Airtightness

Airtightness testing came into force on the 6th April 2006 and is a requirement of part L1a of the building regulations in England and Wales. On each development an air tightness test must be carried out on one unit of each dwelling type selected by the building control body. The dwellings to be tested should be taken from the first completed batch of unit types.

What Is Air Leakage?

Air leakage is the uncontrolled flow of air through the gaps and cracks in the fabric of a building (sometimes referred to as infiltaration or draughts.) To much air leakage leads to heat loss, resulting in higher CO2 emissions.

This should not be confused with ventilation, which is the controlled flow of air into and out of the building through purpose built ventilators that are required for the comfort and safety of occupants.

Timber frame construction offers a superior airtight structure compared to brick and block construction or steel frame construction. Code 4 Timber frame uses a reflective vapour barrier on the external inner leaf walls, this has three main functions the first to prevent moisture from the 'wet rooms' in the house such as kitchens and bathrooms condensing on the timber structure. The second to use its reflective properties to redirect heat back into the home. and the third to help reduce the air leakage through the timber frame structure.

Provision should be made to reduce air leakage through the building envelope the worst acceptable air permeability is 10 m3(hr.m2) at 50pa

In order to meet the requirements builders should adopt one of the following procedures

1 - Use accredited construction details/pressure testing

2 - Carry out Airtightness/pressure tests (pre completion testing)

For further information or to book an airtightness test please click on the link to Sustainable Designs or NHBC below

For timber frame accredited construction details click on the link below:

Timber Frame ACD.pdf

Common Air Leakage Paths

1 - Underfloor vents 9 - Service penetrations through ceiling

2 - Gaps around suspended timber floors 10 - Vents penetrating through ceiling or roof

3 - Leaks around windows and doors 11 - Extractors in bathrooms

4 - Leakage through floor or ceiling voids 12 - Gaps around bathroom waste pipes

5 - Gaps around windows 13 - Kitchen vent or extractor fan

6 - Gaps at the ceiling to wall joint at eaves 14 - Gaps around kitchen waste pipes

7 - Open Chimneys (if Applicable) 15 - Gaps around floor to wall joist

8 - Gaps around loft hatches 16 - Gaps in and around electrical fittings

Changes to parts L & F of the building regulations are scheduled to be introduced in Oct 2010

It is likely that the limiting value for the air permeability of tested dwellings in approved document L1a will remain as 10m3/(h.m2) at a test pressure of 50 Pascals. However for dwellings of the same type which are not tested, then a value of 2m3/(h.m2) more than the tested building can be assumed - meaning that developments with several dwellings of the same type will need to achieve less than 8m3/(h.m2) on the building tested in order that the other dwellings can assume an air permeability of 10m3/(h.m2).

It is also proposed that the number of dwellings currently tested on site be doubled on a development to increase the sample size.

Code 4 have achieved airtight values of 0.6 - 16 times better than current regs.