My new home has to meet the requirements of the Code for Sustainable Homes Level 4. This was mandated as part of the grant of planning permission. This requires a certain (low) level of energy usage. There are three key elements of energy usage: –
- Air exchange with the outside (drafts)
- Heat input (amount and type)
The new house was set a target of 6 m3.h.m2 (volume of air lost by the house per hour normalised for the size of the building). Current building regulations require a value of 10 or lower – so my target was nearly half of that.
The house was carefully constructed to eliminate drafts, and I had gone around before the test to block any holes which will be used for other purposes in future – chimney, soil pipes, etc. Joe the engineer arrived on Monday and set up his equipment
The frame and fan were fitted in the back door with various sensors inside and out. Then the fan was started by the computer and adjustments made to the equipment.
Joe took his first measurement and quietly said we might have a problem. He explained that the house might fail the test as too low! He rang back to the office and said that he was getting a reading of 2.4 and he thought the minimum was 3.6 for normal homes. I was then asked what ventilation system I have installed. The MVHR (heat recovery system) has been built into the fabric of the building and will ensure fresh air throughout the house whilst stopping the escape of heat.
Once this was explained the lower limit does not apply – phew! The powerful fan which is used for the test blows air out of the building and outside air will come back through any gaps or holes in the building. This causes drafts where air is leaking in. As I walked around the house with the fan working I realised that I had left a couple of windows ajar to help cure the screed. Once they were closed – Joe took his final measurements.
My air test certificate shows that the house achieved 1.65 as the final value. This is close to Passivhaus requirements, even though the house has not been designed using those principles. The design features I incorporated (such as North facing windows) inevitably compromise that standard. None the less I will end up with an extremely energy efficient home and with what I think is a very pleasing design