# insulating strategy for exterior wall in old home



## brian85 (Dec 21, 2019)

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. :crying: 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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## Nealtw (Jun 22, 2017)

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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## brian85 (Dec 21, 2019)

Nealtw said:


> 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.
> ...


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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## Nealtw (Jun 22, 2017)

brian85 said:


> 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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## carpdad (Oct 11, 2010)

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.:smile: 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.:smile:


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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## Marson (Jan 26, 2018)

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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## NotYerUncleBob2 (Dec 29, 2017)

brian85 said:


> 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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## Nealtw (Jun 22, 2017)

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-database/1428-What-is-an-air-tight-electrical-box


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## Marson (Jan 26, 2018)

NotYerUncleBob2 said:


> 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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## Porsche986S (Dec 10, 2017)

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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## chandler48 (Jun 5, 2017)

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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## brian85 (Dec 21, 2019)

Nealtw said:


> 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-database/1428-What-is-an-air-tight-electrical-box


Thanks Nealtw! It's helpful to see what you're talking about.


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## brian85 (Dec 21, 2019)

Marson said:


> 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-Insulation-2nd.php?pagename=AirVaporBarriers&dirname=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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## Nealtw (Jun 22, 2017)

brian85 said:


> 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-Insulation-2nd.php?pagename=AirVaporBarriers&dirname=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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## Marson (Jan 26, 2018)

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).


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## brian85 (Dec 21, 2019)

Porsche986S said:


> 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 .


 I pulled a piece of siding off and found white sheets of thin (approx 1/4") insulation sheets. They overlapped and I didn't get to the bottom of them. I probably should dig further down? The nails holding them on were 3" long, and based on how easily they pulled out, the were not in much lumber. 

Was it common to insulate in this way when putting vinyl siding on a very old house?


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## APA (Jul 13, 2018)

brian85 said:


> I pulled a piece of siding off and found white sheets of thin (approx 1/4") insulation sheets. They overlapped and I didn't get to the bottom of them. I probably should dig further down? The nails holding them on were 3" long, and based on how easily they pulled out, the were not in much lumber.
> 
> Was it common to insulate in this way when putting vinyl siding on a very old house?



I would just go for the attic. There are too many unknowns in those walls. 110 years says a lot.


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## APA (Jul 13, 2018)

Insulate the attic and install a coal stove for winter. You can make it as hot or cold in that house as you want.


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## APA (Jul 13, 2018)

brian85 said:


> I pulled a piece of siding off and found white sheets of thin (approx 1/4") insulation sheets. They overlapped and I didn't get to the bottom of them. I probably should dig further down? The nails holding them on were 3" long, and based on how easily they pulled out, the were not in much lumber.
> 
> Was it common to insulate in this way when putting vinyl siding on a very old house?



I would just go for the attic. There are too many unknowns in those walls. 110 years says a lot.


I just don't think tearing into walls during a Minnesota winter is a good idea. Wait til spring.


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## brian85 (Dec 21, 2019)

APA said:


> Insulate the attic and install a coal stove for winter. You can make it as hot or cold in that house as you want.


Thanks APA! Just curious: Do you generally believe that insulating the walls of an old house isn't worth it? Or are you saying that since there's some insulation on the exterior of the walls, then insulating the walls further isn't worth it?


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## APA (Jul 13, 2018)

brian85 said:


> Thanks APA! Just curious: Do you generally believe that insulating the walls of an old house isn't worth it? Or are you saying that since there's some insulation on the exterior of the walls, then insulating the walls further isn't worth it?



I was being a little facetious there. When I was a kid, we would build coal stove fires so hot that the stovepipe would glow orange and the grates would melt. I am not a professional. I just have always read that the attic is where you will see the most benefit. I have also helped in enough old houses to know that digging into the walls is looking for trouble. I also know that the house has lasted this long that waiting several more months for better weather is the best course of action than ripping into a house in cold weather. Use these months to get your ducks in a row and start the work in spring...unless there is something dangerous going on that needs immediate attention.


