My little single-story cottage with the hip roof is finally gutted. Now I need input on how to tie the structure together so I can remove the old ceiling rafters. I understand the basics of rafter ties (the lower the better) but have never dealt with a hip roof. This one is a 24′ square, comes to a point and has a pitch of roughly 8 in 12. Should the hips themselves be tied together diagonally across the space, or is it sufficient to tie the opposite sides of the roof to one another? There have never been any ties in this roof other than what the ceiling rafters provided in one direction. I’m not sure what resisted the thrust perpendicular to those – the lath? The whole structure is nice and square with no sagging or signs of stress. Obviously I’d like to keep it that way. This will be a fairly rustic space, so no problems if they show; in fact they’ll most likely become an architectural feature of the house.
Thanks much.
John in Pittsburgh
Replies
You doubtless have/had ties perpendicular to the ridge, since that would take care of the thrust in that direction. Once the ridge is held up by the commons, the end hip really doesn't generate much thrust, so no ties are needed. That said, I have seen long end hips supported mid-span by struts. Also, the flooring or ceiling system is often planned to supply thrust resistance -- likely in your case.
You might wanna consider getting an engineer or architect involved since you're apparently planning on removing joists (which you call "ceiling rafters"?). Most BIs will want to see a stamped drawing in such a scenario -- I'm guessing yours will as well.
Mike Hennessy
Pittsburgh, PA
Thanks, Mike. You answered my primary question about how much thrust ends up on the hips themselves. There are some aspects about this house that are a little unusual (at least in my experience), most of which make me think it's an old mail-order cottage. The roof (which, by the way, has no ridge - it comes to a point) is framed with 2X4s, and the floor joists meet end-to-end over the beam in the basement - no overlap (which I take to mean they were cut in a factory somewhere). Even what I refer to as "ceiling rafters" (always thought the word "joist" referred only to floor framing) are 2X4s that meet end-to-end over an interior partition with a short floor board scabbing the two parts together. Anyway, you are right to encourage me to get a pro involved in this, but I always like to check in here first to avoid that "what are you, crazy?!" look on their faces when I tell them what I want to do. You've given me what I need to go forward. Thanks very much.
John
There is no ridge when you have a square hipped roof. Itr form,s a pyramid
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"There is no ridge when you have a square hipped roof."
DOH! I missed that it was square.
Deduct 1 point. ;-(
Mike HennessyPittsburgh, PA
Why do you say there never were any ties if you are trying to remove the cieling joists? Those ARE the ties.
You should have an engineering consult
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Right, they are the ties, and I knew I would have to replace (rather than just remove)them for a cathedral ceiling. They run side-to-side, but there is nothing that runs front-to-back to serve the same purpose on the other axis. I will, of course, correct that. It does occur to me, though, that if two opposite sides of a pyramid are solidly triangulated with a strong base (these ceiling members), wouldn't the potential thrust exerted by the adjacent sides on their respective supporting walls be significantly reduced by the fact that the peak of the roof can't fall since it's the top of the solid triangle? If the peak can't drop, what's going to push those other two walls out? Add to that the lightweight framing of this roof, and maybe I shouldn't be so puzzled that it's stayed so straight and square for 70 years. Anyway, I'll be using an engineer; I never ignore Piffin's advice.
Hey, Mike H, I was wondering if you have any recommendations for a heating contractor here in Pgh who specializes in hydronic systems. I'm not putting in anything fancy or exotic, but I want someone who does hot water all the time. I'm in the Homestead area.
Thanks again for the help.
John in Pittsburgh
"Hey, Mike H, I was wondering if you have any recommendations for a heating contractor here in Pgh who specializes in hydronic systems."
Sorry for the late reply -- for some reason, this thread disappeared from my browser until today. Poltergeists, I guess. Homestead? We're neighbors, sorta kinda. My current job is in the Waterfront.
I used to use Energy Reduction on 51 down near McKees Rocks -- great guys, but rumor has it that they've closed up shop. Not sure who I'll use now. Most of my regular plumbing & heating guys are in the South Hills -- M.J. Flaherty & L.S. Hafer. Both are pretty good for what I've used them for, but I don't know how they are in hydronic.
Mebbee Buck can give you a pointer too.
