# Insulation needs



## beenthere (Oct 11, 2008)

Made this its own thread. So as not to have a confusion of who is being answered.


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## Nealtw (Jun 22, 2017)

It would make it easier if you did the math and said this for X per Sq, ft or that for Y per sq. ft. If you do some outside or extra thickness on the inside you gain a thermal break for the studs.


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## jsmith1107 (Sep 1, 2015)

Well, not sure if you suggested this or not but I am doing like STEPHEN BONFIGLIOLI did in his article "Breaking the Thermal Bridge". I really didn't know what thermal bridging was--so this guy says that with the 1" foam strips under the 1x3 I can get R30? Maybe I should just do the rolled R19 insulation then? 


https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge


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## Bud9051 (Nov 11, 2015)

On the outside you would be covering the framing, top plate, all the way to the foundation so the benefits are even greater. But there are guidelines for how much rigid is required on the outside to ensure the inside surface does not get cold enough to form condensation. Zone 6 with 2x6 walls list r-11.25 is needed, that's about 2" depending upon what brand rigid you use.

But, adding 2" to the exterior is another whole project which kicks it back to just max cavity insulation and my choice would be the mineral wool, plus careful attention to air sealing.

Bud
https://www.greenbuildingadvisor.co...the-minimum-thickness-of-rigid-foam-sheathing


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## jsmith1107 (Sep 1, 2015)

So when you say "plus careful attention to air sealing" could you elaborate? Do you mean vapor barrier on the inside and then house wrap on the outside or?


Thanks


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## Nealtw (Jun 22, 2017)

That is what we do here but it depend on where you are.


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## jsmith1107 (Sep 1, 2015)

Nealtw said:


> That is what we do here but it depend on where you are.



I am in Northern Wisconsin. I have read some information that said something about not putting poly on the inside because of condensation?


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## Nealtw (Jun 22, 2017)

jsmith1107 said:


> I am in Northern Wisconsin. I have read some information that said something about not putting poly on the inside because of condensation?



It is all very confused, condensation in the wall happens when air from the house is warm and moist and it leaks past the drywall, passed the insulation where is cools down and it can no longer hold the moisture. So we sheet everything with poly, seal it to the floor tie it into the same on the ceiling. It is called vapour barrier but really vapour does not get there with out air, we wrap outlet boxes and light boxes and no air can get into the wall.


Bud will be along and tell you something is wrong with plastic because it does something yet unexplained but he will also tell you how important it is to stop all air movement with well fit drywall.
I would talk to the city inspectors and ask them what they think it should be.


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## Bud9051 (Nov 11, 2015)

Vapor barriers are not Needed except in the extremely cold and extremely warm climates and upper WI is close to qualifying for the extremely cold climate. But if you add anything on the outside like rigid foam then no vb on the inside. Also, a layer of plastic on the inside would not be considered your air barrier, although is can contribute to that purpose.

The "careful attention to air sealing" involves a lot of caulking of any seams and/or penetrations. I prefer caulk to can foam and the foam has a shorter life span. 

What type of material is covering the outside surface of your framing, referred to as sheathing, plywood, boards, other?

You mentioned housewrap, that would be a water barrier just under the siding that is designed to be vapor permeable to allow drying to the outside.

For caulking I use the large tubes of construction adhesive. Less expensive and will last forever.

Bud


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> Vapor barriers are not Needed except in the extremely cold and extremely warm climates and upper WI is close to qualifying for the extremely cold climate. But if you add anything on the outside like rigid foam then no vb on the inside. Also, a layer of plastic on the inside would not be considered your air barrier, although is can contribute to that purpose.
> 
> The "careful attention to air sealing" involves a lot of caulking of any seams and/or penetrations. I prefer caulk to can foam and the foam has a shorter life span.
> 
> ...


I really need to understand what air gets past poly?