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## Marson (Jan 26, 2018)

brian85 said:


> I pulled a piece of siding off and found white sheets of thin (approx 1/4") insulation sheets. They overlapped and I didn't get to the bottom of them. I probably should dig further down? The nails holding them on were 3" long, and based on how easily they pulled out, the were not in much lumber.
> 
> Was it common to insulate in this way when putting vinyl siding on a very old house?


 Yes, pretty common to find some sort of foam insulation under vinyl siding. Hard to say for sure, but I wonder if that is insulated vinyl siding. They still sell that at Menards https://www.menards.com/main/buildi...yl-siding/vmti4000/p-1444437127943-c-5838.htm Nowadays they use "fanfold" which is a 1/4" foam underlayment. Pretty limited insulation value, but it does serve as a pad to make the vinyl go on easier. There could well be a layer of old wood siding under there too.


Kind of moot really, if your house is drafty and you know from looking from the inside that the stud cavities are empty, you ought to insulate them. Again, it is done all the time. I spent 10 years remodeling old houses in Duluth, and it was fairly rare to find one that WASN'T dense packed with cellulose at some time. Very common practice. Whether you do it piecemeal from the inside or just spend the money and get it over with from the outside is up to you.


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## APA (Jul 13, 2018)

Marson said:


> Yes, pretty common to find some sort of foam insulation under vinyl siding. Hard to say for sure, but I wonder if that is insulated vinyl siding. They still sell that at Menards https://www.menards.com/main/buildi...yl-siding/vmti4000/p-1444437127943-c-5838.htm Nowadays they use "fanfold" which is a 1/4" foam underlayment. Pretty limited insulation value, but it does serve as a pad to make the vinyl go on easier. There could well be a layer of old wood siding under there too.
> 
> 
> Kind of moot really, if your house is drafty and you know from looking from the inside that the stud cavities are empty, you ought to insulate them. Again, it is done all the time. I spent 10 years remodeling old houses in Duluth, and it was fairly rare to find one that WASN'T dense packed with cellulose at some time. Very common practice. Whether you do it piecemeal from the inside or just spend the money and get it over with from the outside is up to you.





I agree about just paying to have it done all at once. I piecemealed our attic project and the house has been torn up to one degree or another for 3 years and it still isn't finished. Pros will have it done and done right before you can even rent the machine. Just get a few quotes...


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## brian85 (Dec 21, 2019)

There's one room in the house that didn't have any plaster or drywall up - just some old insulation. I'm planning to install R15 fiberglass insulation into its 2x4 wall. There a black paper lining the outside of each stud cavity. Reminds me of tar paper. Behind this black paper are horizontal boards that are 3-4 inches wide. I'm not sure if they used to be the exterior siding or if they were just the foundation for the siding. As I noted earlier, currently there's vinyl siding, and I'm not sure what's underneath it (or what the original siding was). 
So here's my question: should I be installing anything on the exterior side of the fiberglass insulation? For example, I could put some Tyvek wrap in each 15" cavity.


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## brian85 (Dec 21, 2019)

ah, just found this related thread

https://www.diychatroom.com/f103/installing-tyvek-barrier-inside-walls-168397/


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## Missouri Bound (Apr 9, 2011)

If you intend to rip off the plaster and expose the studs there is always foam.
It seals everything up and eliminates the need for a vapor barrier.
Although many think the attic is where all the heat goes it amounts to only 30 to 40% of heat loss. Most heat is lost through walls and poorly insulated windows.
The attic zone is a buffered zone with an tempered air space when ceilings are not insulated.
Exterior walls get the brunt of the wind and thermal exposure. If you intend to remove wall covering there is always foam. But the "rock wool" type of insulation is also very good since you can easily cut it to fit exactly. Paper or foil backed insulation is now as easily to work with if you have irregular stud spacing.


