Loft insulation

[Keith Dunbar]

Part of our previously mentioned 17th century Norfolk cottage is a much more recently built single storey annexe. It has a steeply pitched roof (to match the rest of the property) and access to this roof space by a small door in one of the bedrooms. It is wonderful storage space.

The floor timbers are standard 4" x 2" with the standard (then) 4" of glassfibre insulation. It is loosely floored with moderately thin, but adequate planks (the previous owner worked for Boulton and Paul and seems to have access to an inexhaustible supply of timber).

I want to screw down these planks and make the floor more stable - but - what should I do for insulation? Do I raise each floor timber so I can put say 2" more insulation under the floor? Do I cram in 2" more insulation to the existing space? How should this situation be approached - given that funds are quite tight and I'm not really looking to spend much. I suspect some sort of compromise will be the answer - but what?

TIA

Keith

[John Rumm]

Cheap answer is just screw down what you have. Better answer would be PIR foam boards say 50mm thick laid over the joists, and the boards screwed through them. The boards would probably cost £10 - £12 or so each though (for a 2440x1220mm one).

[Keith Dunbar]

Right. Sounds promising, and not too expensive - given that I would only need to put the PIR foam boards where I want to have flooring (I'm going to put 8' x 4' sheets of chipboard on 2" x 1" timbers between rafters for the bulk of my storage).

Two questions. What exactly are PIR foam boards? How does 50 mm PIR foam board compare with 4" glassfibre as insulation?

Keith

[John Rumm]

With rafters being the sloping bits, I am having trouble visualising this...

Polyisocyanurate foam. Common trade names are Celotex, Ecotherm, Kingspan etc. Its a rigid foam with foil covering on each face.

If you take a rough estimate as it being twice as effective for a given thickness, then the two would be comparable.

[Keith Dunbar]

You must forgive my ignorance of the names of all the funny bits of roofs .... (maximise screen to view this best)

| | | | | | | | | | | | | | | | | | | | | | oooooooooo | | ooooooooo | | | | | | | | | | | | | | | | | | |

There is just about room for a 4' width of chipboard at "ooooooooo"

Where would I be best (i.e. cheapest) going to for this PIR board? How strong is it? Can one stand on it? I would need lots of quite long screws to fix the flooring to the joists. Is there any reason why I should need to. Could I create a sort of raft of flooring above the PIR?

Thanks so much for your help.

Keith

[FKruger]

Keep an eye on ebay eg:

you stand on it you leave a slight indentation of your foot but with plywood covering it you wouldnt because your weight is spread.

As for screwing it down I'd suck it and see. I think that the weight of the plywood and the friction would keep it in place. Maybe use a marker pen to indicate werethe joists are incase you want to at a later date. If you are planning on cutting everything up to small pieces tto get it through a small hatch then maybe it should be screwed down.

[John Rumm]

THese pictures only really work if you use a non proportional (e.g. courier) font to draw them and view them....

A specialist insulation provider probably. One of the outfits that can supply "seconds" would be good for this application.

Fairly stiff - stronger that expanded polystyrene for example.

If it is laid flat on the floor then yes. If you are laying it across joists then I would not stand over the centre of the span unless it had a board over the top.

Probably.

If you have a reasonable area of it, and the covering will remain in one lump without fixing then a raft would work.

[Keith Dunbar]

Just out of interest, what is the current requirement for loft insulation - in inches of glassfibre?

Keith

[mail]

Dear Keith Have you considered that 4" joinst as ceiling joists may be adequate but as floor joists particularly storage will not be? If the span is much more than about 10 foot you are risking deformation unless all you are storing is light boxing. If it is heavy storage you will need to put in stronger joists of deeper section to avoid defection if you just want to insulatate - the suggestions made to date are fine. Chris

[Stuart Noble]

A little alarmist don't you think? I've had all kinds of machinery stored in mine over the years without so much as a crack in the plaster below. The bloke has already said that funds are tight

[Keith Dunbar]

Don't the trusses that I tried to depict in an earlier post support the ceiling/floor joists - aren't they effectively hanging from them?

Keith