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Old 07-26-2011, 01:08 AM   #1
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Insulate between 4' OC joists

My 1969 rambler has 3x10s 4' on center with 2x6 car deck t&g subfloor. I had R-30 unfaced fiberglass batts in between held by twine strung across and stapled. Rats had got up on the insulation and made condos and a social club till I bade them farewell. Now I have these expansive joists and nothing solid to span the 45-1/2" tween the joists. Is spray foam the only choice? There is about 24"-30" from ground to joist and no center beam in 24' of joist span. I live near Seattle so we get a fair amount of ground moisture, too. What's the best route?


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Old 07-26-2011, 02:18 AM   #2
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Insulate between 4' OC joists

what about fiberglass with chicken wire over it. maybe tyvec would work for you.


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Old 07-26-2011, 07:20 PM   #3
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Insulate between 4' OC joists

First off let me say I don't really like foam for a number of reasons I am a cellulose guy but this seems like an ideal spot to use foam. I have in the past blown cellulose into a floor like that but it had plywood on the bottom already and was in a fairly dry area. They do make a PSK faced fiberglass product kinda like duct wrap that you can get made almost any size but it is not cheap and it's a special order. It is usually held up with stick clips and or wire . It being fiberglass it is subject to the rat thing also.
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Old 07-27-2011, 11:18 AM   #4
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Insulate between 4' OC joists

With spray foam you will have to cover it with an ignition barrier and a thermal barrier (if it's not code for you now, it will soon be). So along with spray foam comes the need to sheetrock the space. And since you have such large spans that would also entail additional framing.

So I would suggest what DannyT proposed: batts of some sort with chicken wire and tyvek. Chicken wire for the rats, tyvek for the air barrier. If moisture is a problem, lay down some 6 mil plastic on the floor of the crawl space and it will help reduce the overall moisture levels.
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