I am now getting round to the fiddly detail bits. One of these is fitting notched bales between the top the main interior wall and the roof (the bales have to be notched to allow for a purlin) and also putting bales in place above the doorways. It was good to return, one last time to ‘straw work’ athough cutting the notch with a chainsaw meant becoming swamped in loose straw. It also reinforced that by far and away the best tool for cutting or shaping straw is an electric chainsaw (not a petrol one because the straw gets in the air intake and it overheats).
I have also been finishing off the clay around the windows and door frames – using a ‘cobby’ mixture of straw and clay. I want to plaster right up to the window frames, rather than put decorative wooden frames and window ledges in place. I think this sets-off the window frames to best effect, but it does mean plastering over the window sub-frames as well as sticking clay ‘upside down’ to the sub-frame above the windows. To do this I covered the wood in a flour, water and clay paste to give it maximum adhesion. This appears to have worked – although for the final coat I will also stretch hessian or fibre-glass mesh around curve, both to stop cracks developing over the join and also to hold the upside down plaster in place should it feel like falling-off. The job feels a little like being a housemartin, sticking clay and straw to the underside of eaves – and the resilience of their nests gives you some confidence that the clay, with added flour paste, will be sticky enough.
I have found an online supplier (TA Windows) who can provide windows to almost any customised specification. With a straw build you are likely to need customised windows because the basic measurement unit is the width and depth of a straw bale and this tends to rule out designing to use standard window sizes.
Rather than take the risk of ordering all the windows at once – and then finding there was some problem with measurement or fitting, I got one as a trial – which I have now fitted. The key lesson was the importance of undersizing rather than oversizing. Despite knocking-off the recommended 10mm from what I thought was my gap in the sub frame, the fact that the frame was not absolutely square meant that the window didn’t quite fit. This wasn’t a problem, it just meant that I had to fiddle around shaving some wood off the subframe. However, I wouldn’t want to have to do this with every window.
Having to fill a gap between the window and the sub-frame is not a problem thanks to the wonders of expanding foam, in fact having a bigger gap is slightly better than having a very small gap in terms of sealing it with foam. I know expanding foam is not a natural product and I am sure Barbara Jones would not approve, but I figured that it doesn’t intefere with the key natural characteristics of the building – which is breathability and flexibility. When it comes to getting a decent airtight seal in tricky places where straw doesn’t really work, either because you can’t wedge it in or you don’t have sufficient depth, you can’t really beat expanding foam.
The only drawback is that the cans sold in most builders merchants are effectively single use, because the nozzle pipe can’t be cleaned. However, it is possible to get a gun which has detachable / re-sealable cannisters which also comes with a solvent cannister that can be attached and used to flush through the gun nozzle. This makes it possible to do small jobs.
Following this trial window, I have gone ahead and ordered all of the windows and while waiting for delivery have got on with some small, fiddly but necessary jobs such as fitting guttering and putting a galvanised wire mesh around the bottom of the foundation beam to stop rodents getting under the suspended floor. This is a condition of building regs, but I don’t know if this will make a difference, since my experience shows that a determined rat can get around almost anything, including building regs.
Now the render is on, the next task is windows – specifically window cills. Because the windows are set quite deep, I needed a large cill (220mm wide). You can get some bespoke made cills, which have a flat base and angled top cut into them. However, I figured this is only necessary if you are mounting them onto a flat base such a brickwork, rather than something wonky like straw. Instead I got a local saw mill to cut me some oak planks, 220mm wide and 30mm deep and used my router to cut a drip groove in them and a circular saw to make a 15 degree cut along the back of the cill. To fix them I nailed a 10mm bead to form a ledge on the sub frame, rendered the top of the straw up to the top of this ledge to maximise weather protection and give the cill something solid (once it sets) to rest on. I then drilled angled pilot holes into the back of the cill, rested it on the ledge and then nailed and glued it into the frame. In contravention of Straw Works ‘all natural’ specifications, I used silicone sealant to seal any gap at the back of the cill.