Attic Truss Floor

[Yookdew]

My garage was built with attic trusses, 24' OC, for the entire 40 ft length. The attic space is about 10 ft wide and 8 ft tall. I have attached the truss specs to this post.

What would be best to install for flooring in this attic space? Tounge and groove OSB sub-floor, plywood or something else?

 

[billconner]

If just decking and no finished floor or ceiling below, t&g ply or OSB so dirt doesn't filter through.

 

[LopezBart]

Note that from the drawing your trusses have a live load rating of 0 lbs/sq ft on the bottom cord. You have a dead load of 10 lbs/sq foot. What do you plan to store up there?

 

[mm08822]

3/4" osb is ~2.5#/sqft dead load......no bodies or stored items added yet!

You should go back to the structural engineer and discuss what you are thinking of doing. These trusses look super light duty.
Maybe they can be properly reinforced to handle some load but w/o design details and fastening specs. You probably want to stay on the ground otherwise.

What about a mezzanine?

 

[Yookdew]

I was just planning on light storage like Christmas decorations etc.

Can someone explain the live load and dead load on the different chords for me?

 

[WisJim]

The top chord Live Load is snow load or similar non-permanent loads. Dead loads are loads of the materials in the structure, so roof deck, shingles, etc, are dead load for the top chord. Dead load on the bottom chord would be flooring on top and ceiling below. Insulation would also be part of the dead load for either top or bottom chords. My garage/shop has attic trusses with a 24 foot span, and the bottom chord is 2x6 select structural grade, and it's rated for 40psf LL for that area (about 12 center area with good headroom). Your trusses look light to me. I did notice mention on the second page of "bottom chords checked for 10 psf non-concurrent live load". I'm not sure what they mean by that.

 

[duneslider]

It might be worth asking the truss company for some info/clarification, it is weird how they have written the loading.

They say no live load in one spot but then list a 10psf non-concurrent live load. The way I am reading the document is that there is a 10psf dead load and a 10 psf live load. Non-concurrent just means it is independent of the "roof" loads. This is also reinforced in the deflection notes, L/360 live load and L/240 total load, this says to me that they are expecting a live load and dead load.

 

[Yookdew]

Thanks for all the responses.

It might be worth asking the truss company for some info/clarification, it is weird how they have written the loading.

They say no live load in one spot but then list a 10psf non-concurrent live load. The way I am reading the document is that there is a 10psf dead load and a 10 psf live load. Non-concurrent just means it is independent of the "roof" loads. This is also reinforced in the deflection notes, L/360 live load and L/240 total load, this says to me that they are expecting a live load and dead load.

This explanation makes sense to me. I'll contact the truss company and see what I can find out.

If it turns out there is a 10 psf live load rating for the bottom chord, how would I calculate the weight of different options for plywood/OSB etc for some type of flooring?

I just plan for some light storage if the trusses are rated for it so I don't necessarily need a super solid floor, just something that won't break through the occasional times I walk on it to access stored items.

 

[john.k]

Just round from my shop was an old shed with an A frame roof with an attic storage ,rented to car mechanics ..........they loaded up the attic storage with old car stuff , heavy .............one day it collapsed ,taking half the roof and the office with it.............fortunately no one was seriously hurt.

 

[Firebrick43]

Thanks for all the responses.


This explanation makes sense to me. I'll contact the truss company and see what I can find out.

If it turns out there is a 10 psf live load rating for the bottom chord, how would I calculate the weight of different options for plywood/OSB etc for some type of flooring?

I just plan for some light storage if the trusses are rated for it so I don't necessarily need a super solid floor, just something that won't break through the occasional times I walk on it to access stored items.

Find the weight of say 1 sheet of 3/4 osb that is minimum for a 24” span. It weights 80lbs.

If it’s 4’x8’ it has 32 square ft.

80lbs / 32 square ft = 2.5 lbs for every square foot