new roof and insulation on lean to kitchen

[timothydoran]

I was wondering why my kitchen was so cold in the winter. I looked under a couple of tiles and I now know why. No insulation (unless dead insects and dust count) and also the felt has rotted away.

The kitchen is at the back of the house and would originally have been an outbuilding or privy. Built aprox 1900. It measures aprox 3x3m built of bath stone with double roman clay tiles. It is attachced to next doors kitchen on one side.

Internally the ceiling slopes down quite low (maybe 6ft4) so I dont want to loose much internal space. Luckily there are not lots of kitchen cabinets.

The roof rafters are only 750mm deep with the plaster board nailed directly to it.

I want to replace the membrane and the couple of damaged tiles and also insulate it. I cannot have thicker rafters as it is attached to next door.

Any ideas for how to insulate this this would be greatly appreciated.

Thanks Tim

 

[freddiemercurystwin]

So is the ceiling completely sloping?

Replacing the membrane will mean removing the tiles and battens and re-doing. If the tiles are good (appreciate some need replacing) then the membrane is merely a back-up. There are millions of houses with no felt or membrane at all. Are you saying you are prepared to do this?

Insulation would be 50mm Kingspan or Celotex between the rafters and a layer of say 50mm below and then your plasterboard.

 

[timothydoran]

The ceiling is mostly sloping, there is a section of ceiling that is flat.

You suggest 50mm celotex between the rafters which would leave only 25mm air gap. Would this be sufficient?

Thanks for the quick reply to my first post.

I dont really want to fix something thats not broken or leaking, but on the otherhand I dont want to insluate the roof only to have to do the membrane in a few years.

Also if I removed the plaster and found that the some rafter were rotten I would have to replace all the roof or could I just do the bits that were needed.

 

[freddiemercurystwin]

Firstly you only need to repair what’s damaged, if applicable. Do you suspect some timbers to be rotten?

You have to weigh up the costs of doing the membrane now and doing it at the end of the roof tiles natural life, when you’d have to do it anyway. 25mm is an adequate gap if you have no felt (as present) or if you were to fit a breathable membrane if and when you re-do the roof/membrane. As mentioned it really depends if the roof tiles are OK at present, if they are nearing the end of their life it might be worth biting the bullet now. You can still insulate now and re-do the roof later when needs be.

 

[timothydoran]

Thanks Freddy

I think that I shall rip out the plasterboard and then I will be able to work out if the boards are rotten or ok for a while.

I would rather not do the roof if it will last a bit longer, and I am encoraged that I can insulate and then re-tile at a later date.

Between the plasterboard and the celotex insulation do I need to have a vapour barrier? Or if I tape all the joins does that count as a vapour barrier?

If so is this the sort of thing http://www.screwfix.com/p/vapour-ba...mz3FLQk3p6Yq8n9kK8q!1701577020!1367497857704#

Many thanks

Tim

 

[freddiemercurystwin]

If you use a foil backed insulation (like Celotex or Kingspan) then you just stick some foil tape over the joints between the insulation boards, the foil is the barrier.