DIY Doctor UK DIY Forums

HI,
Im looking to cut costs without loosing quality, aint we all.
and I know you get what you pay for ect,ect,
The thing is, wicks do a polystyrene sheet of insulation that is £35 per sheet cheaper than kingspan and celotex. I could save £500 here which would be much needed.

I know the kingspan and celotex are foil faced, which would make a huge difference, but where i work I can get quilted thick foil coated insulation. (about 1 inch thick, this is used to put over frozen food cages to keep them frozen in transit) Bit of a stretch this but could I use 75mm un-faced polystyrene sheeting and stick my own foil coating to the face of it, or am I way off the mark here?

I am looking to use the insulation between joists of a timber frame extension to rear of the kitchen 3m run each side, so only a little project. the joists would be covered in OSB boarding and clad in cedral cement weather-boarding.

also for insulating between roof joists should i stick with solid slab or will loft insulation do, also same question regarding the floor.
thanks for reading this.

rusty

You are writing about polystyrene!
Polystyrene is the generic name for polystyrene closed cell insulation, it is 98% air and 2% plastic.
Air the the item that provides your insulation, if you look beyond the fancy packaging Kingspan is an inert gas wrapped in plastic with a paper face with a foil finish. The foil slows the gas from escaping, the insulation figures are better by a very small amount than polystyrene, and indeed they are based on the expected insulation value when the gas has mostly escaped in 15 years time. After that they end up the same.
If you fix three inches of polystyrene below a ceiling you will vastly improve your insulation. If you place the same insulation between the joists, you are leaving about a quarter of your ceiling uninsulated as the heat from the room below is in direct contact with the plasterboard that conducts your heat into the joists and moves it on to the sky.
I have some rooms with three inches of polystyrene below the joists and between three and eight inches of polystyrene between the joists (basically depending on how thick the joists are) My home is warmer more comfortable and uses about a quarter of the gas we used six years ago. (Accept that every year is different, this year has been particularly cold and miserable....but we have used less power this year than ever before.)

Hi Perry525,

Thanks very much for that, also for getting back in touch so quickly. Like the idea of on top of joists as well.
so don't need to worry about thermal-wraps from work then?

so is polystyrene the way to go in your opinion, over say space blanket loft insulation?

thanks Rustypeg

Aren't which ever type of Kingspan and celotex board you go for both PIR (poly iso cyanurate)? Polyisocyanurate is quite a different material to polystyrene. Does anyone know where I can find some data sheets on the different thermal performance between the two - basically looking to work out whether the extra cost of the PIR over polystyrene is worth it when insulating my shed (it's a fairly posh shed)? Thanks

Kingspan website has thermal insulation data for its various types of board.

Jablite is a trade name for polystyrene and will identify thicknesses and U values acheived.

I would say that you need another 50% thickness in polystyrene to achieve the same results as Kingspan.

hth 99