[Equest-users] 2015 NECB Question, Intersecting Floor and Wall Area

[Jones, Christopher]

Chris,
The NECB 2011 and 2015 assume that the Reference case envelope is perfect and that there are no penetrations of the insulation plane. For the Proposed case, both standards give you the 2% opt out clause – if the total penetrated area is less than/equal to the maximum of 2%, it can be ignored. If the area is greater than 2%, you need to calculate the effect of these penetrated areas on the overall wall R-value. The NECB 2017 mandates calculation of linear transition and point transition thermal bridges but still maintains that the Reference case envelope is perfect – unlike the BC Hydro assumption that applies an insulation derating factor to the Reference case effective insulation.

I did a calculation of the effect of balconies on a typical MURB with 5% total balcony slab edge are total wall area. The Shock balcony thermal break system would take over 20 years to payback – Toronto climate much longer in Vancouver. That is ignoring thermal comfort issues, potential condensation issues, etc.

Christopher R Jones, P.Eng.
T+ 1 416-644-0252

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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Chris Hadlock via Equest-users
Sent: Thursday, April 25, 2019 12:02 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] 2015 NECB Question, Intersecting Floor and Wall Area

Good morning,

For you Canadians, I have a question about how to model the area where a floor slab intersects the exterior wall.

Specifically, Section 3.1.1.7.8) of the 2015 NECB says that "wall assemblies shall be considered to include all related structural framing and perimeter areas of intersecting interior walls but shall not include the perimeter areas where floor or roof slabs interrupt the wall's construction."

There is a reference to Note A-3.1.1.7.(8) which provides an illustration to depict the extent of the surface that is considered as a wall at the intersection with a floor. In this note, it also says "This Code may have different requirements for the perimeter area of floors."

Since I haven't seen any such requirements (how anyone else), I'm not sure how to treat this area.

When I have a building in which the insulating layer in the exterior wall assembly is intersected by the floor slab (thus breaking the insulation plane), I typically model my Proposed building with a separate assembly for the slab edge and assign a low R-value (reflective of a wall with no insulation).

My question then is, in this case, what would people model for the Reference model in terms of R-value at the slab edge (where the floor intersects the wall)?

As mentioned, I have not seen anything in NECB that specifically deals with the treatment of the slab edge (other than at grade level). Would the Reference model carry the same R-value as the Proposed model?

Thank you in advance for your input and thoughts.

Chris

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