Venting a box profile roof

[Nealt]

We are building a house on Shetland. Weve got all our roof/wall sheets on. Now our BW Inspector is insisting on ventilating under the roof cladding. The sheets are fixed to 50mm battens. We used foam sealing strips top and bottom, but they arent air tight. Given the wind in Shetland I cant believe there is a lack of air movement under the sheets. Anyone have any thoughts, suggestions on this issue

[Tom]

You can buy foam fillers with a notch cut out of each "hump" - or just cut a similar notch in the ones you already have. You can also buy ones with wire mesh in them.

[Eric]

With the sheets being on 50mm battens I would say that would provide the ventilation, if you removed the foam strips.

 

House looks smart, is that metal sheets on the walls also?

[Nealt]

10 hours ago, Eric said:

With the sheets being on 50mm battens I would say that would provide the ventilation, if you removed the foam strips.

 

House looks smart, is that metal sheets on the walls also?

Thanks for the response Eric. I dont think removing the inserts is a good idea here. The wind will drive rain under the sheet. Thinking about it the air under the sheets when warm must rise and vent out under the ridge by convection. 

Yes we have the whole house clad in steel

[IanR]

11 hours ago, Nealt said:

Now our BW Inspector is insisting on ventilating under the roof cladding. The sheets are fixed to 50mm battens. 

What are the 50mm battens on? Do you have counter battens or are they on a solid deck? Have you got a continuous gap from ridge to eaves?

[Kelvin]

How else does the BCO want you to do it? 
 

Our standing seam roof is on 50mm battens too. It’s open at the eaves with insect mesh wrapped around it. We cut a slot in the ply either side of the ridge so that it can circulate out. You sometimes see an open ridge cap to serve the same purpose but our roofers said that’s an older way to do it. 

[Nealt]

4 hours ago, IanR said:

What are the 50mm battens on? Do you have counter battens or are they on a solid deck? Have you got a continuous gap from ridge to eaves?

The battens are on the sarking fixed through to the trusses. Yes there is a continous gap up to thr ridge, formed by the peak of the sheets

[Nealt]

2 hours ago, Kelvin said:

How else does the BCO want you to do it? 
 

Our standing seam roof is on 50mm battens too. It’s open at the eaves with insect mesh wrapped around it. We cut a slot in the ply either side of the ridge so that it can circulate out. You sometimes see an open ridge cap to serve the same purpose but our roofers said that’s an older way to do it. 

He wont tell us how. I think what we have provides plenty of air movement

[IanR]

55 minutes ago, Nealt said:

The battens are on the sarking fixed through to the trusses. Yes there is a continous gap up to thr ridge, formed by the peak of the sheets

 

Gaps just at the peaks of the sheets isn't sufficient. If you've not got counter battens to create a full width gap, top to bottom you could try to get the ventilation moving laterally (in line with the battens) but you'd need to change the detail at the verges, your current cuppings are stopping any ventilation.

 

Perhaps you should sketch your build up to make sure its understood. My comments are on the assumption you have a warm roof and don't have a vent gap between insulation and sarking.

Edited June 28 by IanR