Smart Membranes and Cellulose Insulation
Having read a variety of questions and answers on this site over the last
several years certain themes and memes have appeared with regularity.
They aren’t always wrong or right, but they are popular! Here are a few of
them along with a few questions.
1. Variable Permeance membranes are more desirable and superior to impermeable membranes and should be utilized at every opportunity.
Q. Are any of these ideas actually true? I suspect that in many cases
they are not superior (except for the expense) and in many
instances are you would be just as well off with cheap polyethylene.
2. Cellulose is more desirable and superior to most other insulation
material and should be utilized at every opportunity.
Q. What if anything happens to the R-value of cellulose when it absorbs
moisture (apparently it is capable of absorbing about 135% of its own
weight) – what is the R-value at 10%, 20%, etc.? How much settling are
you likely to get in your walls over 8 or 10 years if you have a lot of high humidity and the cellulose you had carefully installed at 3.5 lbs. per cubic
foot now weighs 4.5 or 6 or whatever lbs. per cubic foot? These are the type
of questions that should be asked of all fluffy blown in insulations by the
way, not just cellulose – and don’t get up on your moral high horse and tell
me that they don’t settle if you follow the manufactures installation instructions – there are too many anecdotes out there about people opening
up cellulose filled walls and finding settling. Cellulose in ceilings is not
much of a problem because you can get up there to see it and fix it – but
in walls it can really be a problem!
Enough for today!
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