Friday 29 April 2011

East wind

It's in the nature of this place, up on its high ridge, that it lives in the wind blowing in off the grey Atlantic. Our winds are westerly or southwesterly 70% of the time. Being on the western side of the ridge, my croft takes the full force of them. That's the main reason why I'm designing my croft house to be earth covered, sunk into a natural declivity in the ground. But I don't yet have a croft house; I don't yet have planning permission. So I've built a temporary shelter, my summer palace, which is essentially just a platform in the trees with a crude tent over it. And because the prevailing wind is in the southwest, I've built it in the northeast corner of my wood.

All the time I've been planning and building the summer palace, the wind has been in the west, and the wood has given it good shelter. Today, it was virtually finished. Today, I moved the last of the furniture into it. Tonight I would have moved in completely, but that I have to go to Edinburgh at the weekend, and I didn't want to leave the cats alone in a place they weren't familiar with...

Tonight, according to the met office weather station four miles away, it's blowing force nine. From the East.

My roof is - was - made of two layers of thin polypropylene 'tarpaulin' stretched over a ridgepole which is twenty feet above the ground. It makes a wonderful sail. When I got up there at 19:30 this evening, it had already torn out several of its eyelets and was rapidly destroying itself. It had to come down. But I hadn't designed for it to be taken down easily in an emergency, which meant I had to go up to the ridge pole and untie it at both ends. And I had to do it myself because there was no-one whom I could ask for help who could get there before it was too dark to work.

The first end wasn't too bad but the second end, with four hundred square feet of tarpaulin flapping around in the wind, was bloody scary. However, I got it down, dragged all my furniture into the centre of the floor, covered it tightly with tarpaulin, and left, 'homeward, tae think again'.

This is, actually, a problem. I do have to be out of here, and living in the shelter, in a week. There isn't any slack in that. But the roof as I'd planned it will not survive an easterly gale. So I need to design a new roof, and build it, within a week - and, ideally, without using any additional materials I have to buy, because the money I spend on the summer palace is money I don't have to spend on my permanent house. Reinstating the original roof isn't a solution, because it clearly isn't strong enough.

There are fundamentally three options.

The first is to borrow someone's yurt or caravan. I actually could do this. I'd really rather not - I don't want to be too dependent on other people's help. But it isn't impossible.

The second is to build a bender on the existing summer palace platform. It's what a lot of sensible people have suggested. The trouble is that a bender is claustrophobic, and, in any case, I don't have any long bendy poles to spare (although I could get some from elsewhere).

The third is to make a framed gable roof with round spruce-pole rafters - which I have in quantity - and cover those rafters with carpet and then with tarpaulin. My thinking tonight is that that is what I'm going to have to do. I do have the materials I'd need, and the tools and skills to use them. I'll need to build a lot lower than I was planning, and consequently it's inevitably going to be a bit cramped, but that can't be helped.

Sunday 17 April 2011

Planking the roof

Radial planking

Planking the roof of the cone poses interesting problems. You can plank a cone radially, and every plank is straight. My rafters run radially, but that doesn't have to be a problem; I could put short purlins between the rafters to fasten radial planks to. I can even envisage some rather pretty joinery for those purlins. It isn't impossible.

But every plank would have to be cut longitudinally - identically, so I could make a jig and it wouldn't be a big deal, but it's a significant job. More significantly, radial planking also would not strengthen and stiffen the roof, and I'm still concerned by my friend Pete's comment that the roof could be floppy in strong winds. The tensile bracing which Pete suggested and which I've shown in the last drawings will help, but...

Short tangential

When I originally envisaged planking the dome I thought of short sections of plank between two rafters only. This has multiple problems. There's a lot of work in doing that cutting, and getting it right. In practice, every one would have to be fit and then cut individually, and there would be almost two thousand of them. There's two lots of nails at every crossing between plank and rafter, doubling the opportunity to miss the rafter and end up with ugly exposed nails. Actually more than doubling, because given that every nail is through a plank end it cannot go into the middle of the rafter, and must be on a diagonal. Finally, all those cut ends create areas of roughness which could potentially damage the waterproof membrane which will be laid over them. So it's entirely possible that the roof would have to be sanded before the membrane could be laid, which would be a huge job. The more I think of it the more I see the short-plank roof as a bad idea.

