Author Topic: Old wood house - Insulate walls or not?  (Read 1557 times)

Ty Webb

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Old wood house - Insulate walls or not?
« on: February 18, 2018, 10:32:04 AM »
I own a house in southern Ontario, Canada built in the 1870s. It has wood board and batten siding with no sheathing from what I can tell, and lathe and plaster walls on the inside. There is no insulation in the walls and most of the windows are original. For such an old, drafty house the heating bills are surprisingly reasonable. The siding and exterior trim is in rough shape and will need to be replaced soon. I have read a lot of opinions about insulating houses like this one and creating moisture issues in the walls. When I remove the siding that would be the time to insulate. Should I bother insulating at all or if I should then what would you recommend? Thanks!

bacchi

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Re: Old wood house - Insulate walls or not?
« Reply #1 on: February 18, 2018, 03:39:23 PM »
Yes, you should. Are you putting in sheathing?

Ty Webb

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Re: Old wood house - Insulate walls or not?
« Reply #2 on: February 18, 2018, 04:07:59 PM »
I guess sheathing is the other question. If we leave the existing lathe and plaster and then put sheathing and housewrap that would still allow any moisture to migrate out of the wall to the outside.

Jon Bon

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Re: Old wood house - Insulate walls or not?
« Reply #3 on: February 18, 2018, 07:10:09 PM »
If you don't have sheeting then your wood siding is going to be structural. So if you pull it off you would have to attach sheeting to keep everything tight.

I always like blown in cellulose. Cheap and easy, albeit a bit messy! Depending on your situation, they do make vinyl siding with insulation in it, that would probably help.

But remember as a general rule heat loss happens
1. Ceiling
2. Walls
3. Windows

So take care of 1 and 2 for thousands of dollars before you attack #3 for tens of thousands of dollars.

BudgetSlasher

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Re: Old wood house - Insulate walls or not?
« Reply #4 on: February 19, 2018, 07:14:09 AM »
If you don't have sheeting then your wood siding is going to be structural. So if you pull it off you would have to attach sheeting to keep everything tight.

I always like blown in cellulose. Cheap and easy, albeit a bit messy! Depending on your situation, they do make vinyl siding with insulation in it, that would probably help.

But remember as a general rule heat loss happens
1. Ceiling
2. Walls
3. Windows

So take care of 1 and 2 for thousands of dollars before you attack #3 for tens of thousands of dollars.

I've known many people who have gone the blown in route and are quite happy with it; it is great for adding insulation to otherwise inaccessible spaces with minimal damage (when I help the FIL there was a 1.5-2" hole at the stop of each stub bay to be patched and painted). A down side is that if there is blocking or other large obstruction in the wall it can leave voids below them.

Since the siding is coming down for replacement, the OP will have access to the stud bays for easy installation of batting/foam board. I don't know how well blow in settle in and hold up if it was installed and subsequently the siding/exterior edge to the cavity where removed, perhaps someone can chime in, it may also depend on the way (dry/wet/dense pack) it was blown in. And of course if the insulation is being down at the same time the siding is down and the bays are exposed blown in won't really be contained.

For the windows, they could also take care of 3 with some DIY storm window inserts of with a few dollars of wood per window for the frame and whatever material fits your budget from stretch film to polycarbonate. Just because less heat is lost from windows, or that upgraded R-value windows are less of an upgrade than the other two, doesn't mean that comfort won't be greatly increase; drafty windows with a could wind can be very uncomfortable or even result in a higher thermostat setting and faster heat loss through 1&2.

To the OPs moisture point, as I understand it house wrap is more about keeping air flow down/out and providing a drainage plane for any rain that gets behind the siding. Then vapor barrier goes on the hot side of the wall, in a heating climate the inside, to prevent moisture from getting into the wall. Again as I understand it from research, it is the lack of vapor barrier that allows moisture to get in where it may condense on the newly installed insulation ... and upgraded sheathing/vinyl siding/house warp decrease air flow that would dry out the walls.

If the OP is looking for some detailed information, I suggest reading up over at https://buildingscience.com/. They have some very good articles and other documents (though sometimes it is easier to find what you are looking for on their site with a google search than their own search).

lthenderson

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Re: Old wood house - Insulate walls or not?
« Reply #5 on: February 19, 2018, 01:44:56 PM »
Probably 90% of the cost of insulating a structure is labor so the time to insulate is when the old siding is off. I would definitely add insulation and house wrap before residing the house.

Just stating the obvious, if the siding is structural, you need to do small sections of time and not remove all the siding at once.

Fishindude

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Re: Old wood house - Insulate walls or not?
« Reply #6 on: February 19, 2018, 02:29:38 PM »
It will be quite easy to insulate if you indeed remove the siding down to the studs as mentioned.
Fill the stud cavities with fiberglass, sheathing over that, house wrap over that, then your new siding.   New fiberglass insulation will be the cheapest part of this whole project.

If you're not going to get around to replacing siding for a few years, you could consider getting some blown in insulation installed in the stud cavities.   They will need to drill holes between every stud cavity, then blow in insulation and cap all of the holes.   Caps look kind of ugly, but they can be painted to match current color.

BudgetSlasher

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Re: Old wood house - Insulate walls or not?
« Reply #7 on: February 19, 2018, 04:39:15 PM »
It will be quite easy to insulate if you indeed remove the siding down to the studs as mentioned.
Fill the stud cavities with fiberglass, sheathing over that, house wrap over that, then your new siding.   New fiberglass insulation will be the cheapest part of this whole project.

