Has anyone had some closed cell foam insulation sprayed on the underside of their roof recently? Does anyone have any estimates on what it costs per SF or a general rule of thumb on cost? I am looking at having it sprayed on my roof, but I thought I would see what the boards recommendations are before I bother a contractor. Also, do you know if you can "do it yourself" with rental equipment? Thanks in advance
Foam Insulation?
- Thread starter TEXAS70
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hollisdude
500+ Posts
I have never heard of spraying foam insulation on the underside of the roof. Radiant Barrier paint - yes, but I have never heard of such.
I would ask for three references to go check on before doing something like this. You do understand that foam insulation will do nothing to reflect the heat and in fact would serve to trap the heat once it gets into your attic.
I'm sure you know what you're doing, but this sounds like a bad application to me. Better consult some attic and roof experts before you go this route.
Matter of fact, if this were such a good idea then wouldn't everyone be doing this?
I would ask for three references to go check on before doing something like this. You do understand that foam insulation will do nothing to reflect the heat and in fact would serve to trap the heat once it gets into your attic.
I'm sure you know what you're doing, but this sounds like a bad application to me. Better consult some attic and roof experts before you go this route.
Matter of fact, if this were such a good idea then wouldn't everyone be doing this?
LITNIN HORN
1,000+ Posts
I was not aware that this technique, which has been around for a long time, has gotten traction. I'd have to see a complete thermal analysis before I bought in. They fail to point out that you're having to insulate considerably more surface area under the roof than you would with the ceiling. That would require the spray-on foam to have an even higher R-value to achieve the same heat transfer results. Didn't see that mentioned in the comparison at the link provided. For example, my ceiling is blown-in fiberglass insulation at R-30. Spray-on foam would have to be closer to R-40 to get the same result on the roof which would require 10" of foam.
LITNIN HORN
1,000+ Posts
Actually brntorng...The Link provides answers to all of your concerns, and does state that there is greater up front expense because of more coverage area, which comes with gable ends, roof slope and wall tie ins.
My customers that I have talked to, who have gone this route, are all more than pleased with the outcome.
accuratehorn
10,000+ Posts
I am getting ready to have this done at my house in the walls and under the roof decking. This is far superior to other kinds of insulation.
Make sure you get the "open cell" type if you are in the hot central Texas humidity.
This is "total seal" insulation. The advantages include having your ventilation system inside the "thermal envelope" of your house. If there are any leaks in your ducting, it is insignificant because your attic is part of the conditioned space.
You have to make sure your furnace, water heater, anything that burns gas will be ducted properly with intake and exhaust air, though.
There are different products, but I think they may be similar in performance. Make sure it is water blown. Icenene is a top name brand, with an organic base (castor oil, I think). The bid we got was with a similar product, can't think of the name. I think it is just as good, trying to find out.
I don't think this is something you can rent the equipment for a do it yourself job.
The City of Austin Energy Star department recommends taking all the blown in insulation out and cleaning, i.e. sweeping, the bottom of the roof deck so the stuff sticks well to the bottom of the deck. The contractors don't do this step.
Might hire a helper to do that nasty job.
Closed cell foam is better, is more expensive and doesn't breathe, or let moisture out-not appropriate for this climate, except maybe a wine cellar room or closet.
Make sure you get the "open cell" type if you are in the hot central Texas humidity.
This is "total seal" insulation. The advantages include having your ventilation system inside the "thermal envelope" of your house. If there are any leaks in your ducting, it is insignificant because your attic is part of the conditioned space.
You have to make sure your furnace, water heater, anything that burns gas will be ducted properly with intake and exhaust air, though.
There are different products, but I think they may be similar in performance. Make sure it is water blown. Icenene is a top name brand, with an organic base (castor oil, I think). The bid we got was with a similar product, can't think of the name. I think it is just as good, trying to find out.
I don't think this is something you can rent the equipment for a do it yourself job.
The City of Austin Energy Star department recommends taking all the blown in insulation out and cleaning, i.e. sweeping, the bottom of the roof deck so the stuff sticks well to the bottom of the deck. The contractors don't do this step.
Might hire a helper to do that nasty job.
Closed cell foam is better, is more expensive and doesn't breathe, or let moisture out-not appropriate for this climate, except maybe a wine cellar room or closet.
We had our house in Idaho insulated in part with the closed cell foam (some areas were done in blown-in insulation over 1-inch of foam to save a few bucks). The foam is nothing experimental; it is simply part of "best practices" in building science today. The conditioned attic protects duct work and AC units in the attic, and improves their efficiency, especially where you have long runs of duct work from the blower into your room. The duct work is just too poorly insulated to withstand Texas summer heat (or in our case, Idaho winters). Although it is not a concern in this thread, best practices also include conditioning the crawl space below the house.
The closed cell foam is IIRC rated R-7 per inch, so our 6-inch depth on the roof decking is around R-42. We were told that the performance of the foam was better than R-7, but that was its official rating. The foam is also structural (you can walk on it) so a side benefit is that it will stiffen your house.
After the fact we heard that open cell is better for the roof decking because it will show any roof leaks that may someday develop. The closed cell is waterproof, and will simply collect the water and rot your roof decking. We weren't concerned about Texas humidity in Idaho, but that sounds like another good reason to consider the open cell.
The foam is certainly expensive, but makes for a very well insulated house. Any holes or seams that invariably occur during construction are covered.
