Strengthening Joists- another question
I’ve been reading seiverth’s thread (93333) on reinforcing his floor with interest. My situation is different, so I thought I’d start a new thread and get feedback while the subject’s fresh.
Reinforcing my living room floor is on my long term list of home improvements. I don’t have my notes in front of me, but I can get pretty close on the details. House was built in ’49; has a crawl w/ ~3’0″ clear under the LR. The joist span is ~13′ and they’re 2x10s (IIRC, I measured slightly less at 9″ deep) @ ~16″ OC. Subfloor is diagonal planking, with oak strip over. The room is ~19′ long.
I haven’t checked how much sag there is- likely there’s 1/2″ to 1″. And I’m not dead set on correcting it. But the bounce is just too much- I can even feel our 30 lb toddler walking across the floor when sitting in a chair on the other side of the room.
What I’m trying to figure out is what’s going to be the best combination of effectiveness and low suffering index for doing this, since it involves hauling any materials in ~30′ from the access and I’d likely end up doing most of the work solo.
Candidates include:
1) Full 2×10 or plywood sister onto existing joists
2) Add 2×4 bottom flange to existing joists
3) Add Sonotube footers, posts, and a (say) double 2×12 beam at midspan.
Lately, Door #3 has been the option I’ve had in my head. Mainly because it doesn’t involve a dozen or so repetitions of each reinforcement. Digging and pouring the footers would be a pain, as would getting the beam into place. But it’d be a sure thing as far as taking care of one or both problems. And I’d probably avoid the purchase of a palm nailer.
Any other suggestions or feedback on how nutty this sounds?
Thanks.
Ted
Replies
No doubt I'd go with the beam in a crawlspace. There's absolutely no doubt at all that it will work.
All the other ones are labor intensive, and there's no guarantee that they'll help.
Beam works - but on paper, these joists and layout works, so that tells me something else is wrong, thus my assumption of the checking ends that need repair.
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Sounds very familiar. I had a similar situation, along with a couple of termite damaged joists that needed to be sistered. I chose option #3, which meant that the sister joists only needed to be just over half the length of the original joist. I did not use sono tubes, just 8" deep pad footings.
Sistering floor joists of the same depth and length as the existing can be a frustrating experience.
As someone who has been through the sistering process, I'd be heavily leaning towards option #3 myself! The only reason I had to sister the joists was because I had living space beneath, as opposed to a crawl space.
Setting up a beam to cut the joist span in half is most bullet-proof solution of your three options; I think there's a nil chance that you'll be unhappy with the finished product in terms of floor rigidity.
3) Add Sonotube footers, posts, and a (say) double 2x12 beam at midspan.
Keep in mind that the depth of your beam is dictated by the beam span. If you increased the number of posts, you could decrease the depth of your beam. Based on the 13' joist span cited, a 40+15 psf floor load, and placing the beam at joist midspan, a 4x6 could handle of span of up to about 70", (2)2x8 = 92" span, and (2)2x12 = 136" span (L/480 deflection and #2 hem-fir (E=1.3E6 psi), all cases).
You'll have to decide for yourself whether it's more work to set up additional posts, or haul in a heavier beam. Since you're doing the work yourself, it might make more sense to use a doubled-joist beam; put them in place one at a time that way.
Edited 8/16/2007 3:01 pm ET by Ragnar17
Yeah, the problem is that there was a furnace in there at some point. So, there's a pit about double-wide-coffin size and another 2 feet deep in the middle of the space. So, I'm likely restricted to posts at roughly 1/4 and 3/4 the length of the beam. Thought I'd go deep w/ the beam just to be safe.
about double-wide-coffin size and another 2 feet deep
That a southern dimension?
Sho 'nuff.
Think that's how the home inspector described it when we bought the place.
I'm likely restricted to posts at roughly 1/4 and 3/4 the length of the beam...
Understood. At least you have some span numbers to help guide your decision now.
