Floor joist size for garage??

[AdamCz]

Hi New Member Here! Though I've read through other threads and enjoy the content!

I am building a second floor to a garage that I have and I'd like to span 16' with 4x6 joists. I am wondering if this is doable. They will be rough sawn true 4x6.

The space is a 30'x16' room and I'm trying to avoid having to use center posts. The 4x6 joists will be tied into and sitting upon 2x6 top plates. The 30' will be split equally into two separate rooms and I'm going to use a large LVL in the wall space between the rooms (as in the LVL will span the 16' halfway through the 30'). I also thought that I could incorporate 3x5 steel I beams into the joists for added rigidity (and box them in with rough sawn lumber).

What I'm wondering is if this is safe, will they sag, springy floor? I am going to put 2x6 tongue and groove flooring on top. The reason for the short 6" heigh is a space shortage above.

I appreciate any and all insight.
Thanks,
Adam

 

[PCustoms]

Seems like it won't work.

 

[billconner]

I think there will be a lot of sag and bounce with 4x6s. If you could go to 4x8s 16" in center, should work. And you could drop them for height over.

Or if you could live with some beams below, span the 16' in middle, and then a center beam the 30' framed into it. Simpler might be to beam across 16' at center and quarter points, and them frame with 4x6s between then. The beams probably need to be 12" deep at least if wood or lvl.

Just watched same discussion on www thebuildingcodeforum.com Wanting to span 16' with 2x6s in a garage for living space above. Most said no but one claimed 2x6s 4" on center would do it. I still think there would be too much deflection.

Good luck!

 

[Sumboodie]

The mezzanine floor i have is 2x6s with a 14ft span. It's been fine.
I mean I probably wouldn't do jumping jacks or store too many 3406s or Walmart fatties up there though.

 

[billconner]

Is this storage or living space? I thought it was for habitable rooms.

 

[Kaizen]

Are you somewhere you can't get nominal wood? |Remember fresh sawn beams will dry and crack.
With the prices lately i'd look into engineered I joists. Lighter and stronger. Probably close in prices.
You didnt mention but are you restructuring the 1st floor walls to support the new weight?

 

[billconner]

Remember fresh sawn beams will dry and crack.

I built my entire 28 x 32 barn/garage with rough sawn and had now of that. Just saying. Plus it looks great.

 

[cgrutt]

Seems like it won't work.

Not sure and not familiar with using 4x6s for floor joists but that chart doesn't seem right to me. I think it might be referring to span between posts on a 4x6 beam. You can span a Grade 2 yellow pine 2x6 10'3" (16" OC) for example.

As far as OP, not sure why you're using 4x6 for joist think you would be better off using conventional lumber. Probably need to use 2x10s for 15' span but that's just a guess on my part.

 

[PCustoms]

Not sure and not familiar with using 4x6s for floor joists but that chart doesn't seem right to me. I think it might be referring to span between posts on a 4x6 beam. You can span a Grade 2 yellow pine 2x6 10'3" (16" OC) for example.

I'm not familiar with 4x6 either. I looked at a span table for a 2x6, and it was 9-10' IIRC. Googled 4x6 and grabbed that.

Either way 16' is too much for a "short" joist.

 

[Skiff Builder]

Hi New Member Here! Though I've read through other threads and enjoy the content!

I am building a second floor to a garage that I have and I'd like to span 16' with 4x6 joists. I am wondering if this is doable. They will be rough sawn true 4x6.

The space is a 30'x16' room and I'm trying to avoid having to use center posts. The 4x6 joists will be tied into and sitting upon 2x6 top plates. The 30' will be split equally into two separate rooms and I'm going to use a large LVL in the wall space between the rooms (as in the LVL will span the 16' halfway through the 30'). I also thought that I could incorporate 3x5 steel I beams into the joists for added rigidity (and box them in with rough sawn lumber).

What I'm wondering is if this is safe, will they sag, springy floor? I am going to put 2x6 tongue and groove flooring on top. The reason for the short 6" heigh is a space shortage above.

I appreciate any and all insight.
Thanks,
Adam

Adam, Google 4x6 joist span + Charlie Wing. You'll find reference to a book he had out in the 70's on this. You might get a snip of what your looking for. I've seen spaces spanning 16' with similar sizes you mentioned, at 12.o.c. Species may have been Oak.

In addition to your 4x6 with 2x6 T+G deck, I wonder the strength value added with glued and nailed 1/2 plywood on underside of joists....sort of a tension box.
An engineer let you know what would work within your height saving wishes. Good luck with the project.

 

[theoldwizard1]

Stick with 2x6. Change spacing between joists. Span tables will tell you the answer.

 

[PCustoms]

Stick with 2x6. Change spacing between joists. Span tables will tell you the answer.

Got a table that shows the spacing for a 16' span?

 

[Viper98912]

I'm not a structural engineer, but 16' is a large span for something only 6" tall. And you're complicating things by wanting to add additional 3x5 steel I-beams? In looking at the joist span tables, depending on your load, plus the O/C distance, you're probably up in the range of 2x10 or 2x12's. I personally haven't seen any floors less than a 2x8, and those were for short spans.

