Cold Roof Ventilation??

[peter88uk]

We are doing a garage conversion to the rear part of our garage. At the moment it's at plan

We have an issue with the ventilation above the insulation, we can put softfits in the eaves, but we are unsure what to do as the joist go the short length so for most of it would not cross ventilate to the other side. (if that makes sense).

To try and explain and image:

Any suggestions?

Thanks.

 

[^woody^]

Just fill it with insulation

 

[peter88uk]

Thanks woody.

I briefly spoke to the building inspector and he didn't sound like that was an option (although I didn't suggest it - but I now will). I assume that there isn't any reason why filling it with insulation shouldn't pass building regs?

Thanks again.

 

[tony1851]

Just fill it with insulation

Serious question; would this actually work? and what insulant would you use?
surely not fibreglass. What about interstitial condensation? Just wondering.

 

[^woody^]

It works for SIP's. Just follow the same principles

 

[theoldun]

Just fill it with insulation

Not arguing woody, asking serious question. Have you ever had this approved by any Building Control?

That aside, RFV-FL and Rytons Products both sell flat roof abutment ventilators. We make our own up out of Glidevale FV250 facia vant.
Regards oldun

 

[^woody^]

Yes, if you can demonstrate that your design removes a cold surface for air to condense on, and prevents moist air entering the void then it will be
acceptable

edit - poxy spelling

 

[peter88uk]

BC didn't like that idea woody and said there could still be a small voids somewhere where moisture could develop.

Think we are just going to put a warm deck roof on, more expensive but the easier solution.

 

[noseall]

We (Woodnail, Old Codge, Tony etc) have argued about this method, and have come to the conclusion that whilst in principle the method seems sound, building control are probably doubtful over the 'robustness' of some installation techniques.

There would have to be promises of foil tape, foam and mastic galore to prevent the inevitable eyebrow raising from them that need to be obeyed.

 

[CluelessIncompetent]

http://www.londonflatroofing.co.uk/cold-flat-roof-explained/

 

[AronSearle]

It works for SIP's. Just follow the same principles

Yes, if you can demonstrate that your design removes a cold surface for air to condense on, and prevents moist air entering the void then it will be
acceptable

In sips the cold surface is the outer layer of OSB, which is then faced with a breather membrane and a cavity. This sips panel can't be faced with non breathable roofing membranes.

The OP hasn't said if this is a flat or pitched roof, I'm guessing pitched. If it is a pitched roof with tiles, then you could 'possibly' install VCL on warm side, full fill with insulation, OSB sheath, breather membrane, battens and tiles (as you would a SIP panel).

You can download something like builddesk and run a condensation check, or get the insulation company to do it, if it passes a condensation check you can then print of the results for BC.

If it is a flat roof then they need to cross ventilate or do it as a warm roof.