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Old 03-21-2019, 04:44 PM   #1
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Insulation needs


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.
Would you even waste the time of having to do 2 different applications of insulation (both inside and outside) for $299 and go with the wool insulation or should I just put R19 rolled insulation in between the studs and be done with it? Will I save that much in Energy costs over the long haul? I am in upper Wisconsin by the way. I should also state that I currently have 2x4 walls and am adding 1x3's plus a strip of 1" foam board to the existing 2x4's to get them to 2x6.


Thanks!

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Old 03-21-2019, 05:33 PM   #2
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Re: Insulation needs


Made this its own thread. So as not to have a confusion of who is being answered.
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Old 03-21-2019, 05:47 PM   #3
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Re: Insulation needs


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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Old 03-21-2019, 05:56 PM   #4
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Re: Insulation needs


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/201...thermal-bridge

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Old 03-21-2019, 06:01 PM   #5
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Re: Insulation needs


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.com...foam-sheathing
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Old 03-21-2019, 07:40 PM   #6
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Re: Insulation needs


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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Old 03-21-2019, 07:45 PM   #7
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Re: Insulation needs


That is what we do here but it depend on where you are.
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Old 03-21-2019, 07:50 PM   #8
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Re: Insulation needs


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Originally Posted by Nealtw View Post
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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Old 03-21-2019, 08:05 PM   #9
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Re: Insulation needs


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Originally Posted by jsmith1107 View Post
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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Old 03-21-2019, 08:06 PM   #10
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Re: Insulation needs


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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Old 03-21-2019, 08:11 PM   #11
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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
I really need to understand what air gets past poly?
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Old 03-21-2019, 08:35 PM   #12
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Re: Insulation needs


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Originally Posted by Nealtw View Post
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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Old 03-22-2019, 06:33 AM   #13
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Re: Insulation needs


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/docu...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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Old 03-22-2019, 09:00 AM   #14
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Re: Insulation needs


Quote:
Originally Posted by jsmith1107 View Post
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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Old 03-22-2019, 09:22 AM   #15
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Re: Insulation needs


Quote:
Originally Posted by jsmith1107 View Post
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.
Would you even waste the time of having to do 2 different applications of insulation (both inside and outside) for $299 and go with the wool insulation or should I just put R19 rolled insulation in between the studs and be done with it? Will I save that much in Energy costs over the long haul? I am in upper Wisconsin by the way. I should also state that I currently have 2x4 walls and am adding 1x3's plus a strip of 1" foam board to the existing 2x4's to get them to 2x6.


Thanks!
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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