Insulating dwarf walls in loft conversion

My loft conversion has dwarf walls (about 1m high) which go up from the floor to meet the pitched ceiling. They currently have 50mm of rockwool insulation between the studs, half of which is falling off.
As I'm about to insulate the loft space itself I'd like to fix and increase the insulation on the dwarf walls as well. But, what would be the cheapest and easiest way to get it done?
The current insulation is held in place by what appears to be heavy black paper stapled to the studs. If I want to make the insulation thicker, that's not going to work.
My two ideas are: 1. Cut down sheets of foam insulation and screw those to the studs. 2. Use some long screws to hold rockwool vertically in place, may be with an few square inches of wood to act as washers.
Frankly given the confined space, I don't much fancy either of them! Does anyone have any better suggestions?
Thanks
Matt
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On 18/11/2013 12:05, matthelliwell wrote:

Is the pitched ceiling insulated as well?

The PIR board insulation would be the simplest - cut into wall height sections, that you can get into place and then fix them in place (cut them tight ish) then a quick squirt of expanding foam to fix them).

The other option would be to dry line the face of the wall rather than the backof it - e.g. fix a layer of foam backed plasterboard over the existing plasterboard. Quicker and less fiddly, but will lose you an extra couple of inches of space.
--
Cheers,

John.
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On Monday, 18 November 2013 12:19:55 UTC, John Rumm wrote:

It appears to have about 100mm of rockwool up there. Ideally I'd strip all the plasterboard back and redo the room but that's not likely to happen just yet so I'm doing the bits I can get to without too much disruption.

Apart from the size of the hatch, they would also have to be short enough to fit around the corners so I can get to all the area so I might be doing a lot of cutting.
Matt
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On 18/11/2013 12:37, matthelliwell wrote:

I recently noticed in my local BM (Selco) a version of PIR that was small boards (Ecotherm, maybe 4 x 2 ft, perhaps smaller) that were tongued and grooved. These could be taken through a relatively limited access then assembled to form a relatively well sealed covering, especially with a bit of foil tape added. When I worked the price out per sq m, it wasn't outrageously more than 8 x 4 sheets (maybe 20% extra). Of course, whether you could get them through your gap is another matter but they might be worth looking up. I did find them on the Ecotherm web site, so sizes available could be checked easily.
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I would use rigid foam. Cut undersize, hold in place with a few nails and seal the gaps with aerosol foam. Very important not to have any gaps at all.
It's not possible to put in too much insulation these days so go well over the top. Take time to do a good job.
You can get the slightly damaged foam boards much cheaper . Google "insulation boards seconds" to find a local supplier.
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On 18/11/2013 17:08, harryagain wrote: ...

...
I suspect that most people would view adding 4ft of insulation inside both opposite walls of an 8ft wide room as putting in too much.
In practice, what is too much will depend upon your personal aims: minimising fuel costs, irrespective of the insulation cost; striking a balance between savings and capital cost (the exact point at which that is achieved may vary depending upon personal circumstances); or simply making the place adequately comfortable.
Colin Bignell
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It cost very little extra to put in 200mm of insulation compared with 100mm.
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On 19/11/2013 16:06, harryagain wrote:

I would expect it to cost about double, based upon Celotex prices.
Colin Bignell
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On Monday, 18 November 2013 17:08:27 UTC, harry wrote:

After due consideration and comparing prices, rigid boards it is. I've just bought a pallet of seconds so I should have enough left over to do my shed next year.
Matt
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