CSA A23.1 expoure class F concrete for exterior balconies 1

[ajk1]

CSA A23.1 requires exposure classification F-2 for concrete "in an unsaturated condition exposed to freezing and thawing, but not to chlorides".
My questions are addressed particularly to those who design or construct a significant number of condos or apartments in Canada:

1. What is the general practice in where the construction joint between the balcony F-2 concrete should be and the type N concrete that would be used for the remainder of the floor that is within the heated building? My opinion is that it would be preferable not to have that joint occur at the window line location, because a) that is a location of potential leakage, and b) that is the location of maximum shear in the cantilever slab, if it is cantilevered.

If you agree, then it would seem that the F-2 concrete should be carried into the heated building space. How far, is my question. Some possible answers seem to me to be:

[ul]
[li]1 metre;[/li]
[li]2 metres;[/li]
[li]3 metres;[/li]
[li]a distance equal to the cantilever length[/li]
[/ul]

2. Given the large number of balcony slabs that I see being repaired over the years, I feel that it would be a prudent extra cost to specify C-1 concrete for balconies. Does anyone agree?

 

[jayrod12]

We are always obligated to provide a thermal break. Especially with the new energy code.

 

[ajk1]

What Standard or Code requires a thermal break?
How do you achieve that with a cantilevered balcony?
Does it apply yet in Ontario?

 

[jayrod12]

We don't do cantilevered balconies anymore. Not unless they wrap them in insulation. The energy code penalty for the thermal bridge that happens here, i.e. -40C on occassion, -30C for an extended period, is not worth the cost of doing something different. And to be completely honest, I'll sleep better at night if I never have to design or seal a cantilevered balcony again.

I've started slinging this idea to minimize the thermal bridge. The tough part is selling the architect on the exposed HSS guardrail. I designed it as a pinned-pinned moment frame in a horizontal orientation. Even taking into account the flexibility of the steel post and designing it for 100 psf the tip deflection is actually quite tolerable. Everything galvanized. Provide a angle welded to the inside of the bottom HSS to receive a pre-cast slab. In my experience, you end up needing steel posts near the balconies anyway since they have massive doors or windows and you can't do it out of steel stud alone.