2 x6 floor joists or Glulam I-joists
For our 17 ft x 32 ft planned home addition, basically an extension to back of house that has raised foundation (not a slab), the architect’s drawings are calling out to use floor joists that are 2 x 6 douglas fir with 16 inch x 16 inch concrete piers with 4 x 4’s connected to the piers that then connect and support the 2 x 6’s.
So, I’m wondering why he did not spec out using those Glulam I-joists (or whatever you guys call them) running in the direction of the 17 ft. If you use those I-joists, doesn’t that mean you don’t have to use those 16 x 16 concrete pads with the 4 x 4’s? It’s only at 17 ft span and there are two internal walls with the length of the 17 ft direction. (He said to use 2 2×6’s where the wall would be above).
After 10 minutes of reading on the web, I see that a 9 inch I-joist can span 18 ft and assume this means with no pier support.
The rest of the original house has 2 x 6 on 4×4 posts that are mounted in concrete piers but ain’t there better ways to do it now. (house was built in 1956 in So. Cal. area). Just looking for advice to make the right decision and learn more before I talk with the architect about this. Thanks for you responses.
Edited 11/6/2009 11:35 pm ET by KWOLSEN
Replies
One thing to understand regarding TJIs or other engineered I-joists is that while they are strong, and they can span a certain distance, the performance of a "barely code" floor may leave you wanting.
TJIs can give a bit of reverberation, sort of like the entire floor platform being like the skin on a kettle drum.
So if going with TJIs, consider upping the deflection of the floor to an L/720 instead of going for a minimum L/360.
No way would I want to see 9 1/2" I-joists spanning 17' You'd be much better off using 11 7/8" deep ones.
Don't bother with the span charts online until you find out what brand and series is available locally. Some of the stuff in the span charts may be very hard to get and consequently very expensive.
If you go to a real lumberyard (not a big box store) or a truss manufacturer they should be able to give you information on what's available locally.
thanks, if using the 11 7/8 " as you suggested, do they still need the supporting piers ?
It does sound as though your architect is carrying period authenticity a bit too far. Most manufacturer's 12" TJs will span 17 feet easily. Of all the other alternatives, such as using 2"x10"s and a central beam, what they are suggesting seems the least practical.
The 11 7/8" I-joists woule easily span 17'. I can't really picture what you're trying to describe with the 2x6 joists and 4x4s .Is it possible that it was drawn that way to keep the height of the floor system down?
The great crime of the 20th century, in my mind, is that we now work harder than ever before. Why is that? To what end is that leading? How are we supposed to free our minds if we spend all our time working? [Adam Rifkin]
"I can't really picture what you're trying to describe with the 2x6 joists and 4x4s ."
It was a very common framing technique in California. Perhaps because of the small dimensional lumber available, the joists were often 2"x6" spanning about 5 feet with a series of small beams supporting them with posts every 6 feet or so. Before sheathing the floor looked like a spiders web or scaffolding of small framing members. I remember seeing Larry Haun building one in FHB back when dinosaurs roamed the earth.
Edited 11/7/2009 12:13 pm ET by fingersandtoes
Thanks for the info - I've never seen or heard of anything like that before.
When the bosses talk about improving productivity, they are never about themselves.
I agree with what the others have said, especially the part about upgrading to 11 7/8 and decreasing the spacing.
Minimal costs will yield a much stronger floor and building to code and not having your dishes walk across the table when you cross the room are two entirely different things.
I'm an architect and I rarely use dimensional lumber for floors anymore. With I joists I can eliminate intermediate support, every piece is the same, no warped or curved pieces, and I can cut big holes in them (although there are rules as to how big and where) for plumbing and HVAC.
Runnerguy
At some point somebody aught to mention the loss of head room. Perhaps there are other design consideration at work that would make it difficult?
Interesting note on the 11-7/8" I-joists and spacing farther apart. The [so called] tract builder for my neighborhood used these (Boise-Cascade) and spaced them on 24" OC. He followed up with 5/8" OSB glued and nailed.
This builder marketed the benefits of the 'silent floor system' but didn't do much to make the floors silent. Because of the spacing, the thinness of the floor decking (ahem, sub-floor), and the lack of screws, this floor system was not silent at all.
I think this was one of the things that caused +3 years to pass before selling enough homes in phase 1 before they could begin the next phase. On phase 2, the builder went back to using the same BC I-joists on 16" OC, but continued to glue and nail, not screw.
