Airtightness & Ventilation Requirements
One of the main aims of Building Regulation Part L is to design and construct homes which are more airtight. We look at the implications and how an air tightness test is carried out as we as the more recent domestic extract fan testing requirements.
One of the main catchphrases of the last decade is ‘Build tight, ventilate right; however, lately it appears to be landing on deaf ears.
Many people in the UK still see the concept of ‘airtightness’ quite unwelcome. They often say that they won’t be able to breathe in an air tight house. Or I’m old school so I ‘I always sleep with the windows wide open, so what’s the point?’ They fear that an airtight house will be unhealthy full of condensation etc. In some cases there is an element of truth to this as many classic Victorian houses were not designed to be air tight in order to expel the coal smoke, with the most common air leakage paths through sash windows, floorboards and through the open fireplaces.
At the time we thought this was healthy; however perceptions are quickly changing. Now, with the growing awareness of concepts like low-energy houses as well as more comprehensive measures such as PassivHaus and zero carbon homes, people are more aware on just how important air tightness testing is in low-energy homes and commercial buildings.
In an airtight house, air quality is much more controlled and it isn’t simply down to random draughts, it is much more planned. As above the ‘ventilate right’ bit of the equation really takes precedent. Airtight homes rely on whole-house ventilation systems. We thus have three essential elements to a low-energy home, they are:
• Lots of good quality insulation
• A good airtightness target
• A whole-house ventilation system
It is essential all three make up the total solution; you need all three working in unison to be truly effective, if you combine all three, you get a low-energy, comfortable home with good indoor air quality.
Testing for Airtightness
Air leakage is the uncontrolled flow of air through gaps and cracks in the building fabric. This is not to be confused with the controlled flow of air into or out of the building through purpose built ventilators. The pressure differential is measured across the envelope of the building be means of a large fan installed temporarily sealed and a range of static pressures and environmental readings are taken. The fan is switched on and the air pressure in the property is gradually increased or decreased and the differential pressure is recorded at each step.
The total air flow required to achieve a pressure differential of 50 Pa is calculated and divided by the total building envelope area to provide the leakage rate in m3/hr/m2.
On each development, an air pressure test should be carried out on THREE units of each dwelling type or 50% of all the instances of that dwelling type, whichever is less.
A block of flats should be treated as a separate development irrespective of the number of blocks on the site.
Depending on the size of the property, the duration of the air tightness test should take no longer than 2 hours with the air tightness test certificate issued some 2 days later.
It is best to make sure that the building is fully prepared for the air tightness test, in most cases the main areas of air leakage are through penetrations in the kitchen and/or utility room and through penetrations in the bathrooms and cloak rooms. Other common air leakage paths are through the wall/floor junction, light fittings and boilers rooms and service cupboards.
Designing for Air Tightness
The key to attaining a good airtightness test result is to design in an air barrier at the outset, and then to ensure that it is properly installed and not tampered with during construction. For instance, instead of allowing plumbers and electricians to drill holes without supervision, the service connections need to be carefully planned in advance and the air barrier penetrations sealed accordingly, otherwise you may have large service penetrations etc. that are not adequately sealed before the installation of kitchen units which can result in large air leakage paths that are almost impossible to seal without removing the kitchen units, which may cause damage to your nice new kitchen.
Heating an Airtight House
If you achieve a good air leakage rate the less heating the house will need further down the line e.g. if you have two identical 3 bedroom houses and House A has achieved an air leakage rate of 4m3/hr/m2 and House B: 10m3/hr/m2, then House A should be 25-35% cheaper to heat each year which can result in some huge monetary savings each year.
Mechanical Ventilation – How does it work?
A MVHR system continuously extracts polluted air from a building. The stale air is passed through a heat exchanger, which is then used to pre-warm incoming fresh air. This ensures a fresher, warmer and more comfortable environment; the Key Benefits of this are
it provides a better quality of clean, fresh and healthy air. It also impacts on energy bills — recovering up to 95% of otherwise wasted heat, ultimately reducing the overall heating requirement. Another notable benefit is the lowering of noise issues as it negates the need for window trickle ventilation.
Mechanical Ventilation Testing
Under Building Regulations Part F all new dwellings will now require post-completion testing of ventilation equipment for dwellings. All domestic ventilation systems should be tested from a basic extract fan test in the toilet (Type 1) to the supply and extract valves in a mechanical ventilation with heat recovery system (Types 3 and 4). We can undertake the domestic ventilation testing at the time of the air tightness testing saving you time and reducing coordination issues.
If you require air tightness or domestic ventilation testing, we have the knowledge and experience to ensure your building passes first time. If you require more information please contact me direct on 07775 623464 or visit the airpressuretesting.net website today.