Long tangential

But, a cone is a developed plane surface; there are no complex curves. So, you could lay your planks perpendicular to one key rafter, and just keep planking like a floor. The problem with this is that the cone has a curvature, and the planks will only bend so much. As you get closer to the peak, the curvature tightens. However, it's a very shallow cone - for most of its area it does not curve much. This means, of course, that the planks will partially wrap around the cone, forming graceful curves themselves which will be visible from the interior (particularly if one in every five or so is stained a contrast colour - see later in this essay).

It also means that if you started perpendicular to one particular rafter, then the natural wrap of the cone would mean that on the opposite side of the dome where the wrap met, you would have planks which were crossing the rafters at a steep angle, and you would need to provide a 'king plank' where the wrap joined. This might look good, but I'm not confident.

The solution I'm presently inclined to try is to start planking perpendicular to the most east-westerly outer rafters, and have a king plank running north-south across the roof. This makes the eastern and western halves of the cone essentially separate structures, but it solves some of the problems of wrapping and I'm confident it would look well. There's a minor problem in that the inner rafters are offset from the outer rafters by 3.75 degrees, so a king plank which is perpendicular to an outer rafter cannot be perpendicular to an inner rafter and vice versa. It will probably look best if it is not perpendicular to either.

In the upper part of the cone, the curvature will get tighter, and the planks won't curve that much naturally. There are a number of possible solutions.

First, I could saw a series of transverse cuts across the plank, halfway through the thickness. It's an old joiner's trick to ease a piece of wood through a curve that's too tight for it. The problems are that the cuts are best done on the inside of the curve, where they would be visible from the interior. The technique weakens the plank anyway, but if done on the outside weakens it more. And the risk is that it snaps, which wouldn't be good.

Second is, I could build a steam box on site and steam the sections of the planks which need to curve most tightly. This would probably work. When steamed, wood goes (relatively) floppy. It also swells, and assembling toungue-and-groove joints when the wood is swollen might be tricky, but this idea has definite merit.

Third, when the curve gets tight I could switch to a different material which can take the curvature more easily. Specifically, for the uppermost 1200mm (or even 1800mm) of the cone I could switch from 22mm tongue and groove planking to three thicknesses of 6mm plywood or one layer of 6mm plywood and two of 9mm OSB (oriented strand board - although I'm not convinced that 9mm OSB will cope with the curvature required, and 6mm isn't readily available).

On colours

In some of my working drawings I've coloured different pieces of timber in bright contrasting primary colours, to make it clearer how joints are intended to work. I never intended that the timber in the structure should be coloured in this way. But I've come back to colour from a different angle.

What I'm building is a frame to support a roof, in Galloway, where it rains. A lot. It can, of course, be covered in polythene when not being worked on; but it's also an exceptionally windy site, so polythene is likely either to get blown away, or, worse, to act as a sail and damage parts of the uncompleted structure. So it would be a good thing if the structure were resistant to wet before it's assembled. Also, the timber needs some degree of protection from xylophilic invertibrates.

I don't like paint, and, in any case, on this scale, paint is simply far too much work - I don't have either the money or the time. But the sort of stains sold for outdoor timber would be quick and not outragreously expensive to apply. They're readily available in a range of browns and greens, from pale to dark, and less readily, in a range of more saturated colours.

So, I'm thinking about staining the main structural frame; and if I'm going to stain it I'm thinking of colour. A forest green frame would definitely be nice. A variety of toning colours, in browns, greens and greys, would also be nice, and could be done either to colour-code the structural function of the element or simply, as in my drawings, to draw attention to and explain joints.

The possibility of colour staining the roof planking, either in a regular pattern or, within the toning range, randomly, also appeals, especially if the 'long tangential' planking technique is used. It would show up the boatlike form of the roof.

All this is slightly complicated by the fact that an exposed timber roof in a kitchen is required to be finished in a fire-retardent varnish, and I assume my singlespace will be considered to be all kitchen from this point of view. But there is no problem with applying fire retardent varnish over a stain, so the solution of staining before erection and then applying varnish to the interior once completed is entirely possible.

