E M
Structural
- Mar 15, 2018
- 41
Everyone-
Have received some help here related to the "design" of load bearing exterior cmu wall requirements as relates to the Florida Building Code. The consensus seems to be that there is no getting around having a 2X 8" high cmu course bond beam at the perimeter of the exterior walls- unless use cast in place "tie beam" at the top of the wall which CAN be 12" high min.
What this effectively means is that top of cmu will need to be 9/4 to end up with 8/0 door and window heads at the exterior.
So, if I don't add a 2x pressure treated plate at the top of the cmu wall (apparently typical construction down here.... bear the trusses on thin metal shim.... possibly fabricated into the cast in place anchors) then my typical interior walls will be 9/4 high.
This is confusing me relative to detailing for a lot of reasons.
Normally (wood frame construction) I would use precut studs to get to 9'-1 1/8" plate height.... but this won't work with masonry construction at 9/4.
Also, the interior walls will be an odd height and if 9/4 ceilings, will almost certainly need to go with all 8/0 interior doors as well. Could potentially get by with 6/8 interior doors for the 9/0 ceilings but pushing it imo so 7/0 ideally better. Really another topic for discussion but factors into the equation.... added expense for 7/0 or 8/0 interior doors.
So one approach is to just use 108" actual precut stud lengths (assuming they are readily available here) and that gets me close but would need to either:
- shim trusses up 1/2" at bearing (pt plywood?.... and anchor bolts rather than cast in place straps and use 2-2x top plates at interior walls (typical wood construction).
- bear trusses directly on top of cmu & eliminate 2x top plate and instead use 1 2x + 1" ACTUAL additional plate for total top plate thickness of 2-1/2". Seems a little odd but since MOST interior walls won't be load bearing would eliminate a lot of the stud trimming. But 1x ACTUAL material probably not readily available.... at least for reasonable cost.
-Strap the bottom of the trusses with 1x material and use 1- 2x top plate (at non load bearing walls and a 1/4 shim.... or just "overlook" the 1/4" and chalk it up to tolerances..... not my preference to pretend descrepancy not there however.
-Raise the bottom cord 1/2 from bearing.... but that seems a little "silly" to me.
-Drop the bottom chord from bearing down to work with "normal" precut stud heights.... but not sure that really makes sense OR, if that can really be engineered in efficiently.
- Or just make the decision to use a cast in place tie beam around the perimeter of X height to work with "normal" precut studs.... but guess here is not a cost effective strategy.
So, after all this is said and done I'm thinking someone besides me has thought this through. And hopefully there is a typical way it's done in this area (other areas?) so that the various trades don't have to go overboard cutting studs/ sheetrock etc. I have no need to reinvent that wheel if there is already a solution so figured I'd ask for opinions on a good path forward here.
Anyone know how it's done down here? Thoughts?
Have received some help here related to the "design" of load bearing exterior cmu wall requirements as relates to the Florida Building Code. The consensus seems to be that there is no getting around having a 2X 8" high cmu course bond beam at the perimeter of the exterior walls- unless use cast in place "tie beam" at the top of the wall which CAN be 12" high min.
What this effectively means is that top of cmu will need to be 9/4 to end up with 8/0 door and window heads at the exterior.
So, if I don't add a 2x pressure treated plate at the top of the cmu wall (apparently typical construction down here.... bear the trusses on thin metal shim.... possibly fabricated into the cast in place anchors) then my typical interior walls will be 9/4 high.
This is confusing me relative to detailing for a lot of reasons.
Normally (wood frame construction) I would use precut studs to get to 9'-1 1/8" plate height.... but this won't work with masonry construction at 9/4.
Also, the interior walls will be an odd height and if 9/4 ceilings, will almost certainly need to go with all 8/0 interior doors as well. Could potentially get by with 6/8 interior doors for the 9/0 ceilings but pushing it imo so 7/0 ideally better. Really another topic for discussion but factors into the equation.... added expense for 7/0 or 8/0 interior doors.
So one approach is to just use 108" actual precut stud lengths (assuming they are readily available here) and that gets me close but would need to either:
- shim trusses up 1/2" at bearing (pt plywood?.... and anchor bolts rather than cast in place straps and use 2-2x top plates at interior walls (typical wood construction).
- bear trusses directly on top of cmu & eliminate 2x top plate and instead use 1 2x + 1" ACTUAL additional plate for total top plate thickness of 2-1/2". Seems a little odd but since MOST interior walls won't be load bearing would eliminate a lot of the stud trimming. But 1x ACTUAL material probably not readily available.... at least for reasonable cost.
-Strap the bottom of the trusses with 1x material and use 1- 2x top plate (at non load bearing walls and a 1/4 shim.... or just "overlook" the 1/4" and chalk it up to tolerances..... not my preference to pretend descrepancy not there however.
-Raise the bottom cord 1/2 from bearing.... but that seems a little "silly" to me.
-Drop the bottom chord from bearing down to work with "normal" precut stud heights.... but not sure that really makes sense OR, if that can really be engineered in efficiently.
- Or just make the decision to use a cast in place tie beam around the perimeter of X height to work with "normal" precut studs.... but guess here is not a cost effective strategy.
So, after all this is said and done I'm thinking someone besides me has thought this through. And hopefully there is a typical way it's done in this area (other areas?) so that the various trades don't have to go overboard cutting studs/ sheetrock etc. I have no need to reinvent that wheel if there is already a solution so figured I'd ask for opinions on a good path forward here.
Anyone know how it's done down here? Thoughts?