You might want to think now about how the beam will interfere with replacing the furnace.SamT
Ted, I would go with # 3. Have you checked for power post beetles? A bunch of 'em here in Georgia.Chuck Slive, work, build, ...better with wood
SamT- no issues with the furnace. It was replaced w/ an outside package unit before we bought the place. Then we replaced that w/ a dual fuel setup w/ air handler in the attic. Only the excavation remains.
I do need to do a general check for insect problems in the crawl. I hate being down there on the old side enough that it takes some psyching up to do it. And then, after a run of working there, it takes about 6 mo.s to get ready to get in there again. I'm about due for a visit.
grpphoto- I'll have to check, but I might be forced into wider spacing by this pit plus getting a reasonable distance from the edge. Will take all of the precast options for support into consideration.
That brings up another question- for the posts, would you do KD or PT? I have another issue w/ a PT post that I will ask about eventually. But the bottom line is that the amount that that 6x6 has twisted in drying out has made me a little gun shy on using PT. I haven't done a lot of hunting, but I'm not sure if KDAT lumber is available here.
I'd go with PT 4x4 on the precast blocks, especially now that I see you're in GA like me. PT will prevent termites from digging through the post requiring them to travel on the outside making it easier for detection. Twist in the 4x4 as it dries can be accomodated in the precast block.
Ways to make it more comfortable while you're down there: cardboard boxes to sit on, lot's of light, fans blowing air, radio, vacuum all the spider webs and whatever else unsettles you at the start of the project.
Re the pit, any reason why you can't install a longer post to make up for the difference in height?
Thanks. I could go w/ a longer post in the hole, but it's really in the wrong spot to work well. That and I trust my abilities to get two posts in at the right length with the beam leveled and all much better than I think I could do more posts.
It's actually not that bad down there. Just depressing to see 58 years worth of detritus and realize how much work removing that there is to do- get the junk out plus taking care of various things (floor insulation, better vapor barrier, re-run phone lines to eliminate AM radio interference, etc). And I've gone to a dust mask as standard for setting foot in the attic or crawl- otherwise the inside of my nose is black with dirt/gunk w/in 5-10 minutes.
The other PT issue that I'll ask about separately is a 6x6 post holding up the corner of our porch that twisted over 1" bottom to top along it's ~10' length. Hack GC who did the work just set the bottom in concrete (like a fence post), and it isn't attached at all at the top. Have to figure how much work I need to do to deal with that.
I understand now...
Post away re: the post (pun intended). Twist might just be an aesthetic thing. Set in concrete is definitely a lengevity issue.
Where in GA are you? I'm in Newnan.
> I'd go with PT 4x4 on the precast blocks, especially now that I see
> you're in GA like me.From a structural perspective, that's great, and it might work well with the inspection situation you have in GA. Here in NJ, a purchaser hires a structural engineer to inspect a place before buying it. The seller doesn't have to fix everything, but the pressure can be on a bit. Some of these guys don't like wood (even PT) that close to the ground.If that's not an issue there, it's at least as easy as the concrete block method.George Patterson
George,
The concrete block/CMUs poses a greater risk than the PT posts here. The blocks open cells create dark/damp Termite Interstates that are difficult to impossible to inspect for termites. Not that a 4x4 is perfect either though. Termite Warranty companies are still suspicious of the 4x4 and anything smaller since the PT treatment is usually a different % level (often untreated portions @ the center)(landscape timbers are the worst) than lumber larger than 4x4. Here in GA, it's not a matter of IF you will have a termite problem, but a matter of WHEN you get a termite problem. Something like an average of 2 colonies/acre statewide.
Piffin is right as usual though, why the sag?
John
Edited 8/18/2007 7:42 am ET by john7g
When I lived in GA, we simply capped the blocks with galvanized sheet metal.George Patterson
Seeing there is such an excessive movement in 13ft with 2x10s what would be the reason for such taking place?
