Looking to take a dip in the usual pool of knowledge…

My father in laws garage roof is shagged to the point of collapsing. Its some sort of cement board crap that will be tested and removed either way as the joists are rotten and the whole lot needs to come up.

What’s the cheapest way to reroof a communal block (owned) garage whilst ensuring that next doors leaks stop coming through?

Current roof is 50×130 joists with ~18mm thick shite board and flat. It’s the end garage so pitching is an option and there is no real issue with access.

Primary concern is keeping it dry for as long as possible. It’s a glorified car port in Cumbernauld, not a lifestyle hut.

A quick pricing up gives me replacement 47×125 joists and 18mm OSB at £366 before we even add sarking or proofing. Would corrugated bitumen or such be a cheaper route?

I was quoted 2k to replace an asbestos roof, reboarsimg and felt

Steel box section?

For finishing of the roof I can’t fault https://www.rubber4roofs.co.uk/

Used them twice, once for a 6m x 3m garage, once for a 2m x 3m porch. 100% waterproof, cheap as chips.

For structure of the garage roof I just used a few 6×2 joists and Stirling board. Whole thing cost me about £500.

Unfortunately he doesn’t have £500 to spare or I’d just be pressing on with what I’ve priced up already. I’m looking for as cheap a solution as possible.

Price up the foam sandwich aluminium panels. I paid a pretty sum to have my old asbestos roof taken away, about 6 new joists, and about 4 new roof panels about 6m long. I asked him for an extra panel so I could create a dry storage area between the garage and fence.

Can’t remember the price but the extra panel seemed bloody cheap (unless he’d made so much cash out of me that he just treated it as pocket money…)

Making it look pretty was simple, using L shaped Aluminium profile you cut with tin snips. Lovely inside as no heat comes through and it’s a shiny white ceiling.

You’d have to make some sort of upstand to avoid leaks I expect.

Galvanised corrugated steel sheets come in at about £25 a piece for 3m x 1n ish so 6 ish to do a single garage? Provided you can get some pitch on them,

So £150 for sheets + timber joists and battens should come in at less than £150

I doubt you can do it for less than £300

You could use fence boards the really cheap 150 x 16mm things and pitch them and lay like tiles might save 50 quid on the job

The galv sheets come in at 133 quid on roofing megastore, screw fix is goodfor the roofing screws

Do not try and put the screws in without driling a pilot hole in the sheet.

If you place your joists in the right places you can get away without battens

Onduline 133 quid for a typical single garage.

5 joists needed .

Expanding foam the edges .

Job done.

It’s what’s on my zwift/home office room (an old concrete sectional garage

Bitchimin board requires complete support so you will still need the OSB or similar.

Coropol 1/4 cheaper than onduline even

Do not try and put the screws in without driling a pilot hole in the sheet.

Why’s that? The tek roofing screws are designed to be self drilling. They even have a drill point on the tip.

Why’s that? The tek roofing screws are designed to be self drilling. Some even have a drill point on the tip.

If screwing through the ridge (and you will unless you want to get wet inside) the force needed to get it started through galv sheet will deform the profile even with tecscrews.

How bad is it? The cheapest will be to fix what you have. Prop the roof, replace the joists, or sister a new one next to the old one. Sealant on any small holes, flash band (with primer) on any cracks. Definitely not the best solution, but functional, especially if it just for a car.

Centre punch drill and then screw..
Just done a roof with 600 tek screws and no leaks

Cheers all, looks like the bitumen board is wining so far, £300 seems reasonable.

How bad is it? The cheapest will be to fix what you have.

It’s literally cheaper to remove the lot*. It’s collapsed in several places, the joists are rotten and would need significant reinforcement (and cost) to build from above after sorting the joists.

*potential asbestos issues aside. The board looks like this mixed with cement and compacted :

Going with corrugated cement board will reduce the chance of condensation, it gets used on livestock buildings.
If you go down the corrugated route, find some one that makes and cuts to size, it will save overlaps when laying. I got some 16′ pieces for my quick re-roofing of our garage. Easier than pre drilling for the roof screws is to use a punch to mark out and stop the screw dancing, the self tapping part of the roof screw will cut through.