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Should we use spray foam insulation in a 130 year old house?

Hi All -

We are in Upstate NY where winters can be well below freezing with lots of snow and ice and very wet and slushy springs. We are restoring an 1880 Victorian that is quite large, and the walls have never been insulated.

Because the plaster walls were in sich disrepair, we gutted all the exterior walls and now are going to insulate from the inside.

We are very interested in spray foam insulation but the trouble is that we only know "some" of what we should and Im not sure Im entirely comfortable with it. I want to know if my concerns are founder or unfounded, and whether we shoudl do spray foam or not. So here goes

1. We have a contractor who says we should use a 2" thick closed-cell spray foam in all the stud cavities. My concern here is that essentially this creates the vapor barrier on the OUTSIDE wall, and the remaining 4 inches of teh stud bays are open to interior moisture. Could that allow warm moist air to condense on the studs that are colder (due tocold conduction from teh outside), leading to mold and wood rot?

2. It is my understanding that wood needs to breathe, especially if it gets wet. If we do spray foam, then we will end up apply spray foam inslation directly to the back of the house's sheathing (and ins some cases, the original dutch lap siding is nailed directly to the studs, there is NO sheathing). If any water at all gets behind the siding (as in between teh siding and the spray foam), wouldnt it get "stuck there" and be unable to dry out because the spray foam prevents air circulation? We dont have any known major water problems, but this is a huge, 3-story 130 year old house and some water in some amounts, especially during tehice melts in the spring, may enter wallss in places we may never know about. Maybe over the last 130 years water penetration has not been a problem because the extreior walls "breathe," but with spray foam might we introduce a problem in this manner?

3. Related to #2 above, a major concern I have is investing 15-20K in a scraping and brand new paint, only to have it peeling off the siding in 2 years because moisture is trapped in the siding and outgases from beneath the paint because it has no where else to go - on accountof having airtight spray foam insulation.

Any opinions? We are really uncertain about the right way to go.

Re: Should we use spray foam insulation in a 130 year old house?

If all of the exterior walls are "gutted" then I can't imagine why you'd even consider spray foam which, in even the best case, is a last resort. Spray foam is a cheap, very bad choice alternative to doing it correctly. It'd be my last choice.

Re: Should we use spray foam insulation in a 130 year old house?

Are we be talking about the same thing? You said Spray foam is a "cheap, very bad choice." Spray foam insulation is the most expensive kind of insultation there is for a home, about 3-5 times the cost of fiberglass. But I am concerned about the framing members of walls breathing.

I am not talking about using cans of "Really Good Stuff." I am talking about a professional crew with a large pump system. If you dont like spray foam, what insulation method do you think is superior?

Re: Should we use spray foam insulation in a 130 year old house?

Thanke for the reply. A lot of old Victorian homes used to nail the 7/8 inch thick dutch lapo siding directly to the studs. I do see that they added a very thick form of "paperish" sheathing beneath the siding which is sort of liek the consistency of very flexible cardboard. The stuff is 130 years old and is sagging and detached in multiple places. For the msot part the siding is in excellent shape, but here and there you might see a little daylight between some sidings but its pretty rare.

We had a professional come and look and he gave us a price. He suggests 2" of closed cell in all the stud bays, and if we wanted to we could add more unfaced fiberglass on top of that to add to teh r value.

Regardless, my main question is whether it is possible for water to sort of seep in between the exterior siding and the spray foam itself, getting trapped and promoting rot.

Almost no one seems to be able to address this question - - it would seem to be an issue for any old house that was gutted but never insulated.

I supposed we could staple tyvek into teh stud bacys first (conforming to the studs and exterior wall), but I think that might keep the spray foram from adhering.

Anything on the moisture question would be appreciated,

jaros bros.
Re: Should we use spray foam insulation in a 130 year old house?

To answer your question about water getting behind the siding, that is happening right now. It will happen with the foam as well. The reason the paint peels off of wood siding has to do with a number of issues. First, the wood has to be sealed on every cut and on the backside with a good primer. If this is done, you've got a good chance of the paint sticking on for 10-15 years between repaints. The right way to do it is to add a rainscreen before the siding goes on. This allows an airspace between the siding and the sheathing so that when moisture does get behind the siding, and it always does, that it will be able to dry out. Usually a rainscreem is composed of vertical strapping nailed to the exterior of the sheathing.
You should be fine with what your insulation contractor is doing. The vapor barrier will be to one side of the wall...and it can be on the outside. I don't especially care for the "flash and spray" method." Why not fill the whole cavity with spray foam? If you only add the 2" you will definitely have to add the fiberglass to finish it off.

