Structural engineer folks: garage attic flooring

orange150

orange150

Well-Known Member
Joined
Mar 20, 2005
Location
Fairfax City, VA
I’ve been thinking about laying 1/2” plywood down in the attic space of my garage, only over the garage door, for storage.
It’s 2x4 construction, do y'all see any issue with this?

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They look like they are 24" oc so they will not support a pile of load but if you want to ensure the chords do not to themselves apart you can always laminate another 2x4 to the bottom chord.

I have way to much stuff sitting on in plywood in my attic with similar construction (I think my roof pitch may be slightly higher). All sorts of car parts and other things that are probably too heavy. No failures but I know I need to reduce the load.
 
@shawn 's spec is important to keep in mind. They're not designed to carry a lot of load in one spot.
Plywood will of course distribute the load.
My concern would be.... psychology. In 5 years when they are covered w/ plywood, is it going to be really easy for you - or the next guy - to not think about how thin they are and pile a bunch of stuff on them in 1 spot?
 
orange150 said:
Thanks y’all.

Is sistering additional 2x4s worth the money? Pretty sure overall span is 22’, and yes 24”oc
Click to expand...
If you're gonna sister something why not go for 2x6 or 2x8?

Perhaps one of the injunears here can calc the load capacity difference to tell if it's worth it.

The root of the problem is that rafter system is designed to hold the load in tension not downward compression.

I have the same problem in my house. Ranch built in the 60s. The builder, who was also the owner of this one, built in stairs over the basement to make it super easy to access the attic. Very unusual for the time.
But like yours it's only 2x4 on 24" centers so you can't really do a lot with it.
 
Anything sistered in really needs to span the entire length if you want to carry significant loads. The truss isn't designed to carry more, and any dimensional lumber will sag under it's own weight at a 20-24ft span.

Stick with what Matt said, just keep it to lightweight stuff.
 
Not a civil engineer, but I specify hanging thousands of pounds of equipment, piping and ductwork, and received countless lectures from civil engineers stating DO NOT hang anything from the bottom chord of a joint. ALWAYS specify extending all hangers to the top chord, as that's how the load is calculated.

To quote Shawn

shawn said:
Do with that what you will.
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CasterTroy said:
Not a civil engineer, but I specify hanging thousands of pounds of equipment, piping and ductwork, and received countless lectures from civil engineers stating DO NOT hang anything from the bottom chord of a joint. ALWAYS specify extending all hangers to the top chord, as that's how the load is calculated.

To quote Shawn
Click to expand...

Not an inguneer, but this is pretty standard. Im not saying to do this, but if I were gonna accept liability of putting stuff in a spot like that id figure a way to carry that load to the top chord.
 
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