I haven't decided on colour. For that matter, I haven't decided on long-tangential planking. But that's the way my thinking is running just now.

Monday 11 April 2011


One of the things I need to consider about the croft is moving around. Not moving me around, my feet or a bicycle do that. And for getting my groceries home, well, a bike or my feet or at worst a wheelbarrow will work. But while building my house I'm going to need to get a fair bit of building materials in, and once it's build I'm still going to need occasionally to move heavy or bulky stuff around.

The planners, of course, will not want a house which cannot be reached by road. But the planners are not me, and I do. At present, you can get a normal car over the hill to the croft... in dry weather. In normal weather, you can't - not because it will sink in, but because you can't get traction. The hill is too steep and you can't get grip.

So what are my options?

One is, construct a track over the hill so that cars can use it. In theory that's 'free' to me, since the co-op agreement is that the company pays for new roads. But the truth is, a new track to my croft is longer than all the other new tracks the company needs to build put together. And money the company spends building tracks is money the company can't return to us in loan repayment. So actually building me a track does cost me money. More significantly, it costs everyone else money, and that doesn't seem very communitarian.

OK, so next, I can depend on borrowing from my neighbours. In theory it's also 'free', although one has to have favours to trade. But that's what I'm trying at present, and it isn't working very well. Of course, when we're all settled things may be a little easier, but I don't want to have to depend on it all the time.

Third possibility, I fit off-road tyres to my little car. That's actually probably enough. But it means that the fuel consumption on-road would go up considerably. It also means that I would tend, lazily, to drive over to the croft too often, which isn't what I want. And it would mean the little car would get more beat up more quickly, as it was used as a general beast of burden (which, to be honest, it is now).

Fourth is, pony and cart. It would be transportation for which I can grow my own fuel. I don't have the skills, but plenty of my neighbours do and could teach me. However, it's probable that it wouldn't get used enough, and the pony would lack exercise and practice. Also, I don't think it would be wise or good husbandry to expect a pony to pull anything very heavy over the hill, so I would still be dependent on charity of neighbours.

Fifth is, get a motor vehicle for farm use. If it was strictly for farm use it wouldn't need MOT or road tax, and could legitimately run on red diesel; alternatively I could sell my little car and get a vehicle which would do both farm and road use, but I won't do that until I'm convinced I can earn my living without needing to drive to cities.

So what are the options for such a vehicle?

I could get what is contradictorarilly known as a 'quad bike'. They are not very expensive, and reasonably simple to run and maintain. They are what the farmers round here use for moving small quantities of stuff, and the farmers are not fools. On the other hand they're noisy, can't pull anything heavy, and might be too easy to get in the habit of using.

I could get a small old tractor like the grey fergie on which I learned to drive fourty four years ago. It would be simple and reliable, would haul a reasonable weight over the hill, and would additionally be able to do  farming jobs like thistle topping, mowing, wuffling and harrowing, and as much ploughing as I'm ever likely to want to do. Grey fergies are something of collectors items nowadays, but you can still pick up a reasonable diesel for a thousand pounds and spare parts seem easy to find. It's definitely possible.

I could get an old diesel landrover. If more than 25 years old it wouldn't need road tax, but (unlike a grey fergie) could be driven into town if I didn't have to go far. It couldn't do ploughing or anything requiring a power take-off, but it too would pull a reasonable weight over the hill. Again, a budget of a thousand pounds would get something usable.

Of course motor vehicles which aren't used very often have to be kept dry, or they deteriorate. If I can store it in the 'communal vehicles bay' in the Void that will be fine, but I expect that space is going to be oversubscribed. Otherwise I'll need to build myself a shed - which isn't a problem, but adds extra cost.

Thursday 7 April 2011


In my last essay I wrote of some unresolved issues in the singlespace design. In summary

  • In a single space, a lavatory poses a problem;
  • In my design as it stood, there was no external storage, for bicycles and firewood;
  • The roof was potentially floppy, and thus vulnerable to damage in strong winds;
  • Drainage on the north, uphill side, is problematic;
  • The cone is an unnatural shape in the landscape, and half of it drains north, aggravating the drainage problem.

