Spray-Foam Insulation
Discover the advantages and disadvantages of spray polyurethane foam-- a high-performance material discovered in the walls and roofing systems of many of today's energy-efficient homes.

Spray-polyurethane-foam insulation is more pricey than other kinds of insulation-- fiberglass batts or blown cellulose, for example-- and it calls for professional setup. So, why do some contractors and house owners swear by it? In a word, performance.

Spray polyurethane foam can be found in 2 variations: open-cell and closed-cell. Both types fill cracks and crevices in walls and ceilings much more successfully than batt insulation, quickly flowing around pipes and wires to produce a reliable air barrier as it cures.

Spray foam is made at the job website from 2 chemicals, the "A" and "B" sides. The two mix at the nozzle of the spray gun, foaming as the elements are united. Installers wear protective clothing and a respirator as they work with it.

Open-cell foam is vapor permeable
Open-cell foam is the lighter and more economical of the two. With an R-value of in between R-3.5 and R-3.6 per in., open-cell foam weighs about 1/2 pound. per cubic ft. Although costs vary, intend on $1 to $1.20 per sq. ft. when filling a 2 × 4 stud cavity.

Installers normally over-fill a stud or rafter bay with the foam and trim back the excess once the foam has treated. This leaves the cavity completely filled.

Open-cell foam makes a good air barrier, but it's vapor permeable. That means water vapor can move through the foam even when the bulk motion of air is obstructed. This ends up being an essential factor to consider when the foam is sprayed in between rafters on the underside of the roofing sheathing to develop a conditioned attic in a cold climate. In the winter season, moisture in the attic air can make its method through the foam and gather on the back side of the sheathing-- a possible mold and decay problem.

In this case, a separate vapor retarder or vapor-retarding paint must be installed over the foam.

Closed-cell foam is a vapor barrier
Closed-cell foam has a much higher R-value than open-cell foam-- about R-6.5 per inch-- and it's a vapor barrier in addition to an air barrier. (One maker, Demilec, states its Heatlok High Lift spray foam has an even higher R-value-- R-7.5 per in.) Closed-cell foam is much denser, about 2 lb. per cu. ft., and it's untouched by water. It forms a tough, dense insulating layer and enhances wall and ceiling cavities structurally.

Closed-cell foam also is significantly more expensive than open-cell foam, costing between $1.75 to $3 per sq. ft. in a 2 × 4 cavity. That's money well spent in some applications. In a wall or roofing where there's limited space for insulation, for example, closed-cell foam uses outstanding thermal performance in a thinner layer than a lot of other kinds of insulation.

Cured closed-cell foam is much more difficult to cut than open-cell foam, so installers do not overfill stud and rafter bays. It's way too much work cutting it back after the foam has cured.

Installers likewise have to be careful not to spray too much foam in a single pass, or "lift." The reason is that the foam develops heat as it cures-- an exothermic reaction. If the foam is too thick, it can catch on fire. Although this is unusual, it has actually happened, and improperly used foam has been blamed for several house fires.

Ensure you know what you're getting
With its really high R-values, closed-cell foam would appear to be a perfect insulation for exterior walls. Simply think: In theory, filling a 2 × 6 stud cavity yields an R-value of 37.75, practically double what a standard-density fiberglass batt would provide.

However, as Green Building Advisor editor Martin Holladay describes in this article, the truth is various. First, the installer will probably not bring the foam all the way out to the edge of the stud. He's more most likely to leave a 1/2-in. buffer so he will not need to cut anything back later. Now the insulation layer is 5 in., not 5-1/2 in.

Then there is the "framing element"-- that part of the wall that isn't insulation: studs, headers, and top and bottom plates. When the R-value of wood (about R-1.2 per in.) is figured into the formula, the whole-wall R-value is more like R-15.4. That's only R-1.9 more than you 'd get with open-cell foam, however at a much higher expense.

Environmental factors to consider
Regardless of some undeniable performance advantages, some home builders and designers will not use spray foam. Supporters of foam-free construction don't like the petrochemical origins of spray foam, or the possibility, nevertheless remote, that incorrectly blended foam will develop a chemical risk or lingering smells in the house.

In the case of closed-cell foam, there is the matter of the blowing agent—the chemical additive that gives foam its froth and its high R-value. Open-cell foam utilizes water or carbon dioxide as the blowing agent, but the industry-standard blowing agent for closed-cell foam has actually been a hydrofluorocarbon (HFC) with a worldwide warming capacity (GWP) some 1300 times higher than CO2.

With the dangers of global warming and climate change becoming better understood, this alone is enough to make some designers run the other method. However, a next-generation blowing agent, Solstice, developed by Honeywell, is a chemical, a hydrofluoroolefin. It has a GWP of 1 or less, making spray-foam solutions that use it no more hazardous in that respect than open-cell foam.

The spray-foam market is slowly switching over to this more recent blowing agent, and the Spray Polyurethane Foam Alliance anticipates the transition to be complete at some point in the next year or more.

