Insulating below exisitng ceiling below flat roof (rather then tearing down perfectly sound ceilings)

I have a large area of flat roofed accommodation (dining room 22m2, kitchen 14m2 and utility room 9m2). The existing insulation over all the flat roof area appears to be 1" of fibreglass!
I've just installed Celotex between the rafters of 2 bedrooms after the ceiling had to be taken down due to a leak in the flat roof (yes, I have an AWFUL LOT of flat roof!). Seems a good and simple solution in a case where the ceiling has to come down anyway.
I really don't want to have to tear down the perfectly sound ceilings in these other rooms, but I'm conscious of the enormous heat loss that must be taking place with the pathetic original insulation. (The external covering is less than 2 years old, so I don't want to spend a lot of money having that redone for a warm deck solution!)
It seems however that I have only two options - one is to tear down the ceilings, insulate between and below the joists and have the ceiling reboarded and finished.
The second option - because these ceilings are very high compared to the rest of the house and I have 170mm to play with under the existing ceilings while still maintaining headroom the same as the rest of the ground floor - is to follow the "advice" from Celotex to fix 150mm "battens" at 600mm centres, insulate between with 150 mm and board and finish.
This second option seems to be as expensive (although less dirty) than tearing down the existing ceilings and insulating between and below the existing joists. Can anyone suggest an economic and practical solution?
I am a competent diy'er and cost my time at 0 as I am retired, but would need a professional to board and finish and have no help available to fix 6x2" 6m long "battens" under the existing dining room ceiling!
I couldn't get a coherent answer from Celotex to my question about vapour barrier in the kitchen - in fact no response to that part of my enquiry at all.
All suggestions really welcomed: unfortunately I don't appear to qualify for any grant-aid towards improved insulation.
many thanks in advance
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no spam here, thanks wrote:

use 150mm fibreglass instead of celotex, it's a fraction of the cost.

steel joist hangers - about 2 each, affix them in a straight line along opposing walls andfix your joists in these - but they don't need to be 150mm seeing as they will only be carrying the weight of a ceiling and not the roof or floors above....one point to note here is that it's easier to affix one side only of the joist hanger, then insert the joist, then affix the other side of the hanger (they bend quite easily.)

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wrote:

Good idea! Thanks!

Also top tip! Except .. don't I need 150mm joists if I'm fitting 150mm fiberglass? I was meaning 150mm x 50mm (or 6x2 in old money).
I'm assuming the plasterer will need 50mm to aim his nails at, and I'll need 150mm for the fibreglass.
But that joist hanger suggestion is such a brilliant tip - makes the whole job immediately more practical, Thanks a bunch!
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no spam here, thanks wrote:

yes but you can use 4 X 2 and set them 50mm down from your existing ceiling.

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wrote:

!Flash! I love those blinding glimpses of the obvious: what a triffic bit of lateral thinking!
But not too bouncy in the middle of a 3.7m length? Well, !FLASH! A noggin in the middle.
Brilliant suggestions, thanks a bunch again.
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no spam here, thanks wrote:

Rockwool slabs are easier to handle than the rolls
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On Fri, 21 Dec 2007 17:13:43 GMT, Stuart Noble

Yes, and less of an irritant too - I have birds and a wife to think about (ahem - parrots). But cost is a consideration, so I'll have to balance the two when I choose the solution.
Thanks for the pointer.
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no spam here, thanks wrote:

What about an industrial grade suspended ceiling..pre finished, no plastering? the sort that goes in offices. Just add 150mm glass on top and the job is done.
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wrote:

My immediate thought is 'Yikes, that's an expensive solution!' Need it be? And is it a DIY job? OK for a kitchen? (I'll need to do some resarch on that). Ta for thoughts ...>
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no spam here, thanks wrote:

No. Its a cheap one, because peopel who do that sort of thing do large spaces on low budgets. Its all screw together strip, preformed fiberboard panels and that's it.
And is it a DIY job? OK for a kitchen? (I'll need to do some

Have a look see. I've had it done in offices I have converted, some time ago. It was not as I recall that expensive.

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no spam here, thanks wrote:

why not blow poly beads into the cavity through a few easily repaired 1" holes?
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Steve Walker wrote:

fire risk.
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wrote:

I had thought of that, but even the idea of getting the beads one-by-one into the end of the straw left me completly knackered, let alone actually blowing billions of the little bleeders into the cavity .... and catching them as they fly out of some previously undetected hole ...
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wrote:

Dear msht I have done this on walls and ceilings (albeit sloping attic ones) What size and span are the existing roof joists? If ok then consider the merits of using TP10 or any equivalent p- urethane (preferably cheap seconds) slabs 8 x 4 I would go for 4" but 2" or 3" will do Here is the good bit - buy a pack of the stainless steel pins and large plastic pink washers that they use for putting this stuff up on external walls and pin or (if you are particulary worried screw) the slabs to the ceiling joists (which you will have to find and mark on the walls then ceilings) IF, additionally, you are able to glue with plasterboard adhesive (depends on existing ceiling surface) you will get better adhesion Then (at different centres) tack on plasterboard with the same fixings scrim the washers and Pink it (suggest you get a pro in for this?{ End product has no need for structural joist BUT and it is a BIG but you will need to check if the existing joist are man enough If not then existing suggestions best Chris
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On Sun, 23 Dec 2007 03:45:32 -0800 (PST), snipped-for-privacy@atics.co.uk wrote:

Thanks for that: I was wondering about that approach. I think, tho, that if I want 150mm (6") insulation I might be asking a bit much trying to get fixings through the plasterboard, via 6" of insulation into a 2" target! More importantly, though, I'm not sure the joists are man enough for the job. 4" x 2" x 3.7m unsupported at 16" centres.
I think I'll wait and ask me man what he thinks when he comes in to do my other ceilings.
Thanks for the suggestion though ....at least someone else thinks it's theoretically possible!
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