24x24 2 story with open floor plan on 1st floor. How do you support second story

[kiaman5]

Looking to do a 24x24 2 story with a total open floor plan in 1st floor (other than about 8x8 guest bath in one corner). Not understanding what would support 2nd floor joyces. 2nd story will also be totally open floor plan with exception of master bath and walk in closet. Just one big bedroom basically. I plan on getting code and all, I just "googled" some things and you guys came up. Read a few posts and thought I could use your help and maybe be helpful for some others. Thanks in advance for any ideas.

[akwoodchuck]

You can get a glulam beam that'll span 24'...it'll be a big'un, but it's possible...

[Don_P]

Or open web floor trusses or I joists instead of dimensional lumber joists.

[ChugiakTinkerer]

You can span 24' directly with an i-joist.  You can get a stiffer floor by spacing them closer together, or by having a deeper I-joist.  This span table from Weyerhauser suggests you can probably use a 14" i-joist spaced 16" on center.  That would give a floor that meets minimum code requirements for deflection (bounciness).

The basic design (not accounting for a stair opening) is like this:



Or you can support 12' joists using a girder, such as a glu-lam beam like akwoodchuck mentioned.   Because of the load it would need to support it would be very large.

Such an arrangement would look like this:

[ChugiakTinkerer]

And welcome to the forum!

[kiaman5]

Thanks I got it. Tinkerer the center beam idea with a floor to ceiling support in the center seems like the way to go to me. Still gotta get codes and rethink all this but i really appreciate all the replies. Gonna keep on here hope i can repay the favors. Thanks guys.

[Don_P]

With a center support post under the girder the size of that beam becomes manageable, probably on the order of a double 11 7/8" lvl. First floor can frame the same way. 2x8's would pass as joists but I'd bump to 2x10's if possible. Don't forget to take the support post all the way down to the footings.

[kiaman5]

Thanks Don. I planned on 2x10 joists but what is an 11 7/8 lvl? Sorry new to this.

[Don_P]

Laminated Veneer Lumber, it looks similar to plywood with all the plies running lengthwise along the length of the beam. 1-3/4" thick x widths from about 9" to 24" deep. 2 plies nailed together then becomes 3-1/2" thick and in this case 11-7/8" deep (one of the commonly available depths). In some markets 11-1/4 deep is available but less common. The 11-7/8" deep was well beyond code in a quick check but was hitting about my limits for stiffness in that type of use. It is roughly twice as strong in bending, twice as stiff and has twice the shear strength compared to regular dimensional lumber. The last ones I bought in that size were about $5 per lineal foot. Available from the contractor desk at the building supply, they will also do the engineering for the beam free of charge as part of the service of the sale. A cordless drill with an 1/8" bit will help with driving 16 penny sinkers or 10 penny commons in your joist hangers, they are dense and tough.

The glulam that ak suggested is the laminated 2x4 or 2x6 stacked lumber style of beam. Also a good option if it is exposed, they look good but are a good bit more expensive. The LVL needs to be wrapped, they are not "pretty".

[NathanS]

Not to go too far off topic, but if you use 2x10s with an open downstairs floor plan you will need to be very careful with your plumbing layout. A 3" drain pipe is really too big to pass through a 2x10. It barely can go through a 2x12.

[ChugiakTinkerer]

With a center support post under the girder the size of that beam becomes manageable, probably on the order of a double 11 7/8" lvl. First floor can frame the same way. 2x8's would pass as joists but I'd bump to 2x10's if possible. Don't forget to take the support post all the way down to the footings.

Having a single post supporting a girder at or near it midpoint goes a long ways in trimming down the size of girders and joists.  It wouldn't have to be an obvious post either.  If it works into your floorplan concept, you could incorporate it as a closet, hutch, or ornamental display of something of interest.