Foam Insulation

I just inspected an older home with a hip roof. There is a floor in the attic and all areas of the roof are sealed with foam insulation, from top to bottom. There is no visible ventilation in this space and minimal insulation under the flooring.
The attic access is not sealed or insulated and is fairly large, 2x3 feet located in the basement stairway.

Has anyone seen this type of insulation applied to this extent without ventilation visible? (soffit vents are visible outside but not inside). My concern is the lack of ventilation, however, the amount of foam installed effectively turns the area into a semi-heated space (no actual heat) so is ventilation really needed here?




It’s a good idea if done correctly. I’m not qualified to judge what is correct, but try this:


Thanks Mark. Good find.

This technique is being used by partners of Building Science Corporation (Joe Lstiburek’s firm) in the Building America program. Others may also be using it now since it’s been used for 4-5+ years by BSC partners.

The house is a system. When you foam the rafters of an existing structure you now have an effect on other aspects of the house. For example, the A/C should have been sized for the old insulation and ventilation. When you foam the rafters what happens to the moisture that was vented out of the attic and by the supposedly properly sized A/C? Have we now created short cycles on the A/C? Retrofits should be done with the whole house system kept in mind.

This may help also Bob.

Unvented Attics with Sprayfoam

Might want to pay attention to where it says, if accessible for equipment in attic etc., it needs to have an ignition barrier. :slight_smile:

Get ready to see more and more of this application as the IRC is already working on the next generation code cycle which will require another 25% gain in energy effiency that will make it a total of a 45% gain in 6 years. mechanical eguipment will not be able to keep up with these ever increasing effiencies and nor will traditional methods of construction and new methods like the isolene spray foam will have to be utilized to meet the new requirements. Wow sealed attics after growing up in the industry that has always pushed ventilate,ventilate it is hard to believe.
How about this if the attic is sealed it is no longer an attic but an adjacent space and since it is sealed then in theory you could locate the air handler in the attic and use it as a plenum and draw air from the adjacent habitable space with out the use of duct work?

If the proper type of foam is used (open cell) this is a preferable system. The open cell foam does allow for some minimal amount of water (like from a leaking roof) to seep through so the homeowner knows to replace the roof.

If the foam is soft to the touch (the consistancy of sponge cake) it is open cell foam. The hard stuff is closed cell (like red can Great Stuff).

The heating and cooling equipment can be lowered in size if this is done. It also stops the stack effect in the house.

Make sure that all vents (bathroom, kitchen, etc) are vented outside and not into the attic.

I have recommended this to many people having hoses built, where I am doing phased construction inspections. The problems that I see are always in the GC not taking this into account and informing the subs to change the usualy way that they do things:

  1. Exterior venting of kitchen abd baths.
  2. Don’t install roof or soffit orridge vents, or cut openings for them.
  3. HVAC has to be re-sized.
  4. Replace the roof when it looks like crap and don’t wait until it actually is leaking through the ceiling.
  5. Icynene foam instead of polyurethane because of fire rating.
  6. Use an installer who has actually been factory trained.

Hope this helps;

Just a little added info on open cell and closed cell. :slight_smile:

Numerous homes have been done with Icynene, Sealection 500, Biobased.
NCFI and Corbond. Spray foam is a chemical.
The difference between different brands is the recipe used in the chemistry. Icynene, Sealection 500 and Biobased are referred to as open cell foams. (although Demilec, Biobased and NCFI manufacture closed cell foams as well). Open cell foams typically weigh between .4 to .6 lbs per ft3 fully cured.
As opposed to closed cell foam which weighs 1.6 to 2.2+ lbs ft 3.
Open cell foams use water as a blowing agent where as closed cell uses a zero depletion blowing agent, typically Enovate manufactured by Honeywell.

