Flat roof repair products

Hi all,
I've had a few previous posts about the flat roof on my extension and what to do with it, but for the short to medium term at least I am going to need to do some repairs. What I found the other day when I went up there is that water had got under some of the felt, and though it has not come through the next layer I and the next dry day I obviously need to get the water out and stick this edge back down. Although a lot of the rood is in good condition there are a few bubbles which I think it would be best to cut out these bubbles and patch, and then I was thinking to cover the whole thing with one of those roof seal compounds. I like the idea at least of these products and a continuous seal, rather than the joints in the felt where water can be seeping under as it has done in this case.

There are obviously bitumen based products, and stuff like Thompsons High Performance Roof Seal and Isoflex Liquid Rubber, I have never used any of these before and was hoping anyone with experience can advise on products or their experience using them?

Also, best products for sticking down the felt, and I presume any standard felt is fine for patching before putting on the roof seal?

Thanks!

i'm afraid you've got problems with that roof - starting with the original design, and then how its been covered and detailed.
the construction framing was poor - perhaps due to inadequate support framing when the Velux's were installed, and you've got pooling in the gutter. maybe a lack of adequate falls?

cutting out and patching air/gas bubbles is not the modern best practice.
where the felt join edges are lifting is no simple matter to solve - even if its even doable as a repair.
theres no way that i know to "get the water out" - water vapour thats now in the roof will continue to bubble and lift any felt weak spots.
painting the roof cover with some kind of sealer ight give relief for a bit but i doubt it for long term.

a simple start would be to remove all debris from the roof and gutters, and check the soundness of the bay window roof felt.

i know you've come on here for advice but you really need an experienced eye on site - there are RICS surveyors out there that claim to specialise in roof work.

Thanks bobasd. I recognise that there is a problem with the design, not just the lack of sufficient falls and detail. The design in fact is a can of worms because as I have discussed in other posts, if I am going to spend the money on re-roofing I would have liked to get it converted to a warm roof, but with the current design and sloping slate front that is impossible, which means a complete redesign and rebuild of the roof. Aside from building regulations, I am also in a conservation area, which means I can't even start with building control until I have gone through planning, and I can't start with planning until I have a new design and drawings.

All of this would obviously take some time which is why I am where I am and thinking about patching and sealing. I am in the process of getting some roofers out also, to get opinions of best way forward and rough idea of cost for those options, but I doubt I will have everything in place, including funds, until another winter has passed!

P.S. I have already cleared up all that rubble, its the only pic I had handy and was just after the stone masons had finished with the wall. The pooling in the drain channel in the pic is mostly due to the rubble, and it drains freely now that is clean, but the pooling to the left of the channel is permanent.

So, still at this. Did get a quote to re-felt the roof, which was £10k. To be fair that is to convert to a warm roof, with 100mm insulation, and 3 replacement skylights, but there are some complications in converting to a warm roof due to height of windows and the slate sloping section, so I suspect it would go up above this quote by the time it was all over.

Trying to get them to give me a quote to just replace the felt (which is what I originally asked them for!) and leave as a cold roof, and also waiting on another company to quote to get a comparison. Anyone got a rough idea of what to expect for around 35 sqm?

Also, would still appreciate any comments from anyone who has tried roof repair products in case I need to act quickly as the rain just keeps on coming here!

Thanks

I had similar problems with our flat roof, being very exposed the storms earlier this year the wind got under the roofing felt and stripped it back, being an urgent repair, I overboarded the complete roof, applied roofing silicon between the boards and applied flash banding over the joins, I then gave the roof two coats of roofing compound, this has appeared to solve the problem , I hope to apply a further coat of roofing compound at the latter end of summer . I was given estimates of around £15.000 to do the roof and garage. I appear to have made it watertight for less than a grand . Maybe not professional but this is a DIY Forum .

Thanks bosswhite. That's interesting, so you actually screwed boards down over the existing felt, then applied the roofing compound to the boards? Or did you strip the felt back first.

I'm not against paying for it to be re-roofed, but my concern is that the roof design itself is flawed and if I pay thousands for someone to re-felt and then have the same problem again a few years down the line. the drain channel can easily get backed up which means there will be water sitting against the felt joins.

I did not have the time to strip the old felt off completely, although I lost most of it within a couple of weeks due to the Storms, the roof is at the back of the property and I have open fields at the rear of the property and am situated about a mile or so from the open sea so it gets rather draughty during the winter. My theory was that after a couple of other severe storms if it was re felted the wind could strip it back, its going to take a Hurricane to remove the boards this time , as I said before plenty of roofing silicon between the joints of the boards covered with wide flash banding, couple coats of roofing compound and then a coat every year or so . I could have gone down the road of Insurance claim , but this sort of claim is dependant on length of time felt has been down and the workmanship (more trouble than its worth .) If the boards last ten years it will still be a great saving .

Kaymo said:

Thanks bosswhite. That's interesting, so you actually screwed boards down over the existing felt, then applied the roofing compound to the boards? Or did you strip the felt back first.

I'm not against paying for it to be re-roofed, but my concern is that the roof design itself is flawed and if I pay thousands for someone to re-felt and then have the same problem again a few years down the line. the drain channel can easily get backed up which means there will be water sitting against the felt joins.

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You could put wood over the existing roof if you wanted to. I've had to do this up in Stirling recently because they didn't want to strip the old felt back.

I went up over the weekend and cut away the felt that the water was getting under. The felt underneath in the drain channel is sound, and it seems as though the felt in this section was the termination of the section coming from the garden room end (the bit of the L that juts out in the pic), terminated in a fairly stupid place where water running into the drain channel would put pressure on the join. I just put some bitumen trowel mastic around the join where I cut it as it slopes down into the drain channel on the other side, and in a few other spots around the roof where there were small gaps. My biggest concern was the water running down the channel under the felt and putting pressure on other joins, so at least that part is sorted.

Roof seems to be temporarily ok now at least, and no water has come through at any point so that gives me some breathing space at least. Having had a good look around a lot of the felt is ok, there are just a few spots where the felt is bubbled up or I am not confident for the long term. Maybe I could get away with just cutting out these sections, patching then going over with a roofing compound if necessary. Don't think I need to overboard anything in this case, and wondering whether it might just be worth patching the few remaining concerns and painting over it all with bitumen.