Closed, open or fiberglass?


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Old 12-07-13, 05:58 AM
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Closed, open or fiberglass?

Looking to insulate a cabin we are remodeling. The roof is 2x6's and the walls are 2x4's.

We would like to do spray foam everywhere but it is expensive. Two contractors have recommended closed cell due to how close they are to the water and to get a higher r value with our limited space.

So should I be using closed cell on the roof? It is pretty close to being a cathedral ceiling with the only Alice being in the center of the house (1foot high).

The floor so over a crawl space so closed cell was also suggested here.

So should we do closed everywhere ? $$$
Open cell everywhere except crawl space floor? $$
Closed cell on the roof and floor with fiberglass r13 on the walls? $$

Any other suggestions?
 
  #2  
Old 12-07-13, 02:51 PM
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Need to go back and add your location to your profile for better answers.
Not sure how being close to the water has anything on how you insulate a home.
 
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Old 12-10-13, 02:21 PM
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+1

Gotta know where you are for vapor permeance recommendations.

I don't like foam as a primary insulator and definitely not closed cell. You can do everything that foam does with rigid board or a combination of flash and batt.
 
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Old 12-11-13, 08:26 AM
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I am in Massachusetts. We initially looked at spray foam because the roof is made of 2x6's, with parts of the ceiling being cathedral. Also, there are no soffit vents, just the roof vents along the back side.

Spraying the roofline would eliminate the venting issue and give us a higher R value than we could get with fiberglass.
 
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Old 12-11-13, 12:47 PM
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True but even 5.5" of closed cell will not get you R-38 that is code required.

Is the roof coming off? If so, some rigid foam on the deck with another layer of plywood would really make the roof system perform.
 
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Old 12-11-13, 12:51 PM
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You will need to use closed cell on the roof because you won't be venting. At 2" or thicker, closed cell becomes a vapor retarder. If you do flash and batt, you need to have at least 50% of the R-value in foam.

I don't see a need to insulate the floor above the crawl space. It would be cheapr to insulate the walls of the crawl instead. Although, doing the floor would be better if you have a problem with radon. Rigid foam board would be a good choice for that area. It will be cheaper than the spray foam. If you use rigid foam, do more than one layer and over lap the seams so prevent air infiltration.
 
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Old 12-11-13, 01:40 PM
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The roof is not coming off. The shingles, plywood and rafters are all in good shape.

I know we could not achieve r38 but we would be far lower with fiberglass.

We wanted to spray the floor for a couple of reasons. The joists are rough cut 2x6's so space is a concern and we're try to cut down on the possibility of rodents nesting in the insulation. Insulation the crawls space walls could be tough. It is build on piers. There is a stone retaining wall around the house that is very irregular.

Is rigid foam effective in between joists? It seems to me that there would be a ton of gaps depending on how well it was cut. I would do it myself but I know it would not be air tight.
 
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Old 12-11-13, 01:51 PM
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Here's an article on "Cut-and Cobble" rigid foam installs. They work and cost less. Thought you would enjoy.
Cut-and-Cobble Insulation | GreenBuildingAdvisor.com
Bud
 
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Old 12-11-13, 02:47 PM
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Thanks Bud,
I guess it would work under the house. Just not sure what I would save. I would probanly need two layers of 2" foam.
I talked myslef out of using spray foam on the walls. However, a lot of the bays are 24". The highest R value I could find is 11. I may have to split the bays to get r 13 or 15.
 
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Old 12-11-13, 03:26 PM
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A recent article discussed the importance of air sealing. Once well sealed, a cavity can be insulated with just about anything and provide similar performance. Allow any leakage and fiberglass loses over half its value. I like Roxul and it is very dense and if spacing is consistent you get a great fill. Very old home with 14" to 26" stud bays are a lot of work.

One of the tricks to cut and cobble is to leave a big enough gap for the can spray foam to be inserted. That also makes measuring and cutting less of a problem.

Bud
 
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Old 12-11-13, 04:15 PM
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Is rigid foam effective in between joists? It seems to me that there would be a ton of gaps depending on how well it was cut. I would do it myself but I know it would not be air tight.
My thinking was to put the sheets over the joists, not between. If you have too many things hanging or in the way like those piers, it probably won't be worth your time.
 
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Old 12-11-13, 05:14 PM
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Its not too bad. The piers are connected with beams. I could run the foam right up to the beam. Only concern is that it wouldn't be tight enough to keep rodents out.
I could fill the bays with R19 then add the foam. I am going to try and price it out.
Are their online calculators? I seaeched but didn't come up with much.
 
 

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