Standing Seamed Roof

[Ryan Bazeley]

Hello,

 

I am roofing my SIP using steel standing seamed sheets. The installer has said it can be fixed straight to the SIP but I am sure as like the cladding a ventilation gap is required? I am assuming the best way is to fix battens to the SIP then an 18mm OSB/PLY, breather membrane then steel sheets? Has anyone fitted a metal roof to their SIP build?

 

TIA

[IanR]

I was planning to use Colorcoat Urban originally and Tata, at the time, said they were investigating using their product directly on the sheathing of a Warm roof, without a ventilation gap. They did come back to me and say all their analysis showed it "would be fine".

 

I wasn't willing to take the risk personally - in the end I went with an Aluminium roof (for other reasons), and a ventilation gap. As you say, battens and 18mm OSB.

[Ryan Bazeley]

Thanks For your advice Ian great help. Out of interest why aluminium??

[IanR]

When first quoted late 2016, Colorcoat was the best value, and I had a company lined up to Install. When I pushed the button mid 2017, the install company had just got busy with a development of properties and Colorcoat's pricing seemed to have gone up 40% (plus they appeared to be having some internal issues)

 

I went back to re-quote all the options and Falzonal was now the better value. I also liked that all the flashings could be hand worked in the Aluminium, rather than introducing another material.

[Alexphd1]

Ventilation gap for me. We diy installed stainless steel and had a 2 inch air gap below. Very belts and braces but I did read a Danish report on standing seam (think tin) rotting out very quickly.

There is also a felt on the market that creates the air gap (haven't used it ourselves) https://www.roofing-tools.com/klober-permo-sec-structured-underlay-c2x9252015 

[Ryan Bazeley]

This stuff has been recommend by the installer, he said it is a waste of money and not necessary to construct a ventilation gap?

[SuperJohnG]

How big are you guys making the ventilation gap? 

[IanR]

1 hour ago, SuperJohnG said:

How big are you guys making the ventilation gap? 

 

50mm gap between sheathing of warm roof and 18mm OSB deck for metal rain screen.

[Tosh]

Agree with everyone else. Just note that to warranty the product then you need to follow the manufacturers recommendations for the build up and use an installer accredited by them to install it. I would suggest that anything outside of that and you're on your own if anything goes wrong i.e. corrosion. Appreciate steel/aluminium is not so fickle as say zinc but you get the picture i.e. moisture build up on the underside of the SS. I also looked at the permosec stuff but again some manufacturers approve of it, others don't. 

[SuperJohnG]

9 hours ago, IanR said:

 

50mm gap between sheathing of warm roof and 18mm OSB deck for metal rain screen.

Thanks - I was more checking as I have slates but there aren't many threads on the actual size of the ventialtion gap. I have a 25mm batten planned, then 22mm sarking. But as the sarking is not spaced as such, does it mean that my ventilation gap is only 25mm? 

[Ryan Bazeley]

Had a few issues with the installers but have found a new one who use GreenCoat PLX. They have said they will only install if there is a vented cavity and an 18mm deck. They seem to know there stuff and said they have roofed many SIPS.