Floor support check and questions
Beardoh
| Posted in General Questions on
I am hoping to get confirmation that I am thinking about the supporting walls (in the basement) for my floor correctly.
House is a 1 story 46’ x 32’, simple rectangle. North is up in the floor plan. CZ6A
The supporting wall in the basement is based off my mother’s place, which was built 5 years. Span is the same, so I thought I could replicate some of the ideas.
I am trying to get away from a long girder running down the middle. At my height – meaning 6’5” tall, it seems like an unfortunately low placed thing…making door entries ultra short, etc.. I didn’t love it in the last house I built.
In this basement, where most of the ‘open’ space will be for woodworking tools in my guitar building, having a long wall running down the middle is not an issue. The space will be plenty big, and I don’t mind the forced separation of some space, as I will likely have a machine-free zone of the shop. I realize I left out the door between the two halves in the main section. Location TBD.
The long wall near the center is meant to hold up the TJIs or Trusses that would span the full width – 32’ – (north to south) of the floor. The short wall on the north side of the stairs would support the TJIs or Trusses coming from the other side…and be there to nail in the stair stringers. I’d have my concrete guy do a long trench footing for that long wall and then likewise for the short wall on the north side of the stairs. One of the attached photos shows a short bit of the supporting wall.
The developer who did my mom’s place used 12” deep TJIs with 2” flanges installed at 19.2 OC. It is OK, but only OK. I dislike squeaky or bouncy floors, so I am guessing that going to 16” OC and having 3 or 4” flanges would eliminate a bit of the bounce that I notice in her place.
My Questions:
1-Is my plan for the supporting 2×4” walls good? Any downsides to this plan?
2- I am thinking that TJIs will be much cheaper. I’ve been told floor trusses are 15-20% more. A friend should be able to help me with a decent HD discount on the TJIs, I am guessing that differential will only increase with that discount.
3- Is 12” TJIs with 3” flanges at 16” OC good for a solid floor with these spans?
4-For subfloor, I was planning to use LP Legacy subfloor from HD. I see it is $40 retail vs $62 for Advantech. Is LP Legacy decent? I’ve only used Advantech, which was fine.
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What you're proposing can be done. But it needs to be engineered, there aren't "standard" ways of doing it, you have to calculate based on this house and the materials you choose. Your local inspector may insist that a licensed engineer sign off on the plans.
A bearing wall may not be any cheaper than a row of posts spaced every 8' or so. You could then build a non-bearing wall around the posts. The advantage is if you ever change your mind about the layout you can take the non-bearing wall out.
Also, if you're worried about clearance, it costs almost nothing to make the basement taller in new construction.
Do you mean making the basement through taller concrete forms. The difference between 8 and 10’ walls is at least $6000. Are you proposing something else?
I am leaning towards the 10' walls...but things add up.
OK, maybe "almost nothing" is the wrong choice of words, but it doesn't cost any more than the cost of the taller footers. It's become the norm in new construction around here, because finished basements are the norm, and the taller ceiling makes everything easier, you can drop big soffits and run all of your mechanicals below the joists.
I am with DC, consider taller basement walls. This will give plenty of room for ductwork and utilities. Make the basement a neat place to be, warm, dry, storm shelter, people cave.
I'll likely be spending a good amount of time down there....both building instruments as well as cabinets and furniture for the home. 10' would feel pretty nice...and allow for some higher storage for wood.
I've got 9' 6" ceilings in my garage and love it. I can pull in my full size truck with the racks on it or swing a 8' board around without worrying about it. It's a nice upgrade if you're going to be spending much time down there.
