I have one half of a duplex, which is separated by a brick wall (looks like a triple brick?). While refinishing my basement, I'm trying to determine the insulation requirements in my local building code (Ontario, Canada), but no matter what I punch into google I cant find the right reference.

Can anyone suggest the search term I should be using to find the correct part of my local code?


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    Whatever language there may be will be about the fire-rating of said party wall, not thermal insulation. If the neighbor is not prone to leaving the house unheated in winter, there should be little temperature variation across the wall, on average. When that differential shoots up to 900 degrees, it's good if you can leave the house before a fire breaks through... – Ecnerwal Jun 27 '17 at 2:18
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    Will the space behind the wall be about the same temperature as your space? If so, what do you expect insulation to do? – Harper - Reinstate Monica Jun 27 '17 at 3:58

There actually aren't any (at least in the Model Codes)

The reason you're coming up empty handed is because the Code makers, by and large, have not addressed this when writing energy conservation codes. Party (common) walls are generally not considered part of the building thermal envelope, which is actually rather OK, as insulating them poses special challenges.

From the Building America Solutions Center page on the topic (italics in original):

The model energy codes do not address minimum insulation requirements for common walls because the common wall is not defined as part of the building thermal envelope.

If you want to insulate and/or air seal them, you must respect the wall's fire rating and listing when insulating in order to be Code compliant. You may wish to speak with your AHJ on this, especially considering that you are dealing with an older style of party wall which behaves differently from modern residential party walls.

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The article and discussion found in the article referenced by @ThreePhaseEel indicates no code reference specifically to party walls. However, all major codes reference energy compliance for "Dwelling Unit's Walls". I think the article is misleading when it implies there is no energy code requirements for "party walls."

Yes, the code is very specific for fire separation for "party walls" in multi-family structures. (By the way, as of 2014 Code, fire sprinklers are also required for 3 units and more.)

However, all party walls have "sound wall" requirements. I'm not sure what your party wall's sound transmissions class (STC) is, but I'm sure the brick wall does not meet the required "R value" for walls in a "dwelling unit"...as required by all codes.

We try to "kill two (or three) birds with one stone" and use thermal insulation in a party wall design to meet sound wall requirements and fire wall separation requirements.

So, I'd suggest use the same thermal value in your party wall as your exterior walls to meet the energy requirements for dwelling units.

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  • The prime concern I'd have with insulating a party wall is that combustible insulation materials (foam, celluosic) could void the fire wall listing/rating depending on the existing construction and means of installation. Air sealing could also have an impact on this as well... – ThreePhaseEel Jun 30 '17 at 2:51
  • @ThreePhaseEel I don't think you can get a "fire rating" using combustible insulation. I've never heard of it. Can you? – Lee Sam Jun 30 '17 at 2:59
  • Well, ICF walls are often considered to have some degree of fire rating performance AIUI even though the forms will burn off the exposed side after the finish is no longer able to hold... – ThreePhaseEel Jun 30 '17 at 3:06
  • @ThreePhaseEel Hmmm...my UL Fire Rated Listing Manual doesn't have ICF listed. Are they? – Lee Sam Jun 30 '17 at 3:23
  • Interesting -- my understanding could be wrong, at least for first gen (foam sandwich) ICFs. (There are what I call "second gen" ICF technologies (such as Apex Blocks) that use a foam-aggregate PCC -- these do have an official fire rating, at least if the specification sheets are any guide.) – ThreePhaseEel Jun 30 '17 at 3:27

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