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Old 11-15-2017, 07:05 AM   #1
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Replace wall insulation?


Renovating a bathroom in the corner of the second floor, so there are two exterior walls. House was built in 1968, 2x4 walls, and insulated with R13 fiberglass. Question I have is since I have the drywall off is it worthwile to replace the insulation? Some of the batts are faced with a paper/foil and others are not. My concern is that since not all batts are faced that I do not have a proper vapor barrier. But since I am not going to pull down all of the walls in the house, I am wondering how much benefit I will get from doing an 8' and an 11' wall in a 2500 sqft house.

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Old 11-15-2017, 07:40 AM   #2
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Re: Replace wall insulation?


What ever best practice is for your area. Do a room or wall when you can, you never know what will happen and for a couple bucks you would hate to have the room with most of the moisture the only room not done.
Any other room I would say to add to the wall for more insulation but being a bathroom you likely can't do that.
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Old 11-15-2017, 07:40 AM   #3
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Re: Replace wall insulation?


If you don't see any signs of deterioration of the structure by not having some of the batts faced don't bother replacing it being it's been that way since 1968. Any change in R value would be negligible.

If it would make you feel you've done your very best and get a better night's sleep, by all means remove and replace. If you replace consider the 2x4 edges would like to have a vapor barrier too. That's what those flaps are for.
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Old 11-15-2017, 08:27 AM   #4
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Re: Replace wall insulation?


Since your house was built they have osculated between needing and not needing a vapor barrier. Currently it is more on the "not" side. They have also determined that the facing on fiberglass insulation isn't a very good VB, more like a vapor diffusion retarder of some unknown value. The good news is, what you have will do just fine.

Being a bathroom and your somewhat cold location installing a VB might be desirable. Simply use unfaced batts and cover with a sheet of plastic.

But, here comes the real opportunity. Replacing the old insulation will allow you to upgrade to R-15 (I prefer Roxul but they also make high density R-15 fiberglass) and air seal those cavities very well. A typical omission is insulation in the corner which will be difficult to inspect but if it is void then can foam is your friend. They make a large gap version but be patient so you don't overfill. You will want the warmest day possible for can foam.

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Old 11-16-2017, 04:42 PM   #5
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Re: Replace wall insulation?


Your r-13 fiberglass is unlikely actually r-13, probably closer to r11.

You should put a proper vapour barrier on the warm side sealed to the framing - not just stapled, cuts down on leakage and prevents condensation.

For insulation to do it's job well, there can't be air movement due to leakage.

The plastic vapor barrier over the entire wall assembly improves thermal performance of the wall, stops air movement through the wall, so you get rated r-value.

R-value of fiberglass with a lot of air movement is zero!

Only rigid foam insulation and dense packed cellulose stop air movement and can do well without a vapour barrier. (for cellulose dense packed without vapour barrier, you need good drying potential as it's not perfect)

It's air movement that causes condensation issues in walls. Air carries moisture which hits cold surfaces as it leaks out causing condensation. Have poor drying potential to the outside, and moisture accumulates, leading to structural rot.

It was thought at one point that vapor gets into walls mostly by diffusion through the wall material. Now we know, diffusion is not a very significant factor.

It's air movement.
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Old 11-16-2017, 04:53 PM   #6
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Re: Replace wall insulation?


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It's air movement that causes condensation issues in walls. Air carries moisture which hits cold surfaces as it leaks out causing condensation. Have poor drying potential to the outside, and moisture accumulates, leading to structural rot.

It's air movement.
Do you really need a vapour barrier to have an air barrier though? Doesn't painted dry wall act as an air barrier?

I didn't think you'd have much air flow through painted drywall - unless you have protrusions like plumbing pipes, light fixtures etc. - which can be caulked to block air.
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Old 11-16-2017, 05:12 PM   #7
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Re: Replace wall insulation?


There's leakage through cracks, gaps, penetrations. There's a gap at the floor covered with trim.

Can caulk trim but better, more effective to just have a properly done air/vapor barrier.

Don't think drywall or plaster is super air tight even if painted.

The plastic air/vapor barrier is brought right up to the electrical boxes and is also sealed to the framing with acoustic sealant. Seams have to be tuck taped as well.

You can look up how vapor barrier is done around these penetrations.

If the wall is open anyhow, why not bring it up to modern air tight standards?

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But, here comes the real opportunity. Replacing the old insulation will allow you to upgrade to R-15 (I prefer Roxul but they also make high density R-15 fiberglass)
If you do the math, the energy savings from going from R11ish fiberglass to R15 aren't that great, probably not enough to justify the cost of new batts. Especially considering the r-value of the studs.

Once you have insulation in there, the greatest savings comes from having a tight wall assembly and reducing thermal bridging.

Where I am builders are starting to put rigid insulation on the outside to reduce thermal bridging. But we have some of the strictest energy codes in north america for new builds.
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Old 11-16-2017, 06:04 PM   #8
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Re: Replace wall insulation?


Here's one discussion on vapor barriers and it has a list of related articles.
http://www.greenbuildingadvisor.com/...stop-air-leaks

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Old 11-16-2017, 06:13 PM   #9
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Re: Replace wall insulation?


