Warm roof concern

[speccy]

We had some concerns with our roofers and quality of work so called out a reputable roofer to check out the work on our warm flat roof with the intention to possibly take over the job.

He immediately noticed breathable roofing membrane had been used instead of a VCL (vapour control layer). I checked the architect drawings which clearly also state this should be VCL. It seems building control just signed it off without really checking. The new roofer suggested this should be replace with the proper membrane as will cause issues. Im awaiting building control who seem to be really poor and slow to respond here, if it really is an issue i want this rectified before we continue. Appreciate anyones input here.

Just to confirm we currently have

Joist
OSB
Breathable membrane (should be VCL!)
PIR Foam
OSB
EPDM

 

[harrythefurrysquid]

Yeah that should be a VCL. How does a roofer mess that up?

 

[speccy]

Yeah that should be a VCL. How does a roofer mess that up?

Thanks Harry, indeed a good question, does show their lack of competency. So all has to come off and be replaced i guess?

 

[harrythefurrysquid]

I would think so, otherwise you're going to get condensation soaking the top OSB layer and insulation, which will presumably then go mouldy and rot.

You want a professional roofer's opinion, but it sounds like you already got one.

Edit: BS5250:2011 (latest version I could find online) says:

With all warm flat roofs there is a risk of interstitial condensation forming
between the thermal insulation and the waterproof covering; to avoid that risk,
an AVCL with vapour resistance at least equal to that of the waterproof
covering, should be provided immediately above the supporting structure. The
AVCL should be wrapped around the edges of the insulation and sealed to the
waterproof finish at the perimeter and all penetrations.

Various roofing system manufacturers produce convenient diagrams based on the standard highlighting the VCL:

 

[speccy]

I would think so, otherwise you're going to get condensation soaking the top OSB layer and insulation, which will presumably then go mouldy and rot.

You want a professional roofer's opinion, but it sounds like you already got one.

Our building control officer claimed 'it should be ok' as the foiled backed pir foam acts as a VCL?! I feel we can trust noone, apart from this new roofer, is that bs?

 

[harrythefurrysquid]

Sounds doubtful to me.

Did they tape it? And if they did tape it, surely they'll have taped it across the top, not the bottom - which would put the "VCL" on the cold side - and it seems like that's putting a lot of faith in the tape to stay perfectly sealed.

 

[speccy]

Sounds doubtful to me.

Did they tape it? And if they did tape it, surely they'll have taped it across the top, not the bottom - which would put the "VCL" on the cold side - and it seems like that's putting a lot of faith in the tape to stay perfectly sealed.

Tape it no did they fck... well it seems after asking the building control again after asking them 'what would you do if this was YOUR house' we had the obvious answer of make them do it again properly. Hopefully that will happen this week sometime. Thankyou for your input here.

 

[Notch7]

Tape it no did they fck... well it seems after asking the building control again after asking them 'what would you do if this was YOUR house' we had the obvious answer of make them do it again properly. Hopefully that will happen this week sometime. Thankyou for your input here.

the PIR should have foam in every gap and then all joints foil taped.

and a decent VCL



Theres no firrings mentioned - it’s vital these go under PIR boards as must not be any air void between insulation and deck OSB.

 

[datarebal]

With the spec above the vcl would never be perfectly sealed anyway. It's punctured with screws .

 

[Notch7]

With the spec above the vcl would never be perfectly sealed anyway. It's punctured with screws .

That’s very true.

 

[noseall]

It's a warm roof! Fix duplex plasterboards and forget about it.

 

[noseall]

We had some concerns with our roofers and quality of work so called out a reputable roofer to check out the work on our warm flat roof with the intention to possibly take over the job.

He immediately noticed breathable roofing membrane had been used instead of a VCL (vapour control layer). I checked the architect drawings which clearly also state this should be VCL. It seems building control just signed it off without really checking. The new roofer suggested this should be replace with the proper membrane as will cause issues. Im awaiting building control who seem to be really poor and slow to respond here, if it really is an issue i want this rectified before we continue. Appreciate anyones input here.

Just to confirm we currently have

Joist
OSB
Breathable membrane (should be VCL!)
PIR Foam
OSB
EPDM

A warm roof does not rely on a robust VCL but benefits from belt and braces. Fit Duplex boards and forget about it.

 

[harrythefurrysquid]

Rip the ceiling down to fix it (but maybe it's not in yet)? And I guess you need extra care if there are penetrations for downlighters etc, and achieve a good seal around the edge by some means.

That does sound like a solution to go with if you were trying to cheaply fix a problem with an existing roof that was out of warranty.
Is it right for this situation though?

 

[^woody^]

Membrane can be used as a VCL. Taped joints and the right way around.