Frequently Asked Questions

1. What is air tightness?
Air tightness is the control of how much air/heat is lost through unwanted gaps and cracks in the fabric of a building. Since 2006, all buildings constructed in Britain must adhere to standards set out in Building Regulations, and achieve a target score (Design Air Permeability, found in SAP calcs) specific to that building.
2. Why should I build to a high airtight standard?

Up to 40% of energy usage is due to heat lost through leaky building fabrics. It’s difficult (but not impossible) to bring the existing housing stock to high standard of airtightness, but new builds should be designed with high levels of both airtightness insulation as the norm. Leaky, draughty buildings mean higher fuel bills and an uncomfortable living environment.

The air tight vapour check also ensures that interstitial condensation risk is minimised, ensuring no structural damage from moisture, mould, rot and damp.

3. What is an “intelligent air tight system”?

The technology used in Pro Clima membranes ensures that they may become more vapour “diffusion open” when required. This means that they have the ability to alter their vapour diffusion resistance depending on the average relative humidity surrounding the vapour check. During the winter period the membrane remains diffusion tight and will resist the diffusion of vapour from the internal fabric of the building into the insulated layer. However in summer Pro Clima membranes may become more vapour open. This allows any moisture which may be trapped in the insulated fabric of the building to back dry.

4. Why does moisture accumulate within building elements?

Unanticipated moisture may be present in buildings due to diffusion directly through the membrane or air leakage, and also at the construction stage where the building may have been exposed to rain and frost. Using an intelligent Pro Clima vapour check ensures that this moisture can dry as quickly as possible due to its unique diffusion properties.

5. Is it difficult and costly to install for air tightness?

Achieving an airtight seal isn’t difficult, but the focus needs to be on design and planning, and attention to detail at installation. Poor installation will result in air leakage which will be detected at the air tightness testing stage. The cost can be as low as 0.5% of the total build cost.

If you have a question, please give us a call on 01938 500 797 or email us at and we will endeavour to help you out.