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spray foam from outside?

Cape20895's picture

Has anyone heard of spraying foam insulation from the outside of the house?  We are removing old siding and sheathing and would like to insulate with spray foam but don't know if it can be done this way.  The interior walls are in good shape and most are original plaster so we don't want to disturb them.  I have e-mailed this question to a couple of spray foam installation companies but never heard back.  Maybe they think I am crazy!?

(post #109450, reply #1 of 18)

I think that it's the ideal way to retrofit a house and make it air tight.


(post #109450, reply #2 of 18)

Does that mean it is possible?

(post #109450, reply #3 of 18)

"ideal" WOULD seem to imply not only possible but also fairly straighforward.

It would be about the only way to take, or instance, an 80-year-old house and bring it up to or exceed typical modern construction in terms of energy efficiency.

Take the extra effort to expose all the entire building envelope.  If you can completely seal with spray-on foam, not only will your energy use go way down, but you will solve the problems caused by the movement of humid air before they start.


David Thomas   Overlooking Cook Inlet in Kenai, Alaska
David Thomas   Overlooking Cook Inlet in Kenai, Alaska

(post #109450, reply #5 of 18)

Absolutely it's the way to go and it's been done countless times.


(post #109450, reply #4 of 18)


I would be very nervous over the idea ofremoving all of the sheathing from your house at once.

Interior wall finishes DO NOT  provide adequate lateral bracing.

be very careful about how much you take of at any one time without providing some temporary diagonal bracing

my two cents worth...

Mr T

Slow or Expensive, pick any two.
. .

(post #109450, reply #6 of 18)

Thanks for your input.  We do plan to take a section at a time and thanks to your warning we will exercise more caution. 

(post #109450, reply #7 of 18)

I was thinking about the same thing during my adventure in replacing the claps with fibercement on my home. Why are you removing sheathing? Thought you would need 2" hole in each stud bay at top.

The problem you are maybe going to run into is a question of timing. The foam guys will have a minimum job $ and multiple trips may send you over budget. Please keep us posted as to how you make out as I may be following in your footsteps. Lots of luck.

(post #109450, reply #8 of 18)

We have a few reasons to remove old sheathing.  First, cellulose insulation was blown in (from the outside) probably 15 to 20 years ago (and has settled) so that will have to be removed before we can reinsulate.  Second, the sheathing is 8 inch boards run on a diagonal with gaps as big as 1 to 2 inches between in some places.  Third, we found some dry rot/termite damage at the sill which was repaird but who knows what other damage there may be once we start tearing off the old vinyl siding.

We have not yet figured out the scheduling for a project like this.  Since we probably can't do the entire house in one day for safety/shoring and weather reasons I fear that it may be difficult to find a sub to spray insulation over several days.

Is spray foam something that can be DIY?

(post #109450, reply #9 of 18)

Is spray foam something that can be DIY?


What prices are you getting in your neck of the woods? The prices for foam varie tremendously from one area to the next.


(post #109450, reply #10 of 18)

Now that we know it can be applied from the outside we can talk to installers about price.  I am sure that we won't find any bargains on foam insulation in the DC area, unfortuantely.  Will get back with prices.

(post #109450, reply #11 of 18)

Now that I see you're in DC, try 301-937-4710 (I think that's Insulators of Maryland) and ask for Terrence. He quoted me $2/sq foot for 2x4 stud bay with a $400 minimum. Reading from some notes I took, this price was for "closed cell foam" and lead time was 3 to 4 weeks.

(post #109450, reply #12 of 18)

Thanks for that reference.  They are on my "call" list... and now, since I have a name, they are at the top of the list.

(post #109450, reply #13 of 18)

Just make sure when they spray it to account for any overspray. 

I had a neighbor from h--- a few years ago who tried spray foam insulation on his "project" house.  He didn't bother to watch that the overspray was drifting down into the driveway and all over the front of his truck. 

I could tell you where he went for weeks following - the only bark blue pickup in town with a yellowish pebble finish coat.


(post #109450, reply #16 of 18)

In my humble opinion, diagonal board sheathing is the a higher quality sheathing than the typical OSB installed these days.  I would replace diagonal board sheathing reluctantly.  The boards provide excellent racking resistance (bracing), and are far superior to sheet goods at allowing any moisture in the wall to dry to the exterior.  Recent Canadian studies point to the difficult that plywood and OSB have to dry out once they get wet -- they dry much more reluctantly than framing lumber or boards, and can rot before they dry out.  Why replace good sheathing with so-so sheathing?  You can always top up the stud bays with more cellulose if the existing cellulose has settled.  You'll save a bundle of money compared to your spray foam plan, and you won't end up putting your house at risk of structural collapse by removing the existing bracing.

(post #109450, reply #17 of 18)

Thank you for sharing your view on this issue.  We had never considered the diagonal sheathing to have any positive attributes - then again, we aren't professionals.  We will do more reasearch before starting this project.

(post #109450, reply #14 of 18)

If you are interested in doing it yourself you can order the stuff ( not exactly the same stuff ) from FOMO @ Order their two part foams and you can insulate as you open up the walls. These are refillable kits and so you can pay as you go. Good Luck

(post #109450, reply #15 of 18)

Thanks, we'll check it out.  Doing it ourselves would certainly solve the scheduling problem.

to answer your questions (post #109450, reply #18 of 18)

to answer your questions about outdoor spray foam, go to 'youtube' an type in, how do i use outdoor spray foam outside my home. there are videos that will explain in full details of the type of outdoor spray foam insulation to use. one of them i no is called foam it green. thay sell high density spray foam to do it yourself for outside your home and roof.