Mike HennessyPittsburgh, PA
Thanks, Mike. Gee, small world, huh? I never had much reason to go to the Waterfront before I bought this little place; now I'm there all the time (usually at Lowes). Anyway, let me know if you should hear of anyone who gets a good recommendation. I'm sure there are plenty of companies that do both very well, but I think central AC has made forced air the way to go for most folks these days. I know a guy who does work on the boilers where I work, but it's obvious he's winging it. I'll need to make a choice soon; this strangely beautiful weather we've had through August and September can't last much longer.Thanks again.John
FWIW on one of the TOH shows they looked at another home that that had cupulo like observation room that was an all open. I believe that they said that the top plate was a structural (square) ring. I think that this was smaller, maybe 12x12. And most likely not something that could be retrofitted.But I still think that it was a neat idea..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yes, I think I remember that too. When I began thinking about this issue, I tried to figure if what I know about domes could apply to a square structure. My recollection (from some PBS show no doubt) was that they used a chain to encircle the base of immense domes way back when. Then I noticed something about my house that I missed at first: There's an extra (third) top plate on the sides parallel to the ceiling framing (the sides that are not tied together structurally).
What I'm leaning toward now is beefing up every third ceiling 2X4 significantly and removing the rest. That would leave the tie system at its lowest possible point while creating a space that's open enough.
Only with the engineer's OK, of course.
Thanks!
John
If you do diagonal ties that are sized and placed properly, the hips become structural, in effect, and the rafters are all just hanging and delivering point loads.
When I say "sized," I mean they should be of sufficient strength to handle the axial loads. Steel rods or cables can be used, but the connections should be engineered.
You said "cathedral" so I am presuming that you want to open up all inside space to the bottom of the roof rafters, although this means that in a 24x24 building with an 8:12 hipped roof, your floor to roof reach at the middle will be about wall height plus eight feet, perhaps sixteen feet if your exterior walls are eight feet tall.
Ten, twelve, fourteen, and sixteen feet of space above the floor is OK in one of the ballrooms in the palace at Versailles, but above smaller rooms as might be in your place, it will seem wierd.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Well, Gene, I guess it's a matter of personal preference in terms of the height of a cathedral ceiling relative to the room size. Now that the place is gutted to the studs and rafters, I can say that the height feels very good to me. Part of it is the warmth of the time-darkened framing and sheathing. One thing I know I don't want is a drywalled box that comes to a point. But the other thing is how different a hip roof feels in terms of the sense of height compared with a gable roof. Even though it is about seven feet from the old ceiling to the peak (meaning the total floor-to-peak is 15'), there is a cozy feel to the room. Again, I think that has a lot to do with that aged framing's toasty color, but I'm planning to finish the underside in something warm and woody. Chances are, by the way, that the interior will not extend all the way to the peak; the ventilation for the roof will claim the top 18" or so. But you're right to encourage me to be sure this is what I want. Cathedral ceilings are trendy, and we've all done things we wish someone had suggested we think through a bit more thoroughly. And thank you for the input on the diagonal ties. I'd almost forgotten that it was my original question!John
If your whole 24x24 building just has one room inside, like maybe a church would be, then the large vault would not be out of scale.
Here in the northern Adirondacks of far upstate NY, most everything that gets built is some sort of a getaway, and great camp style prevails, some of the owners going to great expense to either maintain the c. 1885 campy-ness, or if building new, do it like the old.
Planked hipped ceilings are quite common, but they rarely if ever vault up to the top. Here is a typical room finish, in a new build. In some of the great old places, the finish in a ceiling like this is all birchbark panels rimmed in half-sawn sections of bark-on cedar logs.
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If you are dividing the 24x24 square plan into various rooms of varying sizes, any room with one or more outside walls, if you desire ceiling vaults, will vault with the roofline at those outside walls. This is a given.
What you will need to decide is how you want to do those rooms. An outside-wall room with an 8:12 pitch up on side of the ceiling, is going to feel quite unbalanced if the other sides of the ceilings don't pitch up equally.
I am in favor of the hip-and-flat approach as shown in the pic above, and raising the flat for larger rooms, then bringing the flat down for smaller rooms.
Any room that is not rectangular or square will require decisions about how to treat the ceiling. Some are inclined to do a flat ceiling at wall height for the smaller ELL part of such a ceiling, and hip-and-flat the larger.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
That's kind of spooky, Gene. Your description of the camp/getaway tradition in your area is exactly what I'm working to create. At first I had some trouble explaining to friends why I was so excited about this little place, but when I finally said, "It's the getaway cottage you don't have to get away to," they got it. The other thing you wrote that resonated was the mention of a church. Among the properties I looked at were (really small) churches, again for the opportunity to work with a single open space. I'm a singer who spends a lot of time in different churches doing weddings and funerals, so I think the vertical component of a space is just in my blood at this point.
So yes, it will be one big room with one bedroom in the basement and the other in an enclosed porch that will need to be rebuilt for several reasons. Your photo is a good example of where I'm headed, so I'm grateful for the visual inspiration. Thanks again for your input.
John