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Old 10-04-12, 08:29 PM   #11
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Put it on the walls. Pull the siding, put the foam over the existing sheathing, seal the joints with "foam in a can", tape the joints, then side over that. You will need to either replace the windows, or move them out by the thickness of the foam.

The inside of the foam is your new vapor barrier. As long as that surface is above the inside dew point, you will not have any condensation.

I know of three houses built this way. They all need mechanical ventilation. One of those houses is heated with propane. The owner fills the 500 gallon propane once per year, in the summer when he can fill it cheap.

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Old 10-05-12, 02:14 AM   #12
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How much money are you willing to spend to install the foam board 20 30 thousand ? if so rip off the siding like was suggested otherwise put it on the crawl space walls and ceiling.
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Old 10-05-12, 09:51 AM   #13
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I agree that putting it on the outside is the best bet. You must not have a vapor barrier in the wall already though or else you create a vapor barrier sandwich and the wall will have drying issues. There is a ton of information out there on how to do it but basically you screw the foam to the studs through a piece of strapping and then attach the siding to the strapping. The screws you use are made by FastenMaster and are called HeadLOCk. They have a really flat head and are super strong. I have also heard rumors that SimpsonStrongTie is making a similar and cheaper screw but I have yet to find them. The biggest problem will be the window details. You don't want your walls willing up with bulk water from rain. If this is too much or you don't have enough foam then put it under the floor and make sure to tape all of the seams and foam around the edges or it will do little. I worked on a house where they had done this and didn't air seal the boards. It made almost no difference until the air sealing was done.
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Old 10-22-12, 01:17 PM   #14
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Have you decided what to do with the foam boards yet?
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Old 10-31-12, 11:53 PM   #15
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Looks like I will be installing some of it where the rafters meet the ceiling and some around the light fixtures in the attic. Also on the attic access door.

After reading the responses and the article that Exeric posted under "Spray Foam Experiences", it looks like it would be a waste of money to use it on the rafters.

Here is the article Exeric posted.
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Old 11-06-12, 12:18 AM   #16
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In regards to the vapour barrier, I have docs from the Ontario gov't that says it's OK to go without one if one uses a vapour barrier paint. Aren't most paints like a vapour barrier? Continueing on this theme, wouldn't this justify the act of simply putting the foam board on the outside of the studs?

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