I can only wonder what the builder saved in screws and 33% less joists in order to pass off the family room (16'x18'). And these I-joists were of the narrow stile variety making even nailing into a chore that was barely accomplished--or caught by inspectors.
In defense of the builder, I have noticed that the distance between Ijoists appear to be less and less at 24". At one time that was considered the norm. Not anymore.
The squeaks in the floor really has nothing to do with joist spacing.
I humbly disagree. The combination of spacing, thin stiles, lack of screwing, and the use of 5/8" sub-flooring all added up. The only thing the builder changed between phase 1 and 2 homes was spacing, and behold a non-squeeking floor.
BTW, my phase-1 home isn'y an isolated case. Otherwise, I would have concluded differently.
Actually what you are probably missing that is more important is the subfloor adhesive.
I have seem too many new home framers miss this and it s crucial to whether a floor squeeks or not.
Screws are not necessary and most framers should be using ring shanked nails that when shot with a gun are extreemly difficult to remove. I believe they hold as well or bette than screws.
From what it sounds like, your builder left out some steps in building a good home.
Width between floor joists will decrease or increase deflection, which is not a cause of squeaks if the other steps are followed.
Oops, I should have included poor supervision considering the number of nails that stuck out of the sub-floor facing down into the basement. Missed nails. :)
What you don't see, and this is not necessarily true for your builder, but I have missed nailed, renail right besite that catches the joists.
I really suspect that you have a lack of glue.
You can glue 'till the cows come home but too large spans for floor sheathing will still cause squeaks. Stand between joists on a 24" floor with 5/8" ply and I bet you can make the tongue squeak. I can and I'm only 160 lbs.
Would would use 5/8" ply with 2' centers?
The guy we are talking about did. See posts 35 and 37.
Sounds like he pushed the practical limits of the floor a bit. BCI have a method of spacing 19.2 inches, I think. There is a logic there, but I forget what it is or how it works. But it strikes the balance between 24 oc and 16 oc.
5/8 seems way too thin for any floor IMO let alone 24 oc. Penny wise, pound foolish it sounds to me. My BCI rep would ALWAYS inform me of code AND practical deflection ... she would say ... it meets code, but do you want it to deflect 0.35" as you walk on it? If you say, uh no ... she points you to a little beefier combination.
There are a number of factors here - I'm hoping you are referring to a center line of support and the 2 x 6s aren't spanning the full 17' width.
Nothing wrong with #1 or #2 D fir dimension lumber BUT you may find 2 x 6s problematic with regard to penetrations which are limited by the depth of the beam (1/6 rule).
I-Joists will tend to give you a flatter more trouble-free floor and no joist crowning is necessary BUT they have to be sized and detailed properly.
Jeff
I agree with Henley. You should double check your elevations. An increase in floor height can have consequences at doors, stairs, roof lines, etc.
Beat it to fit / Paint it to match
Yeah, it's important to consider the whole picture before deciding which type material is best for any particular application. If I hire an architect to design something it's because I believe she'll do a good job and I can communicate with her. If she calls out something I question, I question HER, not somebody in Nebraska.Came back to say no offense to anybody in Nebraska. That was meant as an example.
Edited 11/7/2009 12:16 pm ET by jimblodgett
jimblodgett-
well, you must not have read my initial post in which I was looking for advice on this forum before I ask my architect. I dont care where in the world replies come from , just looking for advice from people who know alot more about I-joists than I do. Your the first person in my many postings to finehomebuilding to make such a rediculous comment.
I don't think the change in materials would affect floor height. It is a new addition so the floor height can be set at the same level, and the stick framing with 2"x6" has dropped beams so the crawlspace height will be slightly higher with TJs.
The house was built in the 50's in Calif. I'm guessing he only has an 18" crawl space. If that is the case he does not have room for a taller joist.The girder depth does not count as part of the 18" minimum. I've been under plenty, it's a real treat.Actually, if he rat proofs with concrete I think he can go less than 18". Won't be accessible though, except for the cat.John
He said he was on a foundation. If that is poured and the elevation established, it could be important to know if deeper floor joists will raise other parts of the structure and effect some of the things I've mentioned. Just a guess since we know very little about the addition. If the facia needs to meet with what is existing on the house, even an extra inch will have to be taken into account.Beat it to fit / Paint it to match
I took it as being still in the planning stages. If the foundation is in that changes things. But unless there is some really good reason, why would they pour a crawlspace where a difference of a couple of inches of wall made you use 2"x6"s?
