Insulating a roof at rafter level....

[Geoff Flegg]

Just in the final stages of buying a Victorian semi, which needs a new roof covering.

As the roof is being re-covered, the job needs Building Control approval from the local authority - who tell me that you now have to get the roof up to 0.2 u-value.

Problem is, the house was built from new with attic rooms, so there are (perfectly good) lath and plaster ceilings attached to the bottom of the rafters.

Stripping the roof obviously gives the chance to introduce insulation - there's none at all at the moment. You only have the rafter depth to use though - 4" - and 1" of that needs to be left empty under the (new) breathable-type roofing membrane. To insulate right up under the membrane would involve using counter-battens under the roof tiles, which I can't do as that would make my roof higher than my neighbours (remember it's a semi ! )

Using the likes of Celotex or similar, I can't get the u-value I need with only 75mm to play with. Which means having to strip the ceilings out, insulate underneath the rafters as well as between, then plasterboard and skim to get a new ceiling. This also reduces the (already not great) headroom.

Anyone got any bright ideas on this one? I've considered the "superquilt" insulation from YBS (http://www.ybsinsulation.com) but hear mixed reports on it's effectiveness, plus you are supposed to use it running across underneath the rafters with a vapour barrier etc, not between the rafters with no vapour barrier.

It just seems such a shame to destroy perfectly good ceilings!

 

[biffvernon]

Have you tried saying to the Buildings Control Officer, "I am not going to destroy the historic fabric of the lath and plaster ceiling. What do you suggest ?"

You can read an extremely long thread about multifoil insulation over on the Green Buildin Forum that started with a pot of coffee and eventually involved some of the main players in the industry.

 

[Ian Bond]

Hi

Just wondering why the house needs a complete new roof covering, so falling under the building regs?

Is your roof slates, stone tiles, clay tiles, concrete? Roofs fail for many reasons, and mine failed through the failure of iron pegs holding the tiles in place. A good proportion of the stone tiles could be re-used, and so the job was a repair.

Having said that, it still makes good sense to insulate as best you can - it's your money going through the roof. But it makes no sense to destroy a perfectly servicable ceiling, and it would be a horrible waste to remove it just to fit insulation.

 

[Geoff Flegg]

It could be repaired - like everything, really - but it's reached that point where the cost of repair is close to the cost of re-covering the roof.

One of the problems is that it's a very tall house, so you have to hire scaffolding to get up on the roof safely - and that scaffolding costs around £1500. If we went for the repair option, it's likely that as the tiles themselves are failing ones that are good now would start to go in a few years time - so we'd need to get that expensive scaffolding in again, probably more than once. There's no way you'd get me up on that roof - way too high and too steep a pitch - so it means getting a roofer in every time.

The roof is covered with plain clay tiles, and for much of the roof they appear to be nearing the end of their life - when disturbed they fracture and in some cases crumble, almost as if they were made of shale! I guess that your stone tiles are just naturally more durable.

Also, the way the roof is constructed means that to insulate it at all you need to rip a lot of ceilings down, unless you take the tiles off - which is why I guess it's never been done! If it was down to me I would just insulate between the rafters, it would still be much better than it is now.

The BCO tells me that there's no time limit to completing works though - so I suspect that I will get the roof done, insulation in between the rafters, and leave the ripping ceilings down and insulating underneath until I get around to it - could be some time!

It would be nice to use the sheep's wool insulation, but as thickness is such an issue I don't think I've got any choice other than to use the rigid foam Celotex / Kingspan type to get to a decent U-value. Still, environmentally and financially it's got to be better than not having any insulation and wasting all that heat.

The old tiles coming off the roof that are good won't be wasted - one side of the roof is better than the other, it must be more sheltered. The roofer reckons he can salvage enough good tiles for me to roof a double garage that I want to build.

Has anyone had any bad experience of using the concrete replicas of plain clay tiles? That is what the other half of the semi was re-roofed with, about 10 years ago. I have to say they look fine - I would never have known that they weren't clay if the roofer I asked to quote hadn't told me. It is obvious that the neighbours side of the house has been done and mine hasn't, but they don't look out of place, and the roof structure seems to be fine with them. The roofer reckons they have a longer life than clay - anyone care to comment? They are cheaper.

 

[GK]

Well, someone may post a 'concrete is bad / environmentally damaging' message.

I too have heard that concrete plain tiles last longer than natural clay. And they don't look bad at all, when compared with a machine made clay. I wonder why they're cheaper? Wouldn't they cost more in manufacturing and energy than firing a lump of clay dug out of the ground? Are plain clay tiles more expensive just because those specifying them aren't likely to consider anything else?

 

[biffvernon]

Have they forgotton how to make clay tiles? Mine must be more than 200 years old with no sign of decay. How about yours GK?

 

[GK]

They haven't forgotten how to make them round here. There's a tile factory just a few miles from me where they turn out goodness knows how many machine made clay tiles and quite a few handmade ones as well. The clay is dug out of the ground next to the factory, which is next to a canal, which, AFAIK, digging it out was how the top quality clay was discovered

This might lead to an aerial view of said tilery:

http://local.live.com/default.aspx?v=2&cp=53.736237~-0.698366&style=h&lvl=16