I was at the house when the foam was sprayed and it was definitely not a do-it-yourself job. The subcontractor, after days of covering things he didn't want foamed, wore what looked like a diving suit (one of the old baggy ones with hoses that lead outside to a fresh air supply and air pump). The foam went everywhere and expanded upon release onto the decking. He had to drag around the hoses for his sprayer and air supply, while applying an even coat and periodically measuring the foam to assure consistent and adequate depth. The foam drys really fast and produces a lot of heat, so the guy was miserable inside his "diving suit". Unless you are doing a really small area, this is one job where you will be glad to have a subcontractor. I believe I've seen some rental rigs on home improvement shows though.
Good luck!
The closed cell foam is IIRC rated R-7 per inch, so our 6-inch depth on the roof decking is around R-42. We were told that the performance of the foam was better than R-7, but that was its official rating. The foam is also structural (you can walk on it) so a side benefit is that it will stiffen your house.
After the fact we heard that open cell is better for the roof decking because it will show any roof leaks that may someday develop. The closed cell is waterproof, and will simply collect the water and rot your roof decking. We weren't concerned about Texas humidity in Idaho, but that sounds like another good reason to consider the open cell.
The foam is certainly expensive, but makes for a very well insulated house. Any holes or seams that invariably occur during construction are covered.
I was at the house when the foam was sprayed and it was definitely not a do-it-yourself job. The subcontractor, after days of covering things he didn't want foamed, wore what looked like a diving suit (one of the old baggy ones with hoses that lead outside to a fresh air supply and air pump). The foam went everywhere and expanded upon release onto the decking. He had to drag around the hoses for his sprayer and air supply, while applying an even coat and periodically measuring the foam to assure consistent and adequate depth. The foam drys really fast and produces a lot of heat, so the guy was miserable inside his "diving suit". Unless you are doing a really small area, this is one job where you will be glad to have a subcontractor. I believe I've seen some rental rigs on home improvement shows though.
Good luck!
I'm not saying it's a bad approach to insulation, but I don't think the website addresses one of my points that increases the cost even more. Since the roof is significantly more surface area than the ceiling, the total R-value of the roof insulation will have to have a higher value than the alternative ceiling insulation to achieve the same amount of total heat transfer. Think of it this way: for every square foot of equally R-value insulated roof or ceiling--regardless of the material--the same amount of heat will transfer through that square foot. Since there are more square feet of roof than ceiling you will lose(gain) more heat using the roof method. As a result, to achieve equivalent total heat transfer, the R-value of the roof method will have to be higher--proportional to the roof area:ceiling area ratio. So, if the roof area is 1.5 times more than the ceiling area, the total roof R-value needs to be 1.5 times higher than an equally effective ceiling insulation.
I have blown-in fiberglass and the ducts are completely covered by insulation. I don't think I lose much through my ducts as a result.
Another thing to be aware of if you go with the roof insulation approach is to be sure the house doesn't get too tight. My conventionally insulated house is already marginally too tight. An insulation method that makes it even tighter could result in health issues.
I have blown-in fiberglass and the ducts are completely covered by insulation. I don't think I lose much through my ducts as a result.
Another thing to be aware of if you go with the roof insulation approach is to be sure the house doesn't get too tight. My conventionally insulated house is already marginally too tight. An insulation method that makes it even tighter could result in health issues.
LITNIN HORN
1,000+ Posts
I think The Link addressed all of your issues about coverage, R value, greater area to be insulated and specifically stated the thickness would need to be approximately 6".
As for tightness, there are differing philosophies on that. If you have proper ventilation, operable windows and a good HVAC system backed up with carbon monoxide detectors, you should have no worries.
accuratehorn
10,000+ Posts
The benefit of the blown in insulation is not in the R-value. Forget R-value, because other forms of insulation lose their R-value, or you never get all of it, because they are difficult to install where the insulation completely seals the surface it is supposed to seal. The actual R value won't be what it is supposed to be covering because of numerous leaks around beams, wiring, fans, ducts, and other intrusions. The blow in stuff goes in and expands into every nook and cranny, and it really seals it up tight. Then it shrinks up over time, or gets damp, or the roof leaks on it, or someone cuts holes in it to add a new light fixture-stuff like that.
The other forms of insulation depend almost entirely on the skill and diligence of the installation crew, who were out at the Landing Strip the night before working on your house buying jello shots for themselves and several sweet young ladies.
The other forms of insulation depend almost entirely on the skill and diligence of the installation crew, who were out at the Landing Strip the night before working on your house buying jello shots for themselves and several sweet young ladies.
Just had this done on a new house, closed cell variety. Caulking the bottom and top plates, windows, and any stud seams is still necessary. Like accurate said, its the SEALING of the entire house that is the key. We had our grages done with cellulose and you can just see how it wont seal nearly as well.
But I would say you need to double check the installation, we had spots that got missed just by plain laziness, others were missed becasue they were verry difficult to see. You gotta get up in the attic and check the rafters etc, also check any complicated framing jsut above your top plate, quite a bit missed there, particualrly where the rafters and joists met in close quarters. Also had a copuple large gaps uninsulated where we had a some strong back framing runing near the rafters.
We are combining this with a geothermal system, so we should be set.
But I would say you need to double check the installation, we had spots that got missed just by plain laziness, others were missed becasue they were verry difficult to see. You gotta get up in the attic and check the rafters etc, also check any complicated framing jsut above your top plate, quite a bit missed there, particualrly where the rafters and joists met in close quarters. Also had a copuple large gaps uninsulated where we had a some strong back framing runing near the rafters.
We are combining this with a geothermal system, so we should be set.
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