Josh Jaros

Re: Should we use spray foam insulation in a 130 year old house?

Jaros Bros.,

You said that there will be "a vapor barrier to one side." The contractor has said that the 2" of closed cell foam IS the vaopr barrier and that is all we need.

If the spray foam is put in there there will be NO gap at all between the foam and the siding. On the original house there is no sheathing.

The question is: will water get in there and become trapped between the foam and teh siding, or, will teh foam adhering to the "back"of teh siding essentially prevent water from even touching it?

jaros bros.
Re: Should we use spray foam insulation in a 130 year old house?

The foam will act as a vapor barrier. It is going to be your vapor barrier if installed. That is my point exactly.
Secondly, water does get behind your siding. No matter what you do, it will get there somehow. And when it does your paint will peel if these conditions are not met...your siding needs to be backprimed and sealed on every cut with a quality primer. This is the very least. A rainscreen would be better.
I could tell that you were concerned that the foam might affect your paint job. It might, there's no way to tell. When it rains your siding gets wet and the wood is probably soaking up a lot of moisture. Right now I am guessing your ancient siding(unless you had it sided properly lately) is not backprimed or sealed well. This means that your wet siding now has to release the water to dry. It will push the paint off a lot of the time or dry off wherever it can. With the foam sealing up the back and sticking to it, that reduces one more avenue that it can dry by.
There's no easy way to do what you're doing. Turning an old drafty building into a new tight efficient place takes money. The right way to do it would be to strip all the siding off, add 1" foam, run vertical strapping for a rainscreen, and then install new siding, fully backpriming it and sealing every cut.
In the end, you might justify doing this because painting it every 5 years compared to painting it every 10-15 is a big difference. And also if you put the 1" foil faced foam on the outside you could skip the foam contractor and use fiberglass on the inside and install it yourselves. That would be the way to do things the right way without having to worry about all the issues you are thinking about right now.

Josh Jaros

Re: Should we use spray foam insulation in a 130 year old house?

It sounds to me that you are thinking about this a little to hard. If the siding on the out side is in good condition, tight to the studs and to it's self, a good coat of primer and quality paint, caulked where it should be, then NO water will get in, Right?. Paint is designed to shed water but let the material breath.
As for the insulation you need at least 2" of 2 lb foam to get your vapor barrier. 2lb foam is closed cell, so that means the foam will not obsorb water, like a door closed. 1/2lb or Icynene will absorb water it is open cell, like a sponge. As for the off gasing leave off the drywall for a few weeks, it is not necessary but you can. Also with 2lb the cavity does not need to be full.

jaros bros.
Re: Should we use spray foam insulation in a 130 year old house?

If paint was waterproof, why do we have rainscreens?

Josh Jaros

Timothy Miller
Re: Should we use spray foam insulation in a 130 year old house?

Howdy closed cell foam is water proof so the moisture cannot travel threw it to then hit the inside of the outside walls. Foam also stops air infiltration- major cause of drafty homes and high heating costs. Foam is very $$
With the walls open much less expensive to install fiberglass with a plastic moisture barrier on the inside and it caulked to the ceiling plat and floor wall plates so the moisture cannot enter the insulated wall cavity. The peeling paint is likely caused from moisture traveling from inside home out to siding.

Re: Should we use spray foam insulation in a 130 year old house?

HellNY, I think you have raised some very reasonable questions about your house.
There isn't a wall made that doesn't allow water to get inside in some fashion. Nowadays we tend to limit how far the water can travel by using house wraps and solid sheathing. Even vinyl siding which is essentially waterproof will allow water to be blown under it, which then has to be drained off.
Then we have to be concerned about trapping moisture either because of vapor being trapped in the wall or getting into the wall from outside.
With the original uninsulated wall with no sheathing or even strapping any water that got in would dry eventually.
I would be leery of placing foam directly against the siding too.
Also placing fiberglass directly against to siding might allow the moisture to wick into the insulation.
Any chance the studs are 2x6, then you could put in 3 1/2" fiberglass and keep it off the siding?
Sorry, no real answer here.


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