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## jsmith1107 (Sep 1, 2015)

Nealtw said:


> It is all very confused, condensation in the wall happens when air from the house is warm and moist and it leaks past the drywall, passed the insulation where is cools down and it can no longer hold the moisture. So we sheet everything with poly, seal it to the floor tie it into the same on the ceiling. It is called vapour barrier but really vapour does not get there with out air, we wrap outlet boxes and light boxes and no air can get into the wall.
> 
> 
> Bud will be along and tell you something is wrong with plastic because it does something yet unexplained but he will also tell you how important it is to stop all air movement with well fit drywall.
> I would talk to the city inspectors and ask them what they think it should be.



I do understand what you are saying and my thought was 6 mil vapor barrier on the inside of the wall. I planned on putting Tyvek on the outside of the house as well. I would think if I put the 1" foam under the 1x3's I put on top of them and then mineral insulation, I should be good---actually much better than it is now.


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## Bud9051 (Nov 11, 2015)

Hi js, can you detail what your proposed assembly will look like. Not sure where the 1x3's are going and the 1" of rigid foam.

Also, what foam do you have in mind, foil faced or plain? Even plane 1" is considered a vapor retarder. If on the inside I would question the need for the plastic.

I'll add a link to help explain why I'm not fond of plastic, as it was a mistake from the start.
https://www.buildingscience.com/documents/insights/bsi-073-macbeth-does-vapor-barriers

Bud

Note, we should be adding plastic vapor barriers only under special circumstances and not having to debate removing them from every home. Bad habits are hard to break.


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## Nealtw (Jun 22, 2017)

jsmith1107 said:


> I do understand what you are saying and my thought was 6 mil vapor barrier on the inside of the wall. I planned on putting Tyvek on the outside of the house as well. I would think if I put the 1" foam under the 1x3's I put on top of them and then mineral insulation, I should be good---actually much better than it is now.





What we can all agree on is insulation works best if it is dry and between studs no insulation will stop all the air from passing.
If one side of the wall is sealed from air and the moisture it carries, we don't have drafts and the insulation works as intended. 



We can accept that windows and doors, no matter what quality will have condensation and eventually leak. Maybe that is not always true but it is a good belief to have.
So if you are making a house tight you should look at rain screening. Which is just an installation method that captures water and gives it a path out. 



Sidings like stucco and brick that absorb water have been given a drain plane and a drain path for years and now that same idea is used on all siding to give the back side space to dry, that is also called rain screening. 



So no matter what you do with insulation you want to look at that.


I agree from the outside with a foam board you can get a better coverage for over all the framing members but is is hard to include everything like other framing attached to the house like decks, porches or extra roof against the house.


We don't see a lot of how to's on how to air seal outlets and light fixtures on the outside of a house. 



I think both sides agree that keeping inside air out of the wall is important
and having a hole into an otherwise sealed cavity is no big deal.
But if the house is sealed on the outside it is more important that air cannot travel from one opening to another opening is even more important.
We do better with that now when we fire stop holes for plumbing, wiring and such. 



If I was doing it today I would do the batt between the studs and do 2" foam board on the inside. I would seal that with tape and caulk and I would treat outlets and fixtures just like I would with a poly barrier.


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## Spyder (Jan 11, 2019)

jsmith1107 said:


> Hey everyone--reading this thread and wondering opinions on the below since it is on the same topic basically.
> 
> 
> Insulation needs---R23 Owens Corning Thermafiber MineralWool Insulation Batt 15”x47”. Need 42 ata cost of $24.99 per bag. Cost isroughly $1050 minus 11% rebate ($115.50)=$934.50. To use Fiberglass rolled R19 I would need 15bags of Guardian Unfaced Insulation 15”x39’ at a cost of $21.99 per bag. Cost is roughly $329. To get up to R23 of the Wool Insulation Iwould have to add ¾”X4’x8’ (R4)Owens Corning Foam Board. I would need 30 of these at a cost of $12.81per piece. The cost on this would beroughly $384.30 making my total cost on R19 fiberglass plus ¾” foam board $714 minus11% rebate ($78.54)=$635.46 making a difference of $299 to do wool vs. thecombo of fiberglass and foam board.
> ...


All these guys have good ideas on insulation. I would definitely go with a combo of foam board and either fiber or mineral wool on the inside. The foam will help with the thermal bridgeing.

I think the foam board should be a given, its what you put inside that is the question.