If you're not going to get around to replacing siding for a few years, you could consider getting some blown in insulation installed in the stud cavities.   They will need to drill holes between every stud cavity, then blow in insulation and cap all of the holes.   Caps look kind of ugly, but they can be painted to match current color.

The insulation will definitely be the cheapest part of the project, unless maybe the OP hires out spray foam for the insulation; still I would recommend doing some research of the cost and benefits of various types of insult, personally I am not a big fan of fiberglass in general and especially where there could be incidental moisture and air movement.

The FIL and I discussed the holes when he did blown in in his farm house. What he decided to do was punch the holes on the inside through the plaster/drywall and then patch them like any other wall damage. Of course that meant repainting every exterior wall, but the end result is that you cannot tell it was done.

zolotiyeruki

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Re: Old wood house - Insulate walls or not?
« Reply #8 on: February 20, 2018, 08:20:03 AM »
I'm not sure simply filling the stud bays with insulation is a good idea.  You'll definitely want to add some sort of vapor barrier on the warm side of the wall so you don't get condensation inside your insulation.  Spray foam is the most effective at both insulating, vapor barrier-ing, and air sealing, but it is the most expensive option.  You could also use styrofoam sheets, adhere them to the back of the lathe/plaster walls, fill/seal any gaps with expanding foam, and then fill the remaining cavity with batts or blown-in insulation.  The problem with that approach is that it's labor-intensive to custom fit each piece of styrofoam, and also the back of a lathe/plaster wall is not likely to be smooth.

If it were me, I'd inclined to go with the spray foam for sealing and moisture control.  I'd do a thin layer for cost savings.  The rest of the space between the studs I'd fill with cellulose or some sort of batt insulation.

bacchi

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Re: Old wood house - Insulate walls or not?
« Reply #9 on: February 20, 2018, 02:16:40 PM »
The OP isn't removing the interior walls so a vapor barrier on the warm side can't be put in place. Any vapor barrier on the outside would trap moisture inside the walls.

What the OP needs is an air barrier with high-perm. A rain screen is a good idea, too, if the siding is flat against the sheathing.

https://buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers/view

Quote from: buildingscience
The key point that needs to be made is that although air barriers are a good idea everywhere, vapor barriers are not.

Densely packed cellulose would work as both insulation and (almost) an air barrier.

https://buildingscience.com/documents/insights/bsi-043-dont-be-dense

Quote
Dense packing a wall does not eliminate the need for an air barrier in new construction. But in retrofit applications we often get so close that we can typically live without one. Besides, there are no other practical alternatives short of completely reconstructing the wall assembly. So “rock on” and dense pack walls. The approach is practical and cost effective.

zolotiyeruki

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Re: Old wood house - Insulate walls or not?
« Reply #10 on: February 20, 2018, 03:32:57 PM »
The OP isn't removing the interior walls so a vapor barrier on the warm side can't be put in place. Any vapor barrier on the outside would trap moisture inside the walls.

What the OP needs is an air barrier with high-perm. A rain screen is a good idea, too, if the siding is flat against the sheathing.

https://buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers/view

Quote from: buildingscience
The key point that needs to be made is that although air barriers are a good idea everywhere, vapor barriers are not.

Densely packed cellulose would work as both insulation and (almost) an air barrier.

https://buildingscience.com/documents/insights/bsi-043-dont-be-dense

Quote
Dense packing a wall does not eliminate the need for an air barrier in new construction. But in retrofit applications we often get so close that we can typically live without one. Besides, there are no other practical alternatives short of completely reconstructing the wall assembly. So “rock on” and dense pack walls. The approach is practical and cost effective.
I wasn't trying to talk about the interior walls, but rather the back side of the interior face of the exterior walls.  Or, what you see if you strip the siding off the house and there's no insulation.

bacchi

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Re: Old wood house - Insulate walls or not?
« Reply #11 on: February 20, 2018, 04:11:08 PM »
I wasn't trying to talk about the interior walls, but rather the back side of the interior face of the exterior walls.  Or, what you see if you strip the siding off the house and there's no insulation.

Right but a few others have mentioned a vapor barrier. That can't/shouldn't be done in your case.

You need an air barrier with a high-perm rating to allow water vapor to pass out of the house.

zolotiyeruki

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Re: Old wood house - Insulate walls or not?
« Reply #12 on: February 20, 2018, 07:00:01 PM »
I wasn't trying to talk about the interior walls, but rather the back side of the interior face of the exterior walls.  Or, what you see if you strip the siding off the house and there's no insulation.

Right but a few others have mentioned a vapor barrier. That can't/shouldn't be done in your case.

You need an air barrier with a high-perm rating to allow water vapor to pass out of the house.
Why would you want to allow the water vapor to pass through the walls?  That's how you get condensation in the middle of the insulation, and eventually, mold.  Am I missing something?  What's wrong with blocking the water vapor on the warm side?

bacchi

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Re: Old wood house - Insulate walls or not?
« Reply #13 on: February 20, 2018, 07:24:37 PM »
I wasn't trying to talk about the interior walls, but rather the back side of the interior face of the exterior walls.  Or, what you see if you strip the siding off the house and there's no insulation.

Right but a few others have mentioned a vapor barrier. That can't/shouldn't be done in your case.

You need an air barrier with a high-perm rating to allow water vapor to pass out of the house.
Why would you want to allow the water vapor to pass through the walls?  That's how you get condensation in the middle of the insulation, and eventually, mold.  Am I missing something?  What's wrong with blocking the water vapor on the warm side?

No, I'm missing something. I misunderstood.

You're right -- a thin layer of CC foam against the interior wall is the way to go.