Sunday, 17 November 2013

Strawbale house, phase 3

The season's progress in 18 seconds....

...and for an overview of the whole construction process, go to

Building progress

We left the house in the autumn of 2012 with the solar panels installed, and the strawbale walls being harled with lime mortar. The second coat was put on later than we'd hoped, and there was a danger of frost damage, so the fresh mortar was draped in sheets of hessian to insulate it. There was some surface damage - easy enough to repair next year.


To my surprise, the below-ground kitchen area stayed dry through the winter - but then there hadn't been much rain or snow. But it needed to be properly sealed, so I gave the floor and walls two coats of Aquaprufe, a water-based bitumin emulsion. But when it did rain hard, there were ominous puddles on the floor. (Dealing with rainwater was a theme for the year.) It was difficult to get the Aquaprufe into all the nooks and crannies of the very rough concrete surface of the floor; I thought it might be still letting water through, so I covered it with a ready-mixed self-levelling screed and painted it again with Aquaprufe. Again, wet patches appeared. Perhaps, I thought, water came through the join between floor and walls. The summer was dry, and the problem was shelved. 

Meanwhile, Donald Ingram had taken out a large tree stump just to the north of the house, and while he was doing it, he excavated a large hole to become the rainwater soakaway. All we needed to do was back-fill it with large stones, and dig trenches to take the water from the three downpipes. Digging trenches is not a pleasant job (as I remember from a volunteer workcamp in Hungary back in the late sixties, when the boys were digging a railway drainage ditch on the north of Lake Balaton, while the girls were picking peaches on the other side of the lake. But that's another story.) Inevitably, large rocks were encountered - in some cases so big that they were immovable without Donald's digger and we had to reroute the trench. Another time we broke into a drainage pipe that we should have known was there (it was put in to service the new house just 2 years earlier, so at least it wasn't in use yet).  Establishing a proper gradient all the way down to the soakaway was more difficult than it should have been. The only flexible ducting we could find was meant for field drainage, and was perforated (to let water in), so to make sure the rainwater didn't simply seep back into the ground by the house, we inserted solid black rainwater pipe inside the ducting until it was a few metres clear of the house. Nick helped a lot with this; he was on site most of the summer, busy renovating the main house before letting it again.

(The old family home - converted from a roofless ruin in the late 1980s.)

Getting the rainwater well away from the walls seemed to stop water leaking into the kitchen area, but of course a proper seal was still needed, so my next idea was to use bitumin paint - a thick black paste, much more promising as a sealant than the thin water-based Aquaprufe. I painted it thickly around the base of the walls and onto the floor, and now wait anxiously for a heavy downpour to test it. [Update, late October; Nick reports small wet patches, apparently around the shoes at the base of a couple of posts. Will have to coat those thoroughly with bitumin. The holes for the resin-fixed bolts broke through the damp-proof membrane, but the resin was supposed to seal it again.] 

The serious job this summer was joining the new roof onto the old steading roof, leaving a covered passage underneath, where the front door will be. Simon was up for a long weekend to help with the really heavy work, putting up the beams; extensions from the eaves beams in the new house across into the old roof, purlins at such a height that they meet the ridge of the steading roof, and a ridge beam continuous with the beam in the new house - which is considerably higher than the steading ridge.

Supporting the beams and joining the new rafters to the rafters in the steading roof required a lot of extemporising; it didn't help that nothing in the old roof was regularly spaced, and the top of the steading wall didn't have a continuous wall plate to support the beams. At the far end of the new roof, a small hipped roof was needed to join onto the slope on the other side of the steading roof. How exactly to do this came to me while lying awake one night - and I remembered it in the morning, and it worked! Putting the sarking on was tricky, as the boards had to meet the steading roof boards at a complicated angle.

Trial and error again. Inside, I fixed battens onto the existing sarking to support the free ends of the new boards. The sarking was covered with breather membrane – so at last there was no need to drape tarpaulins over the open space above the workshop to keep the rain out. 

Intrepid brother-in-law Richard gave invaluable help with the upper reaches of the roof.

The space inside the new roof above the old was closed off with a partition wall - with access through a hatch from the steading workshop. Alistair slated the roof extension, declaring himself satisfied with my joinery – the join with the main roof is invisible. 

We'll have a solar thermal panel fitted on the south side. Incidentally, the solar photovoltaic panels on the main roof generated about 2900 kWh in the year since they were fitted - a little less then the theoretical output, but I was warned that shadowing from the trees to the west would have an effect. In the middle of the day in summer (and even into September) it was great to see the meter climbing towards 3.5 kW!

The windows were fitted in August, and the doors in October. The house was windproof - except for the great gap between the ring beam on top of the bales and the roof. This was to be filled with a fascia board - or rather, three boards, lapped together. The two lower ones were planed 150x50 larch, and heavy.

Simon was up for another long weekend and helped with this. I have to admit that the house is not quite regular - the roof, at least on the south side, dips a bit in the middle. So getting the boards to line up and fit together and look OK was a challenge. The uppermost part of the fascia was between the rafters, and for this fiddly job I used lengths of planed sarking. So now the house is more or less wind-tight and working on the inside during the winter should be pleasant.

By November, the new roof was slated and the solar thermal panels were in place. The team from Mortar and Lime came to put the final coat of harling on the walls: the hessian drapes were to protect against frost.
At the end of the month, Andy Newcombe came to inspect the harling and remove the hessian. He - and we - were very happy with the way the house is looking.