I just bought Mineral wool at home depot at the bulk pricing at $32 per pack for R15, 59sqft. How are you getting such great pricing? I called 2 yards and neither carried the mineral wool, so I finally just bought at HD.

When I did my house, I did 3/4 foam board and R15 fiberglass. I regret not doing foam board then doing a flash and fill with closed cell foam followed by fiberglass. I definitely get air leaks and I feel that would have helped.


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## jsmith1107 (Sep 1, 2015)

Bud9051 said:


> Hi js, can you detail what your proposed assembly will look like. Not sure where the 1x3's are going and the 1" of rigid foam.
> 
> Also, what foam do you have in mind, foil faced or plain? Even plane 1" is considered a vapor retarder. If on the inside I would question the need for the plastic.
> 
> ...



Hey Bud, thanks for the reply. The link below is what I plan on doing. 
I think this explains it really well and breaks the thermal bridge issue. The more I read it, I am not even sure he used poly. Let me know your thoughts please. 


https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge


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## jsmith1107 (Sep 1, 2015)

Nealtw said:


> What we can all agree on is insulation works best if it is dry and between studs no insulation will stop all the air from passing.
> If one side of the wall is sealed from air and the moisture it carries, we don't have drafts and the insulation works as intended.
> 
> 
> ...


Hi Neal, thanks a lot for the reply. When you say the batt between the studs, are you talking the mineral wool or fiberglass? What do you think of the proposed method in this article? https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge 
You would do 2" foam board on the inside in addition to what I have planned from the article above? How would you attach sheetrock to that? And let's say I do the method I am thinking of mineral wool and then like the article says? Would you do poly and seal off all the electrical outlets, etc.?


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## jsmith1107 (Sep 1, 2015)

Spyder said:


> All these guys have good ideas on insulation. I would definitely go with a combo of foam board and either fiber or mineral wool on the inside. The foam will help with the thermal bridgeing.
> 
> I think the foam board should be a given, its what you put inside that is the question.
> 
> ...



Sorry, you did 3/4 foam on the inside or outside? Can you explain what you mean by doing a flash and fill with closed cell foam followed by fiberglass? 


I am buying my insulation at Menards--that's where I got the pricing on it. 


Thanks


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## Nealtw (Jun 22, 2017)

jsmith1107 said:


> Hi Neal, thanks a lot for the reply. When you say the batt between the studs, are you talking the mineral wool or fiberglass? What do you think of the proposed method in this article? https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge
> You would do 2" foam board on the inside in addition to what I have planned from the article above? How would you attach sheetrock to that? And let's say I do the method I am thinking of mineral wool and then like the article says? Would you do poly and seal off all the electrical outlets, etc.?



No I didn't mean both that system would be good, then you could make the wall deep enough to use 5 1/2 inch batts, rock wool or, or, 

I was thinking of the 2" foam instead with the foil face for the barrier. But with that you still loose the break at windows and doors so that system might be better that way. And that still leaves you the question of a vapour barrier. 

Even if you don't do the vapour barrier, I would still treat outlets and lights like I was with the poly wrap so you could apply sealer to it when you drywall and ave no air leaks thru them. 



These are the easiest


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## Bud9051 (Nov 11, 2015)

A little back of hand calculating, but if you calculated the net r-value of a standard 2x6 wall with mineral wool and then compared it to a 2x4 wall padded out to 5.5" as the article describes it would increase the net r-value of that wall assembly by 0.4 r-value. In one case you have the r-value of the wood and in the other 1" of that is replaced by r-4.

Bottom line would be zero difference in interior comfort level and a very small difference in energy costs. if you want i can crank out all of those numbers, that is part of what I do with my energy consulting

Bud


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> A little back of hand calculating, but if you calculated the net r-value of a standard 2x6 wall with mineral wool and then compared it to a 2x4 wall padded out to 5.5" as the article describes it would increase the net r-value of that wall assembly by 0.4 r-value. In one case you have the r-value of the wood and in the other 1" of that is replaced by r-4.
> 
> Bottom line would be zero difference in interior comfort level and a very small difference in energy costs. if you want i can crank out all of those numbers, that is part of what I do with my energy consulting
> 
> Bud


He is also gaining the R5 from changing from a 2x4 to a 2x6 wall.


