Last week my brother-in-law (who is a proper builder) and sister came across for a couple of days to tackle the drains and also the studwork for the bathrooms. Drains are relatively simple, but given it is so important to get them right it is very useful to have someone who knows what they are doing to set them out properly. The electrician also came across – so in the space of a day and-a-half the the drains were put in, the flooring was finished, the studwork for the bathrooms (the only internal walls other than straw) was put up and first-fix electrics was done.
It has just remained for me to chase-in the electrical conduits and secure the switch and socket boxes into the straw. The chasing was best done with a claw hammer and the boxes were secured using hazel pins about 30cm long as massive rawl plugs (see picture). These provided a reasonably firm fix – but I wouldn’t use them for fixing anything too large or heavy to the walls. For things like kitchen units I will probably revert to chasing 4×2 uprights into the straw and fixing these to the floor plates and then screwing horizontal batons into these. (Note the picture shows the boxes and conduits as the electrician left them – they are not secured into the straw).
For holding the conduits in place I used some smaller hazel pins and put a bent nail into the end and hammered these into the straw beside the conduit (see picture).
I have also had to prepare one corner for the installation of a pellet boiler. The view from HETAS is that you need a fireproof plasterboard and a 12mm air gap between this and the straw – so to be doubly sure I rendered the corner with one coat of lime, then put a 2×1 frame onto this, screwed top-and-bottom into the ring beams and also secured against the straw using hazel pin rawl plugs and then attached the fireboard. Final job to do here is make a hearth out of quarry tiles and we will then be ready to get the pellet stove in – which will provide heat and be very useful for helping dry out the clay plaster (next big job).
I have spent the last couple of weeks putting in all the flooring and ceiling joists as well as the actual flooring in the living area. The flooring in the bedroom / bathroom area will have to await putting in the drains and be coordinated with creating the studwork for the bathrooms. This will happen next Thursday, under the direction and assistance of brother-in-law Nick – who is a builder and therefore knows about these things.
The one piece of advice worth passing on for the non-builder, concerns the slight absurdity of the fact that sheeting products such as floor sheets are generally available in imperial sizes (i.e. 4×8 foot whic is approx. 1220mm x 2440mm) whereas plans always specify metric gaps – such as 400mm or 600mm. However, this should not lead you to space your joists at imperial-friendly gaps (e.g. 610mm) because, if you are using tongue-and-groove flooring sheets these are 8ft long but this includes a 10mm tongue – so the actual length of the sheet is less, making it sit perfectly on joists at metric 600mm spacing.
I have also become an even greater fan of expanding foam, especially the type with the attachable gun, because this makes it possibe to do ‘precision welds’ along joins (see picture) rather than the rather messy results you get with the conventional single use cans. No exactly natural building, but you could say eco-friendly in terms of creating good airtight seals.
We spent the weekend attacking brambles and some small hedgerow trees (but mostly brambles) that run down the field boundary that is one edge of the area that will be the garden. The result is that we now have a view out over the fields from the house. It is a good view.
I didn’t get around to finishing-off the render right up to the final purlin / roof joist at the front of the house. This left a small gap which I figured I could stuff with straw and render as part of the general finishng-off process. Some wrens have taken advantage of my tardiness and turned this gap into a winter roost. I say ‘some’ – when I was out yesterday at roosting time (16.40) I counted 15 going in in a 5 minute period. I reckon there most be at least 30 in all bedding down there every night. Now, I don’t really want to fill it in, although come the spring they will probably all move out, although some may try to nest there. I should probably therefore try and make some roosting / nesting boxes since it would be nice to have some resident wrens.
Looking back over my posts I saw that last year’s task between Christmas and New Year was the construction of the roof trusses. This year’s has been putting in the suspended timber floor.
The I Beams arrived just before Christmas. I sourced them from Pasquills, who were very helpful – I just just sent them a copy of my plans and they produced a design which specified the size and spacing of beams required for each span (220x65mm in the most part with some chunkier 220x97mm to support water tanks in the attic space) and supplied all the necessary hangers. A 220mm beam will also allow the 200mm of insulation required to get a U-value for the floor of 0.18
Thus far I have put all the beams in place in one half of the building, including putting down a weed-proof membrane and layer of gravel, and completed the isulation in half of this. The insulation is carried on a 4mm ply sheet which is glued and nailed into the bottom flange of the beams. I also decided to put the ever-useful expanding foam to seal the gaps at the ends of each run and the join between the ply sheets – just to improve the air-seal. Straw Works don’t specify this in their plans, but I expect this is because they don’t like expanding foam and there isn’t really a natural alternative.
I would estimate that time required to put in each section (hanging a beam, putting in noggins at the ends, cutting and putting in the ply and then laying the insulation) is about 45 mins. I haven’t put the chipboard flooring sheets in yet, since they will lie crossways to the beams, thus all the beams plus insulation need to be in place before doing this.
I have now finished putting in all the windows (sort of). Putting the frames in was very quick and easy, however painting and then glazing them was a real pain. Each window comes with glazed panels held in place with wooden beads tacked in with a couple of panel pins. You have to take these out to screw the windows into the sub-frames, but in putting them back in you need to put sealant strips around the glass, plus fill the voids between the units and the frame with industrial quantities of silicone sealant. This probably takes almost an hour per unit.
I decided to simply tack the units back in place in order to get the building weather tight and will do the fiddly permanent glazing later. None-the-less, it has probably taken as long to get this far with the windows as it took to put on a coat of render.
Next job – flooring.
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.