Floor advice

[jashv]

I am about to build a room above my 24'W X 26'L block garage. The builder that is giving me estamates says he wants to use 2X10's 14' wide, he said that would give about a 2' hangover where he can bolt them together in the middle. He was then going to put down 1/2" plywood. He is going to remove my current gable roof, build 9' walls then use joist hangers to hang the floor about 2' above the block wall. This way I have a 7' wall and an additional 2' of height in the garage below.

A. Does that sound like it will support a room with light furniture?
B. Is there a website that tells you if you have a span X long you need X size material to safely go the distance?

Thanks

[Rich]

SPF 2x10's @ 16" o.c. with light loads (30+10) would be able to span 17'2. I would assume that would mean you have a wall or girder down the center of your garage.
The issue I see with the whole thing is the 1/2" plywood. It will be spongy / bouncy especially if he plans on putting the joists at 24" o.c.. If @ 24" o.c. I would then get a little worried about the joists also, even though they should be able to span 14'. I would suggest putting down 3/4" tongue and grooved plywood and attached with screws with at least 1" penetration into the joists. Some type of PL400 or Liquid Nails is also recommended between the joists and sheathing.
Here is a good span calculator. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/

[doyle]

If there's not a center beam or wall for the joined 2x10's to rest on where he plans on overlapping them, then there's no way that it would work.

If that's the case, get rid of him right away and hire a competent contractor!

If you want to span the whole distance without any type of support underneath, you will have to go with some sort of engineered floor truss or I-beam.

[man_water]

I'm not sure about minimums for the floor, but here's a calculator for floor stiffness needed to tile. http://johnbridge.com/vbulletin/deflecto.pl

If it'll hold tile, I would think you've got what you need. I don't know if 1/2" would be stiff enough even if you aren't tiling. I know it's light for tile.

[mjpliv]

:lol: I love the graphics on that last URL posted :lol:

[jjcold]

Wow, that Johnbridge site is cool. I currently have a 15' span with pro150 (10") TJI I beams 16" on center. Way too much floor bounce. The johnbridge site quotes a deflection of .566" Too much!!! My plan is to put extra support beams in this summer cutting the span to 7.5' that will make the deflection .064, or something like that. Hey, that should be better, huh???!! Plus, now I can install a slate floor in my living room if I wanted to!!

[mjpliv]

The deflection criteria L/360 or L/480 can be quite subjective. You would think these minimums would represent the total deflection allowance for a floor member.

It is in fact the ratio of deflection to length of component (joist, rafter, beam, etc.). If I design a joist with a deflection criteria of L/360 with a span of 10' then that joist would be permitted to deflect only .333 inches (120 inches divided by 360) when fully loaded. If I design a joist with the same criteria at 20' span it would be permited to deflect .666 inches (240 inches divided by 360). Yet they are designed with the same stiffness criteria.

To acheive the same deflection value for these two joists I would have to increase the live load deflection criteria for the 20' joist to L/720.

When you are planning a job that involves large spans, take a few minutes with a calculator and determine your own deflection criteria for each floor area based on the spans and projected loads on the floor. Then you can order your joists in the correct depth and from the correct series.

Keep in mind that, by most standards, the deflection criteria used in specifying components is the live load deflection only.

[jjcold]

What is considered live load and dead load? I would suspect live is weight of people, furniture, etc and dead is weight of the walls, decking, house components?

[mjpliv]

If you will excuse the expression - "you hit the nail on the head".

[jjcold]

Thank you.