After the house has been made weather-tight, we’ve been focusing our efforts on first fix electrics and plumbing. You might ask: but how does that work with straw walls? Our strategy has been to run the main services in the dedicated service zone under the roof and distribute most of the final drops in internal partitions. For the very few power points and pipes on external walls we’ve taken advantage of the timber frame studs or installed ply pattresses, thus avoiding ‘chasing in the straw’. I know other straw builders have successfully chased into the straw and used timber pegs to fix the sockets to, but we’ve managed to avoid this without compromising the room services layouts (plus our electrician was happier:)
As there’s no mains gas in the area, and we didn’t want to go down the oil or LPG route, hot water will be supplied by a cylinder with integral air source heat pump (Ariston Nuos 200d).
We’ve used 15mm insulated copper pipes for domestic hot water, these also supply hot water to two towel rails in the bathrooms. There’s no other wet heating system in the house – the other source of space heating will be the wood stove, which we’ve described in the previous post. This should give us a much simpler and resilient setup compared to our current unreliable oil burner in the rental cottage.
…to be continued in 2017
Merry Christmas ❄️
No matter how good you think you are with paying attention to airtightness, you don’t really know where you’re at until the first air pressure test. It is a good idea to carry out an early test once the airtightness layer is complete and all doors & windows are installed and sealed, but before airtightness layer is covered up. It is an indicator of how much air passes through the external envelope. Our strategy for airtightness layer is wrapping the Ecococon straw/timber panels with vapour-open airtight membrane on the outside and a more vapour-resistant membrane to underside of roof structure. The wall membrane is sealed to damp proof membrane along the bottom, which in turn is sealed to concrete slab using a flexible sealant.
Paul Jennings came over to carry out the first air test. It was good to catch up with him, he was my airtightness tutor at the CEPH passivhaus designer course 5 years or so ago. Before the test started, we sealed up all the service penetrations (SVPs, ventilation ducts, electrical conduits). Paul then started to depressurise and pressurise the house with a small fan to 50Pa and take 10 consecutive readings for each. Early signs were promising. Nick Grant brought his wizard stick (smoke gun) and thermal imaging camera to detect any air leaks. We have identified a number of small leaks, mainly where the holes for Warmcel insulation were taped up, and around door thresholds. Surprisingly, the big sliding door performed relatively well, so well done to Smartwin for clever double seal design. The wood stove was the weakest point, under pressure the smoke was disappearing through the doors and up the flue, but in absolute terms it still performed well.
We were really pleased with the result of 0.3 air changes per hour (passivhaus compliance figure is 0.6 ach). Bearing in mind the unfavourable form factor of 4+ (long bungalow with a lot of surface area) and the fact that we used mainly membranes rather than rigid boards for airtightness plus fitted a wood stove, it really is a credit to the whole Mike Whitfield building team. Nick is still hoping to air test one of the future houses with a bike pump.
We can look forward to living in a draught free house that will be super comfortable!