Garage roof replacement

booksandbikes

Hello - I'm after some general advice on what to ask for when getting quotes please.

Our garage roof needs replacing; it has the original 1960s cement asbestos and we are thinking of going with EPDM or GRP. Our priority is longevity and good quality.

Is any one of these preferable over the other, given the images below?  The roof has these extended upright bits on either side so I don't know if that makes a difference.

We also would like it to be insulated....we have very bad problems with damp and condensation dripping off the roof so want to eliminate that as much as possible.

Some of the wooden frame is rotten and other bits have signs of historic woodworm so we will most likely get all rafters/joists replaced. Is this a good idea based on the pics below?

We have a gas pipe running through the joist - is that a problem?

Is there anything we need to watch out for based on the pics?

And last question, any idea on cost? I don't have the exact measurements, but I'd say it is probably around 3m x 5m.

ButterCheese

I would certainly get 2 or ideally 3 quotes from established roofers.  Don't assume that big names with lots of vans will do the best job or at the best price.  We found our roofer in the pub by chance, and he's recently done our (converted) garage flat roof and our conservatory roof.  He did the flat roof for £1000 - the quote we got before that was £5000!

Also don't go by check-a-trade.  My colleague got roofing done by a company on their site, asbestos was involved, their kids ended up in hospital and are now on medical watch for the foreseeable future.  They also lost £14k and check-a-trade did not even repsond to their complaints.  The court case is still ongoing.

Anyway, get some quotes.  Nothing in your picture looks too difficult but the asbestos will cost more to properly remove and dispose of.  I think you're probably looking at 5-7 grand

Section62

booksandbikes said:

Our garage roof needs replacing; it has the original 1960s cement asbestos and we are thinking of going with EPDM or GRP. Our priority is longevity and good quality.

Is any one of these preferable over the other, given the images below?  The roof has these extended upright bits on either side so I don't know if that makes a difference.

We also would like it to be insulated....we have very bad problems with damp and condensation dripping off the roof so want to eliminate that as much as possible.

It looks like the roof has a reasonable pitch on it, and if you want to add insulation anyway then I'd suggest plastic coated steel could be a good solution.

The parapet walls are a problem in the sense it is important whatever roof covering you use has appropriate upstand/flashing so you don't get leaks between roof and the walls.  But also a bonus because you can add insulation without either reducing the internal headroom or increasing the overall height of the building.

Metal roofing like steel can be a problem for condensation, but if you add a decent thickness of insulation and the installers take care of doing the job right, then you could eliminate the condensation problem completely.

The gas pipe going through one of the purlins is not good - you might want to speak to a gas engineer about getting the pipe rerouted first, rather than just hoping the workers doing the roof don't damage the pipe when trying to remove the purlin from around it.  And I would suggest replacing the purlins if you are going to the expense of a new covering... they could last for years more, but you may find the top surface has started to rot (from the condensation) and this might not be visible until the asbestos has been removed.

On the subject of asbestos (have you had it tested?) - you'll want to make sure it is removed and disposed of by a reputable company, ideally one which specialises in asbestos removal.  Although people will probably try to convince you it is "safe" asbestos, the truth is all asbestos-containing products need to be treated with caution.  You don't want a contractor who will take a sledgehammer to the sheets and leave your garage (and garden) covered in fragments of asbestos cement.  Likewise, I guess you'd rather the contractor disposes of it responsibly, instead of flytipping it in a country lane.

Tucosalamanca

I've been pricing for jobs like this all week (viewed five garages just this morning). This is what I'd be quoting.

• Strip and dispose of asbestos sheets (following HSE guidance, PPE, wrapping, waste transfer notes etc).
• Carry out replacement of roof timbers where required (some looks in good order, I wouldn't touch the joist with gas pipe going through it)
• Supply and install new 18mm t&g OSB deck.
• Supply and install new vcl.
• Supply and install 50mm tissue faced insulation fixed with thermal broken washers (Kingspan TR 27 or similar)
• Supply and install new single-ply membrane and edge trims (3 layer felt system would be similar cost).
• At perimeter, cut a chase and install Ubiflex imitation lead flashings.
• Clear guttering and downpipes and ensure free flowing.

Cost £6,000 plus vat (£7,200 inc)

It looks like the sheets are bedded into the render, that might increase costs as removal might be a pig of a job (I'd need to see it).

