Rigid Insulation (Pink sheet stuff) vs. True Board Type 1 (White Stuff)


Hi...I am beginning my basement and want to do things right. I have to decide on the insulation first. I am doing all my floors and exterior walls with sheet insulation. Which is better - the Pink Stuff or the White Stuff. Plan on using 1.5 inch on the floors and 2 inch on the walls. Floors will be covered with plywood and walls with drywall. Location is Newfoundland.
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On Aug 5, 5:56 am, snipped-for-privacy@gmail.com wrote:

Lean yourself, google, white is uaualy R 3",,, pink -blue R 5", foil faced polyisocyanurate R 7.2". Learn about what you do before doing it, or its kinda dumb. Also learn about negatives of an exterior vapor barrier, Google is still working the last I heard.
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There are many issues with finishing a basement the biggest being moisture control and/or water leakage through walls or floors. I'll address only your specific question - the pink, or blue, is best. Pink slightly better but go by price as difference not critical.
Closed cell rigid foam sheets have almost double the insulation factor, R value, of open-cell foam. Closed cell is also a good vapour barrier where open-cell is less effective. I would only consider closed cell sheets these are the pink or blue ones. The white sheets are open-cell and thus not the best choice unless economy is critical and you intend to put a vapour barrier on the warm side. The closed cell sheets would also require a vapour barrier if you didn't create a completely sealed interior surface - the sheets installed over the insides of the studs and well glued together. You would need to use the special fastners for sheets so they are solid enough to hang drywall on.
For you project I would stringly advise that you install the sheets over the studs - easier and faster.
Cutting sheets to fit between studs is way too much trouble. If you have to place the insulation sheets between the studs then space the studs for a standard sheet width - I think 2 foot is the narrowest in my area. A 2 foot spacing is OK for basements especially if you foam in the edges which glues the wall together and makes it act as a more solid structural element. Cheapest foam is fine. The foam is almost impossible to trim down so it is only practical if you can build the wall while it is lying flat on the floor and foam from behind. This is so much trouble that the insulate over the studs option looks good.
Finding the studs later to install drywall or hang anything heavy is a problem so take a few pictures and measurements of the studs before you cover them. Make lots of marks so you can run string lines for screws.
The closed cell sheets have an R value of from 6 to 7 per inch of thickness so your 2 inches will give you a total R value of 12 to 14 which is OK but if you used open-cell sheets then you should use twice the thickness and there goes the econony unless you get a super good deal on the open-cell.
There should be air spaces between the back of the walls and floors and the concrete or there will be a wicking action that will draw moisture through even good solid concrete.
You would get some benefit from increasing the insulation thickness in the top part of the walls - above ground exposure down to 2 feet below ground. Maybe put a 2-inch layer between the studs from the top to 2 feet below ground and then put the next 2-inch layer over the studs. Just make sure there is a clear air gap of about 1.5 to 2 inches behind the walls. You could run electric wires through this gap. Again a 2 foot stud spacing is an immense help and will be fine since the insulation sheets must be glued and screwed along every stud. It will be a solid wall.
I don't know what kind of foundation conditions you have but around here the soils swell and shrink and heave the basement floors. We accomodate this by fastening the basement interior walls to the undersides of the first floor in such a way that the wall can move up or down a bit. Hanging ceilings are better because they don't crack with movement. If you have good Newfoundland rock you'll be fine but consider local experience.
The web site below has a lot of good information and details of installations.
http://www.ornl.gov/sci/roofs+walls/insulation/ins_16.html
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Open cell white beadboard is about R4 per inch.

That's about R11, with still air on both sides.
Nick
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