I have an RV garage but no RV. I'm considering building a platform 10ft above the floor. The garage is 14 feet tall and the area that I want the platform is 16ft a 16ft.

The details are stopping me though.

I'm thinking that I'll use a 2x6 every 2 feet as the joists. (see my picture attached.) Would a,b,c,or d be better?

a: each joist runs the full length and is attached to a 2x6 that has already been attached to the wall

b: i split the joists in half and have a middle joist running perpendicular.

c: similar to a but the joists are connected directly to the wall studs rather than an intermediary 2x6

d: combination of b and c.

Maybe there's a better way, so I'm open to suggestions.

Are 2x6s strong even strong enough for this?

Photo attached to show what I mean. The perspective view is to show how it fits in my garage. There are 3 solid walls and 1 open. I'm thinking that the open side will be where the joists are parallel to, (so each end of the main 8 joists will be connected to a solid wall)

enter image description here

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    $\begingroup$ I'm voting to close this question as off-topic because this should be asked at DIY.SE $\endgroup$ – Carl Witthoft Jan 3 '19 at 19:50
  • $\begingroup$ @CarlWitthoft It's not a question about diy. It's about structural integrity. Out of curiousity. what is the link for diy.se though? $\endgroup$ – rudtek Jan 3 '19 at 19:56
  • $\begingroup$ Yes, but the DIY-ers will know the 'rules' for building a platform like this. diy.stackexchange.com/questions $\endgroup$ – Carl Witthoft Jan 4 '19 at 0:29

Depends on the load, but if you guess your load per square feet is going to be near 25lbs, 2x6 is not enough, consider 2x8 @ 16", Doug Fur Larch, grade 1.

You need to use a 2x8 or other means of ledger beam at two ends which is properly attached to your garage framing, so that you nail the joist hangers to it. You should consult a type5 framing sheet for nailing and connectors.

You need to consider earthquake loads and brace the existing garage walls for that. Finally you need to block your rafters at least at midspan.

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  • $\begingroup$ Thanks for answering! I'm not an engineer, just trying to be a diy-er. Most of what you said makes sense, so i looks like option a with 2x8s. Only question is what does "block my rafters" mean? Does that basically make it "b" but the joists aren't cut, the middle line is segmented? $\endgroup$ – rudtek Jan 3 '19 at 16:39
  • $\begingroup$ Also, would putting the joists closer together allow me to use 2x6? $\endgroup$ – rudtek Jan 3 '19 at 16:46
  • $\begingroup$ blocking means to cut blocks of 2x8x14.5" and nail them in between the continues rafters to restrain them from lateral rolling (buckling) under pressure. $\endgroup$ – kamran Jan 3 '19 at 16:49
  • $\begingroup$ Unfortunately 2x6 even @ 12" is not enough. I did a quick calculation and 2x6x 16 feet can't take even 15lbs/sqr ft. even if we allow for L/180 deflection, which is highest for temporary uses. also you need plywood only on top. $\endgroup$ – kamran Jan 3 '19 at 16:57
  • $\begingroup$ one last question. So with this measurement 2x8x14.5" you're suggesting putting the joists every 16 inches? $\endgroup$ – rudtek Jan 3 '19 at 18:10

Whatever joist plan you use , you can make it substantially stronger (and neater appearance) by attaching plywood to the bottom. I used glue and screws because the connection must be strong . This more or less makes an "H" beam , the plywood becomes the primary tension member; chose 1/2 , 3/4 , etc. depending on how stiff and strong you want. With your relatively long span , you could consider steel strapping on the bottom of the joists , they would be covered by the plywood . A little more hassle drilling screw holes but serious increase in strength.

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  • $\begingroup$ i was going to put plywood on top to put things i'm trying to store there. You're saying put it on both top and bottom? $\endgroup$ – rudtek Jan 3 '19 at 16:46
  • $\begingroup$ Yes. The top plywood is in compression which does not add much strength. The bottom is in tension which would provide the primary strength. $\endgroup$ – blacksmith37 Jan 4 '19 at 16:04

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