Truss Uplift With Monolithic OSB Ceiling
I’m building a 24 x 60 house with a trussed roof. I was planning on using OSB as the primary air barrier fior the ceiling, installed before the partition walls. I’m puzzling over how to tie my interior walls to the ceiling to accommodate for truss uplift.
Normally truss clips are installed on the top of the partition walls and fastened to the sides of the lower truss chord, but if I put the monolithic OSB ceiling in first, that cannot be done.
Anyone dealt with this detail before?
I suppose I could puncture the OSB at maybe 4′ intervals for the truss clips and install normally, but how would you seal around that constantly moving hole?
I don’t want to add a deep service cavity because I don’t want to lose the ceiling height. If I add 2x strapping I would only lose 1 1/2″ but 1 1/2″ doesn’t seem like it would be enough depth for the truss clips.
I could reverse the truss clips, screwing them to the ceiling, and runnning the slotted leg down the face of partition walls, but the fasteners and such would interfere with drywall in both planes.
What about using a screw with a very long spin shank, such as a long timberlok, predrilling the top plate of the partitionslightly oversized, and screwing up through the OSB into the truss chord, leaving the head of the screw down an inch or so, so that it is acting as a registration pin for keeping the wall in place, but still able to slide up when truss uplift occurs?
Thoughts? Other solutions?
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Replies
Steven,
Probably not the answer you were hoping for, but my solution would be to eliminate the OSB.
- The function of the OSB as a continuous air-barrier can be done with either poly or a variable perm membrane depending on your climate zone.
- It represents a proportionally large extra amount of additional materials and expense.
- It makes running services - like wiring and plumbing vents - more difficult.
- Except for the continuity over interior partitions, it doesn't buy you much drywall doesn't already provide.
- The solutions you suggest defeat the purpose of having a continuous air-barrier over the partitions.
I debated going that route. How expensive is a roll of intello?
https://www.strongtie.com/strongdrive_interiorwoodscrews/sdpw_screw/p/strong-drive-sdpw-deflector-screw
Now that looks like just the thing...
Just came across this one, which elimates need to predrill: https://www.framerscouncil.org/news/2020/jan/fastenmaster-introduces-non-load-bearing-wall-connector-roof-truss-connections
Steven,
if you go with an OSB ceiling, don't forget to add pieces onto your exterior wall top plates, or your interior wall studs and drywall will all need cutting down.
Done.
In addition to the deflector screws that Tim R mentioned for the interior walls, depending on how you approach connecting the ceiling air barrier to the wall air barrier, you may find that using truss screws to secure the trusses at the perimeter walls makes the air barrier detailing easier at that location.
Here is the Simpson truss screw: https://www.strongtie.com/strongdrive_interiorwoodscrews/sdwc_screw/p/strong-drive-sdwc-truss-screw
I read an article in Fine Homebuilding where they built the attic floor like a typical 2nd floor and put the OSB on TOP of the attic floor joists. Then they put the trusses on top of the OSB floor. This allows the truss installers to walk around on a solid floor, the OSB completely air-seals the attic from the main living space and this method provides a space within the attic floor system for pipes, wiring and can lights to be installed without having to puncture the OSB air barrier.
These are non-attic trusses. No need for a floor up there. That article is by a guy that works in this area.
"Non-attic trusses"? Hmm. Floor trusses?
Well, here's the article for anyone else who might be interested.
https://www.finehomebuilding.com/project-guides/insulation/simple-air-sealed-ceiling-for-a-high-performance-home
Scott,
That's a great roof assembly for the rare projects that can absorb the cost of an additional floor system just to use as a service cavity.
Malcolm, it's an even greater system when you average out the cost of a couple dozen I-joists over the life of the building compared to the savings of creating a completely air-sealed living environment that doesn't leak heat or moisture into the attic from ceiling penetrations.
You're already putting in the drywall, trusses, insulation and air barrier - what's a few more I-joists?
Scott,
It's not just a few I-joists, It's a complete floor system. The joists, sub-floor, rim-plates, and you have introduced one of the most difficult areas in a structure to air-seal and insulate: more rim joists. Especially on a one storey building, that represents a sizable increase in the volume of materials and cost of the framing.
Particularly when you consider the alternatives - bulkheads, plenum trusses - or if the ducts are in the crawlspace or basement, just air-sealing a few wires and electrical boxes, which is really not at all hard to do effectively.
I'm all for an air-tight ceiling, but creating an entirely independent floor system does seem like overkill to me.