Do you have a foundation insulation plan yet? I typically insulate the interior of the walls and under the slab with rigid foam. To reduce thermal bridging, I run 2" foam over the footing. Standard concrete forms are 96" but you typically pour about 94.5" high, which leaves 90.5" with a conventional 4" slab, or 88.5" if you run foam over the footing like I do. That leaves 90" from slab to the bottom of the ceiling joists, or 91.5" if you double up the mudsill. That's not terrible for a basement and I have lived in houses with ceilings that height; it's ok but not great. It would be nicer to use taller forms or add a horizontal form above the regular form, which can get you another foot or two of height, but it's usually a significant upcharge.
It can be hard to schedule the concrete flatwork so one advantage of building a center beam on posts is that you can frame the house and pour the slab later, instead of waiting for the flatwork contractor to get there and the slab to set up before you can continue framing. Rushing the slab to dry is one of the best ways to guarantee that it will crack. Slow-curing helps avoid cracking.
TJIs need to be covered with drywall for fire protection. Triforce open web joists can remain exposed, except for the plywood trimmable ends, as can solid lumber 2x10 or larger. You may want a drywall ceiling down there anyway, but if you don't, it's something to consider.
I often do flush beams to save on height, even though it's a bit more work to install them. They do make it harder to run utilities across the house but there is usually a way to work around that.
Great point on the concrete drying before putting that bearing wall up. I did not think of that. What is a safe time for it to set for a May pour in New England?
I am pretty easily convinced to splurge on the taller forms. When getting concrete quotes over the winter, I was pretty surprised how few concrete guys do a taller 10' wall. At 6'5", 8' ceilings feel short.
Sub slab insulation in basement. You mention 2”, but is that just over the concrete footings, with another 2” below? Or 2” all around. I recall 4" from the PGH book, but now looking deeper, perhaps the 4" was for a slab on grade build, not a slab in a full height basement?
I usually do 5-6" of foam under the slab, with only 2" running over the footing. I often also run 2" foam over any pad footings, around any lally columns, though the energy advantages of that are pretty small and don't always make sense.
If you pour the slab before framing, I would wait at least a week of temperatures above 40° or so, which should get it to 66% strength. If you can wait another week it will be over 80% of its ultimate strength and hardness.
Your mom’s house tji seem like they would have no issue spanning that distance. They should be able to span more at only 480. If you are concerned about floor stiffness I would recommend upgrading to 1 1/8 ply, I don’t think the tji are the issue as even 2x12 should be enough to span that (with support in center). You will get a much sturdier floor. You might consider 2x12, as the cost should be cheaper (might want to double check that) and they are very easy to hang if you decide to bury your girder in the floor.
If you use 2x lumber, or with any floor system, plan you utilities and duct ahead of time.
Thanks - I appreciate the perspective on the TJI at 16" OC with 1 1/8" ply. I recall being in a house 20 years ago that had qty 2, 3/4 ontop of each other. That floor felt outstanding. I forget the joist span.
+1 on a center beam. It will be simpler and cheaper to build and make the space much more flexible.
If you go with trusses, they can be made with beam pockets so you won't loose any ceiling height but will make running utilities harder. The beam can also be pocked with I-joists or dimensional lumber.
You can go with a wide flange steel beam, about 6" tall will span you basement in 3 sections and will still leave some room above. You can also keep one section of beam bellow the joists and run all your across there.
Stair openings can be framed without needing additional support wall. This is usually part of a standard truss floor package. Done with LVLs/I-joists/lumber as well, pretty much the standard way to build.
As for bounce, you can try some o the I-joist calculators ie:
https://www.weyerhaeuser.com/woodproducts/engineered-lumber/resources/tj-pro-rating/tj-pro-rating-calculator/
15' span is not that big, so bounciness is not as big of an issue if you go for a bit above code min deflection (l/480). 12" wide flange I-joist 16OC is overkill.
Thanks - I used a wide flange steel I beam in a build 20 years ago. I liked having that little shelf in the basement...but I didn't like how we did at the time. We put a pocket in the concrete. This gave us a difficult material shape to trim around - I never was satisfied with it, and ultimately a wonderful thermal bridge :)
Thank you all - I am convinced to have:
- 10' Basement height
- Beam on lally columns
How do you all feel about plywood versus the engineered floor products for subfloor?
