Re-sealing a flat concrete outhouse roof

ed110220

With the bad weather recently I have noticed a leak in the roof of my outhouse. It's a single storey structure attached to the main house with a flat concrete roof sealed with bitumen felt. The felt has failed at the junction with the house (it was tucked under the upper storey cladding, but has come away), but as the house has has wide eaves it only leaks if the wind is blowing strongly from the north east while it's raining.

Any opinions on the best way of re-sealing? I'm looking for a DIY solution. Is replacement of the felt with similar the way to go or are there better, more modern solutions?

slipperyshoe

Modern felts (SBS or APP modified) last as long as anything else on the market place. Dont listen to those who know nothing but will happily recommend single ply (TPO,PVC, EPDM etc). All of these are do-able but no cheaper and not longer lasting. Liquid is probably the easiest way to DIY but beware of cheap rubbish. Avoid acrylics or old fashioned 'black jack'.

If the felt is in a brittle aged condition then I would suggest you strip back to the concrete first. If it were me I would go with a top quality SBS modified and polyester reinforced 2 layer felt system. Will last you 35yrs+. Go to a roofing merchant rather than B+Q for materials.

WLM21

Try Thompsons Roof seal over the joints in the felt, or even over al the felt.

I used it on a garage roof last year, over pretty old felt and it has been great.

It was very easy to apply. I actually opted for two coats, 24 hours apart, but I think one is good too.

cyclonebri1

One of the most effective and permanent solutions would be fibreglass, unfortunately it's also the most difficult and messy job you could ever choose to DIY.

I'd do it, but I wouldn't advise you do, not with the onset of bad weather.

Take Slipperys advice

ed110220

Thanks all. I had never actually thought of fibreglass, but if it's difficult and messy I'll give it a miss, though my dad used to do a lot of work with fibreglass repairs.

southcoastrgi

from your post it seems like the felt was run up the wall & stuck to it ?
If this is the case it should have had lead flashing inserted into the wall & dressed down over the felt, anything else is a bodge.

ed110220

southcoastrgi wrote: »

from your post it seems like the felt was run up the wall & stuck to it ?
If this is the case it should have had lead flashing inserted into the wall & dressed down over the felt, anything else is a bodge.

It's a BISF house so the upper storey is clad in steel while the lower floor has a concrete render on steel lattice. The felt is inserted behind the 'lip' where the upper storey cladding meets the lower storey render. I don't think traditional flashing can be applied to steel cladding(?).

Here's a photo of the neighbours' house, which is identical but obviously easier to take a picture of from my landing window!



Thinking about it again, the steel cladding acts as flashing would normally!

southcoastrgi

ah ha pics always helps lol, no you can't stick lead to that, either a strip of new felt stuck down with the correct adhesive or maybe flashband, as i wouldn't have thought you could get anything up & under that cladding unless it's sitting away from the wall.

(doesn't your neighbour get fed up with people walking across his garden to post their letters ?)

ed110220

There's quite a gap behind the lip at the bottom of the cladding, enough to fit the felt behind.

I've never asked if anyone has posted a letter there, but I doubt it as there are only open fields behind with a barbed wire fence at the bottom of the garden to keep the cows in. I don't know if the post office are still looking for it

cyclonebri1

Take the screws out of the bottom level of flashing and insert 300mm wide lead sheet in there. Replace the screws, seal under the trailing edge of the lead with a lead sealant after cleaning the bonding face of the existing felt roof. Jobs a goodun.

Any other issues, replace the lot, that leak may be the 1st of many as it's all the same age. It's a small roof and not too expensive

slipperyshoe

That detail is absolutely fine; felt is not self terminating but under cladding there is no issue whatsoever (so long as cladding doesnt leak!). Saying that the cladding should really be taken off to install this detail, overlap should be minimum 50mm. If you dont do this the risk of fire is great; you are unlikely to actually have a fire but the roofer will be so paranoid about starting one that he will use insufficient heat when welding.

FYI lead free flashing or GRP termination bar are also acceptable details for bitumen felt.

Would'nt go down the fibreglass roof, as poster said it is a good solution for domestic properties, however it is very expensive, can be tricky to properly install and is messy. It also does not have a longer (certified) lifespan than felts. I work in commercial roofing and it is not a viable option on any roofs for say 100m2 and upwards.