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I'm trying to help my grandfather plan for a remodel of his 1950s home. The original structure is 24x24' with 6" rafters spaced about 20" apart on a 6/12 roof. He'd like to be able to have a "vaulted look" by adding rafter ties, removing the ceiling joists and drywalling the rafters - leaving the ties exposed as faux beams. The current ceiling joists are 6" and follow the rafter spacing. There is an overlap in the middle of about 4' and a wall running perpendicular to the joists that I'm assuming helps support the joists at that break. The home is located in SE Georgia, so no snow load to speak of.

  1. Would it be possible to raise the ties up so that he could use a single 20' board for the full span?
  2. Would it be possible to skip every other rafter?
  3. Would doubling the ties on either side of the rafter help alleviate lateral force (see picture)?

This is well outside of my wheelhouse, so any insight is greatly appreciated!

enter image description here

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    The answer to all three is "probably". Without more information about the structure (and more detail about your plan, such as fastening method), no one can say for sure. This is a question for a local engineer. – isherwood Mar 4 '20 at 21:13
  • Hello, and welcome to Home Improvement. As @isherwood says, any of your three questions would probably be too complex for us to answer. And, you should probably take our tour so you'll know you'll know the details of contributing here. – Daniel Griscom Mar 4 '20 at 21:19
  • Yup, you need a local engineer. Sorry. – Aloysius Defenestrate Mar 4 '20 at 21:20
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    I agree it is an engineering question if you can move them up. I doubt you could skip ties on 2’ centers, 20” would be unusual, normally 16 or 24” oc. – Ed Beal Mar 4 '20 at 21:21
  • We looked at something similar for our house, but decided it wasn't worth the money to raise the ceiling one or two feet. Keep in mind that the further up the rafter ties, the more stress on the ties & the joints. In the extreme, you could replace the ridge board (which is what I assume you have) with a ridge beam and remove the ties entirely. That changes all of the forces on the roof, so a structural engineer is definitely needed in that case. – SteveSh Mar 4 '20 at 23:18
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I commented above that the question can't really be answered, but I have a few thoughts to share...

Would it be possible to raise the ties up so that he could use a single 20' board for the full span?
My concerns are that the ties will sag due to the long span, and that the rafter tails may not be adequately anchored to the wall plates if you remove the existing ties. The ~2' rafter tail shouldn't be a concern with respect to flex or strain. That's pretty short for a 2x6.

Would it be possible to skip every other rafter?
Yes, but then you put even more stress on the connections between the ties and the rafters, and between the rafters and the wall plate, for each remaining tie. Connection strength is key.

Would doubling the ties on either side of the rafter help alleviate lateral force?
Lateral force isn't really a concern with respect to tension on the ties themselves. It's a matter of the connections, as I said. Adding more lumber doesn't necessarily help with that.

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  • Skipping every other rafter would leave the ceiling material with ~40" span and that seems quite unreasonable for most material hanging horizontally. – FreeMan Mar 4 '20 at 21:33
  • You're right, but the question mentioned leaving them exposed. The drywall would span just between each rafter. – isherwood Mar 4 '20 at 21:48
  • Ah, valid point! – FreeMan Mar 5 '20 at 12:16
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We made a similar change once. The contractor put up cross-connected ties -- sorry, I forget the proper name -- which run from one wall to near the peak on the other side of the ridgeline. You lose about a foot of ceiling height at the peak (inside) but then you have a cathedral ceiling without any cross-ties at all. Aesthetically much nicer.

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