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I live in a house that was built in 1958. I am looking for the R value of my brick veneer walls. For that I would need to know how the wall was built (there should be the brick, some sheating, insulation etc. This is the part that I am missing: the layers that were used to build my walls. This is in Toronto Canada. If anybody is familiar with this topic I would really appreciate some help Here is what a wall looks like. The house in the back is identical with mine enter image description here

There is good chances that my wall looks like this: enter image description here I am using the Heat2000 program to calculate the thermal values for my house. I decided to go with the below settings. This will give me a conservative R value of 13.5. I will use a second iteration with no batt insulation and see what I get. I need this in order to properly size the furnace, the contractors that I have contacted for this are too lazy for this so I will have to do it myself enter image description here

  • It sounds like you already know the answer: if you want to calculate the R value accurately you need to know the makeup of the wall, including the type and amount insulation (if any). – Hank Dec 22 '14 at 16:12
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    "This is the part that I am missing: the layers that were used to build my walls." So I am looking for info about how the brick veneer walls were built around 1958 – MiniMe Dec 22 '14 at 16:19
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    If you get an IR thermometer, you might be able to back-derive that information from the difference between interior temperature and outdoor wall temperature... – keshlam Dec 22 '14 at 22:57
  • I have an IR thermometer!! How do I do that? (I have an IR gun, and a Seek Thermal Camera -for thermal imaging) – MiniMe Dec 22 '14 at 23:59
  • Are you referring to this: ag.ndsu.edu/pubs/ageng/structu/ae1373.pdf ? This is really easy ... – MiniMe Dec 23 '14 at 0:06
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The only way to know the R-value of your wall is to know everything that was used to build it. Some of the ways you can determine this include by drilling a hole in it or looking behind an electrical outlet. That said, if your house is typical Canadian construction, here's my rough estimate:

  • 1/2" drywall or plaster and lath: R-0.5
  • 2x6 cavity filled with fiberglass batt insulation: R-14 (R-19 batts x 0.75 due to thermal bridging by the 2x6 studs).
  • Plywood sheathing: R-0.5
  • 1" cavity: R-0.75
  • Single-wythe brick veneer: R-0.75

So the all-inclusive "whole-wall" R-value of your wall, if it's like this one, would be R-16.5. However, typically when discussing R-values, you only include the insulation--taking into account thermal bridging by studs. In that case, we would describe this wall as an R-14 wall. If your wall has different cavity insulation, or only has 2x4 studs, or has been retrofitted with rigid foam or mineral wool outside the sheathing, then the numbers would be different.

  • Thanks ..that is very much in line with what I guessed. What period are the above typical for. My house was build around 58 (consider it 60s if you want). I am not sure that the cavity and the batt insulation is there – MiniMe Dec 22 '14 at 16:27
  • Are you familiar with Hot2000? I am using that program and here is an existing typical wall pre configured with the program. i.imgur.com/rvvvLzh.png If I use that I get a 13.35 R value which would probably be conservative considering that I don;t know the structure of the wall – MiniMe Dec 22 '14 at 17:15
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    @user2059078: as you can see looking at these numbers, the insulation accounts for the vast majority of the R value. If you can't get a reasonable estimate of the insulation it's not even worth speculating about the other layers. – Hank Dec 22 '14 at 17:44
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    @user2059078: I'm not saying there's no value in trying to calculate the heat loss, I'm just pointing out that the difference between an R14 and R19 insulation batt is way more important than the drywall thickness or whether or not there is an air gap. If the insulation R value in your calculation ins't correct then it doesn't matter what values you put for the minor things. If you're interested in getting an accurate value you need to find out exactly what type of insulation is in your house. – Hank Dec 22 '14 at 18:47
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    Then for the purpose of sizing your new furnace, you should plug in a value of about R-14 for your wall insulation--either because that's what it already is, or that's what it will be when you have it insulated. – iLikeDirt Dec 23 '14 at 1:03

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