Open vs Closed Cell Under Homes

In light of all the falsehoods and miss-truths that I have heard for almost a decade of inspecting homes I thought I’d put together a list of the Top 10 most uninformed statements concerning open and closed cell under homes:

#1 Open cell will breath.

Yes it does breath. View Insulating a Raised Floor for explanations

#2 FEMA is outlawing the use of closed cell under houses.

Unfortunately some well known local spray foam companies are using this one.

#3 If you spill something on the floor it will soak through and dry to the outside under the floor if you use open cell, whereas closed cell will hold the water.

What? If your spray foam sales person says this (and they won’t be much longer now that this educational page has been added to our site) then ask him these questions.

One, how will this water leak through, move against Mother Nature’s normal flow of vapor travel, and “dry” when it is already wetter down below than it is in the house? Two, what happens if you spill liquid on the floor of a house on slab or has a laminate floor with a vapor barrier below it. Is the water going to drip out of that slab or pass the vapor barrier? Of course not, it can’t.

If you spill water on the floor of a raised house you simply clean it up. I already saw what a leaking washing machine with a fiberglass batting sub-floor in a vented crawl space can do if unknown and unattended to for several months. Open cell surely doesn’t “breath” as much as fiberglass does, yet another spray foam company, after knowing this, actually still quoted open cell.

#4 We install more inches of open cell for a lower price than less inches of closed cell.

True, and how much more money does the sales person make by doing so? It also doesn’t matter how many inches of open cell you install if it does nothing for vapor travel.

#5 It'll dry if it gets wet.

No it won’t. Take a piece of open cell from underneath your neighbor’s house. Leave it in the rain for a while or stab a hose into it and turn it on very little to simulate if there was a long-term leak from above in the house. Now let it sit in the sun to dry. Once the water has worked its way into the foam (which would have to actually occur if it were to “dry out below” as stated) it’ll take a very long time to dry. Now, put this wet piece of foam under your raised house as would be the real-life situation if it did get wet. Check on it a year later.

#6 Our company doesn't sell closed cell spray foam.

The fact is that it can but it chooses not to or steers away from it unless you specifically demand it. Or, they entered into an agreement with a manufacturer which does not want them to sell closed cell.

#7 Our 1.2lb hybrid foam is almost the same as closed cell foam but cheaper.

1.2lb hybrid open cell foam is less expensive but it is nothing like closed cell concerning vapor and water protection.

#8 If you get a leak with open cell you'll know it.

We hear this one more often with spraying underneath the roof decking/rafters but it is now used for the floor also. What kind of leak could this be and when do you go crawling around under your house. If you don’t actually “touch” the open cell and feel its wetness or saturation you won’t know there is a problem for maybe years at which point your flooring may be more compromised now.

#9 The "fluff" of open cell provides better protection than closed cell.

This is actually kind of cute-sounding really. Unfortunately, none of the reputable research organizations full of engineers, scientists, and building science experts have ever used the word “fluff” in their reporting, publications and journals. It does sound cute though.

#10 If the house shifts it'll develop hair-line cracks through which air and moisture will pass and compromise the effectiveness of the closed cell insulation.

We actually like this one. It does sound relatively intelligent after all. Lets elaborate on it a bit. Closed cell is very rigid which is what makes it a premium product. It does, however, have a slight measure of “elasticity” to it. The incredible increased structural integrity (up to 300% shearing and racking) from closed cell will maintain a structurally sound single “plate” of flooring that’ll actually keep it from otherwise bending and twisting as is normally the case with shifting homes. For argument sake let’s assume that it did develop a hair-line fracture or opening and lets air or moisture through. First, this minute amount of space making up this hair line is certainly negligible over the course of the entire 1,000 or 2,000 square feet lets say. Secondly, the percentage of area that allows vapor to pass is in direct correlation with the amount of vapor that will actually pass over the course of the entire envelope of the house. In other words, this extremely small amount is irrelevant. But, this argument does bring up a funny scenario again. If we are concerned with the amount of moisture that this insignificantly tiny hair-line crack (that may almost be visible to the human eye under very close scrutiny and assuming that the house has shifted enough to push this up to 300% increased strength to its breaking point) may allow into one’s home we can certainly appreciate that sales person’s picky sense of perfection when discussing spray foam with their potential client. However, this statement of “letting moisture in” brings us right back to the argument on why NOT to use open cell… it let’s all the moisture in!

As of the end of September 2009 we’ve heard a new falsehood as to why open cell should be used under your home rather than closed cell.

Open cell is less expensive and fits many homeowner’s budgets.

In my opinion it is the ethical responsibility of the insulation contractor to understand his products’ specifications, characteristics and proper application according to manufacturers’ instructions. I’ve seen the competitor’s bids… they usually do not include even a price for closed cell.

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