 

 

 

Spray foam insulation is terrific for the building envelope. Spray foam insulation is a great product. Residences insulated with it can be a few of the most efficient and comfortable homes developed. I've been in lots of these homes and can inform you that when spray foam is set up appropriately, they surpass 99% of fiberglass batt-insulated, stick-built houses. I can likewise tell you that 73% of all stats are made up on the spot, so please do not ask for paperwork of that figure.

Spray foam insulation is a terrific product. Homes insulated with it can be some of the most effective and comfortable houses developed. I've remained in lots of these houses and can inform you that when spray foam is set up properly, they outshine 99% of fiberglass batt-insulated, stick-built homes. (I can likewise tell you that 73% of all statistics are made up on the spot, so please do not request for documents of that statistic.

Spray foam is available in two tastes, open cell and closed cell, and offers both parts of the building envelope-- the insulation and the air barrier. The structured envelope needs to entirely surround the conditioned space, and the insulation needs to be in contact with the air barrier. Since spray foam is both insulation and air barrier, proper positioning of insulation and air barrier is guaranteed.

What's not ensured, nevertheless, is that all spray foam homes will be efficient and comfy. I've seen a number of homes with issues even though they're insulated with spray foam. In order of occurrence, here are the potential fails I've seen, with explanations following the list:


Spray foam isn't thick enough.
Spray foam installers missed out on some of the air leakage websites.
Spray foam installers didn't understand the structure envelope and sprayed either too little or excessive.
Spray foam agreements and pulls away from framing.
Spray foam isn't thick enough.
This is more typical with closed-cell foam, but it happens with open-cell foam, too. Since closed-cell foam has a higher R-value per inch, installers generally spray 2 ″ in walls and 3 ″ in rooflines to satisfy the energy code requirements of R-13 and R-19, respectively. (I'm not going to dive into the energy code here, however, these numbers apply to lots of climate zones, the latter being enabled under the UA tradeoffs rule. See the Energy Nerd's blog on this topic if you want to argue.).

Open-cell foam generally fills the framing cavity completely, so it's easy to tell if the installer has actually sprayed enough. Closed-cell foam doesn't fill the cavity, so you've got to spot check in a bunch of locations to make certain you do not get shorted.

The video below is from a house near Charleston, South Carolina that I checked out just recently, and you'll see that the house owner in this case didn't get his cash's worth. I understood immediately when I strolled into the attic that something was wrong due to the fact that it was hot up there. In a properly insulated spray foam attic, the temperature level will not be much higher than your house temperature level.

The issue was that the installer was doing his first spray foam job ever, and the density of the insulation differed from absolutely no (noticeable roof deck) to about 9 ″. Unfortunately, excellent average density doesn't cut it. The coverage requires to be uniform since a lot of heat will go through the under-insulated locations. (See my short article on flat or bumpy insulation efficiency.).

Spray foam installers missed out on a few of the air leak sites.
Once I got a call to take a look at a 10,000 square foot home that had spray foam throughout, however, the owners had a serious issue in their first summer in the house. When I got here, they took me to the master suite, where two towels were on the floor-- to capture the rain falling off of the supply signs up in the ceiling!

The issue was that the installers missed out on some locations at the soffit in the attic above the master bedroom, and spaces around the tray ceiling allowed the humid air into the room, where it naturally discovered the cold surface to condense on.

As this example illustrates, it's crucial to seal the envelope totally. One of spray foam's most significant selling points is its air-sealing capability, but it can't seal locations where it's not sprayed. Among the good things about using spray foam in brand-new building and construction is that you can do a Blower Door test prior to the drywall goes in. Even much better, you can check for leakages with a fog maker.

Spray foam installers didn't understand the structure envelope and sprayed either too little or excessive.
In intricate houses, seeing precisely where the building envelope is can be an obstacle. If the installer misses locations, it may or may not be an air leakage, but it will absolutely be a thermal bypass because of the lack of insulation. Every part of the building envelope must be insulated, or the home will have excess heat loss/gain.

Another issue I've seen is that the installer sprays additional foam due to the fact that they haven't determined the place of the structure envelope, the border between conditioned and unconditioned area. In the photo listed below, that wall with foam all over it has conditioned space on both sides. The homeowner paid additional and got nothing for it.

Spray foam is squandered on partition walls.
Spray foam contracts and pulls away from framing.
I've seen this just as soon as, and it was with closed-cell foam, however, I've heard of it occurring with open-cell foam, too. I do not know the information, but I've heard it could arise from a bad batch of chemicals, incorrect mixing, or too expensive a temperature. Whatever the cause, it's not a good idea. The picture listed below demonstrates how the spray foam pulled away from the studs. A little bit of uninsulated area like that adds up to a great deal of heat loss/gain when the whole house has that problem, as it did here.

Conclusion.
Do not presume that just because a house is insulated with spray foam that it's immediately a winner. Every item has its risks, and spray foam is no exception. The bright side, though, is that spray foam's problems are normally less regular and easier to conquer with correct preparation and follow-through.