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Framing partition walls in bonus room area….Is truss uplift a problem?

Rick Van Handel | Posted in Energy Efficiency and Durability on

Climate Zone 6A

To make a long story short, I’m wondering if there are any peculiarities to building partition walls in a room in attic area and/or any flooring issues? From what I understand about truss uplift, the bottom chord is typically the one that would move. My bottom chords are structural grade 2x12s. If that’s the case, the bottom chord (which doubles as a floor joist) might rise or contract throughout the seasons. Does the part of the truss that forms the ceiling joists in a room in attic configuration move as well? Do they move in concert? Any thoughts on best practices for framing interior partition walls and how to reduce the likelihood of drywall cracks? Would the arching of the bottom chord affect the flooring?

Details below:

I have an insulated 48′ x 104′ building that was constructed with bonus room trusses above it for the full length of the building. The bonus room area is 20′ wide, with a ceiling 8′ 6″ from finish floor to finish ceiling.

The entire building is insulated, I have partitioned the building so that 40′ x 48′ on the first floor will be a heated wood shop.

I’d like to finish the upstairs (bonus room area) above the woodshop. Due to adding some dormers and hand framed areas to get more natural light, the floor plan upstairs is “T” shaped, with the main aisle 20′ x 40′ and the dormer areas being 10′ x 12′ wings.

I would like to add a bathroom in the upstairs area. The bathroom would be positioned in a corner, so I would need to frame two walls in. One wall is to run parallel with the bottom chord and the other runs perpendicular.

The floor (2×12″) is dense packed fg. Knee walls (full height 8′ 6″) will be insulated with 4″ of recycled eps on exterior and dense packed fg in 2×4 cavities. Ceiling to be r-60 loose fg.

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Rick,
    Attic trusses act differently because their bottom chord isn't tied to the upper ones. For the purposes of truss uplift you should think of the truss members above the bonus room ceiling as being the potentially problematic ones. It's a good idea to use truss clips any time you attach interior partitions. Keep the closest drywall screws a foot from the ceiling wall intersection and you will be fine.

  2. Rick Van Handel | | #2

    Malcolm--Thanks for your advice.

    I have one wall that will run parallel between two of the trusses. I was going to ladder frame 2x4 sections between the trusses so I'd have something to nail the top plate of the hand framed wall. Do you know if truss clips would still be needed in this configuration? If so, I'm guessing I'd have to nail a vertical chunk of 2x stock to the ladder framed 2x so I'd have the proper orientation for the truss clip?

  3. Expert Member
    Malcolm Taylor | | #3

    Rick,
    The clips will work fine with your 2"x4" ladders. There is an illustration of one in this link:
    http://seblog.strongtie.com/tag/scissor-trusses/

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