We have a brick built shed with a concrete roof, which serves me as workshop. Unfortunately when we moved in the torched on felt (the proper three-layer system) had died in a large part, and water could make its way inside. Thus it needed re-roofing.

Now, whilst I have no experience roofing beyond tacking down felt on wooden roofs (which is infinitely simpler than what ended up happening), I immediately decided to volunteer to re-roof it if the landlord would pay. And since it made no sense to do one side, I offered to do the neighbour’s half as well (the shed is semi-detached). The reasoning at the time was that a proper reroofing job would be at least a grand, and the landlord was unlikely to volunteer that for a small leak. More likely he would put some sealer on; the problem would reappear; etc. (I have no evidence this would actually be the case as I did not ask him. But it’s what I’d likely do if someone said the shed was leaking—repair it for a year or so and try to get friendly with a roofer in the meanwhile.) Whereas I wanted to know the tools and wood inside were properly dry. And besides, I’d never done anything of the kind.

The options, then, were:

• seal with some (GRP?) roof sealant and hope for the best
• hire/buy roofing torch, roller, etc and do a 3-layer system as before
• strip the roof and replace with a modern GRP roof-in-a-can
• strip the roof and put down shed felt
• strip the roof, seal it with bitumen sealer, apply a thick bitumen paint layer, and then felt as a top layer

Whilst the modern GRP roofing processes are supposed to last for ever and be completely leak free, where do you go if they go wrong? You can’t exactly buy the stuff at B&Q. Torching was out—I’ve seen a roof burned out in a reroofing job, and I’ve no desire to try to explain that to the landlord. Just slapping down shed felt feels horrible when the current finish has lasted so long. So I went with the latter option.

Firstly, I needed a ladder. They were all rather expensive, so this was knocked together:

Then Lidl had a decent ladder on offer, so I carried one home. Two ladders doesn’t do any harm, after all.

The bitumen sealer is a thin paint, more like wood stain. It waterproofs the concrete largely so the next layer will take without soaking in, but it does provide a degree of sealing in the cracks.

The bitumen paint, on the other hand, is a thick, viscous layer applied ‘with brush or mop’. It forms a layer all in itself, about 3/8" to 1/2" thick. When tacky the felt is placed on top (and rolled down with another roll of felt, since I lacked a roller). The felt was the thickest, longest life no-torch felt I could find, specced for 15 years. Since even a torched roof is only supposed to last 20 years without work, and frequently lasts no longer than 15, I didn’t feel too bad about that.

This bitumen paint is horrible stuff. The professionals use it if torching isn’t possible. It comes in horrible big drums, and after half an hour the solvent had sent me completely light-headed (hold on when using ladders).

But worse even than that was clearing off the old felt. Most of it came fine, but a portion—about 1/3 of the roof—was still stuck down (i.e. 2/3 was flapping loose). Roofers have a proper tool for scraping off old felt—and of course can apply heat. I had a handheld paint scraper. It took several hours and left my right arm and wrist very sore. But once you’ve started a job like this you have to finish.

Then the felt was folded round and glued down, but I was running out of bitumen paint, and the wind was fighting me. I cut it in a hurry with scissors—none too straight—and cleared up the worst of the bitumen run off. Then later I fitted a fascia board, guttering and a downpipe.

Postmortem

All in all there were around 20 heavy-duty black sacks of rubbish when I’d finished, not including all the clothes I’d worn, the brushes, gloves and paint drums. The ladders were cleaned up a bit with white spirit; then the wooden was just painted over and the metal eventually cleaned with tar remover the neighbour gave me. A few things would have made life easier:

• Clamping the side of the felt whilst it glues needs attention before starting work (I ended up making up jigs whilst it dripped).
• Better is to fold round and glue underneath, even if it does mean losing the (cast) drip rail. That way you can just use G-clamps.
• Just because the torched on stuff hung straight down doesn’t mean yours has to (you can just crease it to make an overhang).
• Don’t do anything with bitumen paint, ever. It is pretty good though
• Guttering covers a multitude of sins.
• So does screwing a rain guide board on to the edge. But that would require making fixing holes first.
• Bitumen will never, ever, come out of anything it touches. Fortunately the landlord doesn’t seem to care about the odd streamers which made it onto the fence. I got the worst off.