Foam inulation options in new build house

Old 10-31-13, 01:46 PM
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Foam inulation options in new build house

Hi. This is my first post on here and I am not overly experienced in house building so please forgive any silly questions I may ask.

I am having a new house built in Northern Florida. The prices from the contractor for having the walls and roof insulated with spray foam were way too expensive but I really want it done so am thinking about DIYing. We are having the house built in stages so I would have the freedom of being alone in the shell to do the job.

I am thinking of either using the DIY kits like those available from Tiger Foam/Graiger or using the rigid foam board with reflective backing cut to fit between the studs/rafters and held in place with spray foam from a can/gun.

I was wondering what the general consensus is about which of these options is best in terms of price and efficiency assuming a 2x1" layers of board or a 2" layer of spray foam.

My main queston is this; if I used 2x1" sheets of rigid foam board with a 1" gap between them, the edges sealed by spray foam to hold it all in place, would the air cavity provide a significant enough added insulation layer to make it worthwhile?

Thank you gentlemen (and ladies).
Old 10-31-13, 06:53 PM
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I'm not trying to be a bung hole but last year I got a thermal FLIR camera and am amazed at how rigid foam board and even fiberglass batts can't be cut to fit all the nooks and crannies without air gaps. And, I am no foam expert but I think some of the benefit of sprayed foam will be lost if trying to cut & fit rigid into place. It would take extreme care to cut & fit rigid sheets to fit in stud bays and around wiring & plumbing. Almost impossible on something the size of a house.

Would an air gap between two layers of foam be as good as insulation the whole thickness. NO! Insulation works by trapping hundreds or thousands of air pockets per inch. Two sheets with an air space is sorta like a window. Better than a single pane but not as good as proper insulation.

Have you priced different options? Is it cheaper to frame the walls with 2x6 and use fiberglass batts than to spray foam with 2x4? Is the expense of spray foam even worth it? What is your estimated payback period? If you'll only be in the house 10 years you may never recoup the expense of better insulation.
Old 10-31-13, 10:59 PM
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DIY sprayed-in foam is not user friendly to the inexperienced and the cost is horrendous. I don't like fiberglass and what Pilot stated about its track record of poor installation is generally true as the people that install it don't get paid to do a good job. A rigid foam board job with sprayed-in foam CAN be done well but the time to do so is high along with the difficulty of using the DIY spray foam kits. Honestly, if yo want to have solid, foam insulation walls in new construction the ONLY thing that makes sense is to have it done by a competent contractor.

That stated, there ARE other materials that can be used that are almost as good as sprayed foam. Cotton blown under a breathable scrim, cellulose done either with a binder (adhesive) on bare wall cavities or dense-packed in a covered wall cavity would be better than fiberglass in my opinion. Since you are in a land of primarily cooling AND high humidity the vapor retardant needs to be placed on the exterior of the building, under the finished siding. Note I stated vapor RETARDANT and not barrier. During those times when the outside is cooler than the inside you want the walls to breathe outward.

Now whether or not increased insulation is "cost effective" as Pilot mentions is a debatable point. In my opinion insulation and air sealing in NEW construction should be done to state-of-the-art specifications when ever it is at all possible. It is in retrofitting that the cost factor vs. performance gets turned upside down.
Old 11-01-13, 05:53 AM
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One of the lessons learned is that air sealing is the most important step. Air leaks are the source of most moisture and heat exchange problems. With new construction, attention to details eliminated most of the advantages of spray foam and given recent concerns about the foam itself, going a traditional route will ensure high performance at a zero risk of problems down the road.

A good choice would be a traditional 6" wall with a one inch layer of rigid (pink or blue) foam over the outside. I will defer to Florida codes as to how to do that and meet hurricane requirements. Roxul would be better than basic fiberglass.

Old 11-04-13, 10:35 AM
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Thanks guys,

I was under the impression that spray foam was the best and brightest of insulation and soundproofing. I am not doing any of the building, we have a contractor, but there may well be a time when the property is standing empty as a shell and I could get in there and take my time to get it done.

My idea was that if I can do the hard work myself I could save the extra costs and labour that make it currently unaffordable.

I self built a motorhome in the UK and used the rigid foam held in place with spray foam form a can and gun, it worked really well.

I found that with the rigid foam board the cut doesn't need to be exact, within an inch is good enough as the spray foam expands to fill all gaps and hold it in place.

"given recent concerns about the foam itself"

Can someone give me a quick answer as to what those concerns are?

I have never liked fibreglass, it seems like an outdated material to be putting in a living space, especially in the attic when access is needed for a/c and the like.

I will look into the other materials you mention. I had not heard of them until now.

Thaks again.
Old 11-04-13, 05:08 PM
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You can get DIY CCSF for about $1 a board foot. If you are doing an entire new house, you should be able to have a pro install it for less than that.

You also do fladsh and batt where you use spray foam for the air seal and then install batt insulation to get the rest of your R value.

However, as stated before, there are other options that will perform as well as spray foam when building new. My brother recently had a garage built with 6" of rigid foam on the walls and roof. The inside stays nicely conditioned all year round.

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