Rafter strength question

[Mosby]

I bought a 36x48 pole barn with 18ft walls. It was built around 2005 and was used to store an RV and a few odds and ends for the person who had it.

We built an upstairs apartment across one end of the barn, with one room downstairs on ground level. The rest is all work shop and storage for my boat.

The project is done now, we got all the proper permits, had an engineer draw up the plans and get them approved, etc. So I am satisfied that it was done right. It was built by a contractor who I have a personal relationship with so I was able to help out on weekends and do some of the smaller things myself, trim work, run CATV cable, cat 6 cable etc. So I am pretty familiar with the construction of it. Besides which my father was a carpenter his whole life, while I am definitely not. I am familiar enough to know what I am looking at most of the time, with regards to home construction

The rafters were 4 ft on center. To make the engineer/building inspector happy the framers added 2x4 bracing between all the rafters and nailed up 3/4 inch OSB boards all over the ceiling with ring shank nails. They did this over the entire barn, not just the living spaces.

So my question is, is this "Attic" space strong enough for light storage use? I am thinking Christmas decorations, winter clothes type stuff, not tools or equipment. They installed pull down stairs from the living space, so I have access. And when it was being built you could walk all over the attic with no problem. But I know that's not the same thing as storing stuff up there.

It also has 18 inches of blow in insulation through out, so if we did store anything up there I think I would need to add some kind of raised platform to set the boxes on.

 

[LX-Markham]

.... had an engineer draw up the plans and get them approved, etc. ....is this "Attic" space strong enough for light storage use?

The answer to this seems painfully obvious

 

[tapered-pin]

you've given NO specifics but you're asking a specific question.

Pictures?
Measurements?
Size of your ceiling joists? (rafters are at the roof, joists form floors/ceilings).
Span of each joist you want to store above?

There are people here who will tell you no without knowing any of the specifics and will warn you that your entire structure will collapse if you let a mouse **** in your attic area - ignore those people.

Engineers use anywhere from 30% to 200% safety factor depending on what they're designing.

 

[Homerr]

You're saying 'rafters' but I wonder if you mean 'trusses' or 'site-built trusses' that the 2x4's were added between?

The best answer to your question is 'no'.

However, if you are literally talking about 100 lbs. spread out over a 4x8 sheet of plywood then it's probably fine. Just don't let it creep to include books, papers, other heavy stuff.

That said, with all the volume you must have left int the shop portion there must be somewhere where this stuff could go, like tall shelving accessed by a ladder for this infrequent stuff.

 

[Mosby]

I am not sure what bearings would be, but the rafters are pre-made style using 2x4s. They span the 36ft width of the building and the roof is 11/12 pitch.

I realize this set up won't hold much. and maybe nothing. I am fine with it. The contractor is the one who told me we could use it as storage after they boxed it all in like they did. But honestly I think he did it, because the framing cost went up so much higher than his original estimate, because he left that off the estimate, so I think he was just trying to make that bitter pill a little easier to swallow. But I am suspect about how much strength it added.

Obviously enough to satisfy the inspector and pass the occupancy inspections. But maybe not much more.

 

[Mosby]

I am using the wrong word apparently, I am talking about the trusses. And they are not "site built". They were ordered from wherever you order trusses from and delivered already assembled.

 

[tapered-pin]

I am using the wrong word apparently, I am talking about the trusses. And they are not "site built". They were ordered from wherever you order trusses from and delivered already assembled.

Then you probably shouldn't.


BUT people do it every day, relying on the safety factor incorporated into the design by the engineers to maintain an acceptable deflection.

think about it from this standpoint: when the structure was being built, the guys that were installing the blown in insulation probably stood on the bottom chords of the trusses to walk around and distribute the insulation. the truss manufacturer would never tell you that the trusses will accept an additional 200# per square foot, but they did (unless when the insulation was being installed, one of the trusses failed and a guy fell through the ceiling).

another thing to consider is this:
any interior walls that were built under the trusses will dramatically shorten the design span, thus making the truss overbuilt for the application at that point. (i.e. a truss layout that is designed to span a box with support on the outer walls only, then the box has a couple of rooms built within it and the walls run parallel and perpendicular to the clear span truss layout, the span is no longer from one side of the box to the other, it's now from one side of the box to the longest point where it intersects with the wall.)

 

[tapered-pin]

Again, ignore tapered-pin. I cant stress that enough. A man walking around is not 200psf, it is 200lbs, at one location.

wrong.

a man standing on a single point of a truss/joist/simple beam is a POINT LOAD.
that same man would have to lay down in order to change the distribution of his load.

same reason a man can lay down and move on thin ice he cannot walk across.


dude, your embarrassing yourself with whatever the pros taught you that built your garage (or was it a home renovation that made you an expert?).

 

[mike in tucson]

I experienced this same scenario a while back....in a rent house that was built in 1959. I ran out of garage storage so I figured that I would put the lighter stuff in the attic up thru a 24" X 24" access hole. First up was the lighter stuff like car interior parts, car wiring harnesses, etc. But then, what about the spare wheels that I had? Up they went also. So did the 6 Chevy V8 cylinder heads and a few crankshafts. One day as I drove up to the house, I noticed a sway back shape in the ridge....oooooh. I backed a friend's trailer into the garage and started dropping stuff thru the access hole into the trailer.....scrap yard paid us for 3000 lbs of metal from the attic.....didn't need to do any engineering calculations regarding truss loading on that house!

 

[LX-Markham]

dude, your embarrassing yourself with whatever the pros taught you

If you could only see what you just wrote.


Mosby: it doesn't sound like the building is that old. Do you still (did you ever) have the structural drawings and/or the engineered truss drawings? If so, the design load (including attic storage live load if applicable) should be listed on the drawings.
If you don't have a copy of the permit drawings, then perhaps the original engineer you hired for the building could provide you with a copy. Or the truss manufacturer, or even the City that issued the building permit.