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## Calson (Jan 23, 2019)

You need to have insulation blown into the walls. The choice becomes making the hole on the outside or the inside of the house. With vinyl siding I would make the holes on the inside of the house. Be sure that the quote includes plugging the holes properly by the contractor and check out at least one other job that his people have done to see the level of workmanship.

Adding insulated siding adds negligible R-value and is a waste of money with a payback of more than a century.


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## brian85 (Dec 21, 2019)

Calson said:


> You need to have insulation blown into the walls. The choice becomes making the hole on the outside or the inside of the house. With vinyl siding I would make the holes on the inside of the house. Be sure that the quote includes plugging the holes properly by the contractor and check out at least one other job that his people have done to see the level of workmanship.
> 
> Adding insulated siding adds negligible R-value and is a waste of money with a payback of more than a century.


Thanks Carlson. I'm pretty set on putting fiberglass into this room since I have interior access to the studs. Would you advise to put some sort of barrier like Tyvek on the exterior side of the stud cavity? Or just throw the fiberglass up against the old wooden siding?


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## Calson (Jan 23, 2019)

This is not a simple question as there can be problems with mold if moisture is trapped inside the walls. If the drywall is removed from the studs then adding two-part closed cell foam is a good way to go as it seals air leaks and has double the effective R-value of any kind of standard insulation. An inch of foam has about the same insulating effectiveness as 3 inches of fiberglass insulation in actual practice. 

Important to understand that the times specified for re-entering a space where the foam has been applied assume a certain number of complete air changes in the space (with the outside air brought in and the inside contaminated air exhausted outside of the house along with the very harmful fumes. A manufacturer may state that a space is safe to occupy 4 hours after spraying but in reality when you run the numbers it is going to me more than 24 hours at a bare minimum.

With blown in insulation at least two holes per stud bay need to be made in the walls so you can see that a lot of holes need to be made and then patched.

The EPA produces an excellent guide to sealing and insulating a house and it is not biased toward any particular approach. Don't overlook the benefits from sealing any air gaps in the attic around light fixtures and ceiling fans and air vents and other ceiling penetrations.


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## brian85 (Dec 21, 2019)

Another insulating issue in my house is the knee walls. In all 4 corners of the 2nd level there's a 4' high knee wall followed by a 6' slanted ceiling. Both the knee walls and slanted ceilings are uninsulated. I'm having my roof replaced within a couple of months, and I had been planning to use spray insulation on these 2 places. But this will require ripping up the deck boards on the roof and hiring a spray foam guy. The distance between the slanted ceiling to the roof decking is not much (if any) more than a 3.5", and I still need this space to provide ventilation to the attic, so I could only spray roughly 2" of spray foam (but only between the rafters).
But then I had an idea ... How crazy/feasible is it to put a foam board - probably 1" or 2" - on these 2 surfaces on the *interior? *I mean right on top of the lathe&plaster walls/ceiling!* If *doing so, better to use XPS or polyiso? If I did that, I was imagining putting drywall over the foam board. Here are the pros & cons of this alternative idea. Let me know what you all think!
*Pros*: easier, cheaper than alternative, no thermal bridging on the rafters, no coordination needed between roofer and spray foam guy, better air flow into the attic
*Cons*: lose living space, R-value *might *not be as high as alternative, and seems kinda hackish


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## brian85 (Dec 21, 2019)

I'm a few weeks away from blowing cellulose into my attic, which is located above a basement, main level, and second level. Currently my walls don't have any insulation (*very* old house). While I'm at it, does it makes sense to blow as much cellulose down the balloon-framed walls as I can? I think so, but wanted to check if I'm under-thinking something. I'll have access to over 30' of wall cavity. There isn't a different type of cellulose used for walls vs type used in an attic? Currently there are spots in the attic where you can drop a penny between the studs down to the main level!


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## Missouri Bound (Apr 9, 2011)

Insulate the walls as best as you can.
Remember that attic spaces contribute to only about 30% of heat loss/gain.
The other 70% is wall, windows, doors etc.


