 to J5.4 do not apply to systems installed for commercial or industrial purposes;
and

c. J5.1 to J5.4 do not apply to a building in purpose groups 2 to 7 -

i. where the area heated is 125 m² or less, or

ii. where the system heats or stores hot water for an industrial process.

RULES FOR THE USE OF THIS PART

J1.3* In demonstrating that the Technical Standards are met the following rules apply -

a. when calculating U-values any thermal bridging elements such as normal mortar joints, timber joists and window frames must be taken into account using the proportional area method described in Appendix A. [Note 1];

b. the fabric of a building must be constructed to limit thermal bridging;

c. in a building in purpose group 1,

i. no exposed floor or wall may have a U-value more than 0.7 W/m²K,

ii. no exposed roof may have a U-value more than 0.35 W/m²K;

d. in a building of purpose group 2,

i. no exposed floor or wall may have a U-value more than 0.7 W/m²K,

ii. no exposed roof may have a U-value more than 0.45 W/m²K;

e. in a building of purpose groups 3 to 7,

i. no exposed floor or wall may have a U-value more than 0.7 W/m²K,

ii. no exposed roof may have a U-value more than 0.7 W/m²K;

f. the following are to be treated as exposed walls,

i. external walls, other than those enclosing a ventilated space,

ii. semi-exposed walls adjoining a ventilated space,

iii. any part of a roof which has a pitch of 70° or more to the horizontal;

g. any part of a floor which serves as a roof (e.g. an open deck) is to be treated as a roof;

h. in calculating areas,

i. the area of a floor, wall or roof is to be the internal surface area of each element measured between finished internal faces of the enclosing fabric of the building disregarding partitions, ducts, stairways etc and, in the case of a roof, in the plane of the insulation,

ii. the area of an opening is to be measured internally from reveal to reveal and from head to cill, and

iii. in a shop, display windows at an access level may be ignored;

j. any part of an exposed wall which extends below the level of the lowest floor or above the level of a roof which have the required U-values may be ignored;

k. in the absence of manufacturer's information which has been certified by an independent test house, thermal conductivities and thermal transmittance (U-values) may be taken from the tables in Appendix E.

Note:

1. Thermal bridging may be disregarded where the difference in thermal resistance between bridging and bridged material is less than 0.1 m²K/W. For example, normal mortar joints need not be taken into account in calculations for brickwork but must be taken into account for lightweight insulating blockwork.

J2 Buildings in purpose group 1

STANDARDS FOR BUILDINGS IN PURPOSE GROUP 1

J2.1 A building in purpose group 1 must have provision for conservation of fuel and power in accordance with J2.2 or J2.3 or J2 4.

ELEMENTAL STANDARDS (METHOD 1) [Note 1]

J2.2 Under this method the specified elements of a building in purpose group 1 must have U-values and areas of glazing and doors not exceeding those prescribed in the tables to this standard.

Table 1 to J2.2: U-values of elements and areas of glazing and doors for buildings in purpose group 1 [Note 2]

Notes:
1. For guidance on meeting elemental requirements see Appendix D, Table D1.
2. For information on meeting elemental U-values and areas of glazing and doors 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. 22.5% applies for the indicative U-values, of 3.0 W/m² and 3.3 W/m² for double glazing and doors (for SAP energy ratings not more than 60 and more than 60 respectively). Where those elements have better U-values which have been certified by an independent test house or are as those given in Table 2 to this standard then the maximum area may be amended in accordance with Table 3 to this standard. Single glazing with secondary glazing may be used provided that it has a comparable performance.
6. For information on the Standard Assessment Procedure (SAP) see Appendix C.

Table 2 to J2.2: Indicative U-values (W/m²K) for windows, doors and rooflights for a building in purpose group 1

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/m²K. 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 3 to J2.2: Permitted variation in window and door areas for buildings in purpose group 1
[Note 1]

Note:

1. The data in this table have been derived assuming a constant heat loss through the walls amounting to the loss when the basic allowance for openings of 22.5% of floor area and the U-values given in Table 1 apply. It is also assumed for the purposes of this table that there are no rooflights. Where the proposed building differs from these assumptions this table does not apply and a specific calculation must be made.

TARGET U-VALUE STANDARDS (METHOD 2) [Note 1]

J2.3 Under this method the average U-value calculated in accordance with Appendix G must not exceed the following targets -

a. if the SAP energy rating [Note 2] is 60 or less:

formula

b. if the SAP energy rating [Note 2] is 61 or more:

formula

where -

c. total floor area = the area of all floors, including semi-exposed floors, of the building measured between the internal faces of the enclosing fabric of the building disregarding partitions, ducts, stairways etc.;

d. total exposed surface area = the total internal surface area of the exposed elements of the building measured across windows, doors, rooflights etc. and including the ground floor but excluding semi-exposed elements. Semi-exposed elements must have a U-value not exceeding 0.6 W/m²K and be omitted from the calculation. Areas are measured between finished internal faces and, for roofs, in the plane of the insulation.

Solar Gains

e. The Target U-value equations are based on a calculation assuming equal distribution of glazing on north and south elevations. For this purpose north and south are taken as being between 30° to the east and 30° to the west of true north and south. Where the area of glazing facing south exceeds that facing north, the glazed area included in the calculation can be reduced to take account of solar gains. It can be taken as: the total glazed area less 40% of the difference between north and south glazing. [Note 1];

Heating System Efficiency

f. The Target U-value calculation assumes a gas or oil fired hot water central heating system with a seasonal efficiency of at least 72%. If a dwelling is to be heated in a more efficient manner (having regard for both heating system efficiency and primary energy consumption) a proportion of the benefits gained can be taken into account by increasing the Target U-value by up to 10%. For example: if the boiler in the above system were replaced by a gas condensing boiler this would increase seasonal efficiency to 85% and the Target U-value could be increased by the 10% allowed. As another example, a high efficiency electric heating system comprising a heat pump with a seasonal coefficient of performance of 2.5 (taking account of any heating distribution losses) and a mechanical ventilation system with heat recovery would also enable the Target U-value to be increased by 10%. Other heating systems which provide an intermediate improvement in seasonal efficiency between 72% and 85% would justify a smaller increase in the Target U-value pro-rata. [Note 1]

Notes:

1. For information on Target U-values see Appendix G.
2. For information on the Standard Assessment Procedure (SAP) see Appendix C.

ENERGY RATING (METHOD 3)

J2.4 Under this method the SAP energy rating of a dwelling must not be less than that prescribed in the table to this standard.

Note: U-values must not exceed those specified in J1.3c.

Table to J2.4: SAP energy ratings for dwellings [Note 2]

Notes:

1. For information on the Standard Assessment Procedure (SAP) see Appendix C.
2. SAP energy ratings are for individual dwellings. In terraces or flats this may give considerable variation in the SAP energy ratings for individual dwellings. The construction may therefore have to take this into account.

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