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Structural Can of Worms[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: Structural Can of Worms
- From: "Dennis Wish" <dennis.wish(--nospam--at)verizon.net>
- Date: Tue, 12 Jun 2007 09:26:24 -0700
Tuesday, June 12, 2007
I have a client who is remodeling his condo. It is a duplex located on the golf course of a gate community in the Palm Springs California area. The home was originally constructed as a tract development and this home was part of a phase constructed in 1977. I did an investigation of the roof and ceiling framing by climbing into the attic space with the owner. I discovered that the roof is connected to any of the interior or exterior walls. Rather, the roof is a post and beam system that is in most areas of the unit, four feet above the ceiling and in the living room where the ceiling is 10 feet, the roof is 12-feet. The exterior walls and all walls that may have been originally designed for shear are supporting the ceiling and that the built up 2x4 columns supporting heavy timber (6x25” DF #1 or better) beams is integrated in the walls. The roof framing slopes down from the heavy timber to create a mock mansard roof. It appears that in some areas the soffit from the exterior comes back to the top of the exterior walls where there is some light framing to the roof but no sheathing in the enclosed area. Essentially, the roof is floating above the walls on post and beams. The roof is slightly sloped (1/4” per foot) until the mansard then drops at about a 4:12 pitch. The mansard cantilevers out six feet from the exterior face of wall.
Let me first briefly explain that the work I am to do does not actually change any of the lateral load distribution to the building. Since none of the walls I need to remove to open the plan to from the kitchen/dining room/living room area are extended to the roof, they represent non-shear walls and bear only the weight of the ceiling. The built up 2x4 columns below the heavy timber roof is embedded into these walls and my job does require removing one or two columns from the ceiling down which I had planned to replace with a steel beam and two columns as well as to undermine and beef up the existing pad foundations for the additional load. I also planned to weld a post base to the top of the beam where the existing built up studs supporting the heavy timber could slip into so as to secure it to the steel without it walking away during an earthquake.
1. I thought I would send a letter to the owner alerting him of the deficiency and explaining that since I am not disturbing the existing exterior walls or modifying the lateral load path of the building, that I am notifying him of the weakness and that any damage during an earthquake to the structure would not be the result of the work I intend to perform (Most likely, my work would keep the area I am involved in upright).
2. There is a small alcove leading to the patio that needs to be enclosed as part of the kitchen. This is where the two critical columns occur, but one column stays and the other is the one I have indicated would be cut at the ceiling and supported on steel. Other than the built-up columns, there is no positive connection between the exterior walls and the roof. The ceiling joists (existing) extend over the walls to create a soffit outside that rises to the bottom of the horizontal soffit of the mansard. This occurs approximately 24 inches away from the exterior walls. I can’t see this as triggering any need for upgrade since I have no control over the neighbors unit on the other side of the party wall of the duplex and if I were to be required to create a load path from the roof down I would have to set off a domino event in probably hundreds of these homes.
3. Lastly, there is a trellis to be constructed, but this worries me as the open structure needs to connect to the fascia of the six foot cantilevered mansard. The only way I can see making this happen is if there were no reaction due to the weight of materials at the fascia and to do this would require setting the beam so that there is a 1:1 cantilever of the trellis. I think we can actually live some uplift force at the connection, but I certainly would not want a reaction at this connection. I could use a suggestion here since I can only put in one line of beams and one row of columns. The neighbors units have the slats parallel to the fascia which may be done by installing a beam below the mansard to avoid transferring load to the fascia and then using beams over columns perpendicular from the home with the 2x3 or 2x2 slats parallel to the home. This way the beam connection can be back to the face of the house where the stud walls can pick up the reaction if any.
Any thoughts on the best way to address these issues and the rationalization for release of liability since I am not changing the existing lateral load system designed (if designed) in 1977?
Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant
C-41250 (Exp. 3/31/09)
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