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We have a 23x12ft room that we are looking at opening up the flat ceiling. The 2x6 rafters are parallel with the long side the the room and there is one beam (3 2x6s) that seems to be a rafter tie running this long length of the room. Looks to have a 2x6 coming down from the peak of the roof at the ridge board down to the beam.

The ceiling joist 2x4s are running at right angles to the beam and rafters across the 12ft span of the room. These joists are below the beam and are tied to it by 2x4. We were told that the joists are not providing structural support and were merely for affixing the flat ceiling.

We had hoped to remove these joists and wonder if the 23 ft beam of 3 sandwiched 2x6s (board seams are staggered) will have any sagging/structural issues if we did. Are there structural concerns with removing these perpendicular ceiling joists?

There are collar ties at in the top third but no other rafter ties besides this beam.

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  • Do you plan to insulate the roof deck as well? Or is the duct purely for ventilation? – ThreePhaseEel Mar 14 '17 at 0:20
  • We will be rerouting the duct work and extending the rafters to make adequate space for insulation and a gap for ventilation in the new ceiling. – McCall Mar 14 '17 at 0:34
  • Where are you on the planet? (Or, equivalently, what are your ground snow loads?) – ThreePhaseEel Mar 14 '17 at 0:56
  • Seattle Washington area. We got an abnormally high amount of snow this winter with 2 storms each getting up to about 5". Google search says our ground snow load is about 15 PSF. – McCall Mar 14 '17 at 1:09
  • an unvented, heavily insulated roof (insulating atop the roof deck) should be practical for you then -- I'd look into that if I were in your shoes, at least as a comparison option – ThreePhaseEel Mar 14 '17 at 1:11
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I believe that you're correct about the ceiling joists being entirely for cosmetic purposes. The rafter tie keeps the walls from spreading, and it appears to be adequately suspended by the roof structure as a whole.

You're probably doing the rafter tie a favor by eliminating the ceiling joists from its bearing, and unless you add substantial weight back onto it I don't have cause for concern.

All that said, I'm sitting here in Minnesota looking at your place in Washington through a peephole. You really do need to get a qualified professional on site to make a more reliable assessment of the situation.

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I have a structural background (somewhat) and I don't get it. There is no reason that the whole thing doesn't fail...how'd they do that?

First, the existing 2x4 ceiling should not be able to span 12' and support the existing gypsum board without cracking due to extreme bending.

Second, the 2x4 roof joists should not be able to span the 23' with just roof ties (and you're even missing one). So, according to my calculations, the 2x4 roof joists at 24" o.c. Should only be able to span about 15' (and that's using the old cut framing dimensions).

Third, there is no reason the the walls are not bowing out due to the thrust the roof structure is placing on the top of the wall. Yeah, I know, the roof ties (and strong-back) are installed to hold the roof rafters from pushing the top of the wall out of plumb. The downward thrust (when loaded with snow, etc.) will cause the flimsy 2x4 roof joists to deflect (bend) and push the wall out of alignment. Having one strong-back is not sufficient to ties the walls together.

I just don't see how you can remove ALL the ceiling joists. Maybe an alternative would be to keep every third or fourth ceiling joist and wrap it with gypsum board. That would make the ceiling appear "open".

Great...now I'm going to be up all night trying to figure this one out.

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  • The rafters are 2x6s though I'm not sure that helps answer your questions. The only 2x4s are the ceiling joists at 24 OC and as you said, that doesn't match any of the span tables I have looked at. I have tried to do a lot of research to get an idea of what questions I should be asking and when to know if the pros I am consulting may be under educated. I am concerned that may be what is happening here. Also, we removed acoustic tiles that were attached to 1x4s running the 23ft length that were nailed into 2 layers of Sheetrock. It was absolutely sagging! everything about this house is strange. – McCall Mar 14 '17 at 4:14
  • Oh, of course, 2 layers gypsum board...not one layer. Ok, so the strong back is supported at the mid-span by the 2x6 vertical up to the ridge. The 3-2x6's can support a total load of about 180 lbs. per linear foot (assuming they are all nailed together properly) for a 11' span (half the 23' minus the width of the 6" walls.) The tributary load transferred to the 3-2x6's is about 90 lbs. per linear foot. So, even if the 3-2x6's are not nailed properly, they'd still support the ceiling joists. Ok, so much for the ceiling joists...now the roof joists. – Lee Sam Mar 14 '17 at 5:17
  • A 2x6 roof joist (old size sawn framing) can support – Lee Sam Mar 14 '17 at 5:19
  • A 2x6 roof joist (old size sawn framing) can support about 40 lbs. per square foot at 24" o.c. for a 10' span. (Half the 23' minus 18" for the roof tie.) Depending on local codes (and snow load requirements), that would allow for about 15 lbs. per square foot for dead load (framing and roofing) and about 25 lbs. per square foot for live load (snow load). That would be fine for my area,but I don't know about your area. So, the 2x6 roof joists could span the 23' with the ties, but they are also in bending. I'm home now and my books / software are at work so I'll have to check that tomorrow. – Lee Sam Mar 14 '17 at 5:33
  • So I am doing my best to follow your technical speak , please correct me if I am misunderstanding... in your first comment it seems like you are saying that perhaps the 23 foot beam is appropriate for providing the necessary support for the roof. But then I lost you when you mentioned the ceiling joists. The ceiling joists are running at a 90 degree angle to the beam and are beneath the beam. It seems like the ceiling joists would potentially be supporting the beam. The snow load for my area is 15 psf. Seattle, WA. Could you give me your thoughts on a bottom line summary for your concerns? – McCall Mar 14 '17 at 5:45

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