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Old 12-28-2019, 10:12 AM   #1
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insulating strategy for exterior wall in old home


I just purchased an old house (110 years). One of the many projects includes insulating some of the exterior walls. Perhaps, eventually, all of them. For now, though, I'm focused on the living and dining rooms of the main level of the house. Punching through the plaster about 3' from the ground reveals no insulation in the 2x4 walls, though it's possible (I'm told) that some primitive insulation has settled down below that. Based on that, heat bills, and the ice on the roof, it seems like there's not a lot of insulation in the house. I'm located in Minneapolis, which is climate zone 6.On the house's exterior there's vinyl siding.



My current strategy is to tear the plaster and lathe off and install R15 (the best I can find for 2x4 walls) kraft-faced batts. At Menards (basically a midwest Home Depot equivalent) yesterday the employee was saying that code calls for more vapor barrier than the kraft backing provides, so technically needing some plastic as well. Regarding whether the kraft-faced batts are considered a sufficient vapor barrier, he added "but it really depends on the inspector."


I know that some people use unfaced insulation and a plastic vapor barrier, but I like the idea of knowing the insulation won't settle because it's stapled in place.



So, several questions:

1) For Minneapolis, what's the best approach? faced or unfaced? If faced, then with additional vapor barrier?

2) If using faced batts and an additional vapor barrier, should one score the facing at all?

3) If using unfaced batts, is there concern that they'd sink down (assuming the studs are consistently spaced)?

4) Some people are quite concerned about mold when using a plastic vapor barrier (in the summer with AC, I think?). How much should I be worried about that?
5) What's the best stapling practice for faced batts? I've read (on this forum) that some think that stapling on the face of the studs adversely affects the drywall screws? But I'm not really sure I understand that argument very well.

6) The Menards guy also pointed out that some old home were "balloon-framed." I'd never heard of this, but in my simple understanding this could mean that the studs on the main level are actually the same studs as the second level (they're very tall), and there's no top plate. I've read that balloon framing increases fire danger as fire can spread up the walls more easily. Upon opening up the wall cavity, **IF** I discover that the walls are balloon framed, then are there other things I should do?

7) What are the odds that plastic was put on the exterior when the vinyl siding was installed)? Clearly having plastic on the exterior and a vapor barrier on the inside of the insulation would cause moisture issues.

8) Other advice/thoughts?


Thanks so much!
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Old 12-28-2019, 11:01 AM   #2
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Re: insulating strategy for exterior wall in old home


The best buck for the insulation is to start with the attic.

If i was stripping walls down to studs for insulation.
1. I hope you are planing new wiring at that time.
2. I would add anther 2" to the walls making them 2x6 for insulation like a new house.
Understanding what vapour barrier can an can't do is the important part of the learning curve.

Mold on a vapour barrier is not the problem but it can happen but it is a symptom of another problem.

If the insulation was installed sloppy so cold air can get to the back of the vapour barrier and warm moist air can get to the inside of the vapour barrier you can get mold. That is true if you use paper faced, poly or just painted drywall.

Most people have the idea that insulation can just be stuffed in and done in an hour.
It is more of a craft job so that it is not missing any cavity so air that is in there can not circulate from the inside surface to the outside surface of the cavity.

If you use paper faced or no VB you want to use exterior wall electrical boxes that have a flange and gasket for sealing to the drywall. If you use a VB there are plastic wraps for the boxes or there are tricks to do the boxes with poly.
If you are not sure what they have put behind the vinyl siding you can unzip it in a few places to have a look see. We can find a video for that.
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Old 12-28-2019, 11:29 AM   #3
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Re: insulating strategy for exterior wall in old home


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Originally Posted by Nealtw View Post
The best buck for the insulation is to start with the attic.

If i was stripping walls down to studs for insulation.
1. I hope you are planing new wiring at that time.
2. I would add anther 2" to the walls making them 2x6 for insulation like a new house.
Understanding what vapour barrier can an can't do is the important part of the learning curve.

Mold on a vapour barrier is not the problem but it can happen but it is a symptom of another problem.

If the insulation was installed sloppy so cold air can get to the back of the vapour barrier and warm moist air can get to the inside of the vapour barrier you can get mold. That is true if you use paper faced, poly or just painted drywall.

Most people have the idea that insulation can just be stuffed in and done in an hour.
It is more of a craft job so that it is not missing any cavity so air that is in there can not circulate from the inside surface to the outside surface of the cavity.

