Reclaimed old growth Douglas fir floor joists — how much is enough? too much?
FHB Brain Trust,
I’m planning a 1.5 story garage using mostly local green hemlock. The 1.5 story portion will be 32′ x 16′ with the upper floor being used for light storage and office space. By the AWC calculator, and the advice I could find on the web, 16′ is on the long side for a a green hemlock 2×12, so I was already wondering about that …
The other day I came across the opportunity to buy 30+ old growth Doug Fir boards, true 2×13.5″ x 18+ ft. long. Removed from a bank built in the 20s. I was planning balloon frame true 2×4 walls with a let-in ledger board, and face nailing the joists to the studs.
I am pretty confident that once these are de-nailed and the ends are cut, they will be PLENTY to span 16 feet. My questions:
– is this overkill?
– should I go with 2×6 studs to support these big heavy boys (I estimate near 100 lbs each)
– should I make the stud and joist spacing wider, e.g. 24″ centers? (or the fabled 19.2″?)
– I’ll probably be buying more than I need: other favorite things to do with old growth fir??
Looking forward to some guidance, thank you all!
Replies
Love the term 'light' when applied to storage. Does it really mean highly illuminated?
Unfortunately most folks have no idea how much weight ultimately gets piled onto a floor designed for "light storage". I'll climb off that soap box.
Old growth lumber is great and it might be helpful to an engineer well-versed in wood design to determine the year that the bank building was constructed. That way he/she could dig back into previous versions of the NDS to determine an appropriate allowable design stress. Using the current tables in a code or the current allowable stresses published in the NDS would be inappropriate for those 2x14s.
If it were me (a structural engineer BTW), I'd consider 2x6 studs at 24" c/c with a 2x14 joist aligning with every stud, using either a let-in ledger or an appropriate framing anchor. Don't forget to install firestops in the stud bays. I trust you're planning to sheath the interior with fire-rated drywall - both for fire protection AND to help stiffen those 2x6 studs. Don't skimp on the upper floor sheathing as well - you'll want that diaphragm to help stiffen the entire structure. Same goes for the exterior wall sheathing - upsize the thickness for a 24" stud spacing.
Thanks very much. I like the idea of connecting the joists to the studs. Plenty of 16d nails and a let-in ledger seems like it will be good and sturdy. Would you place an additional 2x6 under each joist?
Am planning fire blocking; will not drywall if I can avoid it. Looked at various possibilities for sheathing and am planning on plywood or LVL for the second floor decking and the roof sheathing.
Walls will probably be sheathed with horizontal green pine 1x, then covered with tarpaper, then green pine board and batten. Let-in diagonal bracing at the corners to avoid racking.
Upstairs will be left unfinished to dry for a season or so, then batting in the stud and joist bays, 3/4 or 1" shiplap instead of drywall. Going back and forth on a vapor barrier (e.g. Siga) under the shiplap and over the insulation.
Planning to keep all wiring external to walls, in either wire moulding or armored cable.
FWIW I think of "light storage" as "no engines, no bales of hay" lol. Storage tubs of clothes, etc.
I once got sucked into checking the design of a factory interior tool 'shed' that was relocated to serve as a storage mezzanine. All steel framing. The facilities manager figured that since it was steel, there would be no issues. They intended to load the mezzanine with paper records - paper is light right?
The original 'roof' was designed as a dust cover and not as a load-bearing 'floor.' After careful examination of the desired loading, it turns out that a 5' high stack of paper files can weigh upwards of 250 pounds per square foot. Not exactly equivalent to the load of 'dust.'
My point - 'light' storage is never a realistic quantification of load.
LVL for decking? Not sure you have your terminology correct. Plywood yes, LVL not likely.
Without drywall or interior wall sheathing the only place firestopping will be effective is at the upper floor level.
I don't know how your local building official will judge this, if at all. But in my region a garage has to be drywalled & taped using 5/8" fire-rated gyp board. If you can get away with all wood inside & out, good for you. But I'd never to that because I'd want some amount of resistance to ignition - there's "never" an open flame used inside of a garage - right?
I'm a Simpson screw guy instead of nails. What's your opinion on that?
Thanks Yankee. :)
I'm bumming out about the drywall: I would love to have the downstairs walls open and uninsulated, both because of the expense and because I like the look. Any idea if workshops or barns are regulated differently? Realistically, I'm not going to garage cars in it: it will be workshop, storage, gym, and office. (Worth asking.)
LVL: I was thinking of the stuff Advantech sells. Wouldn't that count as LVL?
I'm hoping those 2x13.5 old Doug fir joists are plenty to handle that span!
Yankee, a related question, since you're (almost) local to me: is there a way to get this lovely reclaimed wood inspected and graded? Building inspector here in RI says no stamp, no build. (Code allows an exception for native lumber, but not for salvaged or reclaimed lumber.)
Detached garage?
What is your reasoning for wanting to use ballon framing with a let in ledger over platform framing? Is it just ballon framed at the gable ends or are you planning on having the studs create a short 2nd floor wall on the eave side as well?
You mentioned the 1.5 story portion is 16x32'. What is the size/shape of the rest of the building and are the 2nd floor eave side walls (if there are any) above the exterior 1st floor walls or set in a couple feet towards the interior.
Detached garage, yes. And yes: balloon side walls, forming the first floor and short 2nd floor walls as well. My thinking is that with balloon framing, the joists serve an important role in tying things together, kinda like giant collar ties. Have been worried about a 1/2 story with short side walls being weak. Does that answer your question about the eave side walls?
The plan is to make the other side 14x32', attached as a big shed addition to the side of the 1.5 story portion.