Will try to make a long story short. As part of a kitchen remodel, I'd like to put in a solid oak beam (approx 13' long, would be fabbed by a local millworks) House has trusses in the attic so the beam wouldn't be carrying roof weight and would largely be cosmetic, although it would be helping to correct a dip that has developed in the ceiling over the years. Work will be done by a contractor but haven't been able to get his input on this yet.
Would anyone reading this be concerned about an oak beam deflecting if it was 6"x4" or 7"x5"? I really don't want to go bigger than that to avoid losing headroom (8' ceilings).
I know the easy answer is to consult an engineer and I may still. Just trying to gather opinions
If the oak beam is wet, it probably won't take much of the sag out of the ceiling. If it does take it out at first, it will likely deflect quickly. Not sure about a dried beam, but that is a lot of distance if the center has to take up some load.
Especially if you hope to lift the center of the ceiling, a structural engineer or architect may call for a gluelam or two, which could then be wrapped with 1x rough sawn boards if you could find some straight enough.
If I recall the formula correctly the stiffness of a beam goes up with the cube of the height and linearly with thickness. As far as supporting its own weight I doubt that a dry oak 1 x 4 would deflect any in a 13' span. So the question becomes how much load are you going to require it to support to raise the ceiling? Can't estimate a size until the load is known. I have a 5" tall oak bean spanning 10' and it holds up a roof rafters for a roof that is 10' x 12' with no sag. It is not uncommon in barns to see oak beams spanning long distances. Oak is very stiff, once dry.
and how well you can clamp a 13' long lamination. That's going to be a LOT of clamps! Also hard to keep it straight. Easy to put a curve in something that long.
Is the dip up or down? Isn't English grand? Dip, bulge, sag,...?
Why is there a dip? That may be your question. Is it one truss that deformed? One element in one truss? Or has the support settled and let the trusses move?
The last time I tried to use a beam to jack a truss back into place, the entire thing moved and we just moved the problem to the roof.
If its a single element that warped you may be able to cut it in the attic and install your beam and then repair the cut element.
It will take a lot of clamps- figure two per foot. Titebond is not considered a structural adhesive. Ideally you should use a glue that dries stiff. Glue it up a bit wider than finish and joint smooth and straight. Not a difficult task for an experienced shop.
Select pieces to glue that are rift grain on the edges so there is not clashing grain patterns on the show edge.
I DID say “long story short....”. Just kidding. Longer version is.....
Small Mid-60s ranch. Living room in front and kitchen in back. I believe there once was a full wall between the rooms that was removed. Previous owner put in a soffit and hung cabinetry from the ceiling, causing the downward dip/sag. I can’t see any deformation of the roofline so I’m hoping the dip is confined to the bottom chords of the trusses.
Contractor said he can mitigate some of the sag by doing some sort of strapping in the attic (I have forgotten or didn’t pay close attention to the details). So the beam would (hopefully)be mostly cosmetic but may carry some weight from the dip/sag. I know there will be nail pops and potentially some new drywall in the ceiling.
Hoping to put in a glued-up oak beam in no larger than 6”x4”. I get Bill’s point that the load on the beam is an unknown
Do you know that it is a truss roof? Sounds kind of obvious, but trusses were just coming in to common residential use when your house was built. The 1965 house we're currently remodeling has a conventional framed up roof and lots of internal bearing walls.
One reason I wonder what is really going on is your mention of the sag and the possibility of a wall removed. Those two tend to go together with a conventionally framed roof rather than a truss roof. Truss roofs tend to be clear spans with no internal supporting walls, at least as they are used now.
Another is that you see no sag in the roofline - that indicates, to me at least, that the ceiling and the roof are separate framing.
It's the old removing a load bearing wall trick often employed by renovators seeking that open concept look, that don't have a clue about structural requirements. You now get to pay for their error.
I would definitely recommend getting a structural engineer involved to fix the root problem; i.e. restore the load bearing structure supporting the roof before it gets any worse.
My thoughts initially too but the roof is definitely trusses. Garage is just as deep as the house (25’) with no supports anywhere in that span. I ran all this by a builder friend of mine and his opinion was that the dip could be caused by the hanging cabinetry as trusses are not designed to carry any weight (other than drywall) on the bottom chords.
I’m not ruling out an engineer (as I am not one and not looking to skimp here).
A 5 x 7 will be stiff. I would have no reluctance to drive a car over a 13' bridge made from two of them. I would design for looks and not worry the stiffness. 7" seems a bit deep depending on he look you want to achieve. But do consider what I said about grain on the edge or it will look unattractive.
You could veneer the bottom edge with a thin veneer of oak resawed from 6" wide board. Personally I would choose 1 x 8's that had one straight grained edge. Glue it up and joint straight and smooth to make the 7" depth.
The original post described "a solid oak beam . . . fabbed by a local millwork." Solid and glue-up are two different things with different characteristics. Even seemingly minor miscommunications can result in significant problems.
Some contractors won't want an engineer involved because the engineer may call for a solution the contractor would prefer not to mess with. Some contractors have almost as much knowledge as an engineer, some very little. Every contractor is going to be willing to complete a project, and there is a suggestion that a prior contractor created a problem resulting in the ceiling sag. Without an engineer's study there's no way to know what actually caused the sag, or whether new work will resolve any existing issues.
A house is a significant investment. My suggestion is to start with a qualified engineer, then look at ways to provide the needed support.
Soffits? Are the cabinets short of reaching the ceiling so they put boxing or soffits above them? If the cabinets are against the wall I would think much of the load from the cabinets is carried by the wall. If the cabinets are against the wall bearing the load of the trusses, near the tips of the trusses, I can not imagine applying enough load to create a dip in the ceiling without destroying the trusses. If the cabinets are out in the middle of the room acting as a divider and actually hanging from the ceiling, then all of there weight hangs on the trusses.
I agree with Bill on the beam. Use plain sawn oak and dress the bottom edge or veneer it.
Investigate the trusses or have your builder or Engineer do it. The bottom cord of the trusses are in a sort of odd environment. They may be buried in insulation and kept warm in winter and cool in summer, while the webs and upper cords are baking and freezing. If the bottom cords are made of Juvenile wood (wood from near the pith) they can warp dramatically. Also, your trusses may have been damaged by whomever installed the cabinets if the cabinets are hanging from them. I've seen them with 3/4" holes drilled though them vertically to receive threaded rod. I've also seen them completely cut by plumbers and nearly severed by electricians.
The good news is they are way over engineered and even if mangled along the way, unlikely to fail. And, you are probably far more sensitive to the dip than anyone else, now that you have seen it. Make any structural repairs you need to and level the ceiling cosmetically.