I'd say, rather than complicating your design with multiple factors, just go with something straightforward like 2x12's

 

[theoldwizard1]

Got a table that shows the spacing for a 16' span?

Google "floor joist span table".

 

[PCustoms]

Google "floor joist span table".

I did, did you?

I didn't see anything that allowed a 2x6 to span 16'

 

[mepstein]

My attic had 2x6 as a “floor”. I sistered in 2x12’s and turned it into a living space.

 

[Sumboodie]

Suspect there's limited headroom?

Mine is over an 8ft room, so only 5.5ft, which already *****, so didn't want to further reduce that.

 

[theoldwizard1]

I did, did you?

I didn't see anything that allowed a 2x6 to span 16'

Correct ! Use 2x8

 

[CraigStu]

When we were having our house built, in one conversation the builder told me that standard 2x10 joists on 16in centers were good for 14ft.

 

[cgrutt]

When we were having our house built, in one conversation the builder told me that standard 2x10 joists on 16in centers were good for 14ft.

Varies by species and grade but yes generally between 14' and 15' for grade 2 or better irrespective of species. Can get over 15' with Doug Fir and some others. This according to span table in my DeWalt Construction Professional Reference.

FWIW @theoldwizard1 same table shows grade 2 or better 2x8 is only good for 11' (max 13' 1" with Doug Fir - Larch).

 

[billconner]

What's planned for the attic and what other finishes are planned would affect it. Bedrooms and such can be at 30 psf live load; "light" storage (typical attic) at 20 psf. Based on material it seems like planning for 10 psf dead load makes sense but 5 might be enough with no ceiling, floor finishes, insulation, etc. 1/180 deflection may be ok if no drywall on it. (That's about an inch in 16'.) But 1/240 more typical; 1/360 with drywall ceiling under.

 

[Boon]

The use for the proposed area has not been explained so an informed answer is not possible. My second floor is braced with 14" steel I-beams, per the engineer. No span is more than 11'. It is designed to be able to work on ATVs and UTVs and to support things like commercial table saws. If the area is used for light storage then the requirements would be a lot less.

 

[Kaizen]

I built my entire 28 x 32 barn/garage with rough sawn and had now of that. Just saying. Plus it looks great.

I have no gripes with rough sawn. My point is if its not kiln or properly air dryed and he is insisting on using 4x6 wet wood he should take precautions to allow for shrinkage. The bigger the beams the bigger the potential problem. There is no way to predict the checking that will happen when it dries.

 

[BruceMc]

I own a couple of cabins with that setup - 2nd story sleeping loft, 16' span, 4"x6" RC on 24" centers, topped with OSB. It works for light use, is a bit 'bouncy', but they've been in regular use for 25 years.

I didn't build the cabins, but if I did I would have gone with minimum 4"x8"s. The lofts are A-frame - /_\ - so all the live load is concentrated in the middle. It doesn't meet any code or deflection mins found in any span table, but it works for what it was intended.

 

[jblnut]

I’ll be spanning 14’ with 2x8’s on 12” centers on the loft in my shop and have zero concerns about it. I plan to put all kinds of things up there.

 

[AdamCz]

Wow, thank you everyone for the thorough responses. Regarding why I'm not going with a deeper joist (like 2x12) I have limited headroom above. Which leads to the usage (sorry for not mentioning that before). I am planning on putting 2 small bedrooms above, not sure of the dead load and live load but there will be a full sized mattress, night table, and small closet in each room. I am starting to think that the 4x8 is the way to go. Maybe I don't need to add the boxed in steel I beams?

 

[billconner]

If you have height below, you could drop the joists a few inches to get headroom above.

With the 1 1/2" t&g decking, 4x8s on 24" centers, or 4x10s on 40" centers. Up it to 4x12s, and depending on species if t&g, up to 60" centers!

 

[Joemctag]

Hi New Member Here! Though I've read through other threads and enjoy the content!

I am building a second floor to a garage that I have and I'd like to span 16' with 4x6 joists. I am wondering if this is doable. They will be rough sawn true 4x6.

The space is a 30'x16' room and I'm trying to avoid having to use center posts. The 4x6 joists will be tied into and sitting upon 2x6 top plates. The 30' will be split equally into two separate rooms and I'm going to use a large LVL in the wall space between the rooms (as in the LVL will span the 16' halfway through the 30'). I also thought that I could incorporate 3x5 steel I beams into the joists for added rigidity (and box them in with rough sawn lumber).

What I'm wondering is if this is safe, will they sag, springy floor? I am going to put 2x6 tongue and groove flooring on top. The reason for the short 6" heigh is a space shortage above.

I appreciate any and all insight.
Thanks,
Adam

Since you’re considering some steel, there could be, say, 3 steel beams the 16’ way at 1/4 and 1/2 points down the 30’ length with 7’-6” long joists framing into them. You don’t say where there is a wide ( garage ) door whose header might have to carry some of the extra weight.

 

[CraigStu]

You can also close in the joist spacing. A car shop I worked in wanted some second floor storage. I don't remember whether it ended up w/ 2x10s or 2x12s but I do remember they were installed on 12" centers vs 16".