Insulating a room ,will what i doing be ok?

[canny177]

Hi Folks,
I am going to battern out a room and plaster board and skim it but am thinking about inserting insulation between the frame work for a bit more insulation. I was planning to use 25mm (8x4 cut down)polystyrene sheets. ( the same stuff used for the floor to insulate below the comcrete).
DO you think this will be ok?
I have also studded out the ceiling , leaving the original ceiling in place, could i use 50mm polystyrene for this just to add to the sound and heat barrier? There will be down lighters in the ceiling but i plan to noggin across and line with 12.5 plaster board to create a void for the light area.
What do you think?

 

[markie]

A bit more imfo is needed, when you say a room, is it a....?

 

[canny177]

Hi Mark,
The room is going to be a games room for kids.
I know i could leave the cavity empty on the walls as the exsisiting walls are a good 12 to 24 inch thick ( stone), but i feel if i am able, i might as well infill the spaces between the batterns to warm the surface up a bit.
The ceiling is more of an issue, as i am concerned if it will be a fire spread risk.
I know i will have 2 ceiling in place, The original, which is lats and plaster(30mm thick) and the the new fixed to the original joists with 2 inch timbers then lined with 12.5mm plasterboard.
I know i could use mineral wool, but to keep costs down i would like to use the polystyrene sheets.Would that be safe and legal.
My aim is to make it a little more soundproof without going to the expense of expensive sound insulation

 

[Deluks]

For soundproofing applications mineral wool is about the best you can get, polystyrene is the worst! Think about it, go and bang a piece of polystyrene with your hand, then do the same with a sheet of rockwool. Now imagine that your hand is a sound wave (ie: air pressure)

I often hear (and read) advice from experienced builders who state that kingspan/celotex etc makes for good soundproofing. nonsense, the stuff resonates like a mofo' it's the sheet of plasterboard over the top that's provides the sound insulation.
Rockwool isn't that expensive anyway. From the 'specialist' soundproofing websites, huge markup. From you local builders merch, about 50% cheaper!


You could also just use standard 100mm loft insulation roll. Don't forget vapour barrier on top (or use foil backed plasterboard)

Could also use double layers of much plasterboard for really really good soundproofing.

 

[canny177]

Thanks Mark,
Make sense what you say.
the reason i would like to use the polystyrene sheets is due to being offered them for free. I have fixed some trial bats between the new studs and it does improve the sound and thermal insulation both on the wall and suspended ceiling. I agree rockwool etc is better, but would be happy to go for my polystyrene sheets only, if it is not regarded as a fire risk.
Do you think this would be ok?

 

[Deluks]

Modern polystyrene should be fire retardant if it's for construction use. The plasterboard will provide protection against fire anyway.
If the existing walls are as thick as you say then they will provide pretty good soundproofing already, the only weak points will be windows and doors. Are there rooms adjacent to this games room that you will be using?

 

[canny177]

Yep, a Hall way, shower room and kitchen.

 

[Deluks]

I don't see any major problem other than reduced soundproofing.

 

[canny177]

Many thanks

 

[davy_owen_88]

One point to remember is that PVC electric cables don't react well with expanded polystyrene. Keep them separated unless you want problems later on down the line.

Images provided by RFLighting:

 

[archway]

It is more than don't react well with expanded polystyrene, the data sheets for expanded p state that cables must be sheathed. There is a migration of polymers from the cable to expaned p which results, after time of the cables becoming brittle and a fire hazard.

 

[canny177]

Thanks for that, I'm planning to channel out about an inch both sides of any wires and am also going to box around any downlighters and line with 12.5mm plasterboard

 

[archway]

I think you should also use a plastic conduit.

 

[canny177]

Have just spoken to the sparky and told him to do it. Many thanks