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jdean12002 06-06-2013 08:05 PM

Unlevel Floor Framing Question
 
Hi everyone,

I'm building an 8' x 6' platform on my concrete garage floor--sometimes there is moisture and the ground slopes in 1 direction. The platform is going to hold a home workout area, so between equipment, weights, and person it needs to support at least 1000 lbs. I'm planning to use 2x6 to make the outer frame and 2x4s every 12inches for joists with joist hangers to support. 3/4 inch plywood as the flooring.

Since the concrete isn't level, on one end of the frame I'll need to raise it about 1 to 1.5 inches. I was planning to do this by adding 2 legs (make an "L" with leftover 2x4 and attach it to the frame with a metal joint bracket).

Do we think this will be structurally sound to support the needed weight? And what about the method of accounting for the slope? Will legs do the job and support the weight or is another method more stable? Thanks!

joecaption 06-06-2013 08:13 PM

Odd size and way to build it.
Pretty small for what your trying to do.
Going to need pressure treated wood for the floor joist.
It's going to be a whole lot weaker trying to get by with 2 X 4's.
I'd be cutting the rim joist on a taper so it makes 100% contact with the concrete.

jdean12002 06-06-2013 09:17 PM

Thanks joecaption. I'm a little restricted on the size, but it does what I need it to do.

Is there a better way you'd suggest building it? Do you think 2x6 joists would be significantly stronger than 2x4s? I'm not confident in my ability to taper it.

GBrackins 06-06-2013 10:08 PM

Welcome to the Forum!

how much slope do you have over 6' or will it be over 8'. Most garages have about 1/8" per foot slope, is that too much for your equipment?

if you're planning on making legs for the low side I'd frame everything with 2x6 myself.

GBrackins 06-06-2013 10:11 PM

I would make a level 2x6 frame with "joists" at 12" o.c. cut your legs 5.5" + what ever height you need, for example if you need to raise it 1.5" then you'd just your legs 7" and secure them in the corners of your frame. this way you can secure the legs with screws from two sides.

jdean12002 06-06-2013 10:27 PM

Thanks GBrackins!

Not 100% sure on the slope. When I lay a 6' board and raise it until level, it's 1-1.5 inches off the ground (I haven't measured exactly yet). If I were going to taper the frame, I'd be tapering the 6'.

So you'd make the legs and attach them inside the corner joint (as opposed to directly underneath it)? Just having a little trouble visualizing what you mean.

Lastly--if I were to use 2x6 as joists, what's the word on the joist hangers extending a bit below the frame and becoming a contact point with the concrete (instead of the 2x6 frame). Could that eventually push up the joists and unlevel the plywood?

Duckweather 06-07-2013 09:41 AM

If you want it to bear evenly on the concrete floor you could make what are called sleepers. Take each (PT) joist, block the low end up until level, use a block the size of the space and hold it against the side of the joist. Slide it along the concrete floor while marking the joist with a pencil or Sharpie. rip off the wedge and the joist will bear on the floor it's entire length with no legs. It will take a little more time but have no sagging or bounce. If you do the two end pieces first you can then set the joists on top of them so they are level in both directions, again scribing from the end with the most space and always using the same size block. Sometimes you can use a 2 x 8 and get two pieces from each one with less waste. Your marking block will have to be large enough so the wide end measurement of your first joist is the amount you leave at the top of the 2 x 8. Stand one joist on edge, mark it, then turn the 2 x 8 over and end for end, place it over the next position and mark the second one. You will have 2 tapered joists. Make sure to number them. Depending on your experience level you can use any method you are comfortable with.

jdean12002 06-07-2013 12:52 PM

Thanks Duckweather. I think tapering is probably the most sturdy method, but the one I'm least confident in doing myself. Marking is easy enough, but as far as cutting I'm only working with a small jigsaw--not sure I could make a clean, level cut that long. I doubt home depot would do the taper cuts for me.

I guess what it comes down to is whether or not the leg/joist hanger combo will give enough support for the load. Thoughts? If not I can give tapering a shot. Am I correct in assuming that I should coat the cut edges of the PT lumber?

Thanks everyone! You've been very helpful

GBrackins 06-07-2013 01:59 PM

tapering would be the best bet because then 2x4 framing would be more than sufficient for the load, which works out to about 20 pounds per square foot (1000 lbs/(6'x8') = 20.83 psf

jdean12002 06-07-2013 03:15 PM

Thanks again GBrackins. I think I'll go with 2x6 for everything and try tapering. Will the tapering affect the load capacity at all? I figure each 2x6 joist is ultimately going to have to come down an inch at its end (making it "2x5").

jdean12002 06-07-2013 03:19 PM

Or do you think to just taper 2x6 rim joists and then use non-tapered 2x4 with hangers for the floor joists?

GBrackins 06-07-2013 03:24 PM

2x6 tapered frame, 2x4 joists at 12" o.c. running the 6' way should be fine

Duckweather 06-10-2013 09:37 AM

Quote:

Originally Posted by jdean12002 (Post 1196952)
Thanks Duckweather. I think tapering is probably the most sturdy method, but the one I'm least confident in doing myself. Marking is easy enough, but as far as cutting I'm only working with a small jigsaw--not sure I could make a clean, level cut that long. I doubt home depot would do the taper cuts for me.

I guess what it comes down to is whether or not the leg/joist hanger combo will give enough support for the load. Thoughts? If not I can give tapering a shot. Am I correct in assuming that I should coat the cut edges of the PT lumber?

Thanks everyone! You've been very helpful

Do you have a friend carpenter / DIY er with a circular saw that could cut them for you? good PT should not need coating but you could paint the concrete or put down plastic to keep the moisture out

jagans 06-10-2013 10:18 AM

Quote:

Originally Posted by jdean12002 (Post 1196602)
Thanks joecaption. I'm a little restricted on the size, but it does what I need it to do.

Is there a better way you'd suggest building it? Do you think 2x6 joists would be significantly stronger than 2x4s? I'm not confident in my ability to taper it.

Why dont you just put down rubber mats on the concrete floor?

jdean12002 06-11-2013 01:25 PM

Thanks for the help everyone--I really appreciate it. I finished up last night and am very happy with the result. It's holding all the weight I need it to and seems very solid. And level.

I ended up going with 2x6 PT for the frame, and I tapered the two 6' sections to match the slope of the concrete using the method Duckweather suggested. I went with 2x4's every 12 inches oc for the joists, and secured them with Simpson hangers. I also used Simpson frame/corner angles for all the 2x6 frame corners. 3/4" plywood went on top and was screwed down with 2" screws every 8 inches. Finished it off with 3/4" rubber gym floor.

So thanks again for all the help--I'll put this one in the books as a big success, largely due to all the great ideas you shared with me.


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