Week 25: insulation, airtest and cladding...

Monday of Week 25 started with the Insulation guys turning up. This job is absolutely crucial to the thermal performance of the building and along side the airtightness of the building envelope makes up a crucial element in achieving passivhaus performance.

The job of these two guys was to fill the fairly enormous cavities in the timber frame walls and roof  with Knauf Supafil 34 (read all about it here http://www.knaufinsulation.co.uk/en-gb/more/supafil-34.aspx) which is basically processed recycled glass that is formed into a silicon coated glass wool or fluff. So the way it works is that they bring 'bales' of compressed Supafil in two large transit vans all the way from Southampton.

They then load a bale at a time into a big machine in the back of the van which breaks and fluffs up the insulation into a much greater volume and blows it down the pipes to a jet that the installer uses to fill the cavities. 

This is what it looks like, very similar in appearance to cotton wool or candy floss. 

Here one of the installers fills a wall cavity. There is a cavity between each frame of the house (approx 400 or 500mm apart) so many many cavities per wall per floor. Each cavities has a depth of about 300mm so some fairly massive volumes of insulation. 

The walls took most of the first day. Then on the second day the guys brought two more van loads of insulation and completed the upstairs walls and the roof. The roof is even deeper at 400mm so again a huge volume of material. Below filling the roof cavities. 

Later on in week 25 Jonathan arranged the first airtightness test. Basically shut all the windows and doors, seal up any traps and drains and attach a pump to the house to apply 50 Pascals pressure (suck and blow I think) and monitor how much air leaks out. The idea is this give you a way of determining how leaky your building is. Obviously as low as possible is good. That way you don't have unmanaged heat loss, instead you control air circulation efficiently via the MVHR.

Airtightness testing kit. Pump and monitoring equipment installed in a window opening.

Passivhaus standard requires no more than 0.6 air changes (the volume of the house blown in or sucked out) per hour at a pressure of 50 Pascals. Which is approximately the equivalent of less than 1m3/m2/h @50 Pascals. Interesting to note that current UK Buildings regs are approx 10 times this amount. So how did we do? We got a result of 0.57 air changes per hour. So we were just inside. This was a bit disappointing for us and Jonathan as I think we had all thought and hoped for a figure of more like half of this. However the problem was identified as a number of doors that had not yet been adjusted. The tester through that once this was done approximately 0.2 reduction would be further archived. This is not the final test though as the Certification company will do an independent test at point of certification when we hope to get a better result after the doors are adjusted. Crucially it was not bad enough to hold fire on other work for remedial work to be done. Put another way it allows the plaster boarding and ultimately plastering to continue.  

While all this was going on Zac and Tommy were getting stuck into the cedar cladding on the North, East and West 1st floor walls. Its great to see his go on as it really starts to give and idea of how the finished building will look. The detailing of the 8mm gaps between planks and mitre joints is a very time consuming detail compared with a normal tongue and groove style cladding but its looking really good and we are very pleased. It should also much aid air circulation around the cedar increasing its lifespan.