XPS (extruded polystyrene) foam-board is an excellent insulating material for basements because of its versatility and its built-in moisture barrier. It is installed and supplemented with Tyvek insulation tape and “Great Stuff” spray insulation in this how-to. Learn how to properly insulate your exterior walls before your basement finishing project. XPS insulation is expensive, yes – but it’s not only easy to install, it also has it’s own vapor barrier and is moisture-resistant. It’s a fantastic insulation material. This article will provide tips for installing XPS insulation.
ABOVE: XPS (Extruded Polystyrene) Insulation Installed in Unfinished Basement Remodel in Morristown NJ
The photos above show our use of XPS insulation installed along the exterior masonry walls in a Morristown, NJ basement finishing remodel. The tongue-and-groove XPS Insulation panels were taped at the seam with Tyvek brand insulation tape and gaps were filled with GreatStuff brand expanding foam insulation. We then installed the framing over the 2″-think panels. At R-5 per inch, these XPS insulation panels provide a moisture-resistant R-10 insulation with its own vapor barrier that will hold up even when exposed to standin water.
Rough XPS Foam-Board insulation supplemented with “Great Stuff”
We used “Owens Corning” brand ‘Foamular 250’ Extruded Polystyrene (XPS) foam-board panels. These rigid, foam panels each contain hundreds of millions of densely-packed closed cells that provide exceptional thermal insulation. Extruded polystyrene (XPS) Foamular panels are also virtually impervious to moisture, unlike other plastic foam insulation products, preventing loss of R-value due to moisture penetration.
Also, the product’s built-in rigidity means it can be scored and snapped, cut, or sawed with common tools. Sagging and settling are never a problem. It retains its long-term R-value year after year, even following prolonged exposure to water leakage, humidity, condensation, groundwater and freeze/thaw cycling. XPS foam-board insulation also contains a minimum of 20% certified recycled content, certified GreenGuard Indoor Air Quality for Children and Schools, Energy Star Seal and Insulate Program, and is NAHB Green approved. We used 2″ thick foam-board so that it fit between the nominal 2’x3′ studs. At R-5 per inch, that’s R-10 insulation for the exterior walls.
** NOTE **: When framing a basement it is best to use to standard 2″x4″ lumber or steel framework, and the bottom plate (the framing that touches the floor) should be pressure-treated lumber. 2″x3″ framing lumber is rarely used anymore because of its tendency to warp (bend and bow) over time.
Simple Installation Process:
The foam-board was cut to fit inside the studs and glued directly to the masonry using paneling adhesive specifically formulated for foam panel insulation like XPS Foamular. Even though the product is very easy to score-and-snap, saw and otherwise cut with common tools, there are always small gaps. In order to thoroughly insulate the exterior masonry walls the seams where the panels meet were taped with Tyvek insulation tape. We also used “Great Stuff” insulating foam sealant. This product sprays into gaps and cracks, expands and dries to a rigid, airtight seal that insulates and minimizes condensation. When XPS insulation is deeper than 1.75″ it does not require a moisture-barrier, so none was used here. After the XPS insulation, these walls are now insulated, virtually airtight, moisture-resistant and ready for Sheetrock.
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