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Question of Safe storage in the ceiling

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Forum topic by cbMerlin posted 09-24-2009 03:46 PM 1155 views 0 times favorited 13 replies Add to Favorites Watch
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cbMerlin

98 posts in 2110 days


09-24-2009 03:46 PM

I’m preparing to install a ceiling in my garage (shop) and have a number of questions I’d like your thoughts on. My garage is about 20’x20’ with a 2×4 “W” truss system, 24” OC. Like alot of folks, I’ve got a bunch of crap stored up there. In preparation to put up a ceiling I’ve unloaded it all, what a mess! It ocuured to me that I had quite a bit of weight up there and began to think about the safety. How much weight can I actually put up there safely? I’ve tried to find spec’s on the the trusses to estimate load rating with no luck. They have those metal mending plates dead center on the span. I’ve thought about putting 2×4’s across the mending plate to re-inforce them but have read that doesn’t really improve load rating much. I’ve read numerous opinions on how much they can handle ranging from 10-20lbs per square foot.

Here’s my thinking so far:
1. I want to put 1/2” ply on top for storage.
2. I want to finish the actual ceiling surface with 1/2 ply as well; It’s a bit lighter than drywall & intalled with screws, would be easier to take down if needed, It would also give me better holding and be more versitale holding for lighting, hooks, etc. Might actually increase load capacity by tying the trusses together and distributing the weight. Will be primed & painted white to improve lighting.
3. I’m insulating the ceiling with R13, not the 30+ reccomended, but much better than nothing.
4. Attic space will have two access points, one on either end.
5. I’ve wired for lighting

Any advice, reccomendations or opinions would be greatly appreciated.

-- Sawdust looks better in the garage than cars, explain that to your wife!


13 replies so far

View Kindlingmaker's profile

Kindlingmaker

2654 posts in 2216 days


#1 posted 09-24-2009 05:41 PM

If you put plywood on both the top and bottom of your 2×4’s ( a boxing of the frame work ) make sure you stagger the plywood joints/seams, and this should add more strength. Be careful in that your truss system was not designed for inside loads but to support the roof…

-- Never board, always knotty, lots of growth rings

View GFYS's profile

GFYS

711 posts in 2160 days


#2 posted 09-24-2009 06:14 PM

a 10’x10’ area with 20 pounds per sq ft is 2000 pounds.
I can’t recommend storing anything in your roof structure.
I have a 20’ wide structure with similar trusses that were built on site.
I have a few light weight items like plastic pipe etc stored in the spaces.
You might call your local supplier that sells trusses. They can tell you what the
designed load bearing capabilities of similar trusses are.

View Dan Lyke's profile

Dan Lyke

1485 posts in 2814 days


#3 posted 09-24-2009 09:07 PM

You can start with a joist load calculator, like the American Wood Council Maximum Span Calculator for Joists & Rafters, with the caveat that your trusses have loads on them that aren’t simply represented by a floor, as kindlingmaker suggests. The neurons I’ve got dedicated to floor loading aren’t being cooperative right now, but the simple answer is that a ceiling should be no problem, but there’s no way that storing anything on those trusses will ever be code compliant, so if you really want to use that space you might think about how to run a secondary set of joists.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/User:DanLyke

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Kindlingmaker

2654 posts in 2216 days


#4 posted 09-24-2009 10:27 PM

Dan Lyke, The ceiling structure of having plywood on both sides of the 2×4’s would resist bowing more so than plywood on one side only BUT the load factors of the trusses still must not be stressed.

-- Never board, always knotty, lots of growth rings

View TopamaxSurvivor's profile

TopamaxSurvivor

14873 posts in 2365 days


#5 posted 09-24-2009 11:24 PM

Wouldn’t plywood both sides add strenght like a torsion box?

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View cbMerlin's profile

cbMerlin

98 posts in 2110 days


#6 posted 09-25-2009 12:28 AM

I’ve seen truss designs that have a verticle in the middle of the “W”, making storage pretty much worthless. I always thought the verticle piece was a way of telling you not to use the area as storage. With mine, the distance between the bottom elements of the “W” is about 6 feet wide and probably 4 feet to the peak. It’s almost begging me to store stuff up there, however, I have enough issues cutting straight lines without dodging falling roof parts!

Prior to this project, I probably had 500 lbs of misc. stuff up there. I have it all down right now, but don’t want to push my luck, I guess it ain’t going back up. Another factor that just dawned on me was snow load. My garage has always been heated and without insulation the snow doesn’t build up over the garage, it just melts off. With adding insulation, it might be something I need to consider. I guess I better re-think my storage problem, damn.

More thoughts are welcome!

-- Sawdust looks better in the garage than cars, explain that to your wife!

View Dan Lyke's profile

Dan Lyke

1485 posts in 2814 days


#7 posted 09-25-2009 06:06 PM

cbMerlin (and others), when I said “never going to be code compliant” that doesn’t mean “is definitely gonna break and kill everybody”, but if you live in earthquake country like I do those one in a thousand events take on a little more meaning. When using those truss span calculators, it’s also worth noting that the default deflections are set up for “don’t crack the wallboard in the ceiling if someone’s walking on top”, failure is quite a bit more than that.

Your attic trusses should be engineered for snow load, so I wouldn’t worry too much about adding insulation, but it might be worth talking to an architect or Googling around a bit to find a reference on what the projected lbs/sq.ft. for snow load is for your area (40? 120?), and double-check with your truss manufacturer (or someone similar). But think about what the various elements of the truss are doing under roof load: The horizontals you’ve been stacking stuff on are going to be under tension when there’s more roof load (because the weight on the rafters is going to be trying to make the walls spread), which will likely make them deflect towards the floor less.

In short, if it was well spread out I wouldn’t worry about 500lbs spread out over most of the ceiling, but by the time you add flooring and ceiling, even though as others have pointed out there should be some box-stiffening effect there, it might be time to double-up on the 2×4s that your trusses are using as rafters.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/User:DanLyke

View cbMerlin's profile

cbMerlin

98 posