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bauer09 · Jan 24, 2009, 05:19 PM

Hi, I have a question that I hope I can provide enough details for to get some opinions.

This is a situation that existed in my house when I purchased it, and wasn't mentioned by the home inspector.

The home has a 1 1/2 car garage (not quite 2... ) with a steeply pitched roof. The previous owner converted the upper area into a small walk-up storage attic by running attaching 2x8 joists directly to the rafters (with lag bolts) and running them the full length of the garage (approximately 20'). He then laid 3/4" plywood on top. I was always a bit skeptical of the strength of those 2x8 joists spanning such a large area, especially because they are only 24" o.c. While the storage area above that the joists are supporting is not a full 20' (knee walls block off some of the area), it is still a substantial span.

After looking through some code books I have, it seems that this is a much larger span than is specified by code for 2x8 lumber 24" o.c. --- any thoughts? If it is indeed unacceptable, is there any way I can firm it up short of replacing all of the joists?

Thanks in advance for any opinions...

bones252100 · Jan 24, 2009, 05:56 PM

Try joining the joists together for collective support. (Together, we stand; divided we fall.)

21boat · Jan 26, 2009, 05:04 PM

Basically add more joist and split the 24" oc or put more sister joist beside the joist there.
I'm am curious why the 2x8 weren't put on top of the wall plate to begin with.
I prefer splitting the span simple the 3/4 play would be better supported with less span than 24"OC.
Bones Picture will add sharing of the floor load a Little with out a doubt but that configuring works much better of joist being 16" O.C.
They heavy ply also helps that.

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bones252100 · Jan 26, 2009, 07:29 PM

Concur with 21boat. In our area, 16" O.C. (on center) is the current code for nearly all joists. The horizontal supports are a work-around for an existing condiition

ballengerb1 · Jan 26, 2009, 08:51 PM

And it all depends on the weight of the load you plan to put up there. What you started with was minimal old code for no load at best. You can double up your rafters and add an extra set and still bow them if you store too much weight in the attic space. Can you tell us roughly the load planned/ You might need a header crosswise on a post.

21boat · Jan 26, 2009, 09:26 PM

Bauerer09
Ballengerb1 Brought up a good thing to think of
Here is a basic chart on how to figure out you loads and what the floor can Ruffly. I forgot I even had this.
Thanks to all here!

American Wood Council Understanding Loads and Using Span Tables

Here comes my disclaimer I'm not and engineer here but through out the general practices of building there are basic standards that can be applied

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bauer09 · Jan 28, 2009, 02:03 PM

Thanks for the input...

I am assuming that he didn't put the joists on the top wall plate because he wanted extra headroom in the garage -- just an assumption. And they are spaced 24" because that's what the rafters are spaced -- so if I wanted to add some in between to make up the difference, where would I even attach them?

Thanks for the feedback, all the points are good -- I considered but would like to avoid adding a header with posts at the midpoint. As for storage, the upper level is split into two halves. They are both for general attic storage, but the one half is supporting a washer and a small dryer.

I can't imagine trying to sister these joists being that they are 20' long, that would be major pita. How much support does adding the extra blocking between the joists provide? That seems to be the easiest option, basically I just don't want any problems down the road especially on the washer/dryer side. I don't plan on increasing the weight load anymore than it already is now.

21boat · Jan 28, 2009, 02:51 PM

2x8s aren't that hard to handle. I would go the ends of the original joist and cut two 2x8 to fit between those ends doubled up on opposite ends and nail them in between the original joist Now you have a place for a metal joist hanger. Use a scrap of X and gage the new joist hanger and nail the one top side of that so it can swing do same on other side. Now all you have to do it take the new X joist and slip it the pivoting hanger flip it and the new joist and finish nailing hanger. This would be fairly easy and as far as lineal feet doing it this way would be close to the cross bridging way as the drawing bones did and putting in the joist being now 12 O.C> splitting the 4 O.C> would be close in strength for the whole floor system if it were 2x10 16 O.C.
Do the math and see how it works in lumber cost as to what you get out of it in strength. I will guarantee the way above here is the best way for the buck and the time for this is close to the same as adding all of the scabs the pic is above. Bones was good on the pic if that your only option. But Its not as strong as this option. Two guys and a day its done the easiest is not always the best especially here. Just think if it as 20' is two 10s together

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