Jump to content

Warm roof build up - Air cavity - Metal sheet.


Recommended Posts

Ok, I have a warm roof, Pavatherm above the rafters. About to fit Tata Steel metal roof but not on OSB sheet but batten fixed vertically at intervals to support the pan.

Do I have to have a 50mm ventilation cavity as its on batten not OSB which would not need a cavity for a warm roof. Is it necessary?

Thanks all,

 

 

Link to comment
Share on other sites

Same as me. Warm roof, pavatex, non tenting breathable membrane, vertical counter battens, horizontal battens,  box profile roof sheets.

 

Battens then counter battens = 50mm gap anyway.

  • Thanks 1
Link to comment
Share on other sites

I don't think you need a ventilated void under the metal roof because all of the structural woodwork (rafters) are on the warm side of the insulation. Any condensation should run harmlessly down the membrane.

 

I would double check with the metal roof supplier just in case they want a ventilated void under the metal or other reasons? Such as preventing corrosion/rust?

Link to comment
Share on other sites

@Temp @ProDave

Thanks for your replies. I have spoken to my BC and has said cavity is not necessary as its a warm roof. I would like a cavity so 25mm is fine, no counter battens needed.

Tata want a solid deck of OSB, provide you with 40mm nails which go straight through the OSB and puncture breather membrane which does not work for me.

 

Link to comment
Share on other sites

Are you ever going to walk on the roof? I don't think I would want to walk on a tata roof that doesn't have some sarking board beneath it.

Edited by jfb
Link to comment
Share on other sites

@JamesP

the normal build up for a warm roof with an impervious roof finish like metal is to either (a) ventilate properly under the metal or (b) install a proper vapour barrier on the warm side of the construction.

Link to comment
Share on other sites

I have aTata roof and this is on 18mm structural osb. DO NOT under estimate how much IMHO that you need a solid continuous support underneath the metal roof. When you are doing the ridge pieces and general finishing you will need to stand on the roof. Even a roof ladder will mark/dent your roof. I would contact Tata and talk to them. My roof make up is a warm roof with a 50mm ventilation layer and the nails have punctured the membrane but everything is fine. My/insp said we did not need a v/layer as he was not overly concerned about moisture due to us having mvhr and the level of airtightness but the timber frame manu built one in anyway.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...