Lowering ceiling

[Hellraiser2666]

Hi there,
I moved to my current 1950s house last year which has a flat roof with little are no insulation inside it & during the cold nights i decided i would try insulate the roof from under the plaster board ceiling to try make things better next year,

I`ve thought of attaching 47x50mm timber across the ceiling joists using 120mm screws at 450mm intervals & then putting celotex 50mm between the 47x50mm timber battens & then attach 12.5mm plasterboard over that.

Just wondering if the ceiling/roof joists will hold the extra weight of the battens / celotex / plasterboard the joists are 2inchs by 9inchs on 18inch centres

Any Help Advice Would Be Great
Thanks..

 

[ladylola]

How wide is the room?

 

[Hellraiser2666]

How wide is the room?

The room is 8ft 11ins wide & thats the way the battens will run & its 15ft long & the joists run that way there are 6 joist in this bedroom & one hiding within a internal wall so was going to use some L brackets on the end of the batten & screw it to the wall to allow for the missing joist,

i have not looked in the landing or the other bed room for the joist was takin it one room at a time but the other bedroom is 9ft by 8ft 10ins & the landing is 4ft 7ins by 8ft 10ins

 

[PrenticeBoyofDerry]

Have you thought of metal stud suspended ceilings?

 

[Hellraiser2666]

well i`m using 47x50mm because i don`t really want to loose to much ceiling height & i thought using celotex would give me the best isolation for the small 2inch lowing of the ceiling & i`ve never worked with metal frame are know the cost to buy it,

 

[foxhole]

What condition is the flat roof in? if it's worn or near the end of it's life it's a good oppertunity to add additional insulation to the roof from above [and re-roof] without encrouching on the space inside.

 

[ladylola]

To address your original concern about the extra weight-
There is a simple rule of thumb to determine joist depth and that is "halve it and add two (or sometimes one)" i.e. half the span in feet + 2 gives the depth in inches. Therefore 15ft divided by 2 =7 1/2 +2 = 9 1/2 or 8 1/2 if you are adding one which all means that your joists will be ok.
Rather than fixing 2x2's to the ceiling and insulating between I think a better (and probably slighty lighter) method would be to fix the insulation up in full sheets and then screw on 2x1 tiling lath sandwiching the insulation between ceiling and lath. You would need longer screws as you would have something like 3 1/2" to go through before hit the joists and you would lower the ceiling by an extra inch but your insulation would be continious.
If you are still worried about the weight you could try fixing something like a 6x4 across the center of the room fixed to the wall by steel angles.