Wood framed partition walls same height as bearing walls?
Wood framed partition walls same height as bearing walls?
(OP)
I want to find out what occurs in other areas of the country on wood framed partition walls. Here all bearing and partition walls are framed at the same height. This ends up leading to drywall cracking in multiple story structures where partition walls are located in the midspan of a truss. The truss can't deflect, and ends up "bearing" on the partition wall. This causes the floor joists or sheathing to support loads that were not originally intended. The floor joists then deflect more than intended causing drywall cracking in the ceiling on the lower floor. I have done a lot of distress inspections recently where this has been one of the causes for ceiling cracking. We specify that the partition walls be framed a fraction of an inch lower than the bearing walls to make sure the trusses have room to deflect without transferring load to the partition walls. However, I am positive this is never done in the field. I want to get some input as to what others do to preserve the intended load path.






RE: Wood framed partition walls same height as bearing walls?
I think Simpson makes some sort of slip track for wood stud walls, but I have never heard of anyone using it.
However, with cold formed steel stud walls, slip tracks are used all the time.
DaveAtkins
RE: Wood framed partition walls same height as bearing walls?
The cracking I mentioned is only on large span trusses. The most recent one being a 39'-0" roof truss. The partition wall is located right at the midspan. This particular model has been built multiple times and in every unit there are drywall cracks right at the end of the partition wall. The crack runs parallel with the existing trusses which leads me to believe that the crack is from differential deflection of two adjacent trusses. One truss can't deflect because of the partition wall located at the approximate mid span, the other truss can deflect fully where there are no partition walls in the entire span due to a hallway. The builder wants me to come up with a way to construct the future units to prevent the drywall cracks. We could make this a bearing wall with a header, but it seems to me if we used the slip track from Simpson, this could solve the problem instead of spending more money on beams, footings, etc.
Jeff
RE: Wood framed partition walls same height as bearing walls?
RE: Wood framed partition walls same height as bearing walls?
RE: Wood framed partition walls same height as bearing walls?
RE: Wood framed partition walls same height as bearing walls?
You would need an expansion joint between wall and ceiling all along the partition wall.
Also, if this is a home based on the IRC or something simillar, the interior walls many times serve as the empiracle shear walls that provide stability to the structure. Slip tracking these walls reduces that lateral capacity and stiffness.
Better to design the trusses to be supported by the interior walls and add bridging where necessary to minimize differential deflections.
RE: Wood framed partition walls same height as bearing walls?
As for the floor joists, I generally do not use the DTC clips for partition walls. Technically I should. Just never have, but with no problems as long as the salls generally stack. I also spec double joists under any interior partition wall parallel to the joists that span over 50% of the joist span length.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Wood framed partition walls same height as bearing walls?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Wood framed partition walls same height as bearing walls?
BA
RE: Wood framed partition walls same height as bearing walls?
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Wood framed partition walls same height as bearing walls?
JAE: Yes there is the dilemma of possible cracking at the joint between the ceiling and the wall, but I myself would prefer this over the crack off of the end of the partition wall. The partition wall in this instance is not a bracing element.
woodman88: In Arizona they typically provide a 1-1/2" gap between the trusses and the partition walls? Is there a lot of cracking at the joint between the ceiling and the walls as some have suggested could occur?
RE: Wood framed partition walls same height as bearing walls?
From my experience this is a builder driven practice and they are accepting the fact they may have to come back and repair drywall.
RE: Wood framed partition walls same height as bearing walls?
Making the partitions short doesn't prevent gyp board cracking unless the ceiling doesn't connect to the partition. When a roof load is realized, the ceiling commonly moves down a good part of an inch, and so cracks the joint. I have designed slip joints for such a case using picture mold, lapped trim, or a reveal to close the apparent gap. It isn't hard to calculate, but it takes time to detail. No matter what the plans show, the structural engineer wins over the architect, because his stuff gets there first, but then the woodwork wins over the engineer, showing no respect. It really is true that the structure doesn't care what we figure.
RE: Wood framed partition walls same height as bearing walls?
RE: Wood framed partition walls same height as bearing walls?
BA
RE: Wood framed partition walls same height as bearing walls?
Long spans will lift up, some places more so than others. Especially when the attic ventilation is not adequate. Number wise, trusses that bear on "non-bearing" walls between panel points fail.
Also if these are pre-manufactured trusses, look at the details and recommendations that come with the design package (usually in tiny type).
There can also be other problems such a lumber shrinkage, sill crushing, placing the sheet rock inside before the final roofing is installed. Consider if a 38 foot span rests on exterior walls of a number of storeys: Count the number of plates and then check the shrinkage when the plates dry out from 15% to say 8% or 9%. The vertical shrinkage can get fairly significant.
RE: Wood framed partition walls same height as bearing walls?
1) Engineers deflection of truss needs to be accurate (often not)
2) Carpenters need to install the vertically sliding ties/clips along the top of the stud wall correctly (often not done right)
3) Cornice is not to be set to wall to allow movement (I have seen many cornice set to wall and ceiling)
4) Painters are not to paint 'wall to cornice' junction - what client would accept that?
And then what happens where loadbearing walls are adjacent non-loadbearing walls - how does cornice junctions work here? Or where trusses run parrallel to masonry party walls - do we really expect the cornice to slide up and down these walls with wind unscathed?
I think alot of the time the loads we expect to hit the roof after the finishes are applied never occur, so there is no problem. When the deflection is achieved you see the cracks as described by the OP.
Design the truss to be suported on the internal walls and follow the load path down
RE: Wood framed partition walls same height as bearing walls?
I don't think its a bad idea to spec a small gap at the T.O. wall and a vertical slip connection, as much for dead load deflection as for truss uplift action due to thermal/moisture cycling. This causes cracking and separation along wall-ceiling joints all of the time, I see it doing forensic investigations and had it happen in my own house. Ideally this joint should not be finished with gyp compound but caulked or covered by a crown molding detail that will accommodate movements.
In my line of work I see a lot of places where expansion joints should probably be located but it is not standard practice. And so you have cosmetic cracks and separations which we all know are not a structural issue, but lay people do not and they are the owners of these buildings. Therefore, it becomes a problem...
RE: Wood framed partition walls same height as bearing walls?
RE: Wood framed partition walls same height as bearing walls?
RE: Wood framed partition walls same height as bearing walls?
Stucco and other cementitious compounds and gypsum joint compound make very poor crack and joint filler materials due to their lack of elasticity, I see their failures every week... Something to keep in mind.
RE: Wood framed partition walls same height as bearing walls?
I am not turning every wall into a bearing wall, just this one partition wall on this one unit.
a2mfk,
I have told pretty much the same thing to the contractor as far as how susceptible those materials are to cracks. He wanted to know a few options so he doesn't have drywall cracks in the same location on the newer units.
RE: Wood framed partition walls same height as bearing walls?