Expert: Richard Taylor, AIA - 1/7/2010

Question
I have a 1960s split-foyer house with some kind of blown-in insulation in the attic.  It looks kind of like a combination of cardboard and dust.  It looks like it covers the entire ceiling of the top floor.  The roof has a vent on either end, and under the eaves.  Is the existing insulation any good, or should I have it replaced or added to (and if so, with what)?

Thanks!

Answer
Good morning Joe - thanks for your question!

You have blown-in cellulose insulation in your attic - which is in fact, cardboard and dust!  Good call!

Insulation gets its heat-blocking value by trapping air; in fiberglass insulation it's the air spaces between the fibers; in foam it's the air-filled bubbles; in cellulose it's the air trapped in the "fluffiness" (that's the technical term).

Cellulose insulation is pretty much just ground up newspaper.  It's mixed with a wet binding agent and pumped through a hose, and sprayed between the ceiling joists.  Once it drys, it stays "fluffy", trapping air and providing insulating value.

It's relatively cheap, but there are downsides.  Older cellulose insulation may not have the fire-retardant additives that newer cellulose has.  And the older it is, the more likely it is to lose its fluffiness, and therefore most of its insulating value.

And as you've already seen, it has a tendency to "dust" quite a bit.  I wouldn't have it in a home if the occupants have allergies.

Definitely DON'T add more insulation of any kind to it - the weight will compress the cellulose and take away all its value.  If you think you need better insulation, have it removed and replaced.

Best products for replacement include fiberglass blankets (the big pink rolls with paper on one side) - but make sure you get the kind you can use exposed (some paper backings require covering with drywall) and get the right thickness for your ceiling joists.  Once you remove all the old cellulose, you can pretty easily install FG yourself.  One of my least favorite jobs, though!

You could also install new blown-in cellulose; it's very commonly used in older homes where access is limited.  Check the prices between fiberglass and blown-in for the best value.

My personal favorite (and unfortunately, the most expensive!) is expanding foam.  It has the highest insulating value by far, completely seals all the "gaps" in the construction, and lasts more or less forever.

In all cases, there's a right and wrong way to install insulation.  Most important is to avoid blocking air vents in the soffits and rafter spaces.  The insulation manufacturers will provide you with all the info you need for proper installation - do it right or risk damaging your house.

Hope this helps,

Richard Taylor, AIA
www.rtastudio.com
www.rtastudio.blogspot.com
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