Insulating a floored loft?

[mrswee]

Hi we are buying a house with a large loft that has been floored, eventually we will covert the loft to have a bedroom in. Currently it has no windows as yet.

When I went up there to have a look I noticed it was very warm so heat is escaping into it.

How do we go about insulating it? where does the insulation go?

The loft I have now is not floored or used for storage and has insultion above our ceilings in what would be the floor of the loft between the joists.

thanks, I have no idea about these things!

We were told that we could buy the insulating sheets that are used inside cavity walls and cut them to fit between the joists and under the boards. I think the brand name is celotex and standard thickness is 100mm.

We've not got round to doing it yet tho so I can't say if it works

When we did our loft conversion building control required oodles of insulation but we used insulation that is also acoustic. Are you sure the joists are suitable for a loft conversion? They may need upgrading for a habitable room even if there is a floor on them at the moment.

if you went up there in the last week or so (sunny weather) the loft will have been warm due to the sun beating down on the roof. There is generally no insultation under the tiles. Loft spaces can be unbearable in summer.

As remembering says, if you are going to convert it into a habitable room later, the existing loft flooring will almost certainly have to come up anyway, since the timbers will have been designed to hold the ceilings up, not people and furniture

We have Celotex under our loft floor, DH had to raise the floorboards to fit it but not a huge amount of work, and worth it even for short-term.

I am not at all sure if the joists are strong enough, so good advise there! We would obviously be finding out that when we do the planning though.

So the insulation still goes in the floor not in the roof under the boards and tiles? or is that a daft question? or do we eventually put insulation in both areas?

if the loft is a loft and not a habitable room, put mineral wool quilt between the timbers that the ceiling below is fixed to.

If the loft is converted, insulation will be needed between and below the roof timbers that the felt and tiles are fixed to. It will be necessary to change the ventilation of the roof space and the area under the tiles to prevent condensation.

Celotex (and Kingspan which is similar) is a rigid plastic foam board which is a better insulator than mineral wool or polystyrene of the same thickness, and for some building purposes is better. However it is a lot more expensive, and is not so suitable for insulating most lofts as it has to be cut to a precise fit, as it will not squash to fit like mineral wool does.

Thanks for your reply pigletjohn very helpful info!