Where to buy rigid insulation boards?

[Sherman]

My cold water tank is currently uninsulated. I've set myself a project of building an insulated 'box' around and above it by fixing rigid board insulation to the wooden frame on which the tank sits. This way the tank will be in its own insulated 'mini-room' in my attic, with heat coming up into it from the uninsulated attic floor below. The rest of my attic has 10 inches of insulation everywhere except directly under the tank.

Would my local builders' merchant sell the stuff I need? I assume it would be Kingspan or the like that I ask for - I've seen it on television, about 3 inches thick rigid board with foil on either side which is easily cut with a blunt saw. What kind of price would I be looking at? Apologies for all the questions, but I want to sound like I have even a small clue as to what I'm talking about before I go ringing builders' merchants!

Thanks in advance.

 

[ClubMan]

Why not just affix polystyrene from goods packaging to it to insulate it? You'll probably have plenty of it over Xmas with all the presents etc. Costs nothing.

 

[dmac]

You will get what you want in your local builders merchants, they should have a range of thicknesses in stock, yes you can use Kingspan or Xrtatherm, they are know as insulation board and you can get PIR board or phenolic board, they sell these in 2ft x 4ft bales so one bale should be enough if you use 2 or 3 inch or like Clubman said just use polystyrene, this can also be bought in bales from your local building merchant

 

[Sherman]

That's perfect, thanks for the help dmac - at least now I'll know what to ask for!