I've tried to address these issues in a new variant of the design, longeaves.

Firstly, the shape in the landscape. In the first singlespace drawing, the frontage was very stark and basic. The roof overlapped the front edge of the building very little, making the geometric regularity of the fenestration very obvious. I tried to address that in the second drawing by extending the front eaves out from the building, but I still did this with rotational symmetry, and it still looked, in my opinion, very artificial.

Considering the need to add additional space - somewhere where, in the longer term, a water closet might be installed, and also somewhere where bikes, firewood and other outdoor stuff could be stored - led  me into reconceiving the roof. If one has a conventional building, the most convenient way of adding an additional space is to add a leanto - essentially, a space under deliberately extended eaves of the roof. Well, OK, let's build the roof with long eaves on the sides, deliberately creating additional space. Let's build the retaining wall to accommodate that space. Suddenly the roof has changes shape; it's no longer a neat truncated cone. Now it has an asymmetric skirt. And if we fair that asymmetric skirt into the main roof in a fluid curve, then we have a shape which does not look quite so artificial in the landscape. The energy costs of doing so are remarkably small; the eaves will not shade the windows at noon, because they are extended only at the sides, nor will they at evening, when the sun is low.

I could, of course, build these eave-extensions on both sides of the building, and initially that's what I thought I'd do. However, but the time I'm old enough to need an inside water closet I shall probably be too old to ride a bicycle over the hill, and the shape of the depression in the ground into which I want to put my house will make it easier to have an extension on the west side only. So my present plan is to have only one such extension, arranged for now as an external store but designed with the intention (and thus with the insulation and damp-proofing) which will allow it to be incorporated into the internal space later. Again, increasing the asymmetry decreases the landscape impact by decreasing the obvious artificiality of the shape.

As discussed in the previous essay, the obvious solution to stiffen the roof is to add tensile bracing like the spokes of a bicycle wheel. My aesthetic temptation is to use rope; Hempex brand polypropylene such as I plan to use for the ring beam lashing is sufficiently durable and looks good, but I think the tensile bracing needs to be very, very low stretch indeed, so stainless steel wire with turnbuckles for tightening is probably more sensible. I might compromise and go for steel rod (which would also be cheaper than stainless). These new drawings show how this could be done, and it looks reasonably persuasive.

I thought a lot about reshaping the roof to merge it into the hillside better, and I've decided not to. Adding a gable (which would be possible) detracts from the structural simplicity, and thus elegance, of the space; the gable adds cost and complexity, and replaces a cone in the landscape with flat planes in the landscape. Making an irregular shape strong is even more complicated, and adds costs not just in materials but in time. The simple cone isn't a natural shape; but it is a simple shape to build and it does have elegance. And I think that in this version it won't shout in the landscape - particularly if I plant gorse on the roof.

This leaves the issue of draining the uphill side. I started with the idea of an underground house. That, in the end, turned out to be too expensive. Singlespace still has a turf roof, which makes it less obvious in the landscape, and it's nestled into a natural hollow. The question is, do I dig it back into the hollow and berm natural earth up against the walls? I can do. And there are well documented solutions to draining this sort of design. They aren't absurdly expensive. To be able to walk from the natural hillside onto my roof with no obvious transition seems a good thing to me. And building back into the hillside definitely decreases wind exposure and increases insulation.

But Galloway is very wet. Water will be moving down that hillside in wet weather, and the drains will be critical - digging them out after the building is complete would be difficult and expensive. My friend Pete, who's given me a number of good steers in this design process, doesn't think I should dig right back into the hillside. He thinks I should leave a walkway behind the building  to make drains maintenance easier...

He's quite possibly right. And, if I went that way, I could use straw bale for the back walls rather than concrete block and polystyrene, increasing the insulation and decreasing the energy cost. It isn't impossible, but I'm very resistant. Digging back into the hillside feels like the only part of my original concept I've got left.

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The fool on the hill by Simon Brooke is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License