Get Your Building Airtight


The building regs require that all new dwellings achieve an air leakage of less than 7m3/hm2.


In a residential build, the test result will be passed to the DEAP assessor who will then update the calculations


Some mechanical vent systems have a heat recovery function (MVHR) which draws heat from wet rooms and recycles it for use in the rest of the house.

Once a build is complete, an essential part of our work is testing for air tightness.
Air Permeability Testing is a crucial phase of any build as the result will significantly effect the energy performance of the building.
Here we are going to give you our top tips for ensuring your building is as air tight as possible.

But first some background for the uninitiated…

Air Permeability Testing – What you need to know

The building regs require that all new dwellings achieve an air leakage of less than 7m3/hm2. That is the air leakage rate per hour per square meter of envelope area. If we are being precise, there are a few caveats around DEAP BER Calculations and dwelling types which can affect this, but broadly this is the rule. The m3/hm2 figure is the headline ‘pass or fail’ number produced by the air testing engineer and demonstrates how much air is being sucked into the building through ‘leakage’ when the fan is operating at 50 Pascals.

Uncontrolled Air Leakage

The key is that this test measures uncontrolled air leakage. It is not concerned with trickle vents, extract fans or ventilation systems. Controlled ventilation sources will simply be taped up or sealed prior to testing.
Therefore air permeability testing is looking for gaps and cracks in the fabric of the building.

Certification

Some certification schemes look to go further than building regs standards – for example the Passivhaus standard requires all new builds to reach a maximum of just 0.6 air changes per hour.Whilst this is a huge improvement against a ’10′, it should be noted that there are slight variations in the testing metrics and procedures.

Whilst testing may take place at any time in the build process, it is common for air testing to take place in the final throes of a project prior to issuing of final DEAP Calculations and an BER.

In a residential build, the test result will be passed to the DEAP assessor who will then update the calculations, establish that a pass has been achieved, and issue final reports and an BER.

Effects on BER

Importantly, the DEAP BER rating will be significantly affected by the air leakage rate, as high levels of uncontrolled air leakage will reduce the energy performance of the building.A BER Assessor will generally set a design air permeability target of between 5-10m3/hm2. This is a reasonably achievable performance although in some cases this may need to be set lower.

Why?

Well the dwelling may be struggling to meet its emissions targets and a low air leakage may compensate for other areas, either arising from poor design, or factors beyond the developers control. Whilst it would be great for our heating bills and DEAP Calculations if we produced super airtight houses every time, this obviously can cause issues when a dwelling is not designed for very low levels of ventilation.

Ventilation specialists will generally quote an air tightness of ’3′ as a healthy rate for a naturally ventilated house. That is, ventilated only with extract fans, trickle vents and windows. Anything tighter and some form of forced ventilation will be required, i.e a mechanical ventilation system. Some mechanical vent systems have a heat recovery function (MVHR) which draws heat from wet rooms and recycles it for use in the rest of the house.

Our Top Tips

During the course of testing hundreds of different buildings, we’ve learnt a few things.


Waste and Supply to Kitchens and Bathrooms

Ensure all waste and supply pipework is sealed to walls and floors with expanding foam or mastic. Most leakage will come from hidden holes, gaps and cracks behind bath panels and cupboards


Drylining

Plasterboard installed with dot and dab can lead to problems, as any missed leakage in the brick or blockwork has a potential path from behind the board to the floor slab. Try to use solid lines of adhesive around all sides of the board and any cut outs for sockets. Its not always possible to seal around skirting boards so this can really help


Kitchen Base Units

Kitchen base units often hide issues – walls with no skirting, and services and waste which are often not sealed in


Downlighters

These can be a real problem either due to leaky joists or draughty loft spaces. Some units are better than others, and you can now buy LED downlighters with sealed units, although they are really intended for wet rooms


Windows and Doors

It’s amazing how many window and door frames we see which haven’t been sealed or fitted properly. Ensure there are no gaps or cracks around all jambs, sills and lintels


Rad Pipes and Manifolds

“Manifolds from underfloor systems and radiator pipes are often not sealed into the floor screed – this is then covered up with flooring or carpet. Also many radiator pipes penetrate the wall behind a rad – which again is very hard to spot unless you are looking for it”
Design it out

“These are very much superficial fixes – we can quite easily identify these problems in a pre test check without even running a fan – and pretty much guarantee a pass against building regs standards. However, there is no substitute for good air tightness design right from the architects drawing table. Passivhaus builds and the like are different beasts and will need a lot more thought around air tightness barriers in the construction itself. The most important point on any build is to get all the trades onside and get them thinking about air tightness as they go. If everyone buys into the air tight theme, with good practices from the start, you can avoid the problems later on.”


For more reading see:

Air Testing – Which and How Many?

Air Permeability Testing – the Info

Air Permeability Testing

New Build Compliance Pack

Just give us a call on 01 4428924 or send us your enquiry – we’ll get straight back to you.

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