Insulating converted loft

[David]

Hello helpful people,

I have a few questions regarding our converted loft which is currently my bedroom!

Situation: No insulation between rafters at all, this makes the room feel very very cold in winter (drops to around 8=BAc in the cold). There is only a small amount of insulation under the floorboards between the joists, it's extremely old and has turned black with dirt/dust. There is a 1.7kw radiator in the room which does heat the room to a comfortable temperature but an awful amount of heat is lost from the roof - snow melts quicker than any other house on the street.

The ideal solution I am told is to remove all insulation between joists, removed plasterboard which is covering the rafters and insulate using Kingspan or Celotex boards and then fix the boards back on.

However this will cause a lot of upheaval to the room which is not desirable.

I am thinking of a good compromise that could be made. In loft space there are storage compartments which can be accessed from doors in the loft like this:

storage space looks like this inside:

of the room (view from storage area)

this picture here you can see: arrow points to a gap which can be accessed from all the storage areas.

Would it be possible to slide some insulation board up these gaps to at least stop the heat loss from the main heated part of the loft?

Would there be problems with damp?

I hope you can visualise what I am talking about.

Thanks

[David]

Apologies, first set of links don't work.

Corrected links:

Access to storage area:

storage area:

view of plasterboard which are the walls of the room:

place to slide insulation up:

[John Rumm]

> The arrow points to a gap which can be accessed from all the storage > areas.

You need to leave a gap between the insulation and the underfelt - that will allow air to circulate against the rafters and keep them dry. Ideally you would need soffit and ridge vents as well. However you may be able to get away with stripping out some felt top and bottom.

One option would be to clad the inside with PIR foam backed plasterboard and reskim. Less upheaval, but a loss of a couple of inches of space.

Ideally you would need at least 85 (possibly more - not looked for a few years) of PIR foam insulation under the rafters to achieve modern building regs standards. However even 50mm would make a massive difference.

When I did mine, I did 50mm gap, and then 50mm PIR board between the rafters, and then 30mm underlayer.

[John Rumm]

Should have also said - be wary about taking insulation out from under the floor if this is a second floor conversion. It may be there as much to act as a fire break than for insulation!

[The Natural Philosopher]

I can but please dont.

Insulation that isn't totally airproof is almost useless.

If you cat face stripping the ceiling, dry line it.

[Phil L]

I agree, dog face. :-p

[tim....]

I don't understand this comment.

Normal loft insulation is open to the air (on one side) but isn't useless

tim

[Andy Burns]

But if air can circulate around gaps in the insulation, heat doesn't have to permeate through the insulation, and just shoving insulation up those slots and hoping, rather than being able to tape and foam it will lead to gaps.

[David]

Thank you for all your replies.

So the conclusion is, sliding some insulation up the said gap would not work; it needs to be completely airtight.

I have considered drylining but to be honest I am not very confident in doing it myself and I am considering calling someone in to give an estimate now. The loft was done in 2001-2002 and was used as an office until late 2006.

[nafuk]

Do it properly. Strip the room and fit as much rigid insulation between rafters to leave a 50 mm air gap between the insulation and the tile underfelt. Seal the gaps with spray foam. Then if possible put 30-40 mm insulation under the rafters. Then screw tapered edge plasterboard through the 30-40 mm insulation into the rafters. If money is tight tape the plasterboard joints yourself and fit flexible (rather than rigid) insulation between the floor joists. Check out the many suppliers of 'seconds' rigid insulation. They just have dings and rough edges.

[John Rumm]

I am not as pessimistic as some. If you slid solid foam insulation up, so that it was a snug fit between the rafters, and was in contact with the plasterboard, then the air currents would be on the reverse side of the board. This would not particularly reduce its effectiveness.

The only time air passage is going to be a problem is when you get circulation from the warm side to the cool side such that it circumvents the insulation. With the insulation hard against the inner skin, that can't really happen even if the coverage is not perfectly air tight.

Dry lining would be fairly simple. Mark out the rafter positions, get some long screws and some taper edge insulation backed plasterboard. Screw the new boards to the rafters through the old. Tape and fill the joints, sand off when done.

[David]

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Can you recommend any particular brand of insulation backed plasterboard? It seems a nice solution, any skimming required after the plasterboard has all been screwed in before painting?

Sorry I don't really have much experience with this sort of thing at my age but it seems like a nice project for me especially if it will make my room feel warmer.

[John Rumm]

I suspect it will be a case of take whatever the builders merchant has. While there are lots of brands on insulation, there are only a few big makers of plasterboard.

The insulation bonded PB will be easier to use. Separate insulation boards and PB will probably be cheaper.

Compared to no insulation, even 50mm of PIR foam insulation will make a very significant difference.

[fred]

4dk6n$4g0$ [e-mail]...

Surely this is b****x.

If put a coat on and don't button it up it still keeps me warmer than no coat at all. Perhaps ideally it should be air tight but even then an element of air flow might be desirable

Paul Mc Cann

[PeterC]

messagenews:j4dk6n$4g0$ [e-mail]...

That's my feeling too. I noticed how much difference vertical blinds made - and they're about the worst 'sealed' of anything. Adding net curtains (again, no sealing) resulted in a lot more ice on the windows under like-for-like conditions. I assume that this is due to the convection being greatly reduced, as the 'waterfall' of cold air became imperceptable.

[Grimly Curmudgeon]

It's only partially bollocks. The efficacy of board-type insulation is reduced by air gaps, but in the 10-20% range, iirc. Mind you, that 20% can amount to a fair cost in heating fuel over a few years.

[David]

Hi John, sorry I didn't see this part of your reply last night. Maybe should stick with my first plan then, like I said I am making a compromise and even a small difference would be nice! So I could in actual fact slide something like this:

between the rafters and flush with the plasterboard leaving a gap on the reverse.

Hopefully this will make for a warmer room and house and me not feeling bad seeing the snow melt on the roof quicker than anyone else (even those who have loft conversion)

[David]

But still, it will be better than absolutely nothing at all right?

[Grimly Curmudgeon]

Well, yes; but a bit of care during installation gets rid of the potential 20% loss.

[John Rumm]

> ...snugly between the rafters and flush with the plasterboard leaving

Yup, although I would not want to pay £30 for it! (£15 tops)