Air tightness testing is done to ascertain the air permeability rating of a building. This test is done to meet Part L compliance.
Air leakage is the primary cause of heat loss in houses, which consequently leads to energy inefficiency. Part L of the Building policy states that new buildings must have standard air permeability ratings.
How to do an Air Tightness Test
The testing is calculated in air flow m3 over an hour of 50Pa in every m2 of the building material. Let’s make it simple a typical structure can have up to 400m2 of uncovered material on the roof, walls, and floor. A trial number of 10 give 4000m3 of air flow at 50Pa within an hour.
Before the testing begins, all ventilation must be sealed. Block the external envelope and associated openings. On the inside, all doors are set to open temporarily. Shut down all drainage systems too.
People should not enter or leave the building during the test. So workers remain where they are, in the building or out. Although there might be some noise from the fan used, there is no health hazard-exposed to the workers who are in the construction during the test.
When is the Air Test needed?
To comply with Approved Document L1A, in every private building an air test has to be done in three of the houses or 50% of that housing, whichever is less. The test results are given to the Standard Assessment Procedure (SAP) evaluator who then reviews the calculations, ascertains that normal conditions have been met, and provides a final report.
Document L2A requires testing to of all commercial houses over 500m2. The test results have to be better than the design SAP. Commercial buildings that are less than 500m2 are exempted from this test. However, it is difficult to find buildings that fully comply with these standards.
Tips for a good air test results
- Start with air tight strategies – Before you start building, have talks with your contractor and agree that the building has to be air tight. It helps to have this consensus in the early stages; draw a line that can separate all unheated and heated elements. You can also appoint someone to coordinate this task among the consultants.
- Do random inspections – Leakage can occur if the walls are breached during construction. Random inspections are critical during to avoid this leakage; make sure that the air barrier is not compromised. These inspections will ensure that you evade the high cost of remedial work if the building fails the air tightness test.
- Be vigilant with dry lining – Plasterboards that are fixed using dot and dab can lead to air leakage. The brickwork usually has a possible pathway at the back of the plasterboard to the floor slab. You can either decide to coat the wall or use solid adhesive on all sides of the board and sockets.
- All supply and pipe work should be sealed – Seal anywhere the pipes penetrate walls or the floor. You can use gunned sealants or flexible foam strips for bigger gaps. Avoid using expanding foam; it can shrink and break the seals easily. Only use the foams that are tested for airtight fixing.
- Doors and windows – It’s astounding how many door and window frames you can see in a building that is not properly fitted or sealed. Ensure you use fitting draught strips and seals to avoid cracks or gaps around all sills, lintels, and jambs.
- Loft hatches and cupboards – Many houses are designed with rooms in the roof, and air leaks through the cabinet openings and loft hatches. They are a late addition though; they separate unheated space from the living room so ensure you seal them properly like the windows and doors should be.
- Proper light fittings – Pull all wires in the ceiling and ensure holes around light fittings are well blocked. The fittings must be airtight; alternatively, you can cover the roof void with sealed boxes.