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Foundation Wall Control Joints

Foundation Wall Control Joints

Foundation Wall Control Joints

(OP)
Have a 60' long concrete sandwich wall at the rear of a house. It has a 9 1/2" outer wythe, then 3" of foam and a 4" inner wythe. The wall is designed as a cantilevered retaining wall but is the foundation wall for the house. I have #4 @ 18" O.C. horizontal and #5 @ 18" O.C. vertical. I showed control joints at 20' O.C.
How are the control joints be made? Do they put some bond breaker in the form? Also, should I terminate the rebar at the joints?

Thanks

RE: Foundation Wall Control Joints

Sounds like a bit of an unusual arrangement for a residential basement wall. If it is a cantilevered retaining wall, it must have a heel that is substantially thicker than your typical 4" basement floor?

Not sure what your basement wall height is, but I usually try not to exceed a panel ratio of 1:1.5 for control joint layout. Typically I see them install triangular chamfer strips into the formwork that create a vee notch in the wall when the formwork is removed.

They should oil the forms for easy release. Run the bars through the control joints. That way, when the wall cracks at the control joint, it will still be held together by the rebar.

RE: Foundation Wall Control Joints

(OP)
Thanks Motorcity. It has a bookend type retaining wall footing. It is unusual, but we did not want use the floor system to brace it due to other constraints.

RE: Foundation Wall Control Joints

I assume you mean the 9.5" wall has the reinforcement. I don't know why you would want control joints in that wall, as you won't see it. Is the 4" interior veneer reinforced?

RE: Foundation Wall Control Joints

(OP)
@Hokie66.

It is an unusual situation using a Thermomass wall. The 4" wythe is the actual the gravity load carrying portion. It is reinforced also. The 9 1/2" wythe extends about 14 ft up to the bottom of some high windows on the main level and only has about 5' of backfill on it.

RE: Foundation Wall Control Joints

As motorcity said, the triangular strip is placed in the form where you want the joint. This can be two pieces but should total 1/4 to 1/3 the wall thickness. I'd vote for cutting every other bar. The point is to create a weak spot in the wall so that when the concrete shrinks it will choose to crack at your joint. If the joint is exposed and depending on how fussy the design is, you might also consider how it will align with other exposed elements, like windows.

RE: Foundation Wall Control Joints

Seems like you ought to consider having a water-stop at each control joint too. Vertical control joint are a great idea but I never see them in residential basement walls. Water leaks are (probably) the #1 "call back" item for basement walls so attention to that in this "uncommon" application seems like it would be helpful.

Also curious about the slenderness of the 4" inner wall. As I understand your post, that is carrying gravity loads.
Are the two "wythes" tied together somehow? Not thinking of composite behavior but just bracing for the 4" layer.

Not familiar with the term "bookend". Is that the same as counterfort?

RE: Foundation Wall Control Joints

(OP)

Quote (kipfoot)

As motorcity said, the triangular strip is placed in the form where you want the joint. This can be two pieces but should total 1/4 to 1/3 the wall thickness. I'd vote for cutting every other bar. The point is to create a weak spot in the wall so that when the concrete shrinks it will choose to crack at your joint.
Thanks for the advice.

@Houseboy - The 4" wythe is tied to the 9 1/2" wythe (google Thermomass Walls). Bookend just means a typical cantilevered retaining wall footing - which is essentially how a bookend works.
This is a very expensive house with a high profile Architect as the owner. He does not want to see any cracks if possible. If the majority of the wall was covered with dirt, I probably would not have worried about it.

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