Monday was the air test with Paul Jennings, on completion of external render with windows and doors fitted and sealed. We were pleased/ relieved to get under 1 air change an hour. We did some obvious leaks and got about 0.9, now only obvious one is a door which needs adjusting, Paul thinks we must be looking at disaggregated leakage through the straw and through the roof. So would expect to improve as clay work and warmcell and finishing goes on.
Just to explain, as people have asked me why we are going for airtight layer on the outside, that using the inside plaster layer would have been really hard to achieve, because of the primary frame, especially the long horizontal beams. We're hoping to get the internal plaster down behind it to cover the straw, but achieving a good airtight surface is unlikely. Also there would be a lot of internal penetrations and with big timber sections with shakes, you can't really guarantee an airtight seal.
The problem with airtight layer outside is that moisture from inside could condense in the straw where the air leakage points are, like at eaves for instance. We think that because the whole construction, walls and roof, is moisture permeable all the way thru, this shouldn't be a problem, and the MVHR will also reduce moisture in the internal environment. But we have fitted the AECB Hygrotrac monitors in the straw so that we can properly observe the performance, and will be using an Intello membrane internally in the bathroom ceiling.
Before that we were finishing the strawbale work. The compression of each section took the longest time, but it is so impressive how firm the straw walls are when compressed. Paul did an airtest for Strawworks, before the render started, to see how the straw was performing. It wasn't the figure results which told us anything, as the plastered tapes at eaves and around windows and doors were not in place, but following the smoke, showed how dense and airtight the straw is when it is well compacted.
rendering ready for metal cill
first floor strawbale work complete and windows in
contega tape to base of straw - joint with foamglas
sedge for the ridge
finishing the straw
first coat render
An open afternoon in the village brought about 50 visitors at the end of September, an AECB east anglia group visit brought our most well informed visitors of course! and last weekend the local history group visited, now we are looking forward to joining them.