Open cell foams have an R rating of 3.5 to 4 per inch. Closed cell foams have R’s ranging from 6 to 7.3 per inch.
This means open cell foams usually have to be 2 x the depth to achieve comparable R value of closed cell. Most of the time, this requires open cell to completely fill a 2x4 or 2x6 wall cavity to yield R values comparable to 2 to 3 inches of close cell.
The excess foam then must be shaved off to accommodate drywall. Such activity adds labor cost and waste.
Neither product is particularly great at absorbing sound.
Moisture can move rather easily through open cell foam via diffusion as its permenace is 6 to 10.
Whereas closed cell foam has a perm rating of less than 1.
Since open cell foam has a high open cell content (90%+/-), liquid water can enter the foam rather easily.
Conversly, closed cell foam has greater than 90% closed cell content and resists liquid water quite nicely. Closed cell is used as a weather or rain barrier.
As to which product (closed cell-open cell) is the best choice for your home – the answer is ------It depends. A huge factor is your climate. Can you be assured of indoor humidity levels between 35% to 50%? Is there duct work in the attic. (if not, there is absolutely no good reason to spray a roof deck with foam.)What type of exterior sheathing will you be using? Do you possess the skills to air seal the envelope?
On the practical side, Testing of identical homes side by side with a blower door, it was found, little to no difference in the air leakage rates between an Icynene insulated home and a home with cellulose in the walls and ceilings that was properly air sealed.
Open cell foams are also much more caustic than closed cell,(Corbond)during the installation process.
One of the biggest reasons, I believe there has been an increase in foams being used in homes is that a builder cannot go to the yellow pages and find a contractor that specializes in air sealing.
Since most builders now a days don’t hammer nails and rarely get involved in the actual construction of a home, this is a huge headache for them. Foams allow the builder to delegate the air sealing task to the foam installer.
As far as the differences between Icynene and Sealection 500, it has been my experience that Icynene has little trouble stretching the truth, making unsupported claims about their product while being critical of their competition.
I have not found that to be the case with Demilec, Corbond or Biobased. They seem to stick to the features and benefits of their product which tends to give them more credibility in my book.
According to the ESR’s, it appears that one requires a vapor barrier and the other not.
It also talks about a thermal protection board on both products.

In certain conditions for the Icynene.


You are a freaking walking talking construction referance library. I have been at this for 30 years and a swear i think you have probably forgotten more than I ever learned. You never cease to amaze KUDOS

Hi Marcel, here is a couple of pictures of a kitchen renovation I did recently. We removed the existing ceiling and vaulted it. After the air sealing was completed we installed Insul Web over the framing and then dense packed the walls and ceiling with cellulose.

This was the most cost effective solution for this client and worked well as the house was 100 years old and the framing was not conventional. No ventilation existed prior to the conversion. After the insulation was completed we installed bead board to the slopes and the tray part of the ceiling.

Working on old timber framed homes, this way of insulating is very effective not only for the cost but the performance as well.



Nice Peter. Haven’t seen this system used up here yet. Is that the vapor barrier or just the web to hold the cellulose.?
What is the r-factor for that system?
Do you have a sq. ft. cost? Or board foot cost, which ever way they figure it. I want to rely that info to my Company when they find me work. :mrgreen::wink:

The web is just to hold the insulation. The nice part about it is we us thin wall PVC tubing and have varied lengths in the trailer. We cut a 45 on the end of it and just stab it through the web in the middle of the bay, point it up to fill then point it down. After we finish we cut patches of web and use spray adhesive to cover the hole.

The R value is somewhere between R-3 and R-4 per inch and cost is about 2-3 bucks a square foot, depending on the job.

The product is very green. It’s 100% uncirculated newspaper with the glossy ads removed, treated with borate for fire protection and resists mold and pests. It’s made in NE so it qualifies for most Leed projects.

Find out more about it at

It’s a great system and safe not only to install but for the environment too. Have you ever seen a frame on fire that has spray foam in it? It can be deadly within seconds.

Good point, Peter. Often, we don’t think about some of the other factors until it is too late.

Thanks Peter, I was just reading about it. I was familiar with the wet pack, but that takes 3-5 days to dry in controlled environment. Less expensive but more messy.

I found the web to cost .055 per sq. ft.
The R Factor transalates to 21 for a 2x6 wall which is the requirement for Maine in wall now.
I’ll read up on the link you provided.
I don’t know if anyone in this area does that, I’ll have to check.
Maybe companies like Builders Insulation does it. They have an office for New Hampshire as well as Maine and done work for us before.


Larry, what we have done in the past on that thought for fire rating is install 2" of Corbond SPF in the walls which is an r-factor of 13 and then add a 3-1/2" r-13 on top for a total of 26.

It does two things;
Keeps the cost of the SPF down
Adds the needed r-factor requirement
And acts as a fire retardant to protect the SPF

Corbon Spray insulation does not sustain a flame but the gas would be poisonous.
The batt insulation meets the Flame Spread of <25 and Smoke Developed of < 450. :slight_smile:

That sounds good, Marcel. :slight_smile:

I have no doubt your planning, in the construction realm, is stellar. Good job! :smiley:

Thanks Larry, but it all boils down to the fact that there are a lot of Pros and Cons about any product that you may use.

The key is to agree on one that is consensus of everyone involved. :slight_smile: