Flat garage roof advice

[gogmagog]

My mum n dad have a garage attached to their house. It's rather long, since the guy who built it (previous owner did it himself, we're told) also extended the kitchen sideways at the same time. So, it's the same length as the house (25 feet or so). Neighbour says he used pretty much any bits of chipboard he could find. There seems to be no incline, since water tends to sit it pools on top. It has a few leaks, and has once caused water to pour out of a light switch in the kitchen. I patched that one up, but we're thinking it would be nice to do something so that we can just forget about it in future. Having it properly replaced is out of the question - the money will never be available in their lifetimes. I was wondering if I could cover it all up with some corrugated sheets, making sure they slope down to the back, where there is already a gutter. Is this a reasonable thing to do, or just plain bonkers?

[Phil L]

Bonkers. Unless you get your corrugated sheets and timber for free, but even then it's unlikely that the chipboard would even support your weight if it has been soaked for any length of time.

Cheapo solution - use 8X4 sheets of OSB and get it rubberised by a pro

[gogmagog]

Thanks - that's given me something to start reading up about. Does this require removing everything that's there, or can it just go on top of the old one?

[Phil L]

It could go over the old stuff to save messing, not ideal really but I can't see it compromising the new boarding - the old stuff will just dry out eventually....it may feel a bit spongy underfoot, but the rubber can handle this movement

[Andy Dingley]

Same here.

IMHE (did it to my small workshop, probably doing it to dad's garage next) I'd go with a green roof. This is a clean scrape-off for the old roof, down to the wall tops. Then span it with close-spaced 2x4s, OSB on top of that, then 1" polystyrene insulation, geotextile, waterproof membrane, 1" perlite or vermiculite, geotextile, then 3" of soil. Plant with =A320 of mixed sedums. Split & replant the sedums as the grow, and within two years you can have it covered.

There's a group (Leeds Uni?) who have a downloadable PDF for about a tenner that's the best guide to building a roof at this scale.

[gogmagog]

Okay, thanks very much. Lots to think about...

[gogmagog]

Same here.

IMHE (did it to my small workshop, probably doing it to dad's garage next) I'd go with a green roof. This is a clean scrape-off for the old roof, down to the wall tops. Then span it with close-spaced 2x4s, OSB on top of that, then 1" polystyrene insulation, geotextile, waterproof membrane, 1" perlite or vermiculite, geotextile, then 3" of soil. Plant with £20 of mixed sedums. Split & replant the sedums as the grow, and within two years you can have it covered.

There's a group (Leeds Uni?) who have a downloadable PDF for about a tenner that's the best guide to building a roof at this scale.

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Interesting, thanks. I'll look at any possibility. Actually, it's already covered in moss and sedums.

[Peter Parry]

Bonkers. Probably the most reliable moderately low cost route is to strip the roof and replace any rotting sheets of material then fibreglass over it.

two of many suppliers and have instructions on their sites. I helped a friend do a similar roof and we completed it (including completely re boarding) in two (long) days.

[gogmagog]

Very interesting, thanks. I'd never have thought of that.

[Nightjar]

If the boards are sound the cheapest option is probably a paint on coating:

Bignell

[gogmagog]

I don't know how good they are in general, but some are definitely softened. It might be possible to replace a few after inspection, and then coat it. But that looks like a good option.

[NT]

The cheapest thing that will actually work is to a) strip and replace the deck - chipboard is the cheapest decking, but take care it never gets wet. The roof will fail as soon as it does. OSB is much better. b) felt it

All other options cost more. Where you can save is on labour by diying. If they're plain desperate, felt can be replaced with bitumen and mixed scrap clothing or shredded carpet.

NT

[SteveW]

To cover all the bases. I have two flat roofs that I have fibreglassed (I did want to use EPDM on one, but it is an odd shape and would have been difficult to do) and I covered my garage roof with galvanised steel roofing sheets. I went directly to a company making the sheets and they rolled them from a coil and cut them exactly to the length I required (12' 3") while I watched - that meant they could run from one side of my garage to the other with no joints.

My first fibreglassed roof is okay 13 or 14 years on, the second is only

12 months old and the galvanised sheets look like new 5 years on.

SteveW

[gogmagog]

Thanks all for your excellent advice. There are more options than I'd realised, and you've given me plenty to think about.