Might it be the 58 yearold joists were of a lower strength when originally placed or might drying having contributed to the sag/bounce?
Seeing there is such an excessive movement in 13ft with 2x10s what would be the reason for such taking place?
On the surface, it seems that 2x10s at 16" centers should have handled a 13' span OK. Of course, we don't know what species or grade was used for the joists.
I think the furnace he mentioned played a role -- for whatever reason, the bounciest part of my own floor was right above where the furnace used to be. Must have had something to do with the heat/dry cycles.
The sonotubes is by far the best for a solid foundation but if you were so inclined you could get by with the precast deck footing blocks. Dig/scrape down to good soil and level. I'd go with the sonotubes if there's plenty of room to dig if not, I'd go with the precasts.
> 3) Add Sonotube footers, posts, and a (say) double 2x12 beam
> at midspan.
I wouldn't go quite that far. I would double 2x6s to form a beam. I would haul in the 12"x18"x3" concrete slabs used for landscaping work and some concrete blocks. Lay a slab block where you want a pier and stack concrete blocks up until there's only room for the beam. Put the beam in place and wedge it up against your joists with scrap 2x8 laid flat and 2x4 wedges. Put the piers about 8' apart. If that's solid enough for you, secure the wedges and the beam with 8d nails so that they don't move.
George has the best Idea In my opinion.
2x6s to form a beam.... the piers about 8' apart.
I think the (2)2x6 would be overspanned at 8', George. A 4x6 would only rate about a 70" span per my earlier comments.
If you were really doing a structural beam, I would agree, but you're only trying to stiffen up the floor. I think 8' will be adequate; If not, move the pillars a little closer together.IIRC, the last time I did this, I put the pillars 9' apart, and things worked like a charm.George Patterson
Pouring any concrete should be ruled out since it's too much unnecessary work. You're in a crawlspace so any digging down is wasted effort since it's never going to freeze. Reinforcing the joists should be ruled out because it's too much work if it's possible to add midspan support.
This is a perfect place for those 11"x11"x8" precast concrete deck pads that have a hole in the top for an adjustable post base. Even in the worst soil, the footprint of each will support at least 1,400 lbs which is about what you need if spaced 4' oc. You will be supporting the equivilent of roughly 30 sqft of floor with each pad, which works about right.
I would place a 4x6 across the bottom of the joists, a post/base on each end and others every 4'. Since the metal post base keeps any moisture from the posts, there's no reason to use PT.
View Image
The nice thing about this setup is the screw adjustment of the post bases allows you to take as much bow out of the floor as you want.
One person can complete the job in about two hours with some careful premeasurements of the 4x4 posts that go up the the 4x6. You'll need three 4x6x12' (a bit long, but worst ends can be cut off as needed), 6 concrete pads, 6 adjustable post bases, a pound of hanger nails, enough 4x4 to make up the vertical posts (assume the pad and post base take up 14"-15"). I use deck screws to hold the 4x6 and 4x4's in place while the bases are tensioned and run two 4" Timberloc screws (structurally-rated) into each intersection to keep the overly cautious engineers and nit picky inspectors happy.
6 blocks @ $5, 6 post bases @ $15, 3 4x6x12's @ $20, 3 4x4x8 @ $10, $20 for screws and hanger nails and the whole works is $230 in materials and a couple hours of labor and an extra hour to fetch materials. Done. Cash the check, or pat yourself on the back, whichever is appropriate.
In some jurisdictions a minimum post base footer is 16" x 16" so simply use a precase 16" square x 3" thick block under the precase blocks above and you'll satisfy the requirement since the point load is transfered through the concrete blocks at less than a 45 degree angle to the edges of the 16" footer perimeter. If not required I wouldn't waste the time to meet the arbitrary 16" miminum since the numbers work out with just the 11" sqare bases.
That's how I do it for the most demanding clients if it's inspected or not. It's fast, looks professional, and works well.
Beer was created so carpenters wouldn't rule the world.
