Garage roof replacement

My asbestos cement roof is starting to fall apart on my concrete sectional garage so looking at replacing it. (Yes I know what I’m doing with the asbestos and have former colleagues in the trade). Thinking of  bitumen corrugated roof panels to replace it. Firstly, do these have any issues with condensation like the asbestos has. Do they need something like OSB/ply under them, or would a simple wooden frame be ok? The osb would remove the condensation issue, but is it overkill. The current roof is on a metal angle iron frame.  Thanks

Thinking of bitumen corrugated roof panels to replace it. Firstly, do these have any issues with condensation like the asbestos has.

Yes very much so.

Got corrugated bitumin on the garage out the back – don’t put much in there as it has a condensation on the roof issue half the year

I did my replacement side garage roof in tin in the end from planwell roofing. Still has condensation issues but I insulated the inside and hasn’t been an issue since.

OSB/Ply is usually used when applying bitumen sheets that are melted to give a waterproof membrane onto the ply sheets. Replacing the asbestos sheets is easy enough, you can stick with the previous one, which is usually cheaper and not a huge issue to repair in the long run, you can go for the panels you’ve stated, which can be a little more, or other options with shape and design, but mainly just panels or sheets.

Getting rid of the asbestos can be quite easy, our council have an asbestos skip at the local tips, so we just wrapped ours up and took them down ourselves, saved a fair few quid from the shysters who are around trying to turn this into a very expensive industry!

Oh yeah, condensation issues on any garage is an issue, you tend to have to look at secondary options to fix this, the roof isn’t going to do much to protect this year round.

Any style of roof corrugated roof material will suffer from condensation, condensation is purely warm air meeting cold air, which with a roof of that type is always going to happen, maybe the clear double/triple glazed plastic panels would be OK.

Can you take it off and fit a proper flat roof with joists and felt?

How about making it pitched instead ?

Not just its going to make it more airy, it also gives a bit more room.for storage. You can make a platform up there,or out of the way storage for annoying long stuff.

I replaced my asbestos garage roof with galvanized corrugated steel panels. I did 9mm ply, 100mm mineral wool (between the joists), breathable membrane then panels. Membrane catches any condensation. Ply means when they tried to break in via the roof by unscrewing roof panels they couldn’t. I also increased the pitch.

We had a flat asbestos/concrete roof replaced about 10 years ago with a rubber roof over ply – minimal condensation now.

I did 9mm ply, 100mm mineral wool (between the joists), breathable membrane then panels. Membrane catches any condensation.

That’s what I did too. Worked wonders. Garage stays warm too.

Had mine replaced with insulated sandwich panels, two profiled metal sheets with about 50mm of foam, bright white on the inside and grey or a few other colours on the outside. You get angled trim sections to tidy up the outside, also they come in long lengths so if your garage slopes front to back you can do it in just 3 or 4 panels with no overlaps.

Never had any condensation and you can put fixings into it on the inside with self tappers 

I replaced the roof on my barn about 10 years ago with felt lined coated steel panels which are a direct replacement for your existing roof.
The self tapping screws will go straight through the angle iron.
The felt lining holds the condensation until it evaporates. It works – the only place I get a little condensation is off the original steel angle iron and it’s pretty minimal.

Thinking of bitumen corrugated roof panels to replace it.

I have used this on a chicken shed and I believe it needs fully supporting as it otherwise sags.

Did this at my previous house – Marley sectional concrete garage with corrugated asbestos roof. Removed the roof, installed a wooden ring beam to the top of the wall and built some pitched roof frames with large, open eaves. OSB over the top and then cedar shingles over the top. Never had a problem with condensation again.

The bitchimin sheet require full support of osb / ply or similar. Corrugated sheets are cheapest, you can get them with a anti condensation lining. Cement fibre board are off a little less condensation as they are no as smooth and slightly pourous, this is why they are popular in agricultural buildings with lots of animals inside but these buildings also have lots of ventilation for good animals health.

Thanks folks. The current roof has a shallow apex, (about 20deg ish). I have currently got foil bubble wrap stuff stuck to the underside of the roof panels and almost entirely eliminated the condensation issue, which is why I don’t want to go back there. So thinking that I go OSB, with insulation and bitumen panels on top. Will I need to worry that the osb will get damp and rot and need replacing in 5 yes?

We fitted a corrugated steel ( Rollaclad ) over our steadily failing and leaky probably-but-never-checked-for-sure concrete asbestos roof. A big wooden frame bolted very firmly into the walls and then clad on top. Took the opportunity to increase the pitch angle of the roof at the same time – the lack of drop was what likely caused/hastened the problems with the original roof as water ended up pooling on it in a viscous circle – more water, more weight, more sag, more water.

So we now have two rooves on the garage and it’s dry and relatively warm 🙂

But before that, I tried patching it one end with those bitumen sheets and it wasn’t great. They need full support underneath, and didn’t seem massively durable even then. Doing the job with the cladding was 1000 times better, although cost was about £2.5k in the end; a (poor) job with the bitumen sheets would have been £750-1000 to cover the whole lot.

Id use insulated corrugated panels.

Similar to defblade we fitted a fibreglass roof over the top of the failing asbestos roof using 9mm ply boards and covering/sealing with fibreglass. I have a mate who has a fibreglass company so mates rates applied. There is still some condensation but nowhere near as bad as before.