Garage Attic Truss Ratings?

[Jawgarage]

Whats the thinking here on the MINIMUM Live Load rating I should have my new Attic Trusses built to over my garage? First quote for storage I was given as a bottom cord live load was 40#psf. Then it was increased to 50#psf using 2x10 bottom cords. If we jump to 70# it goes to 2x12's and the price goes up by 50%! Not sure I need more than 50# for basic residential personal item storage in one area, and light office/workshop/storage in the other. I have NO knowledge of trusses but 2x12 trusses seems way excessive to me for what I am doing. Thanks.

Jeff

 

[ssdave]

50 psf should be fine. Normal floor load for a house is 40 psf. Unless you're storing tools or engine blocks or lots of lumber up there, 50 should be quite adequate.

 

[Jawgarage]

50 psf should be fine. Normal floor load for a house is 40 psf. Unless you're storing tools or engine blocks or lots of lumber up there, 50 should be quite adequate.

Thank You for the quick reply AND an answer that I was hoping for. There will not be any mechanicals stored up there as they will all remain on the cement slab first floors. Attic/office will be residential storage, and light workshop/crafts related storage. I like the idea of increasing to 50# over the originally quoted 40#. I also have the option to add support columns under the one section where some day the load may increase beyond what I expect now. Thanks again!!!!

Jeff

 

[Chris705]

Also agree that the 50 psf rating will be fine (actually it's great). Consider using 1 1/8" sturdie floor since the trusses will be 24" oc. Glue & screw the subfloor down for best results. If making wide walk-up stairs, double up a truss and run floor joists between gable end wall and doubled up truss.

 

[Jawgarage]

One more question here......any idea how much more of a load rating I'd get if I went to 16"oc instead of 24"? Current designs for the Trusses are showing a 40psf live load with 10psf dead load on the bottom chords and they quote that as 50psf at 24"oc. This is a 28' span and I'd like to avoid going to 2x12 bottom chords as that seems waaaaay overkill, but I don't want to wind up wishing I had beefed it up more down the road.

Thanks

 

[Chris705]

I would venture a guess that if you specified 40#/sf trusses at 24" oc and used them at 16" oc you would end up with the ability to store between 50 & 60#/sf. But a truss manufacturer can easily tell you that. Call a local truss fab salesperson and ask them your specific questions. Your asking the right questions, a salesperson will go to their engineer to get you the answers.

 

[Radix2]

I would stick with a normal 40psf load unless you are definitely planning heavy machinery up there - lathes,milling ect..

You are also asking about headers and doors below. If you go gonzo up there, you have to follow all that down below as well and that is going to be a ton of cost for stuff you have no plans to ever need.

On my current build for floors we used 40LL + 15DL and for roofs we need 30snow+15DL.
So that gets you 100psf total load on those lower structures (more or less given roof pitch,dormers,girders,ect.). So you might want to think how much extra you want to design for.

 

[Jawgarage]

I would stick with a normal 40psf load unless you are definitely planning heavy machinery up there - lathes,milling ect..

You are also asking about headers and doors below. If you go gonzo up there, you have to follow all that down below as well and that is going to be a ton of cost for stuff you have no plans to ever need.

On my current build for floors we used 40LL + 15DL and for roofs we need 30snow+15DL.
So that gets you 100psf total load on those lower structures (more or less given roof pitch,dormers,girders,ect.). So you might want to think how much extra you want to design for.

Thanks, very very helpful. I don't want to do overkill and there will not be machinery up there at all. It's just a large space so I know overtime it will collect lots of stuff and I want to build for that now. Fully agree on the need to plan for that below too which is why we are going to sister up the current 2x4's likely with a 2x6. I will also ask the Truss guys on Monday about what's involved to beef up the DL to 15 instead of the 10 they quoted on. I'd think 15dl is better with sheetrock below and plywood above anyway.

 

[finn]

I'd stick with the standard 40 lb unless you plan to store old iron block v8 engines up there or are a real packrat.

If normal floor load for a house is 40, remember that considers furniture, floor coverings, and a room full of people.

It's unlikely you will be lugging more than that up (and down) the ladder to your attic in your lifetime. Most household storage items are low density, i.e. a lot of air.

Why reinvent the wheel?