If you use paper faced or no VB you want to use exterior wall electrical boxes that have a flange and gasket for sealing to the drywall. If you use a VB there are plastic wraps for the boxes or there are tricks to do the boxes with poly.
If you are not sure what they have put behind the vinyl siding you can unzip it in a few places to have a look see. We can find a video for that.
Yes, I do plan to completely insulate the attic in the future. The only reason I'm focusing on these exterior walls now is because they're in rooms that we don't want to mess up later.

Regarding the idea to furr the studs out to 2x6, do you think it's worth doing that if most of the walls will remain 2x4? I think it's highly unlikely that we'll rip the lath & plaster off the remaining exterior walls. Perhaps they will get "blown in" insulation at some point.

In terms of strategy, I I did want to widen the walls, would most people just tack a 2x2 alongside the 2x4?
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Old 12-28-2019, 11:50 AM   #4
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Re: insulating strategy for exterior wall in old home


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Yes, I do plan to completely insulate the attic in the future. The only reason I'm focusing on these exterior walls now is because they're in rooms that we don't want to mess up later.

Regarding the idea to furr the studs out to 2x6, do you think it's worth doing that if most of the walls will remain 2x4? I think it's highly unlikely that we'll rip the lath & plaster off the remaining exterior walls. Perhaps they will get "blown in" insulation at some point.

In terms of strategy, I I did want to widen the walls, would most people just tack a 2x2 alongside the 2x4?
Yes that would do it but often they just add 2x2 to around the windows and doors and at the ceiling and floor and just add strips of foam board on the rest of the studs. That gives you a real good thermal break. And some times they insulate the 2x4 and then cover the walls with foam board and make that the VB. They make drywall screws up to 3" long for that.
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Old 12-28-2019, 11:52 AM   #5
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Re: insulating strategy for exterior wall in old home


Wiring is good suggestion, although if in good condition, you don't have to change/upgrade. 15 amp, 14 ga wires, are good, although current rule is 12ga, 20 amp for most wall outlets. You may have to change the breakers as well, so you may not want that ball starting to roll. Older house, so check the wires that show and make sure the insulation is still pliable and the wire ends aren't corroded. If problems, come back to ask. My old house, I had to replace all breakers since one or two were tripping too much. Breakers do wear out.



There are many youtube videos on insulating with fiberglass. One, matt risinger, has a video combining thin foam board (facing outside) and finishing with fiberglass. The foam board with edges sealed, is air seal. I just caulked the stud bay edges with can foam or cheap caulk and plywood sheathing joints, but I think foam board is extra barrier as well as easy way to seal esp if your wall sheathing is 1x boards. Sealing all edges of the boards would be higher cost, esp since boards would have knot holes and splits. Air sealing is just as important as insulation because one can't work well without the other. If I had to choose, it would be to air seal.


I'm in northeast nj. Plastic vapor barrier, as far as I know, is not required here. It looks like it is in colder places. That is because moisture can condense that much faster and in larger amounts where it is colder. If generally required, that is the practice I'd follow. Your spot work may not require a permit but doesn't hurt to ask and pay a little fee. Then you have the paper work and could be a plus if/when selling. But if using plastic sheets, you must air seal the best way. Taping the seams, I think, isn't good enough. Tapes can fail over time. Not sure what, but I'd think about combining caulk and tape. Something that will stay flexible over time. Sorry I can't be more specific, but one thing I see everybody doing is taping and I worry about that. I believe tapes will fail eventually. I don't believe even the acrylic adhesives will last past 15-20 yrs. Eternabond tape, if used indoors away from the sun, I think will have life well past 20, even 30. I used it on roof and I know for certain that its adhesive has close to 20yrs life under outside exposure. It is thicker adhesive, however. I don't, yet, accept manufacturers' claims, although above video guy is claiming good things about acrylic adhesives. But one manufacturer of tape for zip sheathing system, has changed from tape to paint on barrier. I think it has found the tape weaknesses.


BTW all of this is my opinion. I know acrylic adhesive is very good. I just don't know, and time hasn't proved it, about its long term capabilities. Such tapes are warrantied for only 10 yrs, example. Because of air/vapor sealing importance, I think this is a topic worth thinking about. Sorry for the long winded rant.


I think I would use the foam sheets (1"?) on the outside surface and seal all edges with can foam. Then use r13 fiber batts with paper face and staple the paper flanges to the studs. Mark the studs for later drywalling. I would skip the plastic but that is something you can talk to your town inspector.


