I've been doing a bit of thinking about the corrugated iron extension-section of my garage.
It's in a bit of a state, to put it mildly. It was built in a very basic will-this-do manner in the first place, and now it's looking very wobbly.
I've posted this photo before, but here it is again because it's the best pic I've got of the roof - as seen from the back here. But the front isn't any better.
And here's an interior shot, which shows the very minimal timber framework....which is getting more minimal all the time. The two uprights supporting the beam at the bottom edge of the roof (or what is now the bottom edge - there used to be another row of sheets going right down to the low brick wall at the back) and the two Acrow props supporting the next beam in, were put there by me as a bit of collapse-insurance.
Note how the upright timber on the right is sliding sideways, pulling the wall with it. It's all rotten and it all needs to be replaced.
I think the first thing to do is buy a load of
new timber from my good mate Terry. Terry doesn't know he's my good mate yet, but I think we're going to get to know each other quite well.
I've had it suggested to me that I should go for a complete rebuild with a steel frame - and in some ways that would be a better option. But if I stick with a timber frame, it counts as a like-for-like repair (even if the 'repair' is so extensive it's not far off a rebuild), and I won't need planning permission for what would technically be a new building. Some time back I asked a local planning consultant about all this, and the gist of their reply was....stick with like-for-like and nobody will have a reason to ask questions. So that's what I'll do.
However, I think I will improve the design somewhat as I go along, so while the refurbished building will look much the same it'll be better under the skin. In particular, the end wall, which is now sliding sideways, won't be just a load of new timber uprights stuck in the ground to replace the rotten existing ones. That just sets up the same problem to happen again. Instead I'll build a dwarf wall (about 1 metre high) in bricks or blocks, on a proper foundation, and base the timber frame on top of that. I have to remember that there's a river on the other side of that wall - only a little river, but little rivers can get bigger at short notice in the right conditions. So that'll give me a useful bit of flood resistance, too, just in case The Big One ever comes rolling down the valley.
Now....cladding. I want to keep the existing appearance of the building, partly so I don't run into any planning hassle, and partly because it's got a traditional agricultural shed look, which is in keeping with other buildings in the area. I don't want to tart the place up so much it ends up looking like an offshoot of the Slough Trading Estate.
That means a like-for-like replacement of the corrugated sheeting - or, at least, it's got to
look like-for-like.
The existing sheets have clearly been taken off and put back on again at various times over the years. They're dotted with fixing holes in all sorts of places. Some of them are good enough to go again if I ever build a small shed or something, but for the main building I think it would be a false economy to try and re-use the old sheets. I would end up spending my life chasing leaks. So I'm looking at new sheeting.
Basic wriggy tin sheets are
readily available, and aren't massively expensive in themselves.
But what about insulation? It would be nice to have a bit more than 0.7mm of sheet steel between me and the weather.
It's possible to create a 'built up roof', which essentially means a
double layer of roofing sheets, spaced apart by a sub-frame, with insulation in the middle. That's a lot of extra hardware to install, though...
It's also possible to buy ready-insulated panels, in which the bottom sheet/insulation/top sheet sandwich is all one unit. Then you just nail 'em into place like single sheets, no extra framework necessary.
But I don't want an all-over solid roof. I'd like to let a bit of daylight in. That means putting some transparent (or at least translucent) panels up there. And there's not much point in having a fancy insulated roof if it's dotted with skimpy, single-skin, transparent panels that let all the heat out. So my roof windows will have to be insulated, too.
Well, the good news is, it's possible to buy triple-skin (essentially triple-glazed) corrugated polycarbonate panels that let in loads of light but are pretty good at keeping heat in, too. I've got the flat version of this stuff on the back of my house, and it works very well. It's tough, too - some builders working on my neighbours' house dropped a brick on my roof, and it literally bounced right off. So some of this would be ideal for the garage roof windows...
BUT...it looks like there's a problem. The polycarbonate panels and the insulated panels are made by two different manufacturers and they are not compatible with each other. The dimensions of the corrugations are different. The pitch (ie distance from the peak to peak and trough to trough) is 167mm on the insulated panels, and 177mm on the polycarbonate panels. It looks like the radius is different, too, although they don't give any figures for the insulated panels. But going by the illustrations, the insulated panels have a flatter shape than the polycarbonate panels.
I thought it might be an idea to buy a few sample sheets of both types, and try to fit them together as a test, just to see if it could work. Maybe that 10mm difference in pitch could be fudged somehow. It's possible to buy the polycarbonate panels in any quantity, so I could just buy one or two. But the insulated panels have a minimum order quantity of 100 square metres - so that's a nope, then.
I'm not too sure where to go from here....
One slightly lateral-thinking solution would be to clad the entire roof in the polycarbonate panels....and then paint the ones I want to look solid with some sort of brown/grey colour, thus making them look like ye olde corrugated iron. I can't quite decide if that's a brilliant answer to the problem or just a daft idea. It certainly solves the panel-compatibility problem, but would the triple-skin insulation be enough if it was spread over the whole roof? And painting polycarbonate is a bit of a pain, too - it needs lots of prep and priming just to make the paint stick.
Still, now that we're all on lockdown there's plenty of thinking time to figure all this out!
