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Insulating an exterior wall of a brick house with fiberglass batts

Insulating an exterior wall of a brick house with fiberglass batts

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  #1  
Old 01-12-14, 07:21 AM
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Insulating an exterior wall of a brick house with fiberglass batts

My house is a single-story (load-bearing) brick structure where the interior drywall is attached to the exterior brick wall with furring strips as opposed to a 2x stud wall. There are then about 2-inch thick batts of faced fiberglass stuffed between the furring strips.

From within the attic, I can readily feel/see the batts of fiberglass because there is no horizontal (wooden) member over the top of the furring strips, so the wall acts more like a chase (since fiberglass is air permeable).

I am wondering if there should be something at the top to block airflow & improve the overall air tightness of the structure as a whole? I believe the insulation was added to the exterior walls after the fact (probably in the 70s)...but was it done properly?
 

Last edited by IBreakStuff; 01-12-14 at 10:11 AM.
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  #2  
Old 01-12-14, 08:18 AM
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That thin an insulation would be useless. I'd guess it's also been compressed so it's even less effective.
And yes there should have been something horizontal to stop the air flow and act as a fire stop.
Would have been better to have used blue foam or better yet build a wall behind the brick wall.
Ever notice darker vertical areas on the sheetrock caused from thermal bridging?
 
  #3  
Old 01-12-14, 10:10 AM
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Yes, from my research it appears faced fiberglass behind a brick wall is the worst way to insulate that wall, but redoing the insulation is just out of the question. Are you saying a couple inches of fiberglass is useless namely since it doesn't provide much R-value, or are you saying it's useless based on how it was installed?

I haven't visibly noticed anything from the interior, but under IR, I attached what the walls look like near the wall/ceiling corners; definite cold spots vertically & horizontally.

What would you recommend as the most logical/cost-effective fix to stop the airflow at the top? My guess would be cutting out some XPS to cover the gap & foaming it in (after I install some baffles for the soffit vents). Low pitch hip roof too.
 
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  #4  
Old 01-12-14, 11:33 AM
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Those vertical and horizontal "leakage" lines are from the wood framing (no a good insulating material). The framing is a thermal "short circuit" that is common to all materials used to fill the spaces. It is good you do not have steel studs.

Some XPS and foam for an adhesive would certainly cut down the vertical drafting and void circulation.

Obviously, a layer of poly ISO attached to the studs would cut the thermal short circuiting, but that would mean removing the interior drywall and then replacing it.

Thermal imaging can be somewhat misleading when looking from the outside. After a clear cold day of -10F a short in the early evening would show high heat radiation (from the sun heating) from a brick veneer, but the same location early the next morning would show little radiation loss because the thermal inertia of the brick takes many hours to even out.

Heat flow can be very hard to comprehend, especially with different densities of materials and thermal storage.

Dick
 
  #5  
Old 01-12-14, 11:57 AM
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Ok, sounds good, I guess I will go the XPS/foam route & try to fit it as a "top plate".

Thermal imaging can be somewhat misleading when looking from the outside. After a clear cold day of -10F a short in the early evening would show high heat radiation (from the sun heating) from a brick veneer, but the same location early the next morning would show little radiation loss because the thermal inertia of the brick takes many hours to even out.
Very good point...I was kind of onto something like this as it seemed like it takes a while for the house to actually recognize what outside weather it was going through. For example, Monday/Tuesday last week when it was supposedly 40 below w/wind chill, didn't seem like the furnace was working too hard. However, on Wednesday, though it was a lot warmer, seemed like the furnace was working harder than the previous day. Seems like it lags behind the real weather by about a day!

I will say it has been very tough trying to learn about brick construction (as done in the 50s). This is my first house and while it is pretty airtight already thanks to being brick as opposed to the typical stick framed house, wall insulation seems to be the area where I would most-likely investigate prior to trying to acquire another brick house.
 
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