Edited 8/18/2007 1:22 pm ET by IdahoDon
I'm in ATL, FWIW.
Thanks, IdahoDon, for all the detail. I've used the deck blocks before- didn't realize they had a spot to sink the bolt from the post base.
didn't realize they had a spot to sink the bolt from the post base.
There are two types of block, one with a single hole and the other one.
Beer was created so carpenters wouldn't rule the world.
Gotta love HD. I started looking a little for pieces as this project makes its way slowly up my list. My local big orange box has the Simpson EB/EPB post bases, but no blocks with the hole. I've called several suppliers in ATL and all act like I'm crazy when I ask for the pier block w/ a hole in top. Any suggestions (for vendors or otherwise)?
I haven't gone as far as bringing it up w/ the HD store manager, though that would likely be a fruitless exercise. Thanks.
goto http://www.strongtie.com and enter your zip. While you are on that page, find the exact thing you are looking for and ask for it by the specific product number.
Bruce
I'm good to go on the Simpson product. The problem is the deck/pier block with the hole in the top that I can't find. I'm tempted to get the store mgr at my local HD, hold the Simpson post base up in front of him, and ask how they planned for me to actually use it.
you'll just have to drill your own holes
or
pour your own piers with anchor bolts located where you want them
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Edited 10/22/2007 11:19 pm ET by Piffin
Thanks. I've thought about it some more, and I'll probably end up casting my own block using bagged mix and embedding a piece of PVC as a blockout. Maybe a little more time, but it'll be cheaper, since I don't have a hammer drill or rotohammer. Though I guess I could rent one (but I'd still have to buy the bit).
Any suggestions (for vendors or otherwise)?
You could always use a solid cast block of any size and simply drill a hole.
Beer was created so carpenters wouldn't rule the world.
If you're still looking for the connectors, where in ATL area are you? Southwest I use a yard that will get you anything you want without the headache.
Thanks. The connectors aren't a problem- I have HD, Carolina Lumber, and White Cap all relatively nearby. HD even has the EPB adjustable post base, there just doesn't seem to be a post block w/ a hole already in it in existence.
Back when it was built, they did not use joist hangers.
The most common framing method was to notch the joist over a ledger which meant that after a number of years 2/3s of them had splits following the grain of the wood.
If that is the case, your 2x10s could be effectively reduced to a 2x4 or 2x6 in terms of practical load bearing capability.
If that is the case, the solution is to individually jack the load of each, and use PL and ply and screws to stitch the checked ends back together again, then remove the jack an d move on to the next one.
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Piffin's right- the joists are notched at the ends and there's a ledger along the main beam. I'm not sure how big the notch is, and I haven't really looked for checking at the joist ends. In your glued & screwed plywood solution for the joist ends, do you do both sides of each joist or just one?
I need to do some more investigation here, obviously. I was going to quickly see how much sag there is across the room, but I can't find my darn stringline.
At least on paper, in my technical but non-structural opinion, the room is well supported. The beam at one end of the joists has footers at one corner of the room and midway along the long dimension. The other end of the joists is partly against the foundation wall, w/ a 10' or so double 2X beam where the foundation bumps out for a bay window. As for settling, crushing and the like, I'll have to do some more looking.
I agree with Piffin, you should do some more checking into the beam. Something is fishy. Bldg codes are based upon 2D simple analysis that do not take into account the interaction of the joist/deck. With 3/4" diag planking, I am very surprised of vibration prob as the assembly will be much stiffer than just a single joist. As an example, we conducted a full scale load test of an arena arch (120' clear span) and monitored deflections using lab deflection gauges and measured stresses with strain gauges. Until we took into account the interaction of the deck and arch section we were nowhere near the actual observations.
Could be some beam settlement issues, thus the joist span is much greater than you think. I have reviewed similar situations and found undersized footings, inadequate bearing that has lead to beam crushing and many other types of probs.
Best of luck, many here will give you great advice.