Flat roof venting

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Hi all,

I had a really bad job done of my flat roof and since then it has leaked and no come back on the so called professional so I’m going to EPDM cover it myself. It was setup as a cold roof by the roofer but after learning more and checking the work I found that it looks to be poorly vented.

In the picture below the joists run horizontally and it is only vented on the wall side labelled B and opposite at C between the 3 first joists. Wall A is where the flat roof joins a pitched slate roof. All other sides don’t adjoin anything else.

0BA06173-6792-4292-AE48-97D2AB97D1C6.jpeg


There is a 75mm void between the insulation and roof boards.

If I was to turn it into a warm roof it would mean new insulation at £5-600 on top as well as making sure I join into pitched roof ok (as a diyer).

I got a few quotes and some said the venting wasn’t really necessary. One said just vent at one end (C) and others said warm roof only. Quotes were £3-5k so above budget unfortunately.

So, with all the varying advice what would you recommend I do?

The room will one day become a bathroom and a small other room so could be quite a wet atmosphere.

Thanks for your advice in advance
 
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Are you saying youve just had it done, but its leaking and you are concerned about insufficient ventilation of the cold side?

A photo would be helpful to visualise configuration of gutter, upstands, abutments etc.

Importantly how are the falls formed? Horizontal joists with firrings on top of each joist?

Im guessing guttering is side C.
 
Hi, we had it done earlier in the year and the roofing company are no longer around (in that name at least!). Everyone who has seen it says it was not fibreglassed correctly.

There is no gutter fitted at present but it will be on wall C. The falls are formed by the firrings as you guessed.

I’ll see if I can get a picture a little later.

Thanks
 
Stuff it with insulation. Vapour check membrane on ceiling before plasterboard.

Or vent it from side C to A.

What's the actual question?
 
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I can’t vent on the A side as there is no roof vent or suitable voids.

The question is what can I do to ventilate the cold roof as C to A isn’t possible and C to B is only going to vent around 20% of the roof (the joists stop any further air movement)?

Or am I wasting my time and forget about a cold roof and save up for a warm roof? Or another approach as per your vapour membrane and no ventilation idea.

Thanks
 
I can’t vent on the A side as there is no roof vent or suitable voids.

The question is what can I do to ventilate the cold roof as C to A isn’t possible and C to B is only going to vent around 20% of the roof (the joists stop any further air movement)?

Or am I wasting my time and forget about a cold roof and save up for a warm roof? Or another approach as per your vapour membrane and no ventilation idea.

Thanks

Your simplest solution would be as Woody says, stuff with roll insulation.

If its fully open from below you could use a roll type insulation that can be used instead of celetex

http://www.insulation-actis.com/hybrid-system/hybris-uk.html
 
Thanks. So fill the 200mm void completely?

I’m presuming no venting at all with this approach?
 
Thanks. So fill the 200mm void completely?

I’m presuming no venting at all with this approach?
What you need to understand is what the warm/cold roof concept is intended to prevent - damp from warm air and cold surfaces, and high humidity levels leading to mould growth.

Remove the conditions and you remove the likelihood.
 
I am no expert but I researched loads after having a bad roofing job (old style cold roof with no ventilation causing the roof to fail early) and quotes to do it properly were similar experiences to yours, roofers with "25 years experience mate, know what I mean" types giving me quotes which wouldn't get through building regulations for £4k.

Looking at your pic, could you change your facias along wall C to give ventilation across the whole wall and cross ventilate to allow the whole roof space to benefit... of course the other side in wall B would be the ventilation on the other side and I, not being an expert would not know if this is enough ventilation on the other side. Seems a better solution to what you have now at the very least though.
 
Hang on... am I being a weirdo here? :LOL: I missed a totally obvious; ventilate from the long ways ends and use cross ventilation to allow the airflow above the joists.
 

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