Insulating converted loft

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 8ēc 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:
http://i363.photobucket.com/albums/oo71/david938/09092011001.jpg
The storage space looks like this inside:
http://i363.photobucket.com/albums/oo71/david938/18072011003.jpg
Walls of the room (view from storage area)
http://i363.photobucket.com/albums/oo71/david938/18072011005.jpg
In this picture here you can see:
http://i363.photobucket.com/albums/oo71/david938/18072011004-1.jpg
The 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
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<snip>
Apologies, first set of links don't work.
Corrected links:
Access to storage area:
http://i363.photobucket.com/albums/oo71/david938/LOFT/09092011001.jpg
Inside storage area:
http://i363.photobucket.com/albums/oo71/david938/LOFT/18072011003.jpg
Rear view of plasterboard which are the walls of the room:
http://i363.photobucket.com/albums/oo71/david938/LOFT/18072011005.jpg
Proposed place to slide insulation up:
http://i363.photobucket.com/albums/oo71/david938/LOFT/18072011004.jpg
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On 09/09/2011 18:53, David wrote:

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!
--
Cheers,

John.

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On 09/09/2011 18:40, David wrote:

Yes.
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.
http://www.internode.co.uk/loft/insulating.htm
--
Cheers,

John.

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David wrote:

I can but please dont.
Insulation that isn't totally airproof is almost useless.
If you cat face stripping the ceiling, dry line it.

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The Natural Philosopher wrote:

I agree, dog face. :-p
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I don't understand this comment.
Normal loft insulation is open to the air (on one side) but isn't useless
tim
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tim.... wrote:

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.
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<snip>
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.
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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.
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On 10/09/2011 15:01, David wrote:

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.
--
Cheers,

John.

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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.
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On 10/09/2011 20:49, David wrote:

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.
--
Cheers,

John.

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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:
http://buildingsuppliesdirect.co.uk/product/Xtratherm,-Quinn-PIR-Insulation-Foilboard/4163
...snugly 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)
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On 11/09/2011 12:25, David wrote:

http://buildingsuppliesdirect.co.uk/product/Xtratherm,-Quinn-PIR-Insulation-Foilboard/4163
Yup, although I would not want to pay Ŗ30 for it! (Ŗ15 tops)
--
Cheers,

John.

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I think if the insulation were cut as a snug fit, it would get stuck as you tried to push it up. Also there will be some variance in the gap between any two rafters. Either it will get stuck or you will have an air gap. If you can bite the bullet and pull the existing PB off, that's most of the mess out of the way in one session. I really would do this properly; we did ours to regs (then 5 inches deep) and the difference is phenominal. You'll thank yourself for doing it.
Cheers Richard
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Sorry, I don't mean an air gap. You want an air gap, in the traditional sense, behind the boards. I meant you'd get gaps between the boards and the joists, creating cold spots and the potential for condensation.
Cheers Richard
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On 12/09/2011 11:01, geraldthehamster wrote:

I agree, in the sense that yes doing it without the original PB in place will be easier and more effective. I was just highlighting that with the insulation in contact with the back of the exiting PB, there will be little scope for the kind of drafts that would render the insulation ineffective, since the only air available will be that in the actual gaps etc. You will get the cold bridging of the joists thought.
I think the order of preference (in terms of results and quality of job) would be to:
1) strip the existing PB, insulate between and under the rafters, then re board.
2) Dry line under the existing PB, or
3) attempt to retro fit insulation behind the exiting PB.
Only do 2 if you really can't face 1, and only do 3 if you really can't afford the loss of headroom from 2!
--
Cheers,

John.

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To be honest, I would love to strip the whole room, properly fit insulation etc but it's just not feasible, option 2 would cause a loss of headroom and that would not be very good seeing as I can *just* stand upright without touching the ceiling. Anyway, just to confirm, will this board be okay and can I insulate the walls too?
http://www.screwfix.com/p/pitch-roofing-insulation-400mm-centre-x-65mm/28148
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On 12/10/2011 21:24, David wrote:

Its about twice the price I would want to pay, but would appear to be the right sort of stuff.
--
Cheers,

John.

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