I wouldn't go GRP or EPDM as introducing insulation won't be straightforward and any cost savings would be minimal.

If you just wanted a like-for-like replacement with fibre cement sheets, costs would be closer to £3/3.5k plus vat

Albermarle

• Supply and install new single-ply membrane and edge trims (3 layer felt system would be similar cost).
• I wouldn't go GRP or EPDM 

Out of interest what is the single ply membrane made out of ? I would have guessed it would be some kind of polymer membrane, but your comment about not wanting to use EPDM ( which is a kind of polymer) made me wonder.

Tucosalamanca

EPDM (Ethylene Propylene Diene Monomer) synthetic rubber.

Single-ply, mostly PVC membranes, some are TPO but this is becoming rarer.

When public quote EPDM, they're generally referring to rubber based systems (often one-piece membranes that are adhered to the substrate).

To confuse things further, some people will also refer to EPDM as a single-ply membrane.

EPDM is glued to the substrate and relies on adhesives and tape for detailing works (for detailing it's inferior to almost any other product, imo).

PVC single-ply can be glued or mechanically fixed to the substrate, detailing is done with a hot-air gun forming 'welds' for a seamless finish. In my opinion, it's superior in every way (other than cost).

From an installers perspective, EPDM/Rubber is great because the margins are so good. It's my most profitable product but we only use is specific situations (detached garages, roof dormers, outbuildings), where there's a simple shape and no detailing required.
Less scrupulous trades will go EPDM in all situations because they're just interested in profit (or because they don't have the skills/tickets to install single-ply).

Google is your friend if you want find out more.

EPDM Complete Guide | Roofing Megastore
EPDM Vs Single Ply PVC: Which Is Right for Your Project? – Flat Roofing Systems

Albermarle

Thanks for that. I have some background knowledge in the area of polymer based sheets, but not about the actual installation.
Interesting what you say about the different cost and profit margins. From what I know about polymer prices etc it seems a bit odd that EPDM sheet is cheaper than PVC sheet as the base polymer is more expensive.
Must be down to various additives and different processes used in the sheet manufacturing process.
I visited IKO in Clay Cross in the past where they make PVC ( and TPO ?) sheet. Interesting process.

Grenage

I was in a similar position with my garage.  I had the asbestos sheets taken away for £550, and bought full length replacement plastic coated metal sheeting of the same profile for £1100.

Add Section mentioned, condensation can be an issue, so I laid roofing membrane across battens before laying the sheets. Not had a drop in the inside.

tetrarch

FWIW I'm a big fan of EPDM. I've installed a couple myself and had my extension professionally done because I wanted a good join around three skylights that was beyond my competence levels

My 2003 self-install was about 100sq m and is still going strong with no sign of a leak. My (professionally? installed) GRP fireplace roof on the other hand lasted tless than two years before failing at a s seam and basically turning to dust at the edges - not a fan

When I was trying to get an install it seems that many roofers are actualy felters and will go with what they know. Also, it's guaranteed work as they always need replacing at some point - unlike EPDM, which is guaranteed for 40 years

Regards

Tet

booksandbikes

Thank you so much for your replies. You have given me a lot to consider (and google!).

Tucosalamanca - you say you wouldn't go GRP or EPDM as introducing insulation won't be straightforward. Can you expand on that please? Insulation won't work with either of those, or potentialy cause rot from the underside? I will consider single-ply membrane as an option - it's not one I saw regularly mentioned on roofers sites.

booksandbikes

Section62 said:

On the subject of asbestos (have you had it tested?) - you'll want to make sure it is removed and disposed of by a reputable company, ideally one which specialises in asbestos removal.  Although people will probably try to convince you it is "safe" asbestos, the truth is all asbestos-containing products need to be treated with caution.  You don't want a contractor who will take a sledgehammer to the sheets and leave your garage (and garden) covered in fragments of asbestos cement.  Likewise, I guess you'd rather the contractor disposes of it responsibly, instead of flytipping it in a country lane.

Thanks - yes, will definitely make a point of looking out for this. Not had it tested, but it was mentioned in the survey, and then when we moved in the previous owners had left all the original paperwork around construction (from 1967!!) which stated that it was cement asbestos.