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Old 03-22-2019, 10:32 AM   #16
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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.

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/201...thermal-bridge
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Old 03-22-2019, 10:38 AM   #17
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Re: Insulation needs


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Originally Posted by Nealtw View Post
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.
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/201...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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Old 03-22-2019, 10:43 AM   #18
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Re: Insulation needs


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Originally Posted by Spyder View Post
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.

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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Old 03-22-2019, 11:22 AM   #19
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Re: Insulation needs


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Originally Posted by jsmith1107 View Post
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/201...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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Old 03-22-2019, 11:41 AM   #20
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Re: Insulation needs


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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Old 03-22-2019, 11:53 AM   #21
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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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Old 03-22-2019, 11:56 AM   #22
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Re: Insulation needs


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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Old 03-22-2019, 12:05 PM   #23
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Re: Insulation needs


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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Old 03-22-2019, 12:18 PM   #24
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Re: Insulation needs


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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Old 03-22-2019, 12:26 PM   #25
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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
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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Old 03-22-2019, 12:30 PM   #26
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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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Old 03-22-2019, 12:48 PM   #27
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Re: Insulation needs


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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Old 03-22-2019, 12:57 PM   #28
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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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Old 03-22-2019, 12:58 PM   #29
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Re: Insulation needs


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Originally Posted by Bud9051 View Post
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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Old 03-22-2019, 01:10 PM   #30
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Re: Insulation needs


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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