More About Foam Board Insulation
EPS vs XPS foam board insulation - which is better?
This debate was settled when results from a 15-year in-situ study involving both EPS (Expanded PolyStyrene) and XPS (eXtruded PolyStyrene) were published, indicating that EPS has retained 94% of its' original R-value vs only 52% for XPS. In addition, XPS has absorbed over 18% of water by volume, whereas for EPS, this number was below 5%.
EPS is a clear winner both in price and R-value retention, making it an optimal choice for variety of insulation needs.
Applications
Rigid foam board insulation is a great choice for radiant heated slabs, where PEX tubing or electric heating cable is embedded in concrete to create the most quiet, energy-efficient and comfortable heating solution available today. It offers best price-performance ratio and is reliable and easy to install.
Rigid foam board is also suitable for insulating walls, roofs, attics and crawl spaces thanks to it's light weight and very low moisture absorption.
EPS foam board density - why it's important
When foam board is used to insulate floor slabs - above or below grade, with or without radiant heat, it must be dense enough to walk on without crumbling - otherwise it looses efficiency and may compromise the slab itself.
2 lbs/ft³ (2 pounds weight per cubic foot of volume) is the recommended density for slab insulation and is the type available at PexUniverse.
A less common indicator of the foam density is it's compressive strength, which shows how much pressure (psi) needs to be applied to deform the foam by 10% (ASTM D1621 standard). For 2 lbs/ft³ EPS foam board, this number is
25.0 psi.
Foam Board vs Bubble Insulation
These products, although both classified as insulation, belong to slightly different categories.
Reflective bubble insulation has a significantly lower R-value (best is R-3.8, comparable to 3/4" thick EPS foam board), but it is moisture-proof and acts both as a moisture barrier and as an uncoupling membrane - features which the foam board insulation does not have. It can be layered, but with obvious cost increases. In addition, neither PEX nor heating cable can be secured to the foam board.
Foam insulation will, in most cases, require a poly moisture barrier and due to it being in sheet form, will take substantially longer to install than bubble insulation, but it offers higher R-value and allows to secure PEX tubing directly on top with PEX foam board stapler.
Why not both? Used as a bottom-most layer, bubble insulation will act as a moisture barrier, uncoupling membrane and a basic thermal break, while EPS foam board installed on top will provide the necessary R-value.
EPS foam board vs batt insulation (fiberglass & mineral wool) - which is better?
End uses - fiberglass and mineral wool batt insulation types are almost exclusively used in between studs/joists for wall and ceiling/attic insulation. EPS foam has a much broader range of applications, also including concrete and masonry walls and floors/slabs (including slab edges) both above and below glade.
Cost - both have a similar cost per (1) sqft of area with an nearly equal R-value. This means that when insulating a space between joists to achieve R-20 (for example), both can provide the same R-value with the same material length (bay length) at practically the same cost.
Moisture, mold and mildew resistance - EPS is a clear winner over mineral wool and fiberglass. It's highly hydrophobic and does not promote mold or bacterial growth. Unlike batt insulation, EPS will also not sag or clump together and will not lose its' insulating properties from exposure to moisture.
Which foam board thickness - 1", 2", 3", etc. do i need?
The short answer is that 2" is the most common and popular insulation thickness used for radiant floor heated slabs. Attics and crawl spaces are different and may need thinner or thicker insulation.
Over 3" and thicker insulation is generally installed in very cold US climates. The best practice is to do your own research and consult a professional familiar with climate in your area and project specifics.
Note: only 1-1/2" or thicker foam board accepts PEX foam board staples.
Is EPS foam insulation eligible for rebate(s)?
You would need to check with Energy Star (for federal) and your local utility (for state) to determine whether a tax rebate or incentive can be applied.
Layering multiple foam boards
Multiple foam boards can be stacked to reach total desired R-value. It's always best to stagger the boards, so that none of the seams match.
