Spray Foam: Open Cell or Closed Cell?
renosteinke
| Posted in Energy, Heating & Insulation on
As my complete-gut remodel progresses …
I’m stripping the interior drywall, re-wiring, and re-insulating. I am sold on the idea of spray foam, and have approached two contractors. I’m a bit surprised at their gut responses ….
I feel like I’m talking to a Moonie! Their eyes glaze over and they begin chanting a mantra that sounds like ‘open cell.’ I mention closed cell, and they shudder with horror, no, I don’t want to do that! Topic dropped.
So- what’s the scoop? If you were foaming “all six sides” of a house, which would you use? Open, closed, or a mix? Please explain to this rube why you prefer one to the other.
Replies
closed is what I prefer
I prefer closed, especially in a roof. It won't absorb and hold moisture like vapor-permeable open-cell can do.
In walls, I still prefer closed over open.
Open-cell is not a horrible product. I'd still recommend it over FG. Open has a great marketing machine with a lot of money and a lot of misleading information behind it in terms of how they talk about closed cell. In my area there are more open-cell installers than closed-cell installers. when they market their product, they really emphasize that open-cell is a lot less expensive per inch than closed. Without disclosing that it has much less R-value per inch.
Open is roughly R3.5 per inch verus R6.5 for closed. In my area, open is about 60 cents a bdft versus about 90 cents a bdft for closed. So in my area, open-cell is more epensive than closed cell if you want an equivalent R-value. Plus with open you may need a vapor barrier or retarder to protect the foam from absorbing moisture.
If you're into all the eco-friendliness of them, there are open-cell foams made from soy and other more "friendly" things. So i'd say open is more "eco-friendly" than closed. But I think closed is a more effecitve insulator. So maybe you'll burn less energy heating and cooling with closed, making it more friendly in the long run?
Closed is rigid and will improve the structural integrity of the shell of your house. Open is soft, sort of like the foam cushions in your furniture.
Just a few ideas. And yup, my opinion.
Good Info!
I've never seen open-cell, so I appreciate your description of it.
One contractor did claim the two types have the same insulating value, but that open cell was 'half the cost.'
Soy based? Hello! Mice / rats went to town on electrical wires whose PVC jackets was (formerly) soy-derived. That's why wire makers stopped using soy based PVC. I shudder to think what a house filled with soy would represent to the local rodent population.
As you mention, there's far more to foam than just the R-value. It's only one part of the structure. In my case - an older home with board sheathing, tar paper, and ACB shakes - there's a real need for a REAL vapor & air barrier. One 'point' for closed cell!
I'm also atop the epicenter of the stongest quake to ever hit this continent, within 30 miles of the birthplace of nearly every Southern tornado, and at the end of the road for Gulf hurricanes. Plus, I have a freight rail line on my property line- a line that serves the largest steel mill in North America. Do you think my house would benefit from a more rigid structure? Point 2 for closed cell.
(If you're really good with Google, I've practically given you my street address with these statements)
I don't have any data know if there is any difference in the sound transmission of the two types, but I suspect that closed cell would win again ... especially at the lower frequencies of the trains.
Moisture absorbtion? Right now my meter is measuring 99% humidity ... and it's rare for the RH to drop beneath 60%. I swear it has rained every week this year. Small wonder one local cash crop is rice! I think the State flower is actually a fungus. So, again, it looks like closed cell would be a better choice all around.
Where might open cell be of value to me? Well, perhaps for interior walls. Maybe.
The two contractors with whom I spoke particularly liked open cell for attic / roof use. MAYBE for the back side of the roof deck - if there's a leak, you want the water to drain. Otherwise, the last thing I want in the attic is a huge sponge.
For the same reason, under the floor (crawl space) is closed cell territory. I want crawl space moisture to go out the vents, no into the floorboards. I'll take my chances with floor leaks. I do see a need to wrap plumbing penetrations with a piece of removable (open cell) foam, just to allow things to be replaced or worked on.
Considering my options, and my circumstances, I just may wind up insulating the place myself, one DIY 600 board-foot kit at a time.
open in ceilings...
I'd never put open-cell in a ceiling. That's my opinion. I'd rather have a rigid closed-cell foam that won't absorb moisture and will shed it. That shed moisture will indicate itself somewhere, and usually quickly.
With open-cell, the foam will absorb and hold a volume of water and turn into a soggy sponge. Once saturated, THEN it will shed water to indicate a leak.
It's a personal choice though. There's definitely an open-cell camp and a closed-cell camp.
The DIY 600 bdft kits can be effective. But have you thought of using rigid sheets? Not sure fo the scal of your project, but for argument's sake let's say you have 16" oc framing. You can rip 4' by 8' sheets of rigid foam into three 16"-ish wide rips. Rip them a bit narrower than the framing bay is wide so they can easily be set into the framing bay. Set the rip in the bay, then use canned foam (or a DIY foam kit) to fill the gap. the foam will expand tand lock the foam piece in place.
Sheets of 2" polyiso are about $42 in my area. That's about 65 cents a bdft. The DIY kits are about $1 a bdft. The nice thing is with rigid sheet foam you;re getting a solid and even 2" thickness everywhere. With gunned foam, you get a little wiggly-jiggly with regards to getting a consistent thickness in the application.
Just my thoughts.
Doesn't sound like Mother Nature is your friend! Quakes! Tornados! The good life! lol
Insulation, condensation.
I would suggest that you use closed cell insulation board but, consider fitting it on the room sides of the outside walls. The reason for this is, that wood comprises a very large part of every wall, and wood is not a very good insulator.
If you fix sheets of polystyrene over the inside of the frame, and cover it with a water vapor plastic sheet and cover that with drywall, you will keep the moisture you create in the home and not in the wall. The drywall will fill up with water vapor, but this is a good thing as drywall provides a 30 minute fire break.
By all means fill the spaces with insulation, more insulation is better.
House is approximately 1000 square ft, perhaps a 25 x 40' simple rectangle.
Built in 1957, it's a 2x4 frame with board sheathing under asbestos cement shakes, 2-1/2" fiberglass batts,and drywall inside. Framing is minimally acceptable by today's standards - yet there is also far more wood than would ne used today. This is ALL going to change.
On the outside, the sheathing will be covered with 1" foil-faced foam panels, a "rain screen," and hardie-plank siding. Inside, the walls will be faced with a layer of 3/4 plywood, covered with DuRock. I intend to fill the stud bays with spray foam.
I choose spray over board for the stud bays because of the need to work around the electrical (and other) wiring, the HVAC lines, and the plumbing lines. I'll spray the bays with an intumescent coating before spraying.
I see the foam as an integral part of the wall structure- and not just as insulation. Seal it & stiffen it.
With the inner layer of plywood (in addition to the 5/4 board sheathing) and the DuRock, I speculate that the wall would meet minimum penertation resistance as called for by tornado "safe room" standards. Plus, DuRock eliminates some drywall mold issues- and might even stop the errant bullet. (Some of my neighbors are a wee bit casual about their firearms use).
I'm not all that worried about mold .... rather, I have a number of animals in the house, and I want to make things as non-porous and durable as possible. The plywood under the wall will also make it a lot easier to mount grab bars, etc., wherever I want. (Good-bye to the blocking Psychic!)
As mentioned before, I intend to vent the dickens out of my low-clearance attic. I'll use the roof to put the rest of the house in the shade- and use the air flow to remove any heat that makes it through the roof.