Thought I'd post this for the benefit of others who might have been considering this option.
I'm renovating an old property and want to show off the old oak purlins to their best advantage. Pitched roof. The rafters are about 100mm deep.
In an ideal world, and if you believe the manufacturers and even more importantly Building Control accept their claims, then I'd simply have spent the money and put a good multifoil insulation under the rafters and then plasterboarded over the top.
Twas not to be. I could put some foam insulation between the rafters - say about 55-65mm leaving me the airgap as required (50mm or 25mm - depends on the local BCO as far as I can see). That would leave the thermal bridging due to the rafters to sort out. My local BCO wanted more insulation. He wanted another 65mm which would eat into the visible amount of purlin and reduce the room size. I asked if I could use multifoil thinking that that would only take up 25-30mm and he agreed.
He then pointed out that multifoil needed an airgap on both sides and this was news to me. So I checked and he is right. I need 25mm on both sides and so that means a total of 50mm eating into the room.
Foam = 65mm and relatively cheap
Multifoil = 50mm and pretty expensive.
All for a saving of less than one inch. I don't think so somehow.
I'm renovating an old property and want to show off the old oak purlins to their best advantage. Pitched roof. The rafters are about 100mm deep.
In an ideal world, and if you believe the manufacturers and even more importantly Building Control accept their claims, then I'd simply have spent the money and put a good multifoil insulation under the rafters and then plasterboarded over the top.
Twas not to be. I could put some foam insulation between the rafters - say about 55-65mm leaving me the airgap as required (50mm or 25mm - depends on the local BCO as far as I can see). That would leave the thermal bridging due to the rafters to sort out. My local BCO wanted more insulation. He wanted another 65mm which would eat into the visible amount of purlin and reduce the room size. I asked if I could use multifoil thinking that that would only take up 25-30mm and he agreed.
He then pointed out that multifoil needed an airgap on both sides and this was news to me. So I checked and he is right. I need 25mm on both sides and so that means a total of 50mm eating into the room.
Foam = 65mm and relatively cheap
Multifoil = 50mm and pretty expensive.
All for a saving of less than one inch. I don't think so somehow.
