Lots going on at the moment as we try and work out which builder to go with, balancing (expected) cost, experience, availability and a host of other considerations. Not really appropriate to write about all this yet so instead here is why we are going to be spending a fortune on miles of magic tape.
Hand-in-hand with lots of well-balanced mechanical ventilation goes air tightness and super-sealed construction, as we’ve said before – no more period draughts! This is all expressed in air changes per hour ie. how many times the air within the volume of our home is replaced each hour through normal ventilation such as air bricks or in fact leaks in the building fabric. The various standards can be summarised as:
- Passivhaus standard is 0.6 air changes per hour. This is like a single credit card sized hole over the entire building fabric
- Current building regulations are approximately 10 changes per hour , something like a credit card machine sized hole in the building
- Our old house would have been as if someone had driven an armoured van through a wall.
We’re aiming for Enerphit standard which is 1.2 air changes per hour.
Stopping this leakage stops heat escaping and means we can reclaim as much heat as possible through the MVHR. This is done by wrapping the entire house in an airtightness layer stopping all unwanted leakage from the inside to the outside. It needs to be continuous, running all around the building elements floor to wall to roof etc. In addition all the various penetrations must be sealed too – from sewerage pipes to incoming electricity cables. Interestingly the airtight layer is different to the moisture-proof layer – complicated.
Getting this right will requires huge attention to detail and careful workmanship for the building works and an incredible amount of taping, miles and miles of the stuff, some of which will be extremely fiddly such as the junctions around windows. There’s an overwhelming variety of special tape available for every conceivable type of of construction combination, all way more high tech than duct tape. Sadly a lot of plastic and its all pretty pricey (£25 a roll upwards … gulp) but eyes on the prize of very low energy use during the life our the building.
Very exciting, there will be airtightness tests along the way using smoke bombs to see if there are any leaks so defiantly looking forward to that day!