All stud bays now require fire blocks. I think that is every 8-10'. Add the blocks about even with your ceiling and you should be fine. Blocks not tight and gaps, should be sealed. Any pipe or electric cable holes going up, seal with caulk or can foam. There is seaprate foam that is supposed to be a different color (red or orange?) and your inspector will be happier for it.
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Old 12-28-2019, 01:49 PM   #6
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Re: insulating strategy for exterior wall in old home


Hey, I'm in Minneapolis too.






First, I would point out that with vinyl siding it would be fairly easy to blow in dense pack cellulose from the outside without the mess/expense of gutting. With vinyl siding, you can take a piece off in the middle of the field and put it back, so holes can easily be drilled in the outside of your house. This would not be a DIY project though. You need to know what you are doing to pack the stud cavities to the correct density. Properly installed dense pack is superior to fiberglass because it does such a good job of filling every cavity completely and also is better at blocking air. Just a FYI. That is how I would do it.



If you are going with the gutting/ fiberglass route, standard procedure in our area is to use friction fit batts and a poly vapor barrier. You want to limit air movement from the interior of your house into the wall, and kraft faced fiberglass does a very poor job of this. A friction fit batt, properly installed, will not settle. You want to air seal the poly vapor/air barrier as tightly as you possibly can. If you have electrical boxes, they should have gaskets, or at least you want to tape the vapor barrier to the box. You can seal the plastic to the floor with acoustical sealant.



In our climate, we do not worry about condensation forming in the walls during air conditioning season. That happens further south.



Adding 2x2's to increase insulation depth is a good idea, though you're going to have to decide how many other issues that creates with your layout etc.


Here in Minneapolis, insulation qualifies as fireblocking. So it the wall is insulated, no other blocking is required.



In a balloon framed house, you are going to have to take your time and make sure you get that joist area well insulated. Best way (short of spray foam) really would be to slide rigid foam up in there, and caulk you vapor barrier to the foam.
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Old 12-28-2019, 02:26 PM   #7
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Re: insulating strategy for exterior wall in old home


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6) The Menards guy also pointed out that some old home were "balloon-framed." I'd never heard of this, but in my simple understanding this could mean that the studs on the main level are actually the same studs as the second level (they're very tall), and there's no top plate. I've read that balloon framing increases fire danger as fire can spread up the walls more easily. Upon opening up the wall cavity, **IF** I discover that the walls are balloon framed, then are there other things I should do?
It's likely that it's balloon framed, but that's not a big deal. If you're opening up the wall, then you can just fireblock the top with a 2x4 so that flame wouldn't have a direct vent chute to the upper floors and attic.

As far as comfort level in the home, air sealing is more important than insulation. Go after the gaps and cracks that are allowing the cold air to blow in and you'll feel a bigger difference than if you just insulated. Start in the attic for air sealing to reduce the stack effect.

For the plastic vapor barrier, I know it's common in Canada but I've never been comfortable with it. There's a product called Membrain that is a "smart" vapor retarder that changes it's permeability seasonally so that the wall cavity can dry. Kinda like how Goretex will keep rain off you but allow sweat to escape.

Neal has a good point about the electrical upgrade. If you have a knob and tube system (which was the standard when your house was built) you really shouldn't be adding insulation to it as it can overheat and start a fire. You'd have to replace the K&T with the modern Romex type of cable. That's also a good opportunity to get grounded outlets and more of them!
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Old 12-28-2019, 04:33 PM   #8
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Re: insulating strategy for exterior wall in old home


This box is fairly new on the market but they are great for exterior walls, they seal to the drywall and the rubber on the back that seals the wire holes.

https://www.joneakes.com/jons-fixit-...electrical-box


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Old 12-28-2019, 05:43 PM   #9
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Re: insulating strategy for exterior wall in old home


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For the plastic vapor barrier, I know it's common in Canada but I've never been comfortable with it. There's a product called Membrain that is a "smart" vapor retarder that changes it's permeability seasonally so that the wall cavity can dry. Kinda like how Goretex will keep rain off you but allow sweat to escape.