I've heard it said that plywood is good, even in wet New England as it is stronger than Advantech or LP Legacy. Frankly, I am nervous about exposure to rain or an unforseeable delay that leaves it without a roof for a period of time.
Beardoh,
Remember that ten foot forms don't yield a ten foot basement height. You have foam insulation and a slab to deduct from that.
Advantech is pretty much magical the way it holds up to abuse. Now they have a gold-colored "X-Factor" Advantech that's even more water resistant. In 3/4" thickness on 16" o.c. joists of any type, it's good enough for the best houses I've designed or built.
If you want the floors to feel solid, I recommend getting the joists sized for L/480 deflection, vs. the L/360 deflection that is standard.
Do you plan to install a drywall ceiling on the lower level, or leave the joists exposed? Do you plan to have ducted HVAC systems? Those make a big difference on which products I would consider.
Hi Michael - Thanks for your thoughts.
Interesting about the gold factor Advantech. I wasn't familiar. It looks like pricing isn't too much more than standard Advantech.
Thanks for the deflection recommendation.
Yes to drywall on basement ceiling. I figured I could go with TJIs for that reason.
Not planning on a ducted HVAC. Between GBA and the PGH book, I am pretty convinced to go ASHP ductless mini-splits. I think the only ducts we'll have is what is required for an ERV (well, bath and range ducts too, but they won't enter the basement).
I had a project get delayed after the subfloor went down in the very rainy PNW. We used Advantech and it was soaked for many months. Some of the edges did swell a bit by the time it was fully dried in, but a couple hours with a level and belt sander got it all perfectly flush for flooring. I was told that Huber would warranty it if I filed a claim, but considering how long we left it out and how little was needed to rectify it, I didn't bother.
Bottom line is that it takes a lot to get Advantech to swell, and not much to fix it. I haven't seen it swell anywhere else I've used it so I'm not sure I'd even spring for the Xfactor version.
That is quite an endorsement. Thanks for sharing. I’ve read some poor reviews on different engineered products like Advantech or LP, and wonder how the experiences could be very different with an engineered product.
New England has nearly guaranteed rain in June, and tons of projects start at that time.
My house came with Advantech A-frames meant to cover rose bushes, but we put them in our chicken run for the birds to roost on and to hide from sun and predators. They have been sitting on the ground, outdoors, with chicken poop and bedding piled around them, for eight years now. After about five years the bottoms finally started to rot but they are still in place. Regular OSB would have disintegrated years ago, and plywood would have delaminated by now.
Think asymmetrically. Betcha the sweet spot for TJI is something like 24 feet. IF you had a 24/8 split what would the space look like. Ther is about zero reason to be locked into 50/50 if there is a better way.
Aren't stairs self supporting? No need for a structural wall parallel to the stairs I would think
Also is it crazy to have a beam 'in' the ceiling? Joist hangers with no drop beam?
I do like a high ceiling. I have a 16 foot at work and it sure is nice when manipulating 8 and 12 foot stock to not even have to look up.
Thanks for your thoughts - 16' ceilings...that is nice! I don't work with a lot of sheet goods or long pieces in guitar building, but just in working on the kitchen cabinets and some furniture, I think I will enjoy having some vertical space over 8'.
The 50/50 split is pretty intentional. I'd like the ability to rent out the home during ski season, and closing off the area as I've designed is for that reason.
This diagram shows my understanding of what Michael Maines is suggesting for insulation layers below the basement slab. Do I have this correct?
Sorry for the delay--yes, that's how I like to do it.
I'm in the middle of building a new house and I had very similar decisions to make: 10 ft. tall basement walls vs. 9 ft. tall walls, floor trusses vs. I-joists, etc.
