Question about Structural Support
Hello browstoner community
Apologies in advance if this is too long and technical of a post. My wife and I are renovating our 4 story townhouse, and as part of the work, we are introducing a wall of windows at the rear of the home on the garden floor. The townhouse is 23.5’ wide, and has a center masonry/ load bearing wall that goes from front to back on all floors except the top one. The plans drawn by our structural engineer call for a steel moment frame at the rear and a large steel beam connecting the moment frame to the remaining center bearing wall, with a steel post below where the moment frame and steel beam meet. We appreciate the engineer’s expertise, but are very unhappy about the post and do not understand why it is necessary. The response from the engineer was that without the post, too much stress would be placed on the foundation. So we dug two pits in the cellar at the rear of the home and found that we have a concrete foundation. Nevertheless, the engineer opined that they “believed” the foundation wasn’t deep enough – unclear why. I want to let this g o, but I just can’t – I have seen many townhouses in Brooklyn that are 25’ wide and are open front to back which confounds me. I understand that the experts here will likely need more information to opine, but I wanted to get some reactions to this in case I am overthinking it and the engineer is right about the post being required. I am inclined to get a second opinion but don’t want to waste the money if the reasoning appears to be sound. Thank you in advance.
Guest User | 3 years and 3 months ago
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Guest User | 3 years and 3 months ago
Thank you for all of your insightful responses. I should mention that we dug test pits, and confirmed that we have an approximately 12” concrete foundation, but the engineer seemed that insufficient.
Regarding the question about the center bearing wall, it goes from the cellar to the 3rd floor, but the 4th floor has regular plaster walls from front to back. The question about the joists is tougher to answer because we haven’t probed all over. I believe that in some cases the joists may not go from party wall to party wall but instead rest on the joists. I will keep you all posted!
jimhillra | 3 years and 3 months ago
Moment frames at rear openings have become standard on any opening larger than 50% of the wall. This is due to recent structural code changes.
As for the post, if you have multiple stories of masonry bearing wall, that is pretty exceptional. Some of the older or grander brownstones have masonry arches in the cellar and a masonry bearing wall in the basement, with wood framing above, but most have wood framing throughout. If you really do have so much masonry, then that’s a lot of load to transfer to the ground, much more than the wood framing.
Also, if the bearing wall is masonry throughout, then the builders may have used it as an actual bearing wall, not as a “stiffening” wall, which is what most brownstones have. If that’s the case, the joists may not clear span, but instead bear on the masonry, which would result in far more load on that wall than in wood framing where they clear span the full width.
As for the foundation and footing, you should have a contractor dig down to the bottom of the foundation to expose the conditions. There’s no need for opinions there.
kassie319 | 3 years and 3 months ago
I’d ask them what study on their part is required to confirm this belief. If the belief is confirmed your architect should be able to offer them workarounds to investigate- underpin, reinforce, take loads elsewhere.
RobertGMarvin
in General Discussion 3 years and 3 months ago
I don’t think you could get a meaningful technical answer on any online forum. That being said, I think you have only two choices: either accept your engineer’s advice, despite being displeased with the aesthetics, or, because the structural integrity of your house might be compromised, ,get one, or more additional opinions.