For sure the design should see you end up with 1:80 after everything's sagged a bit or seams are taken into account. Trouble is a lot of roofers and DIYers don't take that into account.
Pooling water on felt cold-roof with insufficient slope - Help!
- Thread starter Kingo206
- Start date
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To empty every bit of water off a flat roof, it would need to be 45 degrees +. Tiny amounts by the seems is normal. Flat roofs don't mind being wet.
He didn't take the furring strips all the way to the ends of the joists. Common mistake.
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From Bauder technical:
“According to BS 6229 & BS 8217, flat roofs should be designed with minimum falls of 1:40 to ensure a finished fall of 1:80 can be achieved, allowing for any inaccuracies in the construction. This applies to general roof areas along with any internal gutters.”
I used to set out orangery roofs where GRP was the finish, with a fall of around 1:50 to 1:60 Orangery roofs are quite complicated because the falls have to carry water around the lantern, especially awkward when the orangery had hoppers and not gutters
I'm going to go against the flow, literally, I think it's not even level but slopes back. The water is gathering right on the edge of a seam. When it inevitably freezes in the winter it will push the very edge of the seam open, then a bit more every time until it finds its way through.
My roof was similar - 30 years old and recently refelted when we bought the place but in my case with random dips all over the place mostly due to joists warping slightly over the years. I suspect it was originally built with wet wood.
Yours looks otherwise OK though, which is why I suggested the Black Jack. It's a bitumen paint, i.e. made of the same stuff as the felt, so it bonds and becomes as one with it. You wouldn't be able to peel it off it you wanted to, it's all one sheet of a single material once done. It contains fine fabric threads, so knits itself together. When I did mine I made extra effort to gob it into the seams then finished it by brushing up the joint, leaving a smooth ramp rather than a step.
The silver top coat is to keep you cooler but also prevents the bitumen below getting degraded by heat and UV.
Mine after its recent second silver coat. The paint's still wet here, hence the weird patchy colour. It goes an even silver/grey colour when dry...
You'll also see that it highlights any dips or bumps, less so once dry. It looks like yours won't be visible anyway, so won't matter at all. But the room below was a few degrees cooler the next day, it's good stuff. That lip near the bottom isn't opening up, it's just a shadow. In about five years I'll overcoat with the black gloop again and sculpt this into a ramp.
If you were starting again then the answer would have been rubber, GRP or a pitched roof, although all options come with their own issues and nothing lasts forever. But as you are where you are you'll get decades of protection from a few tins of paint.
My roof was similar - 30 years old and recently refelted when we bought the place but in my case with random dips all over the place mostly due to joists warping slightly over the years. I suspect it was originally built with wet wood.
Yours looks otherwise OK though, which is why I suggested the Black Jack. It's a bitumen paint, i.e. made of the same stuff as the felt, so it bonds and becomes as one with it. You wouldn't be able to peel it off it you wanted to, it's all one sheet of a single material once done. It contains fine fabric threads, so knits itself together. When I did mine I made extra effort to gob it into the seams then finished it by brushing up the joint, leaving a smooth ramp rather than a step.
The silver top coat is to keep you cooler but also prevents the bitumen below getting degraded by heat and UV.
Mine after its recent second silver coat. The paint's still wet here, hence the weird patchy colour. It goes an even silver/grey colour when dry...
You'll also see that it highlights any dips or bumps, less so once dry. It looks like yours won't be visible anyway, so won't matter at all. But the room below was a few degrees cooler the next day, it's good stuff. That lip near the bottom isn't opening up, it's just a shadow. In about five years I'll overcoat with the black gloop again and sculpt this into a ramp.
If you were starting again then the answer would have been rubber, GRP or a pitched roof, although all options come with their own issues and nothing lasts forever. But as you are where you are you'll get decades of protection from a few tins of paint.
After 5 years since the previous paint, the silver had vanished where the water was pooling but the black paint below was absolutely perfect. Definitely no peeling anywhere, the felt below doesn't see either the sun or rain at all.
Thanks, I have had two roofers here who confirm there is a slope up to particular point then it simply becomes flat/level.
I will leave it for now, sort it structurally when it comes to re-felting.
Thanks for all your input.
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