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## jsmith1107 (Sep 1, 2015)

I have a hard time believing that is all that is gained but I could be wrong. The mineral wool is a better insulator than the fiberglass I would think.


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## Bud9051 (Nov 11, 2015)

The calculation I did was the difference from just increasing the framing to 2x6 (all wood) vs 2x6 with the 1" of foam padding. The benefits of thicker cavity insulation would remain the same, just less effort to pad the 2x4's up to 2x6's with wood as opposed to foam and wood.

Bud


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## Bud9051 (Nov 11, 2015)

An all wood 2x6 would be r-1.25 per inch or r-6.875. Remove 1" and you have 5.625. Add in the r-4 and you have r-9.625, an increase of 2.75.

Since the framing that will be covered is about 15% of the total assembly then the resulting added r-value will 15% of the increase or 0.15 x 2.75 = 0.41.

I can double check by doing it the long way if it concerns you. But reducing the bridging is just that, a reduction the heat loss through a lesser area of the assembly. To do it the long way you would need to give me the % area of the wall that would include the rigid foam.

Bud


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> An all wood 2x6 would be r-1.25 per inch or r-6.875. Remove 1" and you have 5.625. Add in the r-4 and you have r-9.625, an increase of 2.75.
> 
> Since the framing that will be covered is about 15% of the total assembly then the resulting added r-value will 15% of the increase or 0.15 x 2.75 = 0.41.
> 
> ...


I miss understood, you are just talking about the bridge. But. even with R.4 that would still be better than just a 2x2 that I often tell people to do with a 2x4 wall. Or do you think it isn't worse the expense.


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## jsmith1107 (Sep 1, 2015)

Bud9051 said:


> The calculation I did was the difference from just increasing the framing to 2x6 (all wood) vs 2x6 with the 1" of foam padding. The benefits of thicker cavity insulation would remain the same, just less effort to pad the 2x4's up to 2x6's with wood as opposed to foam and wood.
> 
> Bud


Ok, I see what you mean I think. So you are saying adding the 1" foam UNDER the 1x3 or basically 1.75" increase in depth of the cavity really doesn't do much (in terms of insulation) compared to just adding a straight wood piece of 1.75" to the 2x4 itself and taking it out to basically the size of a 2x6 (5.25")?


So the 1" foam really doesn't do much for thermal bridging?


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## Bud9051 (Nov 11, 2015)

It does reduce the bridging, but that is only 15% (estimate) of the wall area. And it isn't as if the wood framing has zero insulation value, it has the 1.25 r-per inch. Log homes love it.

As a note, I try to match standard numbers, like 2x4 = 3.5" and 2x6 = 5.5". With mineral wool it wants to fit nicely in the 5.5" space. More space and it leaves a gap. less space requires a bit of compression and less r-value (based upon the reduced space).

Bud


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> It does reduce the bridging, but that is only 15% (estimate) of the wall area. And it isn't as if the wood framing has zero insulation value, it has the 1.25 r-per inch. Log homes love it.
> 
> As a note, I try to match standard numbers, like 2x4 = 3.5" and 2x6 = 5.5". With mineral wool it wants to fit nicely in the 5.5" space. More space and it leaves a gap. less space requires a bit of compression and less r-value (based upon the reduced space).
> 
> Bud



I think we can agree that most people do insulation to fast. Far better to spend the time cut around obstacles and get a great fit. Drives me nuts when I take a wall apart and see they just pushed it in around outlets and things. There has to be huge % of lost R value when they do that.


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## jsmith1107 (Sep 1, 2015)

Bud9051 said:


> It does reduce the bridging, but that is only 15% (estimate) of the wall area. And it isn't as if the wood framing has zero insulation value, it has the 1.25 r-per inch. Log homes love it.
> 
> As a note, I try to match standard numbers, like 2x4 = 3.5" and 2x6 = 5.5". With mineral wool it wants to fit nicely in the 5.5" space. More space and it leaves a gap. less space requires a bit of compression and less r-value (based upon the reduced space).
> 
> Bud




Sorry, sometimes it takes a little bit to get around what you are saying. So, you are saying go with either the 2x2 added to the 2x4 OR the 1x3 plus 1" foam added to the 2x4, it doesn't make much difference. In terms of mineral wool vs fiberglass, if I read what you are saying correctly, you are saying the mineral wool is the better way to go because of the snugness and less compression it offers? 


