Where to insulate with 3.5" Foam Board - Page 2

JRMichler · 10-04-12, 08:29 PM

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.

ecomodded · 10-05-12, 02:14 AM

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.

S-F · 10-05-12, 09:51 AM

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.

Daox · 10-22-12, 01:17 PM

Have you decided what to do with the foam boards yet?

Geo NR Gee · 10-31-12, 11:53 PM

Daox,
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. http://www.buildingscience.com/docum...-sealing-guide

ThomSjay · 11-06-12, 12:18 AM

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?

10-04-12, 08:29 PM	#11
JRMichler Apprentice EcoRenovator Join Date: Apr 2012 Location: Phillips, WI Posts: 109 Thanks: 10 Thanked 30 Times in 25 Posts	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. Last edited by JRMichler; 10-04-12 at 08:31 PM..

10-22-12, 01:17 PM	#14
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Have you decided what to do with the foam boards yet? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

11-06-12, 12:18 AM	#16
ThomSjay Helper EcoRenovator Join Date: Mar 2011 Location: Sarnia, Ontario, Canada Posts: 91 Thanks: 8 Thanked 2 Times in 2 Posts	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? __________________ TomS

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10-05-12, 02:14 AM	#12
ecomodded Supreme EcoRenovator Join Date: Sep 2012 Location: Vancouver Island,Canada. Posts: 1,037 Thanks: 116 Thanked 100 Times in 87 Posts	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.

10-31-12, 11:53 PM	#15
Geo NR Gee Journeyman EcoRenovator Join Date: Jan 2011 Location: Seattle Posts: 326 Thanks: 109 Thanked 23 Times in 18 Posts	Daox, 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. http://www.buildingscience.com/docum...-sealing-guide