After much research, Open vs closed cell foam

[c6matt]

In my new 30 x 48 garage I need to insulate, and I am in the old debate Open vs closed and I was all set to go closed cell, but wonder if the benifits are really realized in my application. I dont mind spending money for a tangable benifit, but I have been told more than once that open cell would be the way to go for my garage by a couple of the companys that came out to quote. So that lead me to do a bunch more research.

Goal : well sealed, well insulated walls (R19) and ceiling (R30)

Lowest open cell quote :5675
Lowest Closed Cell quote 8878 3" walls, 4" ceiling, but I was told that 3" would be plenty on the ceiling and would lower the quote to 7697


R value per inch - winner closed cell

Although the R value is higher, I don't really see a benefit from that as I have 2x6 walls and desire R19, both foams will do this in ~3in


Durability - winner closed cell
I will be putting drywall on the walls, and it will be above a metal ceiling in the garage, so it will be protected from damage, so is it a benefit?

Rigidity winner - closed cell
I know open cell offers little in the way of structure, but with 2x6 wall stick build, and storage trusses, is more rigidity needed?

Vapor barrier/resistance winner- Closed cell
Closed cell wins hands down, but as the garage is fully above grade and has good attic ventilation, is it a concern? I know I have to use a separate vapor barrier with the open cell behind the drywall, but any other benefit in my condition?


What would garage journal do? If the above summary is accurate, wouldn't open cell make more sense? something else I might have missed in my searches?

 

[kj_mustang]

Open cell foam requires more thickness too achieve the same R value as closed cell. Closed cell is R6-7 per inch and open cell is R4-5 per inch. I have both types sprayed in my building so I have been able to compare them. One difference I noticed is it seems that the installer may not get as good a coverage (leaving air pockets) with the open cell foam than the more thick and dense closed cell. The closed cell really flows into areas to totally seal them. I have a pole barn and by using the closed cell on the metal siding it blocked all easy access for insects.

 

[rlitman]

Open cell foam requires more thickness too achieve the same R value as closed cell. Closed cell is R6-7 per inch and open cell is R4-5 per inch. I have both types sprayed in my building so I have been able to compare them. One difference I noticed is it seems that the installer may not get as good a coverage (leaving air pockets) with the open cell foam than the more thick and dense closed cell. The closed cell really flows into areas to totally seal them. I have a pole barn and by using the closed cell on the metal siding it blocked all easy access for insects.

The blowing agent in closed cell foam artificially increases the R per inch. Open cell foam's insulating layer is air. Closed cell starts out with the blowing agent, but after a few years the R per inch decreases as it slowly diffuses out and is replaced by air.

Yeah, closed cell foam has more "pressure" to work its way into spaces. That can be put to good use, or bad if allowed to crush window frames (a good installer will know how to avoid that though).

 

[c6matt]

Open cell foam requires more thickness too achieve the same R value as closed cell. Closed cell is R6-7 per inch and open cell is R4-5 per inch..

That was kind of my point, I have room for the thickness with my 2x6 walls, so does it make sense to pay for the closed cell.... thank you both for the replies!

 

[Bib Overalls]

I used closed cell foam for the ceiling in my shop. One concern was leaks in the roof saturating the open cell foam and bringing it down. I don't, to my knowledge, have any leaks but you never know what the future will bring.

 

[mark52621]

I'm getting solar panels installed some of the cost will be covered by the electric company. To get this I went through an energy audit.

I asked the guy doing the audit if open or closed was better. His response was open. He has seen many bad installations of closed cell foam. What happens is poorly applied closed cell foam can be open on the backside where you can't see it. Water gets in and can't get out.

With open cell if water gets in it can eventually get out. In his experience this outweighs the loss of r value. Infact he said he wouldn't consider using closed cell foam.

 

[c6matt]

I'm getting solar panels installed some of the cost will be covered by the electric company. To get this I went through an energy audit.

I asked the guy doing the audit if open or closed was better. His response was open. He has seen many bad installations of closed cell foam. What happens is poorly applied closed cell foam can be open on the backside where you can't see it. Water gets in and can't get out.

With open cell if water gets in it can eventually get out. In his experience this outweighs the loss of r value. Infact he said he wouldn't consider using closed cell foam.

Interesting, I have not seen that argument brought up before, but it makes sense. But running a vapor barrier would not trap the moisture in the open cell foam?

 

[volleyball]

That guy is full of it. How does closed cell get voids? It goes on in a thin layer and expands. And any moisture if trapped would sit there doing nothing or evaporate through the other surface.
Foam works best when you can encase the 2X's in the wall or ceiling. With a continuous barrier, you don't need as much foam as you think.
How new is the garage? Is the sheathing and roofing up? If not, this is the time to foam outside the 2X's in the walls and ceiling with sheet foam.

