How to fix a corrugated garage roof



1. The Professionals

This roof was fixed by a professional. He cleaned up the existing roof fully, took out all of the existing screws into the rafters, added a top quality perspex clear plastic cover, which matched the original profile and then screwed it all back down into the rafters, with good quality rubber caps over all the screws.

 
 
The closeup shows the profiles matching. This would have been more difficult for me to do myself as the profile is from the 1930's. The professional roofer could just order this directly from his suppliers:

 
 
Because it is now completely dry inside and the rafters all dried out fully, I have insulated the roof and added a false ceiling made from plywood:

 
 
The insulation was added to try and get rid of the condensation that I had as a separate problem. I think this is caused by the thin roof, so the inside of the garage gets really hot in the day and really cold over night. The insulation should stop it all heating up and cooling down quite so much, just like a proper garage, with a full wood structure and bitumen covering. You can see the insulation here, stuffed between the corrugated roof and the new plywood ceiling. I'll show more details further down this page.

 

2. The DIY job
I bought another (very cheap!) garage. This one was in quite a state, with hedge growing over the front doors and Ivy getting under the roof. And it was very wet inside. Clearly, the roof would need sorting out fully.

I thought I'd have a go myself. the existing roof was a more standard 3in profile corrugated concrete thing. Like above but much newer, probably from the 70's at a guess.

The left one here:



I haven't got many before pictures but here is the roof after I have fixed it with DIY options:




ADDENDUM

These concrete roofs are not designed to take weight and they can give way unexpectedly. To avoid any issues I have ALWAYS used a piece of ply to stand on, which is placed over a rafter, as least partly. Also, I do take up a large post, which will span rafters, so if something does give way, I can use that to fully support my weight. So I shouldn't fall through into the garage below.

Typically I used standard roofing screws to simply attach my new sheets through into the rafters. And because my sheets are see through and very thin in fact, I was able just to put them straight on top of all the old roof, not even disturbing the old screws. The sheets were flexible enough to give enough that the old fixings didn't disturb it too much. Here are some of my typical new fixings:




I did have a few problems with some areas and I worked aruond this by adding some simple bolts through the original concrete roofing, just to give the new top some extra hold. You can see I have used some larger (stainless steel) washers over some of the bolts. I did find that this thin uPVC roofing does sometimes split and the larger washers do help spread the load a little. You can see in this shot as well, how the new cover easily bends right over the existing bolts of the original roof. So I didn't have to disturb anything at all to do this job. That is a big plus in fact:




You can see in the next shot how I've used simple small bolts at the edges, just to hold the new covering onto the old (solid) concrete corrugations. I've only done this where I've had to, but in fact, one side of this garage is open to the wind so all along that side, I used this method to secure the top cover:


 

3. Inside the new garage roof

Worth showing a bit more detail on how I prepare inside, to avoid condensation over winter, in particular:



Basically, I want to insulate the inside of the roof so the temparature doesn't vary so wildly from night to day. I'm sure this happens because these roofs are so thin. So I rig up some thin plywood, which in turn holds up insulation. This can be got cheap these days off the internet and I specifically use a non-fibre-glass version, to avoid all the handling problems with that material. See the screenshots below. Basically, I cut lengths that then fit between the rafters and I just keep it up there with the cheap plywood, small size sheets make it easier to handle:

A cheap roll bought off the internet:



Cut to lengths (with scissors) to fit between the rafters:

 

4. Getting on the roof
One last thing worth covering: Getting on the roof. this is not as easy as it sounds, depending on your setup. But obviously, it is critical to get this right. The last thing you want is an accident, just for stopping a few drops of water from getting inside the garage... It's not worth it. So you need to think about this a lot. I couldn't get on my first garge roof at all (the one above). but luckily, this one is on a hill and the back of the garage is not so high up. So my ladder is high enough to let me step off easily, directly onto the roof. This is what you really need, so you can get all your tools up there as well: