Spray Foam insulation: open cell spf vs closed cell spf

12 years ago

Our house has a ventilated crawl space, and the floor(we have hardwood floors and no carpet)feels cold around the year and more so in winter. We live in the San Francisco Bay area to give an idea of the climatic condition. After doing energy audit and after talking to a couple of insulation companies, we feel that doing a spray foam (SPF) insulation barrier under the floor in the crawl space area will provide us enhanced living comfort and some savings in our energy bill. When we looked into the available options there seems to be 2 choices. ie open cell SPF ( ocSPF) and closed cell SPF ( ccSPF). There seems to be pros and cons to both choices. We would like understand the negative/positive implications of the installation of one over the other. Any thing specific along the below lines will be of help too.

- odor due to off-gassing during and after installation. I have a child who has allergies and I get affected when I am exposed to any chemical smell.

- how would any unintentional water leak/spill inside the house dry up.

- future access to crawl space for repairs to plumbing / air duct.

I searched the forum, but did not find any discussion on this topic, so thought I'll post it to get feedback from the knowledgeable folks on this forum. Thanks a lot!

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Comments (3)

energy_rater_la
12 years ago
this has been a pretty hot topic in my hot humid La.
climate.
below is a link for the latest study by LSU ag center
(unbiased information only educational site)
http://www.lsuagcenter.com/NR/rdonlyres/D33F711D-DC4B-4E4C-9ED6-A97DCE9DB026/79806/pub3187insulatingraisedfloorsHIGHRES.pdf

sorry for the long link...its a cut & paste link but it works. take a look at it and then we can discuss methods
of your particular application.

and your ductwork is in the crawlspace? flex or hardpipe ducts? is heating system in crawlspace also or inside house?

best of luck.

basically what it comes down to is this
sweet_home
Original Author
12 years ago
Energy_rater, Thanks a lot for the link! The pdf seems to have detailed info about spray foam insulation. Reading through it. To answers your questions, our ductwork is in the crawl space and it is flex. The heating system is not in the crawlspace though.
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See "Understanding Foundations" from Building Science Corp. "The most cost effective approach involves a combination of rigid insulation and a frame wall assembly .... The least risky interior insulation assemblies from an installation perspective and water sensitivity and drying perspective utilize spray foam--either closed cell or open cell." Either type allows drying to the basement. On my most recent project I used BASF closed cell insulation for the entire basement, rims, garage ceiling and other hard-to-reach areas. On others, I've used open cell insulation at the rim joists and XPS on the walls. I don't like open cell because it requires more to achieve the same R value. Also, when sprayed on cold walls, it shrinks noticeably and I've ended up trying to fill the gaps with hand held spray foam.
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I am in south Louisiana. energy_rater_la, I have no problem with overfilling the walls. I need all the R I can get, and even though I give up R=1 for a 1/2" of air, I get R=1.9 for 1.2" of spray foam, and at $.16/in-ft^2, it still marginally makes sense. For the roof, as I will generally have 2x10 rafters (i.e., 9-1/4" deep), I do not need to have insulation all the way there (the optimal level from an overall cost benefits analysis is at 8".) energy_rater_la, are you saying that I do not have a problem with having some space between the foam and the ceiling sheet rock, unlike for the walls? It would not matter much if I did go all the way to 9-1/4", although I would be paying a little more for the insulation than I would get back in reduced energy costs (using my analysis of the cost of financing and energy cost increase and expected life), as well as not taking advantage of the air space R (value of 1). As for exterior insulation, in general, the costs of the material is so high, that once the wall is at R-12 (net), the total costs of the material and labor are higher than the reduction in energy costs. Actually the cost of material alone is OK, but the extra cost of labor pushes it into being too expensive. There is a new combined structural and insulation sheathing (Dow Styrofoam SIS?), but the material cost is even higher, and it only almost makes financial sense, but with the problems of "this is new, and how good is this going to hold up". However, since the east and west walls get more insolation (and therefore more heat gain), the numbers begin to work out for exterior insulation, and there is the added benefit that the local heat gain is less, which allows those rooms to have the same heat gain as the rooms with non-insolated walls, thereby allowing a more constant indoor environment. I will be putting in an extra 2" of insulation there (which makes integrating with windows easy as all manufacturers make jambs for 6" walls.) This leaves the question of what exact type of exterior insulation should I get. There are so many different types out there - this type of foam, that type of foam, fiberglass, etc. And the idea of vapor and water barriers, foil radiant barrier, with the open cell insulation has me very confused. Fortunately, the price per R is about the same, so I don't have to make a decision based on relative price, but only on what is proper. Here are some of the brands I have researched: ProPink Foamular R-Max R-Tech Which of these is better for my situation? Are there any others I should consider? Thanx again
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Down here we use open cell above grade and closed cell below Building Science articles do mention both cc and oc being used in attics, but they explicitly recommend cc. See "Unvented Roofs for All Climates" and "Understanding Attic Ventilation" (See Link below.) As I mentioned above, cc is excellent in attics as it acts as a secondary liquid water barrier. At the same time, it is permeable, allowing vapour to move both ways depending on the season. As for "hiding" leaks, I have seen commentary from foam appliers who handle all kinds of foam say that in case of leaks cc focuses the water, so it's easier to spot the source. Because oc foam is more permeable and holds water, the R value is degraded, which means the sheathing is more easily reaching dewpoint, which is not desirable. The same logic applies below grade. The one time I used oc foam, it was applied in cold weather and shrunk back considerably around the rim joists; this is recognized in the literature but brushed off as a minor quibble. When I've used cc foam in basements, rim joists, garage ceilings and attics (but not under the decking) I had none of those problems. Clint Eastwood's Dirty Harry had a famous comment about opinions--that I won't use here. That's why I try to reference mine to Building Science, whose principals are among the leading building scientists around; and who are also the source of much info at the US Energy Department --Energy Efficiency and Renewable Energy--Building Technologies Department. Here is a link that might be useful: Vented and Unvented Roof Recommendations
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energy_rater_la
12 years ago
flex in a crawl...sigh the things we do...

you don't get into specifics about the audit
and I've learned not to expect much from a lot
of 'audits'.
but...

ducts leak.flex less than hard pipe.
where they connect to the plenum @ start collar
where they terminate at supply box
and where supply box connects to floor.
just by removing a supply grill inside the house
you can see the poorly sealed cut.

before you spray foam..mastic seal these areas
I listed above. paint on mastic or mastic tape
like hardcast brand #1402
duct leakage is high in existing house. sealing the ducts
with acca ul approved products should be done prior to foam

don't let foam company sell you duct sealing with foam
foam is not a duct sealant. not approved & over time
fails quickly.

if ducts are strapped in between floor joists..how will foam company get foam to floors?
better take a look under there and see if ducts are strapped or loose or lying on the ground. (ducts shouldnt
lie on the ground)

do any duct sealing first...its a pita to dig out foam to
work with ducts...been there done that.

I'd use closed cell.
if you use open cell then a vapor barrier has to be
installed on the face of the open cell once install is complete. unless you have a perfect vapor barrier on the ground...that is still perfect after foam install.

while closed cell will trap moisture
it is the way that it is installed that will make the difference.
install is 2-3" of closed cell in between floor joists.
the joists themselves are not encapsulated in foam
(directly opposite from unvented attics..different product
different needs = different install)
where the foam meets the floor joist is where the
future leaks will exit.
if you go under a house that has had closed cell installed
you will see that in a couple of years the foam seperates
a bit from the joists. closed cell is rigid when dried
and doesn't expand and contract like open cell.
this seperation helps to aid exit of water from leaks.

did the audit cover duct leakage and how to address?
what shape are the ducts in currently?
are they strapped up or not?
your system is in the house in a closet?

shop your foam companies wisely.
ask for customers names that have had similar installs
and speak with them.

as for as offgassing..all foams offgas. but it is outside of the living space and shoudn't be a problem as long as
there are no gaps for the foam to enter the house or the ductwork.
you may want to spend the night somewhere else if you worry
that it will make you ill.

any plumbing work in the future will have to be re-foamed
once work is complete. usually cans of great stuff can be used to seal these smallish areas. if not the foam company has a bigger can of foam that will cover most of these larger areas.

best of luck

Spray Foam insulation: open cell spf vs closed cell spf

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energy_rater_la

sweet_home
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Spray Foam insulation: open cell spf vs closed cell spf

Comments (3)

energy_rater_la

sweet_homeOriginal Author

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sweet_home
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