 

[DEnd]

That guy is full of it. How does closed cell get voids?

Bad installation, and it is easier to install poorly than many people (even some foam contractors) realize.

c6matt: to me the choice depends on your construction details and how much insulation you need. If I were building a wall in your location I would use Building Science Corporations recommendations of 10-20-40-60, and their perfect wall details. ( http://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall ) That's R-10 under slabs, R-20 foundation walls, R-40 above grade walls, R-60 roof. With the perfect wall I doubt you would want to use a vapor barrier foam, as there is already a vapor barrier on the outside of the wall (tyvek is not a vapor barrier) leading to poor drying conditions if the building materials between the two vapor barriers ever get wet. That said if you don't use a vapor barrier and use a rain screen detail (which you should use no matter what, vinyl and aluminum siding basically have these built-in normally) between the siding and the sheathing, then closed cell spray foam can be a good choice.

As for the insulation I admit that those levels may be rather high for a garage, as the majority of your energy leakage is likely to occur through air leaks in the garage door(s). However it is a lot cheaper and easier to install that insulation now than in the future. Where as a garage door can be changed out a lot easier if someone ever invents a much tighter one.

My insulation material of choice for this install? Rock wool. #1 it's fire proof (as Dr. Joe Lstiburek says rocks don't burn). #2 it's fairly easy to install well. That said if you have a bunch of hard to air-seal details then I wouldn't hesitate to look at closed cell spray foam.

Speaking of airtightness you might also want to add some ventilation to decrease the amount of fumes in there while you are working.

 

[c6matt]

How new is the garage? Is the sheathing and roofing up?

as it sits today

 

[DEnd]

Well the good news is you have horrible air sealing. The way you have it built I would put in closed cell foam, and an interior ignition barrier. You should also have a rain screen detail installed when putting on the siding.

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens

 

[yeldogt]

Has anyone suggested doing a skim coat with the foam (closed) and then filling the remaining space with batts to reach the code "R" value? I did this on a recent addition about your size and have been very pleased. The foam thickness is sized based on the dew point in the winter.

Also, why do the ceiling and not the roof deck and use the attic space for storage .. I can't see the truss design ... maybe no space.

The idea of insulating the exterior is a trend that you hear more and more about -- but it requires a different building approach from the start ... I think this is why the zip system is growing in popularity ... I may use this on my next build .... but I'm concerned about trapping moisture.

I'm in the closed cell camp .. used properly it eliminates air intrusion .... and stops the radiant heat gain in the summer. With no air movement and the foam above the dew point ..... all moisture problems are eliminated. I set up the building to dry from the outside and the inside ... no additional vapor barrier. Closed crawl and attic -- with fresh air exchange.

On a garage with the big doors ---- I would be thinking closed cell skim and batts. The closed cell foam really makes for a comfortable structure .. and reduces the size of heating and cooling equipment

 

[c6matt]

Well the good news is you have horrible air sealing. The way you have it built I would put in closed cell foam, and an interior ignition barrier. You should also have a rain screen detail installed when putting on the siding.

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens

From your link it appears I will be fine/ dont require one....??? And the ceiling will be metal, walls drywalled.. ignition barrier?

Because it already has an air space behind it, vinyl siding does not require a rainscreen installation unless it is installed on top of rigid foam that is more than 2 inches thick, in which case it should be installed over vertical furring strips.

 

[c6matt]

Has anyone suggested doing a skim coat with the foam (closed) and then filling the remaining space with batts to reach the code "R" value? I did this on a recent addition about your size and have been very pleased. The foam thickness is sized based on the dew point in the winter.

Also, why do the ceiling and not the roof deck and use the attic space for storage .. I can't see the truss design ... maybe no space.



I'm in the closed cell camp .. used properly it eliminates air intrusion .... and stops the radiant heat gain in the summer. With no air movement and the foam above the dew point ..... all moisture problems are eliminated. I set up the building to dry from the outside and the inside ... no additional vapor barrier. Closed crawl and attic -- with fresh air exchange.

On a garage with the big doors ---- I would be thinking closed cell skim and batts. The closed cell foam really makes for a comfortable structure .. and reduces the size of heating and cooling equipment

the attic has storage, but It will not be heated/insulated. The ceiling and walls were the plan to be foamed

And everything i have read both types of foam stop air intrusion... am I mistaken?

 

[yeldogt]

Open cell foam if applied thick enough will be an air barrier ..... I believe 5" ... but it has been a while since I researched it. Closed cell is a superior product in my climate -- mid atlantic / new england ... so that is all I have used in the past 15+ years.

