Adequacy of existing masonry bearing wall for Residential Addition

[mfstructural]

The other day I received a call to come out and see a house to which the owner is putting an addition on. The addition consists of adding a second story to one side of the house. The current wall consists of a 4" CMU wall with face brick facade. I am not the EOR, the drawings were put together by an architect. Apparently, the architect assumed the walls were 2x4 framed and the drawings reflect this. The owner called me for my opinion because the contractor brought up the issue of adding a 2x4 stud wall on top of the existing 4" CMU wall. The contractor was concerned with the stability. The drawings instruct the contractor build the 2x4 wall on top of the CMU wall (in bearing), then remove the face brick, and rebrick the entire two stories. Personally, I don't feel comfortable with this situation and may recommend building a 2x4 wall adjacent to the existing 4" CMU wall to support the wall above. Has anyone had an experience with this? I've only seen a 4" CMU wall act as a bearing wall in a residence once. Also, would you consider the face brick to aid in resisting out of plane bending? I typically would not, but in this case maybe some credit can be taken...but again this is unconservative.

 

[BAretired]

A 4" CMU wall is too thin to be considered a bearing wall. The architect should be requested to provide revised details as his initial assumption of a framed wall was incorrect.

Face brick does not aid in resisting out of plane bending unless it is properly tied to the masonry so that it effectively increases the moment of inertia of the wall.

Has anyone determined that the foundation is adequate to support a second storey?

I would be careful about recommending anything on this project unless you are prepared to assume full responsibility for the entire design.

BA

 

[msquared48]

I agree with BAretired.

Mike McCann
MMC Engineering

 

[MiketheEngineer]

I agree

 

[InDepth]

Shotcrete concrete against the brick (brick serves as backform). Dig along and add a new footing. This should also allow you to add sill plate bolts to the top of the concrete wall, and then provide easy attachment of new facade.

 

[hokie66]

InDepth,

Your advice is not only confusing, it is probably dangerous. BA has given the appropriate advice.

 

[msquared48]

Hokie is correct here.

Shotcrete, although it will increase the cross sectional area of the wall, does nothing for the reinforcing, assumuing that there is any at all. None has been alluded to in the 4" CMU wall.

To assume here is dangerous.

Mike McCann
MMC Engineering