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## brian85 (Dec 21, 2019)

Missouri Bound said:


> Insulate the walls as best as you can.
> Remember that attic spaces contribute to only about 30% of heat loss/gain.
> The other 70% is wall, windows, doors etc.



Thanks! But I'm not sure what you're saying about my question of whether it makes sense to blow as much cellulose down the balloon-framed walls as I can?


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## Missouri Bound (Apr 9, 2011)

I would fill them up.
Just make sure that the bottom of the balloon framing is sealed so you don't fill up the basement.
Whatever you do will eventually settle even if only a little bit.

And I don't think you are under thinking...perhaps just the opposite.
Insulation will help no matter where it winds up.


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## brian85 (Dec 21, 2019)

brian85 said:


> 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. :crying: 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:
> ...


I was thinking about this more, and I realize that I forgot to mention that between the vinyl siding is approximately 1" of EPS rigid insulation (not sure its perm value) that was simply sandwiched between the original wooden lap siding and the new vinyl. Since the both the lap siding and vinyl siding is not flat, the "fit" between these sidings and the EPS is not very tight and I'm sure that air moves around a fair bit. 

Should I be concerned that when I add insulation to the stud cavity with a moisture barrier on the inside, that I've created a situation with a vapor barrier on both sides of my wall? I don't *think* so, because EPS is not a good vapor barrier, but I'd appreciate others' thoughts!


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## Nealtw (Jun 22, 2017)

brian85 said:


> I was thinking about this more, and I realize that I forgot to mention that between the vinyl siding is approximately 1" of EPS rigid insulation (not sure its perm value) that was simply sandwiched between the original wooden lap siding and the new vinyl. Since the both the lap siding and vinyl siding is not flat, the "fit" between these sidings and the EPS is not very tight and I'm sure that air moves around a fair bit.
> 
> Should I be concerned that when I add insulation to the stud cavity with a moisture barrier on the inside, that I've created a situation with a vapor barrier on both sides of my wall? I don't *think* so, because EPS is not a good vapor barrier, but I'd appreciate others' thoughts!


Have you looked behind the vinyl to see if the foam board was taped or covered with a wrap?


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## brian85 (Dec 21, 2019)

Nealtw said:


> Have you looked behind the vinyl to see if the foam board was taped or covered with a wrap?


It is not covered or wrapped in all of the various places I've seen.


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## Nealtw (Jun 22, 2017)

brian85 said:


> It is not covered or wrapped in all of the various places I've seen.


Have you seen tape on the joins of the board. How likely will water get passed the vinyl and the foam to wet the wall?


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## brian85 (Dec 21, 2019)

Nealtw said:


> Have you seen tape on the joins of the board. How likely will water get passed the vinyl and the foam to wet the wall?


I think it's pretty unlikely, especially since the EPS seems to be in multiple sheets (that sum to about 1") and in the unlikely event that rain does get past the EPS, it's still outside the lap siding.


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## Nealtw (Jun 22, 2017)

brian85 said:


> I think it's pretty unlikely, especially since the EPS seems to be in multiple sheets (that sum to about 1") and in the unlikely event that rain does get past the EPS, it's still outside the lap siding.


Do you use heat more than AC where you live?


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## brian85 (Dec 21, 2019)

Nealtw said:


> Do you use heat more than AC where you live?


Yeah, I'm in Minnesota.


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## Nealtw (Jun 22, 2017)

brian85 said:


> Yeah, I'm in Minnesota.


Your bigger concern is air leaking into the wall from the inside. For years we had to leave gaps in the sheeting outside and drill holes under windows. 
Now they have decided that venting is not required but i wouldn't worry about small leaks to the outside.


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## P_Vilefort (Sep 5, 2021)

brian85 said:


> 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. :crying: I'm located in Minneapolis, which is climate zone 6.On the house's exterior there's vinyl siding.
> 
> 
> 
> ...