In Minnesota, plastic vapor barriers are code, unless you are using spray foam. Minimum 4 mil sheet poly, taped at the seams, sealed to electrical boxes, etc. Used in virtually all new houses for at least the last 25 years that I have been around (again that aren't spray foamed). It's a tried and true system. If it ain't broke, don't fix it.
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Old 12-29-2019, 06:22 AM   #10
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Re: insulating strategy for exterior wall in old home


The first thing I would do is remove a few pieces of vinyl siding to determine what is currently in place . Is there sheet foam installed ? Is there house wrap installed ? As already stated it is soooo much easier to install insulation from the outside because you are not disturbing/ripping out interior sheet rock or plaster .

But if the inspection of wall electrical wiring is a concern then attacking from the inside is the way to go . If money is no object remove all interior wall covering , repair or replace electrical and spray closed cell foam in each wall cavity . The foam adds insulation/rigidity/vapor barrier but is the most expensive way to go . Next way to go would be cutting sheet foam to fit in wall cavities and sealing the perimeter with foam . Next way is traditional kraft faced fiberglass . I also would suggest you have your local utility company perform an energy audit , they know the area/climate and how the old homes were built and perform . It is free advice take advantage of it if nothing else to help build a baseline of knowledge for you to make decisions from .
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Old 12-29-2019, 07:23 AM   #11
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Re: insulating strategy for exterior wall in old home


Bear in mind, too, that the walls most likely have perlins at the midpoint and that would make blowing insulation in from the top impossible. Once determined where the perlins are, 4 holes will need to be drilled, one at the top, one on top of the perlins, one below the perlins and one at the baseplate. A really large jog. If you plan on stripping down the walls (preferred) you can tackle all the upgrades from the past 110 years all at once.
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Old 12-30-2019, 04:32 PM   #12
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Re: insulating strategy for exterior wall in old home


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This box is fairly new on the market but they are great for exterior walls, they seal to the drywall and the rubber on the back that seals the wire holes.

https://www.joneakes.com/jons-fixit-...electrical-box
Thanks Nealtw! It's helpful to see what you're talking about.
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Old 12-31-2019, 08:41 AM   #13
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Re: insulating strategy for exterior wall in old home


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In Minnesota, plastic vapor barriers are code, unless you are using spray foam. Minimum 4 mil sheet poly, taped at the seams, sealed to electrical boxes, etc. Used in virtually all new houses for at least the last 25 years that I have been around (again that aren't spray foamed). It's a tried and true system. If it ain't broke, don't fix it.
Do you know whether a vapor barrier is required/recommended for blown in cellulose insulation in our zone? The Cellulose Insulation Manufacturers Association website (https://www.cellulose.org/Cellulose-...ame=HomeOwners) says "CIMA does not recommend the use of vapor barriers with cellulose insulation, except in circumstances of exceptionally high moisture levels, such as an indoor pool facility, or very cold climates." (my own emphasis on the last few words)

I'd think that MN qualifies as a very cold climate! If a vapor barrier is needed, then is it possible to follow this strategy without tearing the plaster off of the walls?
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Old 12-31-2019, 08:53 AM   #14
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Re: insulating strategy for exterior wall in old home


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Do you know whether a vapor barrier is required/recommended for blown in cellulose insulation in our zone? The Cellulose Insulation Manufacturers Association website (https://www.cellulose.org/Cellulose-...ame=HomeOwners) says "CIMA does not recommend the use of vapor barriers with cellulose insulation, except in circumstances of exceptionally high moisture levels, such as an indoor pool facility, or very cold climates." (my own emphasis on the last few words)

I'd think that MN qualifies as a very cold climate! If a vapor barrier is needed, then is it possible to follow this strategy without tearing the plaster off of the walls?
Paint,oil base and water base both have a value for VB. You would have lots of both on the plaster, you would need to seal up spaces that allow air movement from inside. Outlets and switches and balloons are bad for drafts at the floor because there is no bottom plate.

The tricky part of blowing in is those houses have angle braces on every corner blocking some of the spaces.
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Old 12-31-2019, 12:31 PM   #15
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Yes, the plaster can serve as an air barrier. And there is also vapor impermeable primer available. You can also caulk the base trim to the wall and floor etc. In an old house usually you don’t have to worry about condensation in the walls because they are leaky enough that they can dry to the outside.

If you want to pursue this approach best thing would be to call an insulation contractor and have him look at it. He should have a pretty good idea of how a house your age and in your neighborhood is constructed. Most of the old houses I’ve worked on don’t have much for blocking or bracing but of course you never know.

Retrofitting cellulose is a common practice here in the upper Midwest. Drive around and you often see old houses with holes drilled in them (even stucco).

Last edited by Marson; 12-31-2019 at 12:47 PM.
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