I am trying to figure if I can increase the open floor space in my basement by removing the center support beam running the length of the floor?
The current floor is 100 yr old redwood joists 16″ o.c. measuring 2 1/4″ by 6″ spanning 16′. Midspan there is a perpindicular 4×6 beam with posts every 6′.
I would like to remove the posts supporting the 4×6″ cross beam and need help understanding what size joists I would need to sister next to the existing 6″ joists to have a satisfactory floor for the main floor upstairs.
I should mention that the existing floor already transmits a lot of vibrations (audible through the rattling of our cast iron wood stove) when the kids (40lbs) start jumping and running around.
Any suggestion what size joists would work? Would work well?
Thanks,
karl
Replies
Can you say steel I-beam?
Bill
Any idea how big an I beam for a 22 foot span?Thanks
Karl
"Any idea how big an I beam for a 22 foot span?"Depends what load is above it. Floor only? or walls and roof"
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Real big and real heavy.
Redwood, even the old growth, tight-grained stuff, is pretty brittle and has a much lower ability to carry a span than other common species used for structural purposes.
And you didn't mention what is atop those joists on the upper floor....
And how much headroom is currently available in the basement?
More than adequate headroom to accommodate bigger joists. Head clearance could be reduced by 8" and it still wouldn't be a problem for its intended use.1 by 4 redwood subfloor with 3/4" oak covering that.Thanks for the reply
Karl
Best thing you can do is hire a structural engineer. If the cost for gaining that knowledge bothers you, consider it as the price for peace of mind.
Cost of an engineer really isn't a problem. I was naively hoping there would be a standard rule of thumb ie. 2 by 12 16"oc is good for a free span of "x" feet for a residential floor.It is becoming increasingly clear that there are a lot of variables to consider and a standard rule of thumb isn't going to exist for a question such as this.The vibration in the floor is one thing I really hope to eliminate in the process of upgrading the joists and I assume a competent engineer can address this as well.If I recall correctly Boss Hog as written in the past about bouncy floors. I will do a search to see if he has any info in the archived posts.Thanks for the input.karl
My copy of "Building Construction Illustrated" by Francis Ching, 2001, gives a rule of thumb that a 2x12 at 16" OC is good for 12 to 18' span. 18' span will be more bouncy, of course. It doesn't mention wood species, I assume that's #2 doug fir.
According to the same book, an I joist of 14" depth would just span 22'.
I only mention this because your aware that before you go and do something drastic, this should be looked at more closely by a professional.zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
Zak, I forgot I had that book. I will give it a look see before I ask any further questions so I can refine my questions a bit better.I also did a search for posts by bosshog with the keyword floor and came up with a lot of food for thought.Thanks for the input.Karl
IMO using rules of thumb for selecting structural components is not a good idea at all. A rule of thumb would be useful for knowing when to be concerned and use a real span table or an engineer to get the correct numbers.
I'd bet there are 100 carpenters/builders/remodelers here who could have given rules of thumb off the top of their head, but none have offered that because they see that the info presented by the OP is sketchy and it would be irresponsible to offer a ROT - pun intended :-)
Regarding that book, the fact that it doesn't mention species or grade of wood significantly discounts the validity of the info presented. For it to make a blanket statement that 14" I joists can span x number of feet is equally suspect as I-joists come in several different series, which makes the distances they can span variable.
To the OP: You mentioned that the existing floor has some excessive bounce and/or vibration - so you know first hand what that is. When using span tables, don't assume you can use the full span listed, or even approach it, unless you want another bouncy floor. I like to use an 85% value but have been criticized here for that statement, because it is rule of thumb type thinking. Again though, you can only use a span table if there is no load being supported other than the floor itself. If you Google for "joist span chart" or similar you can find span charts online. For example, here is one: http://ecodes.iccsafe.org/nxt/gateway.dll/Residential/part00382/chapter00657/section%20head00661/section00669.htm/subsection00670.htm?f=templates$fn=main-nf.htm$3.0#JD_TableR502.3.1(2) Notice that the chart has 2 sections - one for 30 PSF LL and one for 40 PSF LL. Regarding span charts for I-joists, consult the specific manufacturer - again most all have their span charts available on the web.