As I've learned new things during the build, there are a lot of things I wish I would have done differently. There are also some things I'm glad I did, which turned out to be valuable in unexpected ways (like adding way too much rebar to my basement walls, which turned out to be maybe enough).
Below are some comments based on my experience. Some of this might be overly technical, but I wish someone had told me this stuff last year when I was designing my house::
1) Footings -- Taller basement walls are heavier, and might require bigger footings than typical. In a perfect world, you would hire a geotechnical engineer to determine your soil bearing capacity and hire a structural engineer to size the footings. In the real world that's expensive, so some building codes assume the soil has 1500 psf soil bearing capacity unless proven otherwise (be careful though, it could be lower). And they have tables of prescriptive footing sizes based on snow load, number of stories, brick veneer vs. siding, wood frame vs. masonry walls, etc. For example, see Tables R403.1(1), R403.1(2), and R403.1(3) on this page: https://codes.iccsafe.org/content/IRC2015/chapter-4-foundations. They assume a 32 ft. wide house with an interior footing exactly in the middle of the house. However, the tables don't include basement wall height (maybe in a footnote somewhere?), so if you have taller than "normal" walls, make the footings a couple of inches wider. Also, although those tables say you can make footings as thin as 6" thick, I wouldn't go less than 8". Mine are 10" thick and I wish they were 12". Put rebar in the footings, on chairs at the proper height. When in doubt, make the footings bigger, just in case. A couple extra yards of concrete isn't that expensive, and you can't make them bigger later.
2) Basement Wall Height -- I went with 10 ft. tall basement walls and I'm glad I did. However, I didn't understand the implications. The soil on the outside of the basement walls exerts force on the walls, trying to push them inward. This force increases as the square of the basement wall height (actually the backfill height, but I'm assuming you're backfilling almost to the top), so 10 ft tall basement walls have roughly 50% more soil force pushing on them than 8 ft tall walls (10^2 / 8^2 = 1.5625). So 10 ft tall walls should be thicker and have more rebar than 8 ft or 9 ft walls, sometimes a *lot* more rebar. It depends on the soil type (gravelly, sandy, loamy, clay) and whether you're backfilling with gravel or not. For example, for 8" thick concrete walls in clay soil (ML-CL or CL), an 8 ft basement wall backfilled to 8 ft need #6 rebar @ 26" centers. But 10 ft tall walls backfilled to 10 ft need #6 rebar @ 13" centers. See table R404.1.2(3): https://codes.iccsafe.org/content/IRC2021P2/chapter-4-foundations. You can use Table R404.1.2(9) to convert this #6 rebar spacing to #4 or #5 bar, since #6 rebar is expensive to work with. It converts to #4 bar @ 13" o.c. for an 8 ft wall, or #4 bar @ 6" o.c. for a 10 ft wall. So essentially, you need double the rebar when you go to a 10 ft wall from an 8 ft wall. Or you could make the wall thicker and add less rebar (based on the tables).
3) Other things to consider with tall basement walls:
3a) You need more sill plate anchor bolts to resist the higher lateral soil loads. This is not called out in the code (it used to be, in the 2006 code, but they took it out). Minnesota has some recommendations in their code, in an amended version of section R404.1., in their table R404.1(1): https://www.revisor.mn.gov/rules/pdf/1309.0404/2020-03-31%2011:43:18+00:00. For example, 8 ft tall walls in clay soil with 7'6" backfill need an anchor bolt every 48". With 10 ft tall walls and 9'6" backfill, also in clay soil, you need an anchor bolt every 24". However, if you read footnote (d), it says you actually needs bolts at half these spacings (24" oc and 12" oc) if you don't countersink your anchor bolt washers. Since nobody countersinks these washers (I wouldn't), you need the closer spacing.
3b) Foundation wall anchorage -- with taller basement walls, you might need something like the Simpson Strong-Tie FWANZ foundation wall angles to help resist the inward soil pressure.
