Windows and doors play a key role in how the building feels and performs. They have to balance visual appeal with daylighting, thermal & acoustic performance and overheating. Many architects’ dream is to have slimline profiles, but this usually comes at a cost and/ or thermal performance penalty. We’ve chosen Smartwin timber windows with aluminium external trims for low maintenance and warm feel from inside. We’ve used a few ground rules for windows design: keep things simple, minimise mullions, have opening lights only where needed, keep sizes to sensible (read: affordable) dimensions, provide adequate shading. It has been super exciting to visit the factory in Slovakia where our passivhaus windows & doors are made. They marry high performance with simple, elegant design – really can’t wait to see them delivered to our site.
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.
Concrete grinding took a bit longer than I originally thought. I don’t know what I thought actually, maybe it was wishful thinking that it would be all done & dusted in a weekend, but in the end it took 88 man hours to get the 100m2 slab to a finish I’m finally happy with. It’s not perfect, but the irregularities in the extent of revealed aggregate and areas where the float created some surface streaks add to the character. In terms of the concrete mix, we’ve used a small local concrete supplier who was flexible enough to allow us to choose a nice warm coloured aggregate mix (as opposed to standard mid grey used in Herefordshire), the rest is 100% cement, red sand and water. We would have liked to use some recycled content (GGBS) and plasticisers to make the concrete ‘greener’ and slow down the drying times, but unfortunately the small supplier wasn’t geared up for this. It did mean we had to work fast during the slab pour, and as a result some areas had gone off before they were floated, so ended up a bit ‘rough’ which, in turn, made the grinding a bit trickier. All in all, pretty happy with the results and hope the effort will be worth it.
So after the concrete slab was poured, rollered and tamped, we covered it up for a few days and started with grinding. The idea is that the slab will be the final internal finish. A day and a bit into grinding the machine had a bit of a fit and stopped working, later we found out one one of its gearboxes gave up. Replacement grinder turned up this week, so I can carry on. It’s quite satisfying to reveal what’s just a few milimeters under the surface…
Monday was a big day. After last week’s installation of Isoquick insulated raft system and necessary steel reinforcement, it was time to pour the concrete slab. We have chosen concrete slab as a base for our house for couple of reasons: it would provide useful thermal mass in an otherwise medium density construction and once ground down, it would provide a durable finished floor surface. Due to tricky site access we had to use a concrete pump and direct the pipes over our neighbour’s garden. Six mini mix lorries supplied 24 cubic meters of concrete with specially selected aggregate. Unfortunately this meant that we had to use 100% cement in the mix, which in turn made the mix go off really quickly – it certainly kept the team working hard until it was all poured, rollered with a giant steel roller and finally tamped with a big float and hand trowels. Can’t wait to start grinding the slab to reveal the aggregate…
AKA insulated raft foundation. Fundamental part of passivhaus design is eliminating thermal bridging and keeping the insulation layer around the house as continuous as possible. We have chosen Isoquick insulated raft system as it is pre-cut to the right shape and individual pieces interlock for greater stability, like giant lego blocks. Local legendary AECB builder Mike Whitfield and his team started on site on Monday 1st August. First they accurately set out the footprint of the house and laid drainage in the 150mm Type 1 stone, and followed by 40mm of gritty sand, which formed the base for the Isoquick system. We started the Isoquick with perimeter L-shaped pieces and finished off with central base, which was made up of two separate 125mm layers, laid in staggered directions. Special Compacfoam high density EPS pieces were installed to support door thresholds. All floor penetrations were meticulously sealed before the waterproof membrane was laid down. Two layers of steel mesh followed on top, providing reinforcement for 225mm concrete slab. There were some tricky details around recessed matwell and shower room – hopefully it will all be worth it in the end!
Our groundworker Greg showing off his skills with the digger. This timelapse video captures installation of 20+ tonnes of hardcore that forms a base for the house. Drainage and ducting for incoming services will be recessed in this layer before insulation arrives on site in August.