Insulation for unheated basement ceiling


Old 09-27-05, 02:23 PM
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Insulation for unheated basement ceiling

I have an old (1860) house with a rough stone foundation and dirt/cement basement floor. The basement is unheated and somewhat damp and I'd like to insulate the ceiling. Your typical recommendation seems to be fiberglass batts paper side up, but I hate working with fiberglass and don't want to create a nesting area for rodents (I removed some really nasty fiberglass with lots of mouse nests previously). Would rigid foam work as both insulation and vapor barrier if fitted tightly between the joists? If so, is polyurethane (thermax) or polystyrene (blue board) better for this application? Thanks!
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Old 10-02-05, 07:43 PM
Join Date: Aug 2000
Location: USA
Posts: 15,834
Extruded polystyrene is made by four manufacturers in the United States. Each uses a different: blue, pink, green and yellow. All four are basically the same. It's resistant to water penetration and is often used to insulate foundations below grade.

Beadboard or expanded polystyrene insulation is very similar to what is used to manufacturer styrofoam coffee cups. It consists of little beads that are fused together. R-value varies with densitiy. It is water resistant.

How effective the rigid panels work as a vapor retarder will depend on how well they are installed, as vapor can find its way around the edges of the panels.
Old 10-04-05, 09:44 AM
Join Date: Sep 2004
Location: Canada
Posts: 71
sadly it isn't rodent proof either...
Old 10-04-05, 09:59 AM
Join Date: Apr 2005
Location: WA
Posts: 117
No, but it would be alot easier to spot a nest, clean it out, and add in a replacement piece.

It seems like a technically sound idea. Cut to the boards to fit joist bays, possibly caulking around the edges of the top board to stop air infiltration.

But my god. Doing it just to avoid working with fibreglass? It seems like an incredible amount of work, mess (what, a table saw to cut the styrofoam to fit 16" oc studs?), just to avoid a possible problem with rodents later down the road.

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