Garage Attic

[MJBaldwin]

I just moved into a new construction home and trying to get my garage cleaned up and storage ideas.  That being said I was planning on adding about 2 sheets of plywood or OSB onto the roof trusses with a ladder in order to create a little storage up there for misc things.  Kids misc things, Christmas items, hockey bag, golf clubs, etc etc. Not looking at a huge weight in my opinion.  I am reading since they are roof trusses I shouldn't do this. Although I had a 1928 home and did this with no issues? Just wondering your thoughts on the whole topic again not going to be weights/steel/etc just some simple storage. 

 

This would be above the 3rd stall being I could get some insulation around the perimeter of it but would have to use batt under the storage... thoughts? Plan on insulating and finish rocking at some point.

 

What type of wood would you use for this? I know i used OSB at my old place and probably only 1/2 if I remember as I had the same thoughts as when I was installing that just to get items up off the ground.

[delcecchi]

You should be able to look up the load carrying capacity of the trusses and figure it out.   The roof load is part of the calculation along with how that load is transfrerred to the walls.

 

Do you have a picture or drawing we could see? 

Edited April 15, 2018 by delcecchi

[cavalierowner]

It's been a while since I've reviewed truss diagrams, but I think the design load for the bottom chord of a standard truss was something like 10 PSF unless a higher load for attic storage was specified. That's why you need to find out what the design load is because things add up in a hurry. 1/2" plywood weighs around 1.5 PSF and 5/8" sheetrock weighs 2.75 PSF. That's a total of 4.25 PSF with just the ceiling and floor. So you've used up almost half of your capacity already. Personally, I wouldn't do it unless I knew for sure what the design loading was and that it was designed for attic loading. 

 

Edit: Oops, just saw that you mentioned 2 layers of plywood, so that makes your total load 5.75 PSF.

Edited April 18, 2018 by cavalierowner

[delcecchi]

8 hours ago, cavalierowner said:

It's been a while since I've reviewed truss diagrams, but I think the design load for the bottom chord of a standard truss was something like 10 PSF unless a higher load for attic storage was specified. That's why you need to find out what the design load is because things add up in a hurry. 1/2" plywood weighs around 1.5 PSF and 5/8" sheetrock weighs 2.75 PSF. That's a total of 4.25 PSF with just the ceiling and floor. So you've used up almost half of your capacity already. Personally, I wouldn't do it unless I knew for sure what the design loading was and that it was designed for attic loading. 

 

Edit: Oops, just saw that you mentioned 2 layers of plywood, so that makes your total load 5.75 PSF.

I was thinking a single layer to make a bigger area with two sheets.   Your interpretation may differ.  

Is it a total or a per square foot load, averaged over some number of square feet?   like I have some trusses.  I throw a couple sheets of plywood over them.  Now I have an 8x8 platform.  How much weight can I put on it?  

This mechanical/civil engineering stuff is strange.  Give me electrons any time. 

[cavalierowner]

As I think about it, my interpretation of 2 layers thick was probably not correct. It's a uniformly distributed load that's assumed. So if the 10PSF is correct and 4.25 PSF is used up, then there's 5.75PSF left to work with. That means a straight calculation of 64 SF(an 8x8 platform) x 5.75 PSF = 368 pounds total spread mostly evenly over the whole platform. If stuff starts getting piled up in one area, then that creates a concentrated load; that's when my brain starts to hurt!! BTW, there are always factors of safety built in to structural design, but you probably don't want to get into those....for safety. 

 

BTW, me and electrons don't get along