Regarding head room, your statements were vague, but, for example, in my state, 6'8" is the minimum required by code.
IMO using rules of thumb for selecting structural components is not a good idea at all. A rule of thumb would be useful for knowing when to be concerned and use a real span table or an engineer to get the correct numbers.
I think that's what Karl's asking here, Matt. This is a fairly simple situation- he has said that there aren't any wall supported, just floor/live load. The information that he needs is general information: that 2x lumber won't span the whole floor, but he could get I-joists that could. The next step would be to contact an I joist supplier and have them design a floor system, or to start thinking about how to support the floor mid span.
As much as I agree with all the poster who say that an engineer is worth the money, I get tired of the threads where no one will give out general, useful information, that is widely published (and widely used). The people who find there way here and ask a reasonably informed question are fully able to find span tables in books- so what's the big problem with making their lives a little easier and just say- "this lumber would span that floor if there are no walls or posts on it, and it has a live load of less than 40 lbs psf, i.e., a bedroom type situation."zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
First, let me state that we are just discussing...
>> This is a fairly simple situation- he has said that there aren't any wall supported, just floor/live load. << Right - but the thing is that the way he asked the Q in the first place pretty much stated that he didn't know what to look for. We had to pull the needed info out and I'm still not sure we have it all. We really didn't have an indication as to what the load on the floor might be until maybe around 10 posts +-. Based on the way the info was provided from the get-go for all we know he has forgot to mention that there is 2 king sized water beds in adjoining bedrooms on this floor :-) Also, at this point I'm not sure if there are any walls on it or not.
>> The information that he needs is general information: that 2x lumber won't span the whole floor, but he could get I-joists that could. << If there is truly no significant load on this floor 2x12s would probably be fine, although I can't say for sure since I haven't been there. IMO, more often than not, when there is a beam supporting a floor system, there is something more on top of that beam than just a floor system. I'm still not sure if we know what is above this 1st floor living space...
>> The next step would be to contact an I joist supplier and have them design a floor system... << Great point re the I-joists that I forgot to mention. As you say, most real lumber yards will design a I-joist floor system for free. One minor point for the OP though is that I-joists really don't span that much farther than solid wood members of the same depth. It's just that I-joists come in much deeper sizes.
And, we really don't know if there may be a head room issue in the basement below. He stated that head room is not an issue, but also stated that he wanted to open the basement area up, which seems like a bit of a contradiction, and I haven't seen too many 100 year old basements with >8' ceilings.
I'm surmising that his goal is is to get rid of the mid span support and deal with the floor vibration/bounce issue at the same time so that would kind of preclude: >> start thinking about how to support the floor mid span. << unless he wanted to go with a flush beam.
>>The people who find there way here and ask a reasonably informed question are fully able to find span tables in books<< Not sure what you are saying... is that it the question was not reasonably informed? Anyway, I did provide a link to a span chart so that he could look it up himself. Sure I could have looked it up (although I didn't need to), but believe it or not I thought the guy might learn a little more if he looked at the span chart first hand. So anyway, >> so what's the big problem with making their lives a little easier and just say- "this lumber would span that floor if there are no walls or posts on it, and it has a live load of less than 40 lbs psf, i.e., a bedroom type situation." No problem at all, although I'm not sure there aren't any walls on it... but now the guy has a better idea of what is involved so that next time he can probably even figure it out for himself, or at least ask a question and provide close to the necessary info the first time around. Also, and possibly most important, I think part of the deal is that it is somewhat irresponsible to give out specific recomendations based on sketchy info.
At the very least you are gonna have to agree that he got way more than his money's worth of info, and all he had to do was wade through a little BS, and answer some Qs to get what he wanted.
