Masonry wall with wood supports for roof

[electronicguy]

Hey, I'm an electronics guy, so this is beyond my engineering expertise, and I would appreciate help.

The builder of our new house constructed our concrete deck and overhead roof, together with wood support posts, before adding the masonry (concrete block covered with stucco) that constitutes a short privacy wall around the entire deck. They built the concrete block wall between the wood posts, and then stuccoed over the masonry wall and wood posts without any additional thought or support. In just a few months, the stucco is cracking at the junction of the wood posts and masonry wall and falling off.

The builder has offered to re-stucco, with chicken wire over the wood posts. I have said that while it might keep the stucco from falling off, it would not solve the basic problem of cracking, and it would still allow rain to enter the intersection of wood post and stucco, thus resulting in on-going problems.

I have suggested that the builder shore up the patio roof, cut the wood posts just above the masonry wall, fill in the masonry wall where the posts were located, and then fasten the posts on top of the new wall with fixtures that isolate the wood posts from the masonry wall.

The builder is pushing back, claiming that the masonry wall, as built, can't support the posts and roof. My reply, so far, has been "that's your problem to solve."

For those of you who understand these issues, what do you suggest?

 

[concretemasonry]

Plain and simple -

You do not support concrete or masonry structures with wood.

Wood it temporary, shrinks and reacts differntly than the rest of the structure. This is especially true with treated lumber that is usually put in place while still wet and will shrink significantly. The long term effects are even greater.

I would suspect that the wood drying shrinkage was so great that the load was shifted from the posts to the block wall. This caused a redistrubution of the loads and caused cracking that may occur again.

I hope there are good footings under the block to carry the loads. It may have been better to just build the block wall and forget about the wood posts and special footings for the posts.

Did this pass the code and inspection?

 

[DaveAtkins]

I think concretemasonry is not understanding the situation.

If I understand it properly, the CMU is merely built between the wood posts, and everything bears on the concrete slab-on-grade.

I would ask the builder these questions:
* What supports the load in the wood posts?
* What prevents the CMU from overturning (if this was a public building, it would be required to be designed for 50 pounds per foot (horizontal) along the top of the wall
* Can the CMU be safely isolated from the wood post, with a control joint?

DaveAtkins

 

[boo1]

Consider use if stucco control joints (two) at the post to isolate the differential movement.

 

[apsix]

As I read it you don't have the wood columns supporting any concrete or masonry, just the roof.

I agree that the existing masonry infill between wood posts and stucco over will be a problem into the future. I would suggest that replacing the wood with steel posts is the best solution, with adequate corrosion protection. Assuming that the wall is not full height, fixing the posts to the top of the wall results in a hinge, and there will also be uplift issues. Both problems are difficult to overcome unless the masonry is reinforced. As it is the masonry infill is probably relying on the posts for stability.

 

[jike]

I would suggest building the masonry around the wood posts but isolated from them. These would appear as pilasters. The stucco would then be fully supported by masonry.

I don't like the idea of trying to cut off the post and resupport on masonry. There will be difficult load and stability issues.

How are the top of masonry walls supported?

 

[JAE]

boo1 - I agree that the control joints would do the trick - the only problem is that at each post you'd have two joints close together (each aligned with the end of the block). That might be a high maintenance issue - or at least sort of ugly looking.

apsix - steel columns still leaves you with an interface between column and block which the stucco won't bridge without cracking in my opinion.

jike - I like it. This is probably the best solution - have the mason come back and fit around the posts with some additional pilaster-type block. This does two things - first, it creates a continuous block surface for the finish material. Second, you have something at least half-way aesthetic to create a sort of column pedestal look that might visually work. (sorry - I'm playing architect here).

 

[apsix]

JAE - you're right, there is still a risk of cracking, but cracking should be substantially less than for wood.
The pilaster solution is good. The only real issue I can see is a possible lack of support at the base.

 

[msquared48]

If you cut off the wood posts at the top of the masonry wall and infill where the wood was with concrete, allowing the post to bear on the masonry wall, you will create a knuckle joint for lateral loads - i.e., a laterally unstable condition.

Better to replace the wood post with a steel pipe column (3" standard would probably be sufficient) This could be inset in a masonry block set into the place of the original wood column. Your stucco problem will go away then.

No worries.

Mike McCann
McCann Engineering

 

[jike]

Re: Lack of support for pilaster

An angle or other steel member could be bolted to the edge of the foundation to support the pilaster projection.

 

[boo1]

Typical residential posts are 4x4 or 6x6.
The plastic stucco expansion / isolation beads we use are 1/2" or 5/8" wide with a 2 1/2" attachment strip/ear on each side.

Installing expansion bead on the post then covering the wall with lathe should bridge across the post.