Last week was quite eventful. Mike’s team finished the tin roof, started with installation of airtightness membrane to underside of roof structure and we had a wood stove installed.
Being a passivhaus with low space heating requirements, our house won’t need much heat to keep it comfortably warm, so putting a wood stove in is a bit of a luxury rather than necessity. The intention is that it will provide bulk of the space heating, topped up with towel rail in bathrooms. For simplicity, we have not coupled it with back boiler to heat water (hot water will be generated via heater with air source heat pump). There have been a couple of technical challenges to overcome – airtightness and air supply. We have used Morso S11-42 stove (with optional airtightness kit) in combination with Poujoulat Efficience triple wall flue to give us a completely room-sealed system. The external cavity of the flue supplies fresh air in from outside directly to the stove, and the inner flue takes the hot air out. This ‘pipe in a pipe’ system also means that there is only one penetration through the building fabric. The flue came with a proprietary airtightness plate with a flexible seal, the airtightness membrane will be taped to it.
It was exciting to see the first fire lit – installation crew from Poujoulat (flue) and Prince&Pugh Knighton (stove) did a great job. Will just have to be careful with keeping the fire under control with all that exposed straw inside!
We will be opening the house up as part of international passivhaus open days on 11 and 12 November – follow this link for more information.
This week’s weather has been kind enough to allow us install woodfibre boards on top of roof I-beams, and wrap the boards with windtightness membrane, held down by timber counterbattens. Larger timber battens will provide support for the corrugated metal roof. It’s good to have two layers of protection above the straw panels.
We have been tweaking the design of junctions between timber cladding and roof with Mike, and decided that it’s best to finish off installation of external woodfibre boards to walls and insect mesh to close off vented cavities before the corrugated roof goes on.
On Saturday Joyce & me finished off sealing the last charred cedar cladding boards, which was very satisfying to see. It’s now all stacked and ready to use.
There was a bit of excitement when a herd of escapee cows passed our site – I wonder if they wanted to have a peek at this straw filled passivhaus? 😉
Things have been moving at a pace on site. Wet weather at the beginning of the week slowed down the progress somewhat, but come mid week, Mike’s team (Mike, Henry, Bisto, Petras, Liam and part time me) got on to taping all the airtightness membranes (particularly around tricky corners), installed timber wall plates and started with the roof installation. It was critical to do all the taping for airtightness before wall plates were in place, otherwise access would be impossible. The strategy is for airtightness layer to switch from outside (walls) to inside (roof), and this swap happens on top of straw timber panels, below wallplates. Unlike walls, which were pre-fabricated as insulated panels, roof is installed as individual timber I-beams, spanning between glulam wallplates and central glulam ridge beam. These 400mm deep I-beams were pre-cut and reinforced in the Ecococon factory, hugely speeding up the installation process on site. Later on they will be fully insulated with blown cellulose insulation. The south canopy overhang is formed with a combination of Douglas Fir rafters cantilevered over wall plates and smaller, 200mm deep I-beams. A team of four of us had all the beams tacked into place in about two hours and Mike’s apprentice Liam topped the house just after lunch on Thursday. This made a huge transformation to the shell – we can really start to appreciate the feel of internal spaces now.
After the mammoth task of concrete slab grinding, a small time window before the straw/ timber frame arrives has allowed me to get on with some prep work: cutting and staining roof rafters and battens that will be fully exposed under the roof. The idea is that these timber members will visually complement charred timber cladding on walls, so I’ve used thinned black OSMO natural oil woodstain applied to sawn Welsh Douglas Fir. This created a very nice effect of maintaining a good wood texture whilst providing a near black stain. Very happy with the results.