I'm guessing that you didn't like my objection to the rule of thumb that you stated. Actually it sounds pretty good, but I just objected to the way it was a little vague - for example you said something like that you assumed it would be Douglas fir. Where I live they really don't even sell Douglas fir except "extra" special order so my assumption would be SPF - so you see the problem with general statements. If some other guy lived in Japan he could be thinking laminated bamboo :-) Maybe it's kind of that I tend to think in terms of data...
Yeah, I guess your objection to a rule of thumb kind of got to me- I don't know what's available in his area, and what the specific situation is, so I can't recommend a particular piece of lumber.
Still, I think rules of thumb are useful, if used wisely. I would definitely use something like span/14= joist depth if I was wondering about the feasability of a project, like I take him to be.
By the way, your link to a joist span table doesn't work for me. There are, as you say, plenty available by googling "joist span table".zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
hummm... the link works for me. not sure why....
>> I would definitely use something like span/14= joist depth if I was wondering about the feasability of a project, like I take him to be. <<
that sounds good - hadn't heard that one.
On the stuff I build it is 2x10s up to 15' (which produces a bouncy floor so <14' is a better number) and then it's engineered floor systems for any span larger than that. We don't use 2x8s for house floor systems except ladder access attic storage space. Also, all new construction stuff has to be engineered so there is not much figuring anyway, but after a while you pretty know what the eng will specify based on the span. Beams are a little more tricky. I just had a house framed that got a triple 18" LVL over the garage door! Didn't look like that much load to me, but maybe I'd have to think about it a bit harder... Used to be that that beam would always be steel, but with the crazy material prices these days, steel is not so popular. I also reciently was kind of shocked when I found I could get open web metal plate floor trusses cheaper than the same depth of I-joists.
Try this link:
http://ecodes.iccsafe.org/nxt/gateway.dll/?fn=main-nf.htm$f=templates$3.0
You can "drill down" through the Contents to R502.3
Second that about the engineer.
If the ceiling is low, you might even be able to pick up a few inches by letting the new steel or laminated beam into the joist level and hanging the existing joists from the sides. I did this on a kitchen remodel once. It's a lot of work, but really opened up the space.
Another reason to get an engineer is to calculate the support required at the ends of the span -you don't want to under estimate this.
Cloudhidden has it right.
BTW - are there load bearing wall(s) above this beam you want to remove? Any point loads? How would you support the ends of these joists you want to sister in? Since you will be lowering the ceiling to sister in larger joists, how much ceiling height is there now?
Thanks for all the input so far.I did neglect to mention that there are no load bearing walls above the joists in question. The subfloor is 1 by 4 redwood and 3/4" oak on top of that.Basement height is not a big issue. I had originally hoped I could just sister 2 by 12 douglas fir along side the redwood joists and have an adequate floor. Given the bounciness/vibration in the existing floor I didn't want to make things worse with a misguided guess.If there are too many variables to specify an adequately sized joist that is fine. I will see what I can turn up for an engineer in the morning.Thanks again,
karl
From your post I am interpreting that the full span width would be 16 feet and currently, you have 6 inch deep joists that are supported mid-span. A few things stand out in this post;
First, I agree that an engineer should be consulted.
Second, If you want to anticipate another question that the engineer might (should) have, I'd say look at the available depth for the bearing of any new joists. If only 6 or 5 1/2" is available, any new joists of 11 1/4" depth would have to be notched and that is way too much of a notch. I would guess that a ledger of some sort will be needed to allow the full depth of the new members at each end for bearing.
I reality, the existing joists will not provide much of the floor support once a new joist is installed that has significantly more depth. In other words, if you place a 2x12 next to a 2x6 (even an old high quality, full size 2x6) the 2x12 is so much stiffer that it will attract 80 to 90 percent of the load. Just something to keep in mind.
The ideas of either adding a new joist between each existing joist or changing out the existing mid span beam to a clear span steel beam seem right. If you can tolerate a couple of new steel posts (with new footings) a few feet off of the end walls, you would be able to improve the steel beam span by cutting the span and adding a cantilever to one or both ends of the steel beam. That will help save some of the depth and weight of a steel beam option and might be a good way to support the beam without placing it on the existing foundation (if that is not practical).