I'm in that situation now myself. Need bottom of exterior watertable to line up with existing and interior floor levels to match. Plus headroom considerations because of septic and basement depth limitations. Presto. Depth of joist problem. Steve
So Steve, how did you solve?
Doubling up the rim and using 2x6 joists with beams and posts strategically placed to have the least impact on the basement space.Steve
Figured something like that.
It'd be nice if KWOLSEN took a minute and enlightened us as to headroom considerations. Especially after all the free great advice he received.
Runnerguy
He has probably been rendered speechless with admiration by the pictures of your barn in the cupola thread. Nicely done.
Thanks F&T. Enjoyed posting the pics which I more or less did as an excercise to get the embedded photo thingy down.
Runnerguy
ok, regarding headroom, the foundation walls are not formed or poured yet, still in design phase. The existing house has about 18 inch crawlspace height. The new 17 x 32 ft addition can be whatever needs to be to accomondate any joist size. Just sounds terrible to use 2x6's. So, I'm hearing consensus that 11 7/8 I-joists would work in the 17ft span direction. Is there code req that says must have certain distance of head room (18 in ?) for crawl space under a house ? Is this space measured from dirt to bottom of joist or to top of joist that connects to the subfloor ?
Dirt to bottom of joist in Calif. You can excavate the addition deeper to make this work for taller joist. As someone mentioned earlier, the outside finishes may not be aligned if that is a concern in this the case. John
Given that this is in a crawlspace yet to be constructed I don't see what's wrong with 2x6's as long as the span they are covering is within normal deflection limits. L/360 over an 8' span (about .26 inches) with 2x6's is going to feel a lot less bouncy than L/360 over a 17' span (about .56 inches). And you could have a sea of beams and posts down there, what does it matter? It's not like anyone is going to be walking around under there.Personally I would rather have solid lumber rather than glue and sawdust anyday if I can accomplish the same thing with the solid lumber. Particularly in a crawlspace.I believe code says that any framing closer than 18" to grade must be pressure treated.Steve
Edited 11/8/2009 10:18 pm by mmoogie
I believe code says that any framing closer than 18" to grade must be pressure treated.
So when you do slab on grade you do PT studs? I don't think that is what you meant, but that is what I'm reading.
I think the code restrictions apply to finished exterior grade. The only restrictions for framing on concrete in our code is a 2" space or the use of sill gaskets under the bottom plates.
Does any code still allow dirt as the crawlspace floor without some type of VB?
On my house, I used untreated wood for bottom plates on interior walls on a slab. My experienced framer questioned it, but it was code allowable. I always read that wood contact w/ concrete had to be PT, but only if w/in 6 in of grade or exposed to the exterior (or something like that; I don't recall the code language exactly). I didn't use any sill seal, either. My BO would have never let me get away w/ such a detail if not allowed; they are pretty persnickity and aware of code requirements.
Not sure about crawlspace floors. In the PNW, poly or other cover was required by energy codes, I think (yeah, a little energy/non energy cross over). Logically, I'm sure why someone wouldn't do it (but that is why it is probably code).
18" may be the code minimum where you are, but without some very good reason, no builder in their right mind would intentionally make a crawlspace less than 24" - especially if there was plumbing going in.
Funny thread this, brings out the regional differences that make some of the questions and answers so off the mark.
Post war Southern California is covered with the type of tract houses Larry Haun built. Hundreds of houses went from initial grade to finished tract in months using those methods.
Those crawl spaces are a SOB to navigate. The posts holding up the floor joists with a short stemwall were SOP until the first slab on grades appeared in the late 50's.
Joe H
Since you have no headroom problems use the I-joists. 2x6's the way the Architect has it makes no sense. Your foundation will be lower that's all. We do this all the time. I'm doing it right now using 14" I-joists with the tops matching existing 2x8 joists with the new foundation roughly 7" lower. Ask the Architect to draw it using whatever size I-joists he feels works. 17' span you can use 9-1/2" or 11-7/8". I've used 9-1/2" I-joists for that span many times and there isn't much vibration at all.Joe Carola
Like Frammer, we match up existing dimensional lumber with new I joists all the time too and I'm an architect.
