17 October 2013

Hickling Strawbale House October Progress

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. 

getting clay plaster in under beams inside

rendering ready for metal cill

first floor strawbale work complete and windows in

stair wall

compact foam ready to be placed below cill of door

compression tape after it has expanded

The windows are from Optiwin, which is a German group of small window manufacturers, this one in Bavaria, they were certified at the 2013 International Passivhaus conference, and are very deep timber sections of 150mm, 5 layers but all timber, with larch to outside face. They are installed with 100mm illmod compression tape, which provides some insulation value to the tolerance gap. Then woodfibre board is fitted externally over the frame before rendering with Contega tape to window frame.

Contega tape to reveal

contega tape to base of straw - joint with foamglas

sedge for the ridge

 finishing the straw

first coat render  

The render is now finished and we will be able to take the scaffolding down soon - the building has looked like a wrapped up Christo sculpture for long enough!

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.

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