Good luck with your engineer.
I concur with the "get an engineer" opinions. As far as deflection goes, the equation is based on the joist length raised to the fourth power, which means that if you double the length, your deflection increases 16 times (2^4th power). And the bounce you feel will seem like more than that.
From what you've given, there's no way to tell if you'd be better off sistering the joists, or replacing that 4x6 beam with steel, or maybe something else. You also need to make sure there's an adequate load path from whatever you do all the way to the ground.
Your 100 year old lumber is probably better stuff than we have now, but it pre-dates grade stamps, so there's no guarantee on how strong it is. Sometimes the old stuff is weak because of really big knots, which we never see any more because nobody can harvest really big trees any more.
There are so many variables that you really need an engineer to look at this in person. Tell us where you are, and maybe somebody here can recommend a local engineer.
-- J.S.
#2 btr 2x12 DF is OK for the 16 ft span, no eng. needed for something that simple.
What you have not shown (take a pix) is how the ends of the existing redwood are supported. You will need to have adequate vertical shear strength at the ends of the 2x12s, or a way to hang them.
If yu can attach 2x12 joist hangers to the end walls, yu are good to go for the 2x12s. For less bounce, add joist bridging 2 places. Bridging does not increast total strenthd, but sure does cut down bounce from jumping kids.
Thank goodness someone finally suggested actually looking at a load chart! For a second I though I was in la-la land.
You don't necessarily need an engineer's opinion, but it helps to have someone with knowledge of how to properly sister the new with the old since it's not always straight forward to properly support the ends, depending on the arrangement of the outer sills and other such details. Creative use of hangers and generic hanger straps can greatly simplify what you're doing.
For a comparison one chart (40/20 lbs L/360) shows a #2 doug fir joist will span 9' 9" at 16" oc, while a 2x10 will span 16' 5" and a 2x12 19' 11".
This doesn't mean the 2x10 16" oc is the way to go since the chart is mostly for new floors. If you have an old floor with a bit of sag, the new joists have to hold up the weight plus have to fight the bend in the old joists. Going up a notch to the 2x12 is a good idea, as would doubled up 2x10s or 2x12s with one on each side of the old.
You could also go with more narrow LVLs, but I don't have a chart for them so can't say what you'd need to span that distance. If basement headroom is an issue this can be a better, albeit more expensive route.
Best of luck
Beer was created so carpenters wouldn't rule the world.
Now that I've read the whjole thread, I see that your problem is not with the enngineering of a beam, but that you want to reduce vibrations. Designing for deflection and vibration are two different things. As Junkhound has said, the floor can easily be spanned with 2x12 @ 16"oc, but you might need to add strapping, blocking, or more depth to reduce vibrations.
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What you have is already near or over the limits
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Taunton University of Knowledge FHB Campus at Breaktime.
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Oh, another item.
If the 4x6 and posts are tightgrain heart redwood 100 YO, you maybe can resell it to a re-sawer if free of nails, etc.
Thank you to all who replied.
I especially appreciated those that actually threw out some sample joist sizes and numbers.
Rest assured I also heard and appreciated the advice from those pointing out all the variables and issues I might need to take into account. The vibration concerns, ability to adequately support the ends of the joists without excessive notching, head room, variety of wood species and their varying strength, etc.
The thorough education I received to an originally simply worded question is ultimately far better than someone telling me to throw some 2 by 12's along side the existing joists and call it good.
Adding blocking to reduce vibration is also information I was happy to get. I did read a bunch of Bosshogs posts on floor vibration and now have a better picture of what to look out for.
I would say you guys pretty well covered everything and I feel very well informed.
I am in Santa Cruz, CA if anyone did have a recommendation for an engineer who is availible for small scale structural advice.
Thanks again
Karl
There is one more item that I amm not sure if anybody mentioned -the attachment at ends is also critcal. If you just glue and nail to the existing joists with 2x12, you will not be able to get your full load bearing capacity. You should be sure to use joist hangers. This can be tricky to install. Photos of the current situation could result in further beneficial advice on how to proceed.
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