DHAPT - Domestic House Air Permeability and Pressure Testing

Conservation of fuel and power

Approved Document L1A

L1A

QUALITY OF CONSTRUCTION AND COMMISSIONING

61 If satisfactory performance is not achieved,

then remedial measures should be carried out

on the dwelling and a new test carried out until

the dwelling achieves the criteria set out in

paragraph 60. In the period up to 31 October

2007, however if the initial test result on a

dwelling is unsatisfactory, reasonable provision

would be to:

a. carry out remedial measures such that on

retest, a result was achieved that showed:

i. an improvement of 75% of the difference

between the initial test result and the

design air permeability; or

ii. if less demanding, a test result within 15%

of the required design air permeability.

b. revise the TER by substituting the measured

air permeability obtained by following

paragraph 61a) for the value set out in

Appendix R of SAP2005, and demonstrate

that the DER is not worse than the revised TER.

This allows some time for builders to develop

the techniques for constructing to reasonable

standards of airtightness, but the poorer

airtightness will be reflected in the Energy

Performance Certificate, which will impact

on the value of the dwelling.

To illustrate the revised target following an initial

failure, if the initial test result was 18.0, and the

design air permeability was 8.0, the revised pass

level to reach in tests following remedial action

would be [18.0 – 0.75 x (18.0 – 8.0)] = 10.5m

/(h.m

)

at 50 Pa. However, if the initial test result was 9.5,

the pass level to be achieved in tests following

remedial action would be 8.0 x 1.15 = 9.2.

62 In addition to the remedial work on a dwelling

that failed the initial test, one additional dwelling

of the same dwelling type should be tested,

thereby increasing the overall sample size.

Alternative to pressure

testing on small developments

63 As an alternative approach to specific

pressure testing on development sites where

no more than two dwellings are to be erected,

reasonable provision would be:

a. to demonstrate that during the preceding

12 month period, a dwelling of the same

dwelling type constructed by the same

builder had been pressure tested according

to the procedures given in paragraphs 54

to 59 and had achieved the specified air

permeability.

b. avoid the need for any pressure testing

by using a value of 15m

/(h.m

) for the air

permeability at 50 Pa when calculating

the DER.

The effect of using this cautious value would

then have to be compensated for by improved

standards elsewhere in the dwelling design.

CRITERION 4 –

COMMISIONING OF HEATING

AND HOT WATER SYSTEMS

64 The heating and hot water system(s) should

be commissioned so that at completion, the

system(s) and their controls are left in the intended

working order and can operate efficiently for

the purposes of the conservation of fuel and

power. In order to demonstrate that the heating

and hot water systems have been adequately

commissioned, Regulation 20C states that:

Commissioning

20C.–(1) This regulation applies to building work

in relation to which paragraph L1(b) of Schedule

1 imposes a requirement, but does not apply

where the work consists only of work described

in Schedule 2B.

(2) Where this regulation applies the person

carrying out the work shall, for the purpose of

ensuring compliance with paragraph L1(b) of

Schedule 1, give to the local authority a notice

confirming that the fixed building services have

been commissioned in accordance with a

procedure approved by the Secretary of State.

(3) The notice shall be given to the local authority:

a. not later than the date on which the notice

required by regulation 15(4) is required to be

given; or

b. where that regulation does not apply, not more

than 30 days after completion of the work.

65 The procedure approved by the Secretary is

set out in the Domestic Heating Compliance Guide.

66 The notice should include a declaration

signed by a suitably qualified person that the

manufacturer’s commissioning procedures have

been completed satisfactorily.

One option would be to engage a member of an

approved Competent Person scheme.

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