Open cell/closed cell foam

[grover]

I have been researching how to insulate my little piece of heaven.  Today I spoke to the insulation company rep.  He advised in my area, which is zone 4a (no interior vapor barrier), that he would use open cell foam in the wall cavitys, (3 1/2 inches), and he would recommend 6 inches of open cell foam on the underside of my roof.
To back up a bit, my roof is metal over 30 lb felt over osb.  Also it is scissor trusses with 12/12 pitch on the outside and 8/12 pitch on the inside.  His plan would give me a conditioned attic space.  Doing it this way would not require any attic venting....no ridge vent, no soffit vents, no gable vents.  My attic space is not very big anyway.  Definitely not somewhere you want to go into after it is finished.
I'm not at all familiar with the concept of a conditioned attic space.  Was wondering what your experience was with closed cell and conditioned attics.
I asked about the 6 inches of closed cell and the lack of enough R value in the ceiling.  I think R38 is the minimum here.  He said the effieciency of the foam was such as that was all that is needed.  Adding more foam than that would be to the point of diminishing returns.

As far as costs...the walls which would be 3 1/2 inches thick and cover approx 1250 sq ft of area = $1500-$1600
The underside of the roof, 6 inches and cover approx 1000 sq ft = $2000

What do ye say?

[MountainDon]

.........that he would use open cell foam in the wall cavitys, (3 1/2 inches), and he would recommend 6 inches of open cell foam on the underside of my roof..

Is that statement supposed to be open cell in both walls and roof, or open in walls and closed in roof??  I ask as 6 of open will not meet the energy code requirements.....

[Alan Gage]

Do some reading on the Building Science website and search for unvented attics. Tons of good information.

Alan

[grover]

Yes Don, open cell in both places.  That's why I asked about the R value of 6 inches of open cell being only about R21.  He said in their experience that was all that was needed.  He talked about closed cell on the backside of the roof too.  He said they didn't like it there because if there is a leak it will never come through the closed cell.  It would just saturate any wood there, joists, decking, etc and rot.

Believe me, I have been reading on that website.

[MountainDon]

Well, I don't know about R21 for a roof or ceiling.   Personally I would not want that little amount in a roof/ceiling. But that's me.  What do other insulation contractors in the area say?  And how does this one reconcile that R21 with the state code?

I've heard the arguments about closed foam making roof problems worse if there is a leak. Seems to me I have also seen papers that state that is a non issue. But I can't find any of them with a quick search and duty calls me elsewhere for a bit. So maybe later. ..... that is assuming that water from a leak comes through all the weather resistant layers and soaks the wood without ever drying out to the exterior.     

I believe one of the big advantages of a conditioned attic space is that the ceiling does not have to be air sealed as well. When air ducts for cooling and heating are in a conditioned space there are lower losses due to improper duct sealing and insulating. That would be big on my reasons for doing a conditioned attic if I was building new. Same for electric perforations and using recessed lights.

I have no idea if this makes any difference, but I wonder if a part time use cabin receives all the same benefits of a conditioned attic or are there some drawbacks as taking longer to warm up the living space below. No idea; that just popped into my overactive mind.

Another thing is open cell is not made with some of the chemicals that are not eco friendly.

If my memory serves me well I believe building science only talks about closed cell foam for roofs; top or bottom of the roof sheathing..   Not sure about that though, but no time to go have another look there.


Till later......

[bayview]

We recently purchased a five year old, 1800 sq. ft. home in North Texas - About 60 miles south of Ft. Worth in October.

The previous owner paid the extra expensive of closed foam insulation, heat pump and an heat exchanger.   The home has all the frills that everyone was looking for.   High (10 ft) ceilings, granite counter tops, tiled floors,  Jacuzzi tub, etc.

We had quite a cold snap recently with temperatures in the teens.   The heat pump could not keep up and went into auxiliary mode at about 30 degrees.  There is no insulation in the ceilings.   So, the heat ends up in the attic.   Leaving the living areas cool.   Accented by the tile floors and granite.   We do have ceiling fans reversed for heat distribution . . .    Creating drafts.

The heat pump runs in the "standard" mode above 30 degrees.   The furnace fan runs on low during this time.   (2 speed fan)   The heat does not reach the floor.    The pump and furnace fan runs continuously until the outside temperature gets above 45-50 degrees.   Again, time for ceiling fans and the draft it creates.

Closed cell foam insulation has an R factor of 7-9 per inch . . .   My walls supposedly have an R-Factor of 24-31.   The attic space roughly R- 35-45     Sounds great.  But including the attic space, I am "conditioning" closer to 2700 sq. ft.   

I have seen on particular high humidity days the 2"X4" wall studs. . .    The cavity is well insulated, but the studs are not.    I can actually seen moisture on the exterior walls where each stud is placed.   On the inside of the house I can "feel" where each stud is.   I can run my hand over the wall . . .    Every 16" there is a cool spot.

There is a 6 degree heat variance from the center of the house to the exterior walls.    The center of the house (bathrooms and kitchen area) can be 78 degrees.   It will be 72 degrees near the exterior walls.

The inlet for the heat exchanger is located in the ceiling.    So, I was taking the warmest air out of the house.   Sending it through the heat exchanger and bringing in cooler air from the outside.   Maybe this works best in the summer time . . .     We ended up turning off the exchanger.   The house is warmer without it running.   We get plenty of air exchanged by going in and out the doors all day.   

