Flat roof insulation.

GSDog

I'm in the process of renovating a house which has a felt on timber flat roof kitchen. It was put on as an extension in the 80's and has no insulation. The kitchen gets unbearably hot in the summer and feels cold in the winter. For those reasons I'd like to do something about it.

I believe the felt was replaced fairly recently and doesn't need replacing for at least another 5 years or so. For that reason I don't want to touch the actual roof.
However, the kitchen is currently completely empty so it probably makes sense to do something about the insulation between the roof and ceiling now.

What are my options?

Any help would be appreciated.

ormus

pull the ceiling down and insert the insulation.
then PB the ceiling again.
and skim if required.

27col

Plaster board is cheap enough. Just rip it down and replace. If you are doing the work yourself use feather edge board and tape and fill the joints. Then you wont even have to get it skimmed if you don't want to. You do not have any other practical options.

muckybutt

just in the process of doing the same to our bathroom, im not using mineral wool or the likes of kingspan, im using actis triso super 10. 30mm of that stuff is equivalent to 210mm mineral insulation, damn good stuff as weve used it before whaen we converted our loft.

GSDog

Thanks, that's what I thought I'd have to do.

What type and size insulation would you recommend?

ormus

as thick as the timber joists allow. rockwool or try the kingspan type.
batts are easier to handle then the stuff on a roll.

iamcornholio

The important thing to remember is to not leave any air voids, especially up under the timber deck - this will prevent the chances of condensation forming.

Completely fill the void with your insulation, and then fit a vapour check plasterboard (foil-backed) or fit a thin polythene layer before plasterboarding and this prevents moisture from entering the roof

Muckbutt's use of Tri-Iso will need the roof to be vented or else there is a significant condensation/rot risk. And incidentally Tri-Iso is still unproven as being equivalent to other insulation types

lucysettle

We've got a similar problem with needing insulation for a number of rooms in our house that have flat roofs. The bathroom in particular gets very condensationy and I'm wondering if that's because the roof isn't insulated.

I heard a rumour though that you could poke a hose through a small hole in the ceiling (like a downlighter hole) and then fill the void with some sort of expandable foam insulation. Is that the case? Does anyone know the name of this?

ormus

screwfix do various brands from 5-10 quid. per can.

ps,
ive never done what have in mind. i suppose it may work ok.

Treadway1

lucysettle wrote: »

We've got a similar problem with needing insulation for a number of rooms in our house that have flat roofs. The bathroom in particular gets very condensationy and I'm wondering if that's because the roof isn't insulated.

I heard a rumour though that you could poke a hose through a small hole in the ceiling (like a downlighter hole) and then fill the void with some sort of expandable foam insulation. Is that the case? Does anyone know the name of this?

I wouldn't suggest doing this if you do have downlighters/spotilights as these type of lights need around 150mm clearance around them to stop overheating and the risk of a fire. Obviously if you put expanding foam in then it will just envelope the light fitting in the ceiling. Coincedentally, that will probably make it very difficult to even change the bulbs, but that's a minor issue after the fire risk.

A more long term problem with expanding foam is if condensation starts to build then the moisture has nowhere to go but in to the wooden (presumably) rafters and will eventually cause rot. All in all, expanding foam would not be a great idea in this scenario.