In the period that your home was built it was very common to use fire stops in the walls. The house I grew up in was built in 1920 and when I built an addition using the long porch on one side, for my father we found fire stops in the first floor framing. This early edition became the starting point for a later first floor bedroom, bathroom and outside porch addition when my parents no longer wanted to climb the stairs to the second floor. The exterior framing was shiplap tightly nailed together. On the outside was 30# felt and then 12 inch wide Washington red cedar board siding with a 5 inch exposure. So the original siding was overlapped 7 inches. When my father bought the house in 1953 he had the original siding covered with cement board siding. Some homes in this time period depending upon where in the USA they were built might have had ship lap only in the corners of the framing and 1 inch thick fiber board sheathing where the outside was either asphalt coated or wax impregnated. In fact in New York state this was still being used in the 1970s.

I suggest that you get a fiber optic scope and do some exploring in the walls before tearing into the walls. Plaster wall are wonderful for allowing vapor to pass through without trapping moisture. In my house the plaster was built up starting with steel mesh reinforced cement board about 1/2 to 3/4 inch thick, covered by galvanized steel expanded mesh nailed through to the studs and covered roughly with cement mortar and this was then covered with plaster. We found out this when my father removed the French doors from the hall near the front door and the stairs to the second floor. With the scope you can better determine what sheathing was used on the house and if it has fiber board sheathing you can figure out where it starts and stops. If you have board sheathing you can insulate with blown-in fiber glass. I would be very careful with anything blown-in with moisture. The fiberboard sheathing, if used would be in the middle portions of the exterior walls. The corner framing would be boards at an angle to the vertical framing.

I would not be surprised if under the vinyl and thin insulation that was used with the vinyl you have cedar lapped siding. If the siding shows lots of chipped paint or paint that looks like it was blistering, then you have evidence of siding that wasn't primed and painted on the backside. Moisture was coning through the wood and pushing off the paint. If you can manage to get off the siding without breaking it, you can reuse it or sell it. That cedar siding is very valuable. If you are residing use Hardie fiber cement siding. It is considered the best in the industry.

Plaster walls are superior to sheet rock. If you are going to really do this right you should do all the work from the outside. Remove the vinyl and carefully remove the cedar plank siding. Then remove the shiplap sheathing or fiber board sheathing. If the shiplap is only in the exterior corners only remove what you actually need to if rewiring. That corner material is keeping the vertical timbers straight. Rewire if you want to, though if you find armored wiring you may want to rethink the rewire. We were going to rewire my father's house until we discovered the armored wire and then discovered that the wire was much larger than what modern codes require, so the only wiring we changed was that needed for the 240 volt wiring. The armor is the ground so most of the time there are only two insulated wires. You can insulate the wall space with unfaced batts like Rockwool. This stuff is nice because it will not absorb water and it doesn't support combustion so it acts as a firestop. You will end up with R15 in the walls. Put on new plywood sheathing, seal the joints, apply a house wrap and then put on furring strips that align with the studs. You can now put foam board on the furring strips. The furring strips give an air and ventilation space for any condensation. You would then use 3/8 inch thick furring strips (plywood) between the foam board and the siding which is the outer most layer. If you seal the foam board joints and any perforations by wiring or pipes, you will end up with a tight sealed envelope. The foam board will take the place of a rain barrier and the furring strips will provide an air space for ventilation in the event wind driven water gets behind the siding.
See this Building Science article: Mind the Gap BSI-038: Mind the Gap, Eh! Note that the foam board should sit on a flashing to protect the edge of the foam from burrowing insects or creatures. The gaps are maintained at the top and bottom of the air space by corrugated plastic in the thickness of the airspace. A finer mesh screening can be applied to the outside ends of the corrugated plastic to prevent insects from using the tubes for nests and to prevent mud daubers (wasps) from plugging the tubes.
See this too for additional information especially on the right hand column: BSI-001: The Perfect Wall


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