People who think a barrier is not needed should open walls and see the dirty insulation where wet moist dirty air has gone thru any and every hole it can find.
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Old 11-16-2017, 06:27 PM   #10
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Re: Replace wall insulation?


I agree, air sealing is a must, but additional vapor barriers are no longer considered necessary. For the op living in S.E. MI I'm not certain their climate meets the extreme cold that would suggest one. But, being a bathroom and maybe cold enough adding a layer of plastic won't hurt.

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Old 11-16-2017, 06:35 PM   #11
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Re: Replace wall insulation?


Quote:
Originally Posted by Bud9051 View Post
I agree, air sealing is a must, but additional vapor barriers are no longer considered necessary. For the op living in S.E. MI I'm not certain their climate meets the extreme cold that would suggest one. But, being a bathroom and maybe cold enough adding a layer of plastic won't hurt.

Bud
We have to have vent holes in the sheeting so the barrier is a must.
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Old 11-16-2017, 07:10 PM   #12
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Re: Replace wall insulation?


Quote:
Originally Posted by Bud9051 View Post
I agree, air sealing is a must, but additional vapor barriers are no longer considered necessary. For the op living in S.E. MI I'm not certain their climate meets the extreme cold that would suggest one. But, being a bathroom and maybe cold enough adding a layer of plastic won't hurt.

Bud
A wall assembly insulated with batts with a well done plastic air/vapour barrier will perform much better than one without one and some air sealing.

Batts really suck at stopping air movement; their r-value only applies when both the hot and cold side are impermeable to air. You won't get the exterior side impermeable on a 1960s house unless the exterior veneer is removed is and tyvec or rigid foam are put on the sheething.


(rigid foam on outside may create problems by eliminating drying potential. however, since it's a complete thermal break, walls done like this may not have condensation issues.)

granted, a house of this age may have tar paper which is helpful.


Local codes over-ride everything though. Where I am they're required.

In the states some areas may have weak energy efficiency codes, allow no barrier. (likely the same states where silly paper backed insulation is used - we never got that crap up here)
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Old 11-16-2017, 10:07 PM   #13
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Re: Replace wall insulation?


When highly respected engineers and scientists can write comments like this I tend to follow their advice.
" Vapor barriers are also a cold climate artifact that have diffused into other climates more from ignorance than need. The history of cold climate vapor barriers itself is a story based more on personalities than physics. Rose (1997) regales readers of this history. It is frightening indeed that construction practices can be so dramatically influenced by so little research and reassuring indeed that the inherent robustness of most building assemblies has been able to tolerate such foolishness."
Ref: https://buildingscience.com/document...vapor-barriers

Strong words and an example of how views on vapor barriers have changed.

We are each entitled to read and judge for ourselves what approach we want to follow, just as many local code authorities have done. My take on vapor barriers has been, if codes require them don't fight city hall and I believe much of Canada still requires them. But in the lower states the majority of the guidance now omits their use until you venture into the deep south where they go to the outside because air conditioning has replaced all need for heating.

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Old 11-17-2017, 11:23 AM   #14
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Re: Replace wall insulation?


There's been research showing the r-value of fiberglass when you have air currents is much lower than rated.

Even if you don't need the barrier to stop condensation in some climates, it's a vital tool in making the wall tight so the insulation can do it's job properly.

I'm thinking in terms of reducing energy use, not just preventing rot to structure.

The writer of the article only seems to be interested in protecting the wall assembly from water, not thermal performance.

Whether put on the outside in a hot and humid climate or on the inside in a cold climate, it helps make the house perform better.

Terms vapour barrier and air barrier are used interchangeably, but it's the air barrier properties that them useful both for stopping condensation in cold climates and for reducing air movement leakage through walls.

It's true, use a vapour/air barrier incorrectly and it can create problems; you need to have drying potential on whatever side the barrier isn't used on.
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Old 11-17-2017, 12:57 PM   #15
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Re: Replace wall insulation?


I'm fully aware of the performance reduction when air is allowed to enter or pass through a wall assembly. Neal (post #11) stated in BC they drill holes in the outside sheathing for ventilation and I have no idea why but down here we don't. But expecting a vapor barrier to do double duty is risky as VBs rarely make it through the construction process without a lot of unintended holes and an air barrier needs to be rigid.

"The writer of the article [Dr. Lstiburek] only seems to be interested in protecting the wall assembly from water, not thermal performance." If you check his credentials you will see he hails from your side of the border:
https://buildingscience.com/users/joseph-lstiburek
"Dr. Lstiburek’s commitment to advancing the building industry has had a lasting impact on building codes and practices throughout the world, particularly in the areas of air barriers, vapor barriers, and vented and unvented roof assemblies. For example, his work with industry partners through the Department of Energy’s Building America program led to significant research into the wetting and drying of walls and ultimately to a major code change relaxing the requirement for vapor barriers in the International Residential Code."

So a Canadian contributed to "relaxing the requirement for vapor barriers".

Disagreeing with me is easy, but Dr. Lstiburek has a considerable background in energy science.

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