More thoughts on shed #2

As I plan for the building of the new shed I have been tossing around all of the thoughts mentioned in my last post, as well as getting input from several people on the Plastic Classic Forum and elsewhere. One of the good ideas was to purchase a pre-manufactured tension-fabric structure (which is basically what the bow shed is) from Clearspan, probably the best manufacturer of these structures in the business. I’m investigating that, as they do make an 18’Wx40’Lx16’H structure which would do quite nicely – but it’s a little on the pricey side, especially when compared to building myself. That particular building has been quoted at $7600USD + tax + shipping, which would bring it to me at pretty close to $10,000… A lot of money. I should be able to build a new bow shed for around 1/4 of that, even including windows and a better foundation, I think.

There were two significant problems with the last shed. These were:

  • The knee walls weren’t stable enough without the bracing system I put in after the fact, and
  • The shrink wrap was only going to last 3-4 years, requiring too-frequent replacement.
    Other than that, I really liked it, and would do the same thing again (slightly longer to give more space at one end for workshop-y things). So here’s my thoughts on addressing the two flaws.

1) Knee walls. By going from 18’ to 20’ bows, I can reduce the knee wall height from 4’ to 2’ or 3’ – that alone will significantly increase their stability – but not enough, so here’s the idea: make the knee walls into a small triangular structure at the base of each bow wall. Like this (very basic drawing!):

The idea is that the knee wall is inherently stable – and I will put anchors in the ground which I can tie into from the top of the triangle every 8’ or so. I can also sheathe it from the outside and store stuff in it from the inside (covered or not – hinged lids would be nice to cut down on clutter). I think I can make these 2’-3’ tall quite easily and get the additional height that I want in a better manner than the old shed.

2) Durability of the cover. While the shrink wrap was brilliant, and didn’t let me down in the two years the shed was there for, it was going to fail eventually, and there was no good way to know when that would be, which always bothered me. This time I’d like to have a shed which can last indefinitely. Making the whole shed rigid is one idea, but exposing any kind of material which isn’t usually used as a roof to the sun and elements is likely to create a maintenance issue, so going with a UV-stabilized fabric that will last well and be “easy” to replace is still a good idea. I was conveniently reminded of a company in the states which sells used billboard tarps in large sizes. They’re 17 mil tarps (more than double the thickness of the shrink wrap I used) that should hold up for several years (10-ish, I’d expect) – and quite reasonable to buy (although I haven’t had a shipping quote yet…). If I get two of them and put them both on then I’ve got a sacrificial outer layer and an inner layer which will keep the shed tight even if the outer layer fails. If it does, I can replace it and I’m back in business without ever having compromised the integrity of the shed. I like this idea.

I’ll also put a long row of twinwall polycarbonate along the south wall to get light in, since two layers of 17 mil tarp, even in white, will not allow a lot of light through. The row of polycarbonate will be 4’ high, and will start right above the knee wall, letting me see out to the south and letting in lots of light – but not lots of heat, since the bows are nearly vertical at their bottom. In the winter, with the sun’s rays slanting a lot it will let in some heat – although the place I have to put the shed has a lot of pine trees to the south, so I won’t expect any miracles of solar heating.

I will probably also sheathe the bottom 4’ of the rest of the shed with plywood and cedar shakes or clapboard to match the south side, and to give me a sense of security. Although any building is easy to compromise, I did used to have a funny feeling about having a bunch of tools just the other side of a 7 mil plastic tarp…

I’ll put a few more windows in to let me see what’s going on around me – it was very odd to be in a building which didn’t keep out sound at all but which prevented me from seeing the source of the sound.

And finally, I’ll put in some decent ventilation since while I never had a condensation problem in the old shed, it seems that I was alone in this – the other three people that I know of who have built either a bow shed or a Clearspan structure have had terrible condensation problems.

That’s where I’m at today, on Beth’s birthday, and that’s as far as I’m going for now!