Calculating Insulation R-Values

Specific Inspection Topics Interior Inspections
#1

Hello!
I am currently studying to become a home inspector and while doing an assignment for the interior / insulation course, I am quite confused about the R-Value.

I live near enough to Toronto where the recommended R-value is quite high. However, when I look at the insulation in the unfinished part of my basement, I can see what I believe is fiberglass batt insulation R8 on 3 walls and R12 on the 4th wall. It is also covered with a vapor barrier (I believe it came as part of a set).
I measured the thickness of the R8 as about 1 inch (maybe up to 1.5 inches) and the R12 at about 2 inches.

How do I calculate the total R-Value for the area? I checked and re-checked the study material and searched online but my answers came up empty.

Thanks in advance!
-Adam

#2

Not sure if reporting total R-Value in your area is within the Canada SOP or jurisdictions but if it is, I’m sure our Canadian members will help you out further. Where I’m located, the R-Value is not apart of the inspection unless it’s an energy audit, OR if you feel that there is insufficient insulation that may be related to other issues or problems that may me directly related to the lack there of.

Of course it’s always good info to provide to your client and even may be required by local jurisdictions, so start there as far as what needs to be addressed and reported.

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#3

Thanks for the info. I also kind of wanted to get an idea for myself as well since I just moved into my own very first house so it’s a great learning area for me too.

#4

Post a couple of pics of what you described in your first post.
My ability to decipher Canuck has been waning lately. :wink:

#5

Welcome to our forum, Adam!..Enjoy! :smile:

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#6

Adam, is there any part of the exterior of your basement that is not backfilled with earth to the approximate 7’ height?

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#7

I don’t calculate anyone’s R-Value, however I do report on inadequate insulation and missing insulation. I have a comment telling what the recommended R value is for my region. Usually I see old insulation that has been compacted and recommended adding insulation to increase efficiency.

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#8

You can guesstimate an R-Value but in a situation like that it would not do much good. Example would be. in an attic Say you have 1000 s.f. of total area and 500 s.f. is insulated with R-38 and 500 s.f. has no insulation. The average Effective R-Value is not an R-19 or comparable to if the attic had an R-19 over the entire 1,000 s.f… It would probably be more like about an R-5 or something. Energy goes to the path of least resistance. There was a study that said something like an attic area that has a 5% void will loose 25% of its overall rated R-Value.
I used to be an insulation contractor and had all this in my head at one time.
One thing I do remember was that an R-38 Batt installed has an effective R-Value of about R-27 (because of gaps and framing members). Blown is much more effective!
Also an R-19 batt is about R-13 if the installer “takes great care” when installing. (a little known fact is that a standard R-19 batt needs a thickness of 6.25 inches and so if you squeeze it down to 5.5 inches (2x6 wall) it is R-18.)

If you really want to get technical and nerdy… you can do these calculation of overall efficiency using ResCheck. (free program, just google it) Which is actually what is or can be used to show energy compliance now instead of saying a certain R-value is required for in a wall or attic. There really isn’t a minimum R-value for a component (wall, ceiling, floor) any more in most States or Jurisdictions. And all houses will be different. even takes in orientation to the sun and windows as well as Climate.

Now how is that for a short answer :grinning:

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#9

No, there isn’t. Sorry for the late reply—my notifications were going into my junk mail. ^^

#10

Very helpful and complicated! Thanks

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