3c) Basement wall design -- typically, basement walls are designed like a closed-top box that requires a rigid top (the subfloor) to keep the tops of the box from being pushed in by the soil. However, it's possible to design a basement like an open-top box, by designing the basement walls as retaining walls. This is expensive and requires engineering, so most people don't do it. But with retaining walls, you're not relying on the subfloor diaphragm to keep the walls from leaning in, so you don't need all the extra sill plate anchors.
3d) Long, straight basement walls are more likely to fail due to soil pressure or hydrostatic pressure. I didn't know this when I designed my house, and I have a 40 ft long straight wall in one section. Oops.
Anything over 20 to 30 ft. long is susceptible. Corners and jogs in the wall help to strengthen the wall more than I realized. If you want to strengthen the wall without corners or jogs, there are a few options: (i) extra rebar, (ii) thicker concrete wall, and (iii) adding external counterforts or buttresses to the outside of the wall, which are basically 2-3 ft wide "kickouts" in the wall (they make the wall T-shaped at the counterfort) that are as tall the wall itself. These counterforts will help to keep the wall from bowing inward due to soil pressure. There's a picture of one on this page: https://hughesconstructionco.com/project/resolution-of-foundation-concerns/. Adding a counterfort every 15 ft or so should help to stiffen the wall. I'm not saying that you need to do any of this, it's just something to consider that I didn't think about when I designed my house. Plenty of basements are are okay with long, straight, tall walls. It depends on the soil, site conditions, backfill height, water drainage, and many other factors.
3e) You didn't ask about drainage, but your insulation diagram only shows an interior footing drain. I would add an exterior footing drain, draining to daylight if possible. Also make sure you have good site drainage of water, so it doesn't collect against your basement wall. Basically, try to avoid water getting near the basement walls, because wet soil is heavier and puts more force on the walls.
4) I-joists vs. Floor Trusses -- I went with floor trusses, and quite frankly they've been a pain. I would probably do it again because I want stiff floors and the span, but it's not easy. Reviewing truss drawings, making sure they're 100% correct (these things aren't easily returnable!), and not being able to make changes in the field is stressful. Also, floor trusses are generally not designed to take lateral soil pressure loads. You can sort of fix this by nailing sheathing gussets to one side of the floor trusses near the sill plate, to transfer lateral loads up into the subfloor (this must be engineered; I had an engineer do mine). Alternatively, you could use top chord bearing trusses (they give a direct connection from sill plate to subfloor diaphragm), but I don't trust them. The truss seat at the top chord just looks flimsy to me. Solid lumber or I-joists can both transfer lateral loads from the sill plate up into the floor, as long as they're solidly anchored to the sill plate, and the sill plate is solidly anchored to the basement wall.
5) Floor stiffness and vibration -- There is a lot to say on this issue, but here is what I learned from researching it First, pick a floor joist size that will meet your span requirements at L/480 when spaced at 24" o.c. Then, increase the joist depth to the next size up (e.g., if 9-1/2" deep works, go to 11-7/8" deep). Then space the joists closer together, e.g., at 16" o.c. instead of 24" o.c. That's supposed to give a stiff floor with minimal vibration issues. So yes, I think that 12” TJIs with 3” flanges at 16” OC is probably around what you would end up with if you do it like this. But it depends on the I-joist manufacturer -- check their span tables and run through this procedure.
But don't let the maximum deflection be more than 0.5". For example, an L/720 floor that is 32 ft clear span (no intermediate support) might seem stiff on paper, but it would have a deflection of just over 1/2" (32*12/720 = 0.53") and would probably feel bouncy. Another caveat: If the floor joists are supported by a beam, make sure the beam is designed for at least L/720, to prevent vibrations and bounce. This can be expensive (especially with longer distances between support columns, which in turn requires bigger footings for each column, and a bigger beam) so a framed load bearing wall would probably be stiffer and more cost effective.
