In January, I blogged about adding insulation to an older home. That article
mentioned both spray-foam and blown cellulose, and specifically stated that
spray-foam is popular and fast, but not always appropriate. Since it appears
that spray-foam insulation is rapidly taking over the world, I wanted to follow
up my last blog with additional comments to help homeowners decide where
spray-foam should be applied.
First of all, since I am a Preservation Architect, this blog will address older and
historic homes, not new construction. For recently-built homes, you can go
crazy and use whatever insulation is recommended for your specific needs. But
if you own or manage an older home – please keep reading.
Anybody can buy a can of spray-foam, bring it home, and spray it anywhere that they like. It’s that easy to use. But as I previously mentioned, older homes are
normally built to “breathe” in order to expel excess moisture in wall and
ceiling cavities. Plugging up these cavities with spray-foam could result in
trapped moisture, damaged materials and could even promote mold growth.
Spray-foam has many popular qualities: it’s easy to apply; it expands to fill cavities and small cracks; and it can bond to materials and become as strong as the structure itself. But these qualities can also harm older homes: spray-foam is
wet applied, which means that it can introduce moisture wherever it is sprayed;
it can expand too much and blow out plaster walls; and being able to bond to
existing materials makes it almost impossible to remove later.
Over the last year, I have talked with several spray-foam distributors who rebutted the negative aspects that I have listed here about spray-foam. Although it appears that newer brands of spray-foam may be addressing some of these issues, not all brands are equal, and there are still many lingering questions about
its use in older homes. Because of this, the National Park Service (the Federal
agency that oversees the weatherization of nationally-significant buildings) does
not recommend spraying foam in wall or ceiling cavities, or spraying it directly
on vulnerable materials such as wood or plaster. Even if your home is not
nationally-significant, it is good advice to follow these NPS guidelines when
insulating an older home.
The NPS does state that spraying foam at pipe penetrations through foundation walls, at by-pass areas (e.g. where chimneys go through floors or ceilings) or where the foundation wall meets the first floor framing are acceptable locations. So it can be used, although in limited applications. To be safe, I would not spray
foam insulation anywhere that you cannot see it, or on any important materials.
What are your thoughts about using spray-foam? Do you have any experiences that you would like to share?