# What type insulation for exterior porch



## Windows on Wash (Aug 30, 2011)

Isn't the porch open air?

Better to insulate that exterior, exposed wall and air seal it than to do insulation on the underside of the ceiling.


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## fisher57 (Aug 30, 2014)

I think we're talking about the same thing. I'm planning on insulating the 2' section of the wall, the part you see in the picture covered with Therma-ply. I don't want to insulate the attic itself, just the house from the attic. There will be a beadboard ceiling on the underside of those sister joists. It's not open-air, but the soffit vents make it the same temperature as outside.


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## Windows on Wash (Aug 30, 2011)

Yes. Spray foam all the gaps, insulated with a foil faced rigid foam. 

We are talking about the same thing.


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## Perry525 (Jan 10, 2010)

*Porch insulation = no.*

Keep in mind that heat always moves to cold.
Therefore, insulation should be on the warm room side, not on the outside.
If you insulate on the outside, all that will happen is, your heat will make its way through the floor, into the joists and frame, and be conducted away by the interaction of the outside of your home and the cold air.
Note, if you box in the joists with sheet polystyrene, or similar, you will stop some of you heat escaping, but it won't be as effective as laying the insulation on the floor - warm air rises, so not much heat escapes through the floor, one inch thick polystyrene laid on the floor, will make a difference.


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## Windows on Wash (Aug 30, 2011)

Perry,

Many of the top building science people in the planet would vehemently disagree with you. 

Putting the foam on the cold side of the wall warms in the interior stud surface and effectively uncouples the stud wall from the exterior. It eliminates the thermal bridge of the stud and brings up the average wall R-Value in the process. 

If they were to put insulation on the warm side of the wall (a physical impossibility here without demolishing the interior of the home's drywall), they would make the outside edge of the stud a cold spot and therefore much more likely to be a condensing location. 

Couple that with the fact that it is impossible to do it in this application without scabbing foam to the interior wall. 

I am not even sure what you are suggesting in the rest of the post but I can't make heads or tails of it.


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## fisher57 (Aug 30, 2014)

I read on Owens-Corning's website that their pink foamboard is supposed to be installed with the sheets running vertically. Do you know if there's a good reason for that. It sure would be more convenient in this case if I could run those boards the other way, just split each 4x8 into two 2x8's and put them in that way. BTW, I asked at Home Depot about 3" cap head nails for installing, and they looked at me like I had a third eye. :huh: They told me just to glue it up with liquid nails.


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## Windows on Wash (Aug 30, 2011)

fisher57 said:


> I read on Owens-Corning's website that their pink foamboard is supposed to be installed with the sheets running vertically. Do you know if there's a good reason for that. It sure would be more convenient in this case if I could run those boards the other way, just split each 4x8 into two 2x8's and put them in that way. BTW, I asked at Home Depot about 3" cap head nails for installing, and they looked at me like I had a third eye. :huh: They told me just to glue it up with liquid nails.


Drainage. Doesn't really apply in your case. 

Horizontal is fine. 

They are dopes there from time to time. Liquid Nail, unless foam formula will melt it. Google rigid foam washers and foam compliant glue.


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## concrete_joe (Oct 6, 2014)

the house is insulated, right? so this is just extra in this area, on the outside. i would 1" rigid it w/o foil. silicone it in place and then add a few 45 degree wood braces to hold it firmly in place. done.


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## fisher57 (Aug 30, 2014)

concrete_joe said:


> the house is insulated, right? so this is just extra in this area, on the outside. i would 1" rigid it w/o foil. silicone it in place and then add a few 45 degree wood braces to hold it firmly in place. done.


Yes concrete joe, this is just an opportunity to add some extra insulation to the wall for the upstairs bedrooms. We had the weather yesterday, so that part's almost done. I used liquid nails on the edges and middle + cap head nails, and an occasional 10d galvanized w/ fender washer to hold the foam where the surface was not perfectly flat.

The brace idea of yours would work but it's probably overkill at this point. Thanks for the input!


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## Windows on Wash (Aug 30, 2011)

Don't rely on the glue long term. It's great to have a mechanical fastener whether by washer or by wedge.


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