8) Insulation under the slab -- I went with something similar to your diagram, except for a couple of details (e.g., I didn't run the insulation up on the column footings). I would at least one change to your diagram: I would wrap the vapor membrane down onto the top of the footing of the lally column, making sure it terminates on top of the footing, and *not* on top of the steel baseplate of the column. Because all of the steel should be fully encased in at least 2" of concrete to reduce corrosion of the steel (otherwise, the steel could end up being trapped below the vapor barrier, in a high humidity zone with no corrosion protection). Another difference is that I ran my insulation up the wall between the slab and wall, so there was no thermal break where the slab meets the wall -- this requires engineering though, due to the lateral soil pressure on the basement wall at this depth (it could crush foam if the foam isn't strong enough). My engineer specified 60 psi high strength XPS for this location (instead of the normal 15 or 25 psi XPS). But it depends on your soil and site conditions -- it needs to be engineered. If you don't have engineering, I would let the slab contact the wall as shown in your diagram.
9) Subfloor -- for 16" oc joists, I would go with 3/4" Advantech. It's worth the price in my opinion -- besides the weather resistance, it's stiffer than comparable products. If you want to make the floor feel even more solid, and reduce sound transmission between the first floor and basement, you could add a second 3/4" Advantech layer as an underlayment (decoupled from the floor joists). Advantech has instructions for this: https://www.huberwood.com/technical-library/2-layer-subfloor-with-advantech-subflooring. But a single 3/4" layer of Advantech on stiff 16" oc joists should be plenty solid for most purposes, except maybe large stone flooring. I'm considering going with the double 3/4" Advantech, but I haven't gotten that far in the build yet (it would go in after the house is fully dried in). I also looked at the thicker Advantech (7/8" and 1-1/8") but they cost almost twice as much as the 3/4" Advantech (actually, 23/32") and I don't really need the extra strength. I just sound dampening and a more solid feel.
The bottom line is there is no perfect decision for any of these items. Every time you fix a problem, you are probably introducing a new different problem that you might not realize yet. It's all just tradeoffs, with a few pitfalls to avoid.
Thanks for all your thoughts. Indeed it was technical but worth saying. I appreciate the time that you put into sharing your experience and decisions made on your project.
I've discussed the long walls with the concrete guy. He proposed using pilasters, which I see all the time down in Mexico.
I need to take some time and go through all of your points more thoroughly, and grab some notes...
Lastly...as this escaped me earlier.
Pocket in the concrete wall for the girder or put lally columns close to the wall?
Having a lally column close to the wall eliminates the thermal bridging, so that would be my preference if you are using a steel beam. When using a wood or LVL beam, I usually pocket it.
What about pocketing the steel beam, could the pocket be lined with rigid? Maybe rest the wide flange on a PT plywood shim?
To me it seems the lally column adds more complication than its worth even if you take a small energy performance hit.
Steel is an excellent conductor of heat so if possible it's really best to separate it from the building enclosure. Setting an additional lally column isn't a big deal. It's not just heat loss but the potential for condensation that's an issue. We've had many conversations on the topic here at GBA and I've dealt with it in the real world as well.
I'll go with wood in this case. QTY 3 2x12s on lalley columns 8' apart.
I did the steel I beam before. It me it is not worth the extra expense of having the machine on site to set the beam. In my previous house I wanted certain areas in the casement to have no walls or posts, so the beam made some sense at the time. Not on this house, however. Plenty of space, and I want the wall down the center or at least some partial walls. I like space to hang stuff in a shop....and the basement will feel large.
I think the thermal bridging should not be overlooked with steel, it was easily felt in my old place. It was not easy to finish around either.
Considering thermal bridging, maybe put the lally column close to the wall, but it might interfere with an interior footing drain. I wonder if you could have an internal pilaster to support the end of the beam? No clue if that's a good idea or bad idea.
