# adding insulation to the outside



## fishhead (Jul 19, 2006)

I was telling a friend that I wanted to add foam insulation to the outside of my house but didn't want to create a second vapor barrier.

He said I could avoid that by simply placing the sheets horizontally so there would be a horizontal crack between the studs.

I've got sheetrock, insulation, box car siding and then masonite siding. I would put the foam between the box car siding and the masonite siding.

That seems like a simple solution but I've never heard of it before. Will it work?


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## ericjeeper (Feb 25, 2006)

Will the nails pull up tight and not let the siding sag?
How will you extend your window trims and door jambs?
How thick are you planning on adding. R-5 per inch of pink or blue board.,


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## fishhead (Jul 19, 2006)

I was thinking of adding an inch.

The siding will probably sag a little but as they sag the nails will pull the masonite siding tighter to the wall so that will help reduce the sagging.

Those are the windows I have to replace anyway so I'll just use wider boards for the trim.


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## fishhead (Jul 19, 2006)

I was thinking of adding an inch.

The siding will sag a little but as it sags the nails will pull it tighter and reduce the sagging.

Those are the windows I'm replacing so I'll just use wider boards.


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## WisJim (Jan 14, 2004)

If you don't seal tightly between the sheets of insulation, you will be losing a lot of the insulation value of the material. If you do seal it tightly, you will have moisture problems. My suggestion is don't put insulation on the outside in your situation, as you describe it. I have seen lots of moisture problems from insulation put on an existing wall under new siding.


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## fishhead (Jul 19, 2006)

Any suggestions on how to add insulation to an old house? I've tried adding cellulose to the walls but everywhere I looked already had fiberglass.


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## SolarGary (Sep 8, 2005)

fishhead said:


> Any suggestions on how to add insulation to an old house? I've tried adding cellulose to the walls but everywhere I looked already had fiberglass.


Hi, 
There are some techniques you can work from the inside -- for example, the Mooney Wall:
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm

Lots of work though.

Gary


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## Intrigue (Jun 11, 2008)

There is nothing wrong with adding polystyrene foam to the outside of the house. In fact, it is a preferred method of insulation, along with batt insulation within the wall cavity and a vapour barrier on the warm side (usually the interior) of the wall.

The National Building Code states that the vapour barrier MUST be on the warm side, so you must avoid having an exterior vapour barrier which would effectively trap moisture between the two barriers......rotting the walls.

Not only does this add extra insulation, but it also insulates the areas where the studs are, a source of heat loss called Thermal Bridge. The other thermal bridge is where the walls meet the foundation, so the exterior insulation would be extended to caver this zone as well.

The trick is to use BREATHABLE foam board. An example would be Terrafoam, but there are other brands as well. You would tape the seams with a special tape made for this purpose.

http://www.beaverplastics.com/beavercurrent/terrafoam.html

Adding things like window extensions is a no-brainer, pretty easy. Some type of exterior siding must be used and is nailed directly over the foam.


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## artificer (Feb 26, 2007)

If you look at the Dow Corning fan fold insulation intended for outside application, you will see it is covered in pin-holes. Its also only 1/4" thick, but it will provide a fairly decent air barrier to keep the wind out.

What I did on my 1890's house was to strip the walls to the bare sheathing boards. I then put on a air barrier, like the Tyvex house wrap. Over that I put on 1" of foam. I did not seal all of the joints, and there are some additional holes in the field of the insulation. I was worried about moisture buildup when I installed it. Since all of the outside trim was original, it was all decayed and deeply eroded. I re-built all of it as I put in the new windows. Siding was Cerainteed plastic. Haven't seen any sagging/problems in the last few years.

On the inside, as I gut a room, I've been putting in 2" of foam board. I seal it in place with Great Stuff. Only R-10, but I'll stack that up to the R-13 of fiberglass in a 3 1/2" cavity any day. NO air infiltration, no moisture problems, and warm.

Even just a layer of sealed house wrap under the Masonite siding will be a big help. Sealing all windows/doors is then next.

Michael


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