If I were to build a home . . .     I would have spent the extra money on . . .
2"X4" walls with an extra 2" of exterior foam with proper condensation protection
9 foot or vaulted ceilings in the living area
8 foot ceilings in bedrooms, bath, etc.   
R-40 blown insulation in a well ventilated attic.
Triple pane windows

BTW:   We never use the Jacuzzi tub . . .    It takes longer to clean it, than enjoy it.   For us, what a waste of space.

/.

[MountainDon]

I'm guessing that the big difference between bayviews home and the one grover is talking about is that grovers has 8/12 interior pitch; not flat. I think the 8/12 is continuous throughout. So the attic space has not nearly as high a volume.

A question arises; what is the alternative to spraying foam on the underside of the 12/12 pitch roof? 

Is there sufficient space between the 12/12 and the 8/12 port of the scissors trusses to blow cellulose up there, laying on the 8/12 air sealed ceiling and have enough depth for a proper R-value right out to the eves or wall tops?

I think any advantages of a conditioned attic that I mentioned before with regards to the heat / cool ducts, does not apply to grovers roof. Or maybe I'm wrong; is there central heating ductwork or not?


I agree bayview; the ideal walls are 2x4 with foam on the exterior. That's what we have ended up with on 3/4 of the house now with the retrofit.

[grover]

Yeah, I'm not liking the conditioned attic idea.  I put a ridge vent in and I'd like to use it.  I'm leaning toward some sort of blown in insulation in the attic floor space, probably cellulose.  The attic area near the walls will be a lower R value area but I will have to accept that if I can't think of a solution.  Maybe some foam board used in that area...not sure yet. 

I like the idea of the open cell foam filling my wall cavities but I need to figure the costs of the foam compared to blown in cellulose.  I would think cellulose would be much cheaper.

I found a product that CertainTeed makes called MemBrain that looks really interesting.  It looks like clear plastic but it adjusts it's permeability with the humidity level.  It looks like a good vapor retarder and air barrier solution in my mixed climate application.

[MountainDon]

How long has the new product been used? I would tend to wait on that self adjusting item until it has been used a lot in order to see if it works as well as the manufacturer says it will. Potential problem with a lot of this stuff is that if it doesn't perform as advertised it is inside the structure and then what? 

Is the wall cellulose the dense pack wet blown stuff?

[grover]

Not sure how long the product has been out.  Might take a little more research.  The dense packed cellulose is not done wet.  I was thinking more like in this video which shows dense packing and also shows another brand of "smart" vapor retarder used in place of the netting.  The brand is Intello Plus. http://www.youtube.com/watch?v=hOhE-UP72xg 

[MountainDon]

I was just wondering on the type of cellulose... I've seen the damp blown (wet is a misnomer) here and thought the nice thing about it was there was no need for any netting or membrane of any kind to retain the cellulose in the cavity. The operator can see that it is going in all the nooks and crannies. Done right any of them work nice.

The one thing I don't like about foams is that they are quite flammable and will produce dense black smoke. I am pretty sure that foam requires an approved fire resistant interior wall or ceiling finish. Like drywall. That doesn't keep the foam from burning but may slow it down or at least keep the smoke and foam fumes outside rather than inside. Cellulose is fire rated itself.

[grover]

The smart vapor retarder sounds like the perfect solution for those of us in a mixed climate.  From another building website...

"Maybe 15 years ago, researchers in Europe began working in a more focused way on variable-permeance vapor retarders. The first such product I heard about was MemBrain, made by CertainTeed's parent company Saint-Gobain (headquartered in France) and available from CertainTeed in the U.S.
MemBrain is a polyamide or nylon sheet with permeance that ranges from less than or equal to 1.0 perms in low humidity conditions to more than 10 perms under high-humidity conditions.
Two variable products are also made by Pro Clima in Germany and distributed by 475 High Performance Building Supply in Brooklyn, NY. Intello Plus is made from a polyethylene copolymer, and it varies in permeance from 0.17 in the winter to 13 in the summer. It comes in rolls 1.5 meters (59 1/16 inches) wide and 50 meters (164 feet) long.
DB+ is a less expensive, paper vapor retarder made by Pro Clima that varies in permeance from 0.8 perms with low humidity to 5.5 perms at high humidity. It is made mostly from recycled paper, and includes a fiberglass reinforcement grid. It comes in rolls 1.35 meters (53 inches) wide by 50 meters (164 feet) long. It is about 24% less expensive than Intello Plus."

Another interesting quote from the same article...

"It turns out that the plain old kraft paper facing on fiberglass batts has this property of variable permeance — as my friend (and leading building science expert) Terry Brennan explained. As humidity increases (in the summer), it becomes more permeable to moisture, while in winter, when the humidity drops, it becomes less permeable and a better vapor retarder. Terry describes it as "poor man's smart vapor retarder.""

It seems Europe got the jump on us on this product.  I don't think it is widely used in the US yet but I think I might give it a try.

[MountainDon]

Yeas, it does sound good and would seem to have an overseas track record. The USA does not necessarily invent the best, first everytime. Look at PEX vs polybutylene.