Whenever insulation is mentioned .. it sets off debate like ....."what oil do you use?". I have seen both wet Cellulose -- and the high packed (blown) in fiberglass ... both interesting products and I'm sure effective if you find the proper contractor.

I like that closed cell is an air and water barrier

I did the hybrid foam/ batts on my house in NJ. The addition has a cathedral ceiling - so I wanted the foam to stop the heat load from the roof in the summer -- and to seal up the typically framed addition .... the small added R value benefit for all foam was not worth the cost as I have NG service.

My other places don't have NG .. it's oil or propane. Since I was building new, I wanted foam to minimize the fuel use and the size of the HVAC equipment.

 

[DEnd]

From your link it appears I will be fine/ dont require one....??? And the ceiling will be metal, walls drywalled.. ignition barrier?

Because it already has an air space behind it, vinyl siding does not require a rainscreen installation unless it is installed on top of rigid foam that is more than 2 inches thick, in which case it should be installed over vertical furring strips.

Yeah like I said earlier if you are doing vinyl you very likely don't need a rain screen.

If you are just doing your walls, then your drywall (at least 1/2" thick) counts as a thermal barrier (more stringent than an ignition barrier, in this part of the code a thermal barrier is not necessarily talking about insulation). If however you are spray foaming the underside of your roof deck or above your ceiling, then things get more complicated. If you have access technically you need an ignition barrier, unless the spray foam has passed the required fire safety test as is. There are spray applied ignition barriers that work in that application, but they must be tested with your brand of spray foam. However if you ever store anything up there you need a thermal barrier, which given you have trusses would be a pain in the rear to install.

More reading on the topic here: http://www.greenbuildingadvisor.com...mal-barriers-and-ignition-barriers-spray-foam

 

[BadgerBoilerMN]

Here in Minneapolis we keep a couple of insulating companies busy as we like to insulate and then design heating and cooling systems for the buildings new and old.

A 2x4 wall can be sprayed with 2# foam to R-19, qualify as an effective vapor retarder and will be stronger than before. The same is true of basements.

Open cell (1/2# foam) will do none of this.

On ceilings we often spray 2" of 2# foam over ceilings and them finish with blown fiberglass or cellulose to R-50.

Both foams usually cost the same per R-value but open cell has limited applications. It does control sound better and does not use those "harmful" blowing agent.

 

[wanderer]

I just had open cell insulation sprayed in my whole house by a reputable installer. I wasn't impressed. He came back and fixed it twice but I kept finding voids and cavities in the installation. Were I to do it again, I would buy sheet XPS or similar insulation, cut an inch smaller than the cavity, screw it in, and then use can foam around all the studs. Much cheaper.

 

[BadgerBoilerMN]

You are mixing DIY with "professional" installation.

Apples to apples, foam is king in renovation. The application, like any other trade, is technician specific. The cost per R-value for XPS vs. open cell foam will vary but I have never seen XPS installed for less than the equivalent open cell.

It is generally easier for the layman to determine the quality and quantity of sheet good vs. foam.

Open cell is a very specific market. We don't use it much here.

 

[yeldogt]

BBMN - You always have good advice and comments ... what is your reasoning for insulating and then designing.. do you learn after the insulation?

I'm actually siting in my one story a framed addition -- all spray foamed 20 x 25. It is 95 out this afternoon and it is 74 degrees just from the overflow from the main house. I have the zone set for 75 .. has yet to come on.

Foam really cuts down on radiant heat gain from the sun.

 

[walrus]

I just had open cell insulation sprayed in my whole house by a reputable installer. I wasn't impressed. He came back and fixed it twice but I kept finding voids and cavities in the installation. Were I to do it again, I would buy sheet XPS or similar insulation, cut an inch smaller than the cavity, screw it in, and then use can foam around all the studs. Much cheaper.

I did this on my addition, 5 inches of cut and fit foam and then one inch over the face of the studs. The addition is 16 by 24, south facing glass and I have no heat in there nor do I need any. Whatever comes thru the door is suffiecient. I think if I were to do it again i'd put in 3 inches and then have them spray in the last 2 inches to stiffen wall

 

[BadgerBoilerMN]

We use a lot of 2" - 2# foam for air sealing, as it is the most practical way to foam a wall or ceiling. On additions and new construction we try to get rigid insulation, like Thermax, on the outside or inside walls to address thermal bridging.

As for foam before heat load. I know from experience, and accepted science, that the large surface areas and normally loose intersections between foundation and framing can use foam. Best to address the obvious loads and add the improvements to the model to get the most accurate heat load analysis and size equipment accordingly.