I've been running some floor joist calculations for myself the past couple days, so I put in your clear span (16 feet, but yours is probably slightly less due to the width of the beam and walls), 16" oc joist spacing, 40 psf live load, 10 psf dead load. I used ForteWeb software by Weyerhauser for some of the calculations, so I also used their I-joists.
See attached tables. Take the results in these tables with a large grain of salt. I'm not a design professional or PE, there might be mistakes, this is just for educational purposes, etc.
There are three categories of performance in the table, they all give slightly different answers for performance. The table cells are color coded -- green is high performance, yellow is okay performance, red is low performance. I arbitrarily assigned the cutoff values & colors, so don't put too much weight on the color coding -- it just helps to visualize the results.
1) Vibration (natural frequency in Hz). Less than 11 Hz is poor (red), 11 to 15 Hz is okay (yellow), and greater than 15 Hz is good (green). These results are based on equations in the vibration article linked at the end of this post.
2) TJ Pro Rating. This is a performance rating generated by the ForteWeb software by Weyerhauser. See the link at the end of this post for an explanation. >= 45 is good (green), between 34 and 45 is okay (yellow), and below 34 is poor (red)
3) L-value of the floor, e.g. L/480 or L/720. In the tables, > 720 is good (green), between 480 and 720 is okay (yellow), and less than 480 is poor (red). I used 40 psf live load, 10 psf dead load, in both tables (even in the 7 psf actual dead load table -- that dead load only applies to the vibration calculations).
Vibration is affected by the actual deadweight of the floor and the stuff on it, so I included two tables, one with 7 psf actual dead load, and one with 10 psf actual dead load. A bare floor with carpet might be around 7 psf. If you start adding heavy things like walls, furniture, etc., it could go up to 10 psf or higher. This will change the vibration of the floor. Vibration also depends on the stiffness of the bearing surface, e.g. a concrete wall vs a beam with long spans between supports. If the bearing is a beam, which also has a natural frequency, it will lower the overall frequency of the floor, which is bad. In simplified terms, you want the beam to be very stiff (much greater than L/720, with relatively short spans between posts) to minimize this effect. Or use a rigid wall instead.
Importantly, only the vibration results consider whether the joists are bearing on a beam with its own natural frequency. Neither the TJ Pro ratings nor L-values take this into account.
To answer one of your original questions, yes, based on these calculations and measures of performance, an 11-7/8" I-joist with a 3.5" wide web at 16" o.c. should give good performance by most measures. Unless I made a mistake, or unless the joists are bearing on a beam with low stiffness and low natural frequency, etc. And remember these are just calculations. In real life, YMMV depending on other factors not considered in them.
Also, different I-joists by different manufactures have different actual stiffnesses (EI values) so check the values for the manufacturer that you use.
Let me know if anyone sees any mistakes in these tables. I didn't error check them closely.
References:
Floor vibration discussion: https://www.finehomebuilding.com/forum/floor-vibration
Floor Vibration Article & Equations: https://web.archive.org/web/20240423194851/https://www.woodworks.org/wp-content/uploads/seaoo_2012_conference_design_of_wood_floors_to_mitigate_floor_vibration_problems.pdf
TJ Pro Rating System by Weyerhauser: https://forteweb.com/Help/Content/D_Design%20Concepts/floor_performance_information.htm
p.s. The upload system made the tables very pixelated. I'm not sure how to fix that.
p.p.s. For floor systems spanning basement walls subject to lateral soil loads, I would recommend a continuous joist from wall-to-wall, so single-piece I-joists spanning continuously over the beam instead of 2x lumber split on the beam. This isn't strictly necessary, since the loads should be (might be) transferred into the subfloor near one wall and then across the subfloor to the other subfloor, but it can't hurt.
Igr123,
Good comprehensive advice.
"And remember these are just calculations. In real life, YMMV depending on other factors not considered in them." If the calculations are done correctly, the performance of structural members closely mimics their predicted performance.