I want to insulate the outside of my house, which type of insulation do you think is best?

J. Ferguson Nov. 15, 2017Updated: July 29, 2020

I live in Southern Alberta and will be replacing my exterior vinyl siding with wood, I also want to add insulation at the same time. It's a 2x4 wall with pink insulation and a vapour barrier behind the drywall,  and only vinyl on the outside. There are a lot of different kinds of rigid foam panel and I don't want to choose the wrong one, which do you recommend and how much will I need? Thanks, Michael. 

Responses (13)

Dave King 4 years ago


We have purchased a 2 season non insulated 2 story summer home that has a 2X4 frame and no insulation. At all. The exterior cedar siding keeps it nice and dry, but with winter at -30C / -22F, we want to make it a 4 season getaway.

We love the painted, open frame interieur look (we can see all the 2X4's) and have decided all work must be on the outside.

We thought about 6" or 8" steel studes on the outside with blown foam insulation to fill in and stopp all air leaks. We would then put new cedar siding on the outside.

Will this work, and what should we modify to make it work?


Ecohome 4 years ago


Hi Dave, 

 The biggest modification I'd suggest would be to ditch the steel. So much heat would be conducted through the metal that it would reduce the effectiveness of the insulation you install by an easy 25% and likely more, read more about that in the link at the bottom.

What you are describing could likely be done with wooden I-joists, though I'd consult an engineer to make sure that the foundation is solid as well as the framed load-bearing walls before you make any modifications. As for spray foam, there are two companies that we know of who have switched to much less harmful blowing agents - Demilec and Elastochem.

You could also swap out the foam for cellulose, that would be cheaper than the spray foam, though there are additional durability concerns so you'd need to ensure there is no water infiltration. 

And here is a link to a product I mentioned earlier that may be a more simple solution, it is an EPS foam panel with a metal rail embedded in the center for exterior insulation that is used to attach it to the wall and that the strapping is then attached to for installing the siding. You would just screw it to the wall, then screw strapping to the same panel for installing future siding, which sure makes the job quicker.  

And one part that will need careful design is the wall-to-roof junction. If the walls aren't insulated then most likely the ceiling isn't either. You may be able to blow insulation into the attic if it has one, or if it is a vaulted ceiling you may also be able to continue whatever wall system you decide on. Definitly have it designed by a professional to ensure not just efficiency, but durabily as well. Without existing insulation it's much less worrisom, but you always need to be careful when drastically changing a wall system to not invite new problems from moisture buildup. 

Here are some other pages on insulation when renovating that may be worth a read: 


Hana Nena
Hana Nena 2 years ago

We have an older brick home from 1960's, can we insulate from the outside?

Mike Reynolds 2 years ago

Hi Hana, yes you can. We always recommend being very careful about the type of insulation and other materials you may install in the process, to make sure they are permeable to moisture and will allow the wall to dry. The page you should read is linked above but here it is again - How to insulate a home from the outside. If that doesn't answer all your questions feel free to write back, and let us know where you live, building for your climate zone is very important

Mark Ollinger 2 years ago

Hello. I have read the commentary and admit to not understanding everything so want some clarification please. Our situation is similar. We have a 75-year-old two storey house and we are looking at a complete exterior redo (most windows, all siding, metal roof over existing shingles, soffit, fascia (sp?), and eavestrough/downspouts) in 3-4 years. We can't add the 7" to the thickness of the wall. I would suspect that some of the insulation between the interior and exterior walls is settled cellulose or perhaps even wood shavings. Is the best bang for the buck to blow into the space between the interior and exterior walls from the exterior with additional insulation clad to the exterior wall prior to vinyl siding being installed? 

John Maloney
John Maloney 1 year ago

We live in Ontario, just north of Oshawa. The back of our two storey house faces north which is all open fields, except for a row of older spruce and spruce trees. Since we have lived here, during the winter months the house is cold during windy days. On those days the back wall is cold. You can feel the draft coming through outlets. I am looking to upgrade the back side of our house (currently has insulated aluminum siding) The three other wallas are bricked. I won't get into why that is. I found out why a couple years after we purchased it.

I have done a couple interior renovations where the room is on the back wall. The house exterior is 2 x 6 framing. I gutted the stud cavity down to the tintest sheathing. And installed 4" of rigid insulation leaving a gap all the way around so as to spray expanded foam to fill the gap between the studs and plates, to create an air tight wall (as tight as I can anyways). The remaing portion of wall cavity was filled with Roxul Comfort Board. Then drywalled. That was possible only becasue I had gutted those two rooms.

The remaining wall sections are in rooms that are not slatted for any renovation. So wanted to tackle this at the same time as replacing the old sheathing and new siding.

What would your thought be in the remaining sections being done from the outside. I was planning on cutting out (or slicing the existing poly vapour barrier so that the interior cavity can breath and no condensation will form. I really don't want to add insulation on to the outside of the studs due to all windows would have to be reset. I know doing this would certainly provide the north wall with a better air barrier as well as increasing the R value. I would sacrifice the loss in R value to the thermal bridging. Anything is better than what is existing.

John Maloney
John Maloney 1 year ago
Sorry I forgot to mention that I will being using 1/2 " plywood for the new sheathing and I'll have to strap the back wall for the new prefinished would siding.