Another consideration is the cost of the piers. I just built a house on a crawl and the cost of the piers (16"X16" masonry on a concrete footing) was $300 each. The fewer of those the better.
Headroom in a crawl is important. That house I referenced above was a teardown I built on the same foundation. The existing crawl was maybe 16" at best. Hard to monitor, keep furry uninvited guests out, etc. For that reason I added two masonry courses to it giving me a nice 32" crawl. Only difference is the old house had 3 steps up to the front porch where now I have 5.
As far as sizing, ask your architect of course but the local lumber yard that sells the things should be able to do that too. They should have all the product lit and with a simple span like yours you can size the floor yourself. It's not complicated.
Runnerguy
I agree use the I-joists. However, the point about the crawlspace depth leaves me thinking the Architect had a method to his approach. So ... respectfully simply ask why not use I joists? Is it because of the depth? He'll explain it to you and either he'll go 'that's a good idea' or no, I have a method to my approach. If he doesn't want to explain it, he's arrogant and I'd dump him.
Maybe you mentioned this and I didn't read it, how is your grade height? There are ways to solve that problem when using taller joists.
>>So when you do slab on grade you do PT studs?<<
Just stumbled on your post...no, PT plates on slab-on-grade with SPF studs. I was referring to floor joists with 18" proximity to grade in a crawlspace.
Steve
edit: here is a small piece of the relevant part of the code, section R323, spelling out when treated lumber must be used:
1. Wood joists or the bottom of a wood structural floor when
closer than 18 inches (457 mm) or wood girders when
closer than 12 inches (305 mm) to exposed ground in
crawl spaces or unexcavated area located within the
periphery of the building foundation.
2. All sills or plates that rest on concrete or masonry exterior
walls and are less than 8 inches (203 mm) from exposed
ground.
3. Sills and sleepers on a concrete or masonry slab that is in
direct contact with the ground unless separated from such
slab by an impervious moisture barrier.
Edited 11/22/2009 5:20 pm by mmoogie
A wood scientist once told me that any wood should have an 18" ventilation between it and ground, even tho it was not codified.Old standard practice here was to keep a house up 18" off ground to keep the ants from making it home.
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There are often very good reasons when doing an addition to follow suit and use same or similar methods to that which already exist.
I would ask your architect why he did what he did.
Could be because of dimensions, could be cost, could be ********, all good reasons.
BTW, an I-joist and a glulam are very different creatures, about as different as a cat and a mouse.
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I suspect some sort of elevation requirement.
PS, just notice how old this thread is. Started while I was gone to FL.
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I like I-joists too, but do you use them in additions to old homes too?
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Sure, if I can. You probably appreciate more then a I do the unique problems of older homes which sometimes preclude the use of engineered lumber but if I can use them I do.
Runnerguy
Me too, but I can well imagine a A NUMBER of scenarios where the 2x6 framing on center beam is a better way to do this. Asking us instead of his archy is not going to get him a decent answer why the design shows this
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going from a 2x6 to a 12" TJI with floor at same elevation would change what top of foundation wall is tho, and we don't know the grades here, but it would definitely effect exterior trim detailing on an addition, and possibly effect grades and surface water flow
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"going from a 2x6 to a 12" TJI with floor at same elevation would change what top of foundation wall is tho,"
If that is a problem the joists can sit on a ledge and the exterior foundation height can be what ever is needed.
As you say, all this is really just speculation without hearing what the architect's intentions were. I'd bet it's all over now exept for here on the board. <G>
Yes, lot of things CAN be done....;)
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>> going from a 2x6 to a 12" TJI with floor at same elevation would change what top of foundation wall is tho, and we don't know the grades here, but it would definitely effect exterior trim detailing on an addition, and possibly effect grades and surface water flowPiffin,In situations like this with low grade and bigger joists the block steps in and the floor joists g0o behind the block allowing for the block to raise above the grade at the proper height. Also, you asked someone else about using I-joist on additions to old homes. We always do this around here.Joe Carola
Edited 11/22/2009 9:01 pm ET by Framer
I hesitate to respond to this, since this is an older post, but you need to know that his advice and comments were very sound and Jim is one of the more well respected members here. It is your presumptuous response that is ridiculous.
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"Is there code req that says must have certain distance of head room (18 in ?) "
Forget code and think common sense for a minute. For a crawl space to be a crawl space, there needs to be space to crawl.
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