Dormer flat roof leak

[Rich-G]

Hi,

I've a leak coming in an upstairs bedroom of a dormer above the window. I suspected it was damage in the flat roof, allowing water in and it will collect above the window. I had a roofer come and look the other day and I'm waiting on quotes back.

They have advised me that the felt is damaged and took pictures to show me, but they've told me the felt has been applied directly to the insulation boards. Knowing nothing of how a flat roof is constructed, and from my understanding from a quick conversation with the roofer, it seems there should be plasterboard, then joists with insulation, or joists with insulation on top (wasn't sure), and then a deck on top of that for the felt to be applied. Because the felt is apparently on the insulation board the felt wont be easy to remove, meaning to properly remedy the situation with the leak I'd need to be quoted to apply an entire roofs length of insulation, then board, then refelt.

Its a 1950s bungalow with an dormer extension (not sure when built).

Is it always wrong to apply felt straight to the insulation board or are some flat roofs like this? Is it true that will mean the insulation boards will need replaced?

If theres cracks in the felt can I get life out of the roof by simply repatching the felt with 1x metre sized squares? Yes I'd like the proper fix but money is tight and theres other things needing addressed on the house first.

I guess without having been up there myself I'm just wanting to make sure I'm not being oversold the job. That this situation I find myself in isn't rare and happens in old houses, and maybe just my luck, and that if felt was applied directly to the insulation that in would indeed all need replacing?

Obviously without anyone actually seeing the roof here, opinions will just be taken as conjecture but I'd be interested to know if what I am being told sounds plausible, as its going to be a big job if these actions are required.

 

[^woody^]

Felt should be fitted to a timber support board layer, not to the insulation.

You can patch the felt, or use a liquid patch product such as Acrylpol, but if the cause of the cracking is differential movement because of how it's been laid, then the problem still exists and could reoccur.

If the issue is age, then patching may just get you a little more time, but normally not worth it.

Photos may help you get more opinion here.

Don't rely on one roofer's opinion or quote.

If you go with a different system such as a resin or fibreglass liquid cover, then it may be possible to just overcoat the whole lot. You'll need a contractor who specialises in such a system to advise if it's viable.

 

[Rich-G]

So just to confirm looking at a slice of a roof, you'd have the felt, underneath that a timbre support board layer, underneath that insulation and then underneath that another board layer, and finally plaster (the ceiling you see from within the room)?

Yeah I'm going to be sent some pics but from what I gather thats correct, they've not bothered for whatever reason to add this timbre support layer, which is making the first roofer say we won't be able to relay felt without relaying insulation.

I've had a second roofer out today who also suggests the felt has been laid on the insulation, but it didn't phase him to remove it, i.e. he didn't force the option of relaying new insulation. I asked him if the insulation was damaged what happens, and they say they can melt felt to patch that up - whether that is correct or not I don't know.

I've got one more contractor coming tomorrow, and then a roofer who specialises in something called EPDM rubber - which would be a different finish, but again not sure what would be involved in that.

The only quote I've had so far is from the contractor today who wants £2,500 for relaying the felt for the back roof only (about the size of a normal one car garage.

 

[ChrisJP]

This all sounds a bit dubious to me. Sure there should be plasterboard fitted to the underside of the rafters - that's what you should be able to see from inside the room. Above that and between the rafters there ideally should be some insulation material, though on an older roof that may not be there. Then above that, fastened to the top of the rafters there should either be a series of timber boards or, more likely, sheets of chipboard or plywood. Then on top of that is the roofing felt. So the roofing felt will ALWAYS be fixed to the "insulation board" as your roofer calls it, and there is nothing wrong with that. In any case, unless your roofer stripped back the existing felt and then cut a bit out of the timber or chipboard below, he'd have no way of knowing how the roof has been constructed. So I fear he is spinning you a line to talk up the job, something which, unfortunately, quite a few roofers indulge in.
I would get another roofer to take a look at your roof.
One way of getting some more life out of aging roofing felt is to coat it with something like Bostik Flexacryl - this has fibres within it and dries to a tough flexible membrane which fills any cracks in the felt and resists further cracking. It won't last as long as new felt, but should be good for a couple of years at least

 

[datarebal]

There Are confused comments here.
Felt can be laid onto insulation , there are products designed for that (in a warm roof situation )
The build up from joists up would be deck, VCL,, insulation and then the felt

The fact you've been told the felt is on the insulation leads me to believe this is a warm roof .

Thermaroof TR24

www.kingspan.com

 

[Rich-G]

Hi all, thanks for the comments so far.

Yes this is warm roof.

Since my original post I've been given the following advice and quotes from roofers. Roofer 1 who initially said he wouldn't be able to lift the felt without replacing insulation, has quoted £7500 which will include felt and kingsan (I beleive thats the insulation).

Roofer 2 says he can lift felt, if he damages the insulation he will melt a bit of felt for patches etc - £2500.

Roofer 3, offered not to lift the felt and instead lay felt over the existing felt. £2000 - with this option I'm worried about the weight of the extra layers of felt. Any advice here would be appreciated.

Roofer 4 specialises in rubber roofs (this EMPG stuff). He commented that the roof is in good enough knick, that they can build the rubber stuff (platform et al) over the top at a price of around £6500, or take the whole roof up doing new vapour layer, insulation etc, and then rubber roof at a quote of £10,000. He also commented he wouldn't be keen laying extra felt over existing felt (roofer 3's suggestion), but didnt go into specifics as to why he was against that.

Obviously very different prices and very different solutions. So any feedback would be appreciated. I don't mind paying the higher prices if the work is done properly and above all else correct. For example roofer 3's solution of felt over felt, seems good on the surface, but I worry about the weight of the overall roof after - is this something I should be concerned about or am I being overly OCD and paranoid?