Thanks and sorry, just need to say it back sometimes to make sure I have it.


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## Nealtw (Jun 22, 2017)

The R-value of anything only counts if the space is full and fit good, I think most people find rock wool better as it is harder to cheat than with fibreglass. So mostly it is just a matter of craftsmanship.
I think Bud's point was adding the foam and 1x2 or 1x3 has very little benefit over just adding a 2x2.


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## jsmith1107 (Sep 1, 2015)

Nealtw said:


> The R-value of anything only counts if the space is full and fit good, I think most people find rock wool better as it is harder to cheat than with fibreglass. So mostly it is just a matter of craftsmanship.
> I think Bud's point was adding the foam and 1x2 or 1x3 has very little benefit over just adding a 2x2.


I have never worked with rock wool before---when I looked on the website that has it for sale and where I planning on buying it, it lists as 5.5" thick. Was thinking--a 2x4 is 3.5 inches plus the 1" foam plus the 1x3 of .75", that only adds to 5.25". 


So, is rock wool "squishy" enough to fit my space given that it is only 5.25" and not the 5.5" thickness that the rock wool comes as?


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## Nealtw (Jun 22, 2017)

jsmith1107 said:


> I have never worked with rock wool before---when I looked on the website that has it for sale and where I planning on buying it, it lists as 5.5" thick. Was thinking--a 2x4 is 3.5 inches plus the 1" foam plus the 1x3 of .75", that only adds to 5.25".
> 
> 
> So, is rock wool "squishy" enough to fit my space given that it is only 5.25" and not the 5.5" thickness that the rock wool comes as?



I am not sure but I think you end up with the R value of the 5.25 which would be the same as if you could buy a 5.25 thickness. 
But you could go the thicker foam strip.


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## Spyder (Jan 11, 2019)

jsmith1107 said:


> Sorry, you did 3/4 foam on the inside or outside? Can you explain what you mean by doing a flash and fill with closed cell foam followed by fiberglass?
> 
> 
> I am buying my insulation at Menards--that's where I got the pricing on it.
> ...


we did 3/4 foam on the outside.
see link below for flash and fill, basically flash 2" or so of spray foam, then fill the rest of teh space with fiberglass
https://www.buildingscience.com/doc...-wall-flash-and-fill-hybrid-wall-construction


FYI, mineral wool comes in 3.5" deep too.

I see the pricing at Mernards, makes sense, its for less coverage than I was getting per pack.


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## Bud9051 (Nov 11, 2015)

You could buy 1.5" rigid and cut 1.25" strips so the 3/4 would bring you out to the 5.5" depth to match the 5.5" mineral wool.

As for fitting the 5.5" batts into a 5.25" space very easy, they come all squished in that bundle. The difference in r-value would be 5.25 divided by 5.5 or 95% of rated value. If that rated value is r-23 then you end up with r-22.

Bud


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## jsmith1107 (Sep 1, 2015)

Thanks a lot---I will do that I think.


Would it hurt if I put 1.5" foam behind and then I would have like a 1/4" gap? Does the gap hurt anything?


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## Bud9051 (Nov 11, 2015)

Personally I would avoid the gap if possible, but doubt it would make any difference.

Bud


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## DallasCowboys (Jan 30, 2017)

Bud9051 said:


> For caulking I use the large tubes of construction adhesive. Less expensive and will last forever.
> 
> Bud



Construction adhesive can be used instead of caulk?
I never considered that ...
Is it done often, do they have different colors like caulk?
Is it used around windows too?


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## Bud9051 (Nov 11, 2015)

I use it strictly in the framing areas. If it will be exposed then use a caulk which would give you color options and paitable. I'm just a penny pincher and usually have the construction adhesive around.

Bud


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