Light Attic Truss - Screwed by Builder?

[kest874]

Seeing some threads on here talking about truss and the ability to support storage has me questioning the trusses in my garage (24 x 24). When we put the contract together I specified light attic storage.

Live south of Nashville Tennessee, we get maybe an inch of snow a year that melts within a couple of hours.

Most of what will go up there is outside Christmas decorations. Stuff I don't really feel like carrying through the house to the above attach garage storage. No plans to put anything super heavy at all.

I installed 23/32 CAT PS2-10 Tongue and Groove OSB Subfloor see picture attached.

https://www.lowes.com/pd/23-32-CAT-...-OSB-Subfloor-Application-as-4-x-8/1000065715

I found the truss specifications that I squirreled away last night and found the BCLL is only 10psf am I screwed? I also planed to use 5/8 drywall on the bottom, should I rethink this and go with metal to reduce weight?

I've attached the truss specs as well for review. Thoughts?

 

[ddurrett896]

Bottom Cord Load is 10 for sheet rock/insulation. Seems correct.
TCLL shows 20 in the middle left which would be fine for storage.

I'm not expert, but looks fine.

 

[Innovate1]

"Light attic storage" is open to a lot of interpretation... Really need a specific loading per sq ft defined when you asked for this or they can say they met it. 10 lb/sq ft dead load and 10 lb/sq ft live load is pretty standard for trusses from what I have seen (which is limited) even without any planned attic load. Some locations around here make you put a sign at the attic access that it isn't for storage and then put some boards making entrance more difficult for final sign off. If the truss is designed for some storage load then the sign and blockage isn't needed.

The specific wording for truss design without the sign/blocking is:
This truss has been designed for a live load of 20.0psf on the bottom chord in all areas where a rectangle 3-6-0 tall by 1-0-0 wide will fit between the bottom chord and any other members.

I recently needed some trusses and got drawings without that note. When I asked for that loading I got EXACTLY the same truss design with the note added. The trusses were good for the loading but they just hadn't added the note. You might check with the truss supplier but I would be very careful about putting much up there without knowing that it can carry more than the drawing shows.

 

[Dagny]

Don't worry about it not even for one second.

 

[Innovate1]

If I'm reading your diagram right, you're designed for a "special load" between the vertical members, from 6 feet away from the edge. I'd call the truss company and verify what that means.

The truss design is a storage type design, and the "special load" is there, so I suspect the truss designer designed for the light storage you asked for.

The bottom cord is 2 x 6 and the diagonals are spread for more center space so it seems some modification for light load was done. Would be good to understand the design limits better though...

 

[kest874]

I'll have to look for the truss manufactures contact information tonight as I don't have that page with me, but googling around it looks like the note BC: From 63plf at 6.00 to 63plf at 18.00 means the center cord supports 63 pounds per linear foot?

 

[finn]

Those are storage trusses, exactly what I have in my garage for light storage.

The next step up when I built would have been a full blown attic truss, at a significant upcharge.

In my experience, the storage truss was a waste of money. I think I went up there twice in the last two years. It’s an inconvenient place to store things without a full staircase.

 

[kest874]

I'll be up there 2x a year for the decorations. 1 to pull them out and the 2nd to put them away. Biggest fear is that I wasn't going to be able to use the space at all having put in the expense to floor it.

 

[WNYflyer]

Looks like the truss designer overrode the traditional "design criteria" indicated by inputting the "special loads". That being said the bottom chord between points J & H looks to be designed for 63 per linear foot (PLF) per the special load input. So if the trusses are 16" o.c. (1.33') then 63 PLF/1.33' = 47.37 pounds per square foot (psf). I figure this is for both Dead Load (DL) and Live Load (LL) since they didn't differentiate between the two. I would say you have a storage truss with an allowable bottom chord/floor live load of approximately 40 psf between points J&H assuming 7 psf is the bottom chord/floor dead load.

The "Maximum Reaction" chart under "Gravity" indicates vertical reactions of 972 # at support points B & F. If you add up all the PLF loads indicated on the "special load" input chart and divide by two you will end up with approximately the 972# end reactions. Doing this is just another way to back check to help confirm you are interpreting the actual design loading correctly.

I would say you got what you wanted.

 

[kest874]

They installed at 24" o.c., so using your formula it comes out to 31.5psf BCDL says 10, so basically 21.5psf of storage load. Hope I did that right.

 

[kest874]

Still can't decide between drywall or tin for the ceiling. Primary use is woodworking so I can imagine it might be a bit louder int here with the tin, but would reduce weight.

 

[WNYflyer]

They installed at 24" o.c., so using your formula it comes out to 31.5psf BCDL says 10, so basically 21.5psf of storage load. Hope I did that right.

Yes your math is correct. I got the 16" o.c. from the Design Criteria chart but tough to read that number so I maybe incorrect. Does the truss design sheet say 24" o.c. anywhere ? Regardless your math is correct.

 

[kest874]

Not on that sheet it may on the others I'll have to look tonight. Short of it is light stuff, no plans to store engine blocks or transmissions!

 

[Innovate1]

Not on that sheet it may on the others I'll have to look tonight. Short of it is light stuff, no plans to store engine blocks or transmissions!

LOL. One place I was looking at building they wanted 2 x 8 on 12" centers for a mezzanine with a 5 ft span (small space over a half bath). When I asked they said someone had put engine blocks/car parts on a similar installation and it fell so they increased their requirements. They gave me the required psf loading. I did the calculations and still came out with 2 x 6 on 16" centers being plenty. We gave up building there. Their logic really seemed dumb as whatever is built it can always be overloaded.

 

[laser3kw]

Still can't decide between drywall or tin for the ceiling. Primary use is woodworking so I can imagine it might be a bit louder int here with the tin, but would reduce weight.

I have approximately the same trusses in my 30 x 40 x 12 w/ "attic" space. I have drywall on the underside and 3/4 t&g on the top side (insulation in between). As other have said, as long as it is light weight items spread out over the floor, you'll be just fine. Mine has been up for over 8 years and handling mid-west 12" ~18" snows and no problems.
Go with "ceiling rated" drywall on the underside, glued and screwed, for the sound dampening.

 

[CraigStu]

I am with Dagny. You will be fine. 2 houses ago we had a 24x24 garage w/ trusses that had the bottom a 2x4. I would hate to weigh all the stuff I put up there over 22 years.

 

[finn]

Go with white barn steel or even liner steel for the ceiling.

Once it’s up, it’s done, and there is no maintenance, probably for the rest of your days on earth.

 

[mike93lx]

Drywall. Install strapping first if the trusses are 24OC

 

[Innovate1]

Go with white barn steel or even liner steel for the ceiling.

Once it’s up, it’s done, and there is no maintenance, probably for the rest of your days on earth.

Could you elaborate on that? Don't know much about this material. I don't have an issue with loading but am looking to finish the inside of a 30 x 40 and insulate the walls and ceiling which means I need something on the ceiling. Seems like steel would be a lot quicker and cheaper than drywall. Only issue I can think of is possibly sweating on the top during our humid summers here when cooling the inside.

 

[peterl]

search for Dura-Panel at Menards

works great on ceilings.

 

[kest874]

If only we had a Menards in TN... nothing but Lowes and Home Depot, callign aorund to get some prices on metal roofing to see what the cost difference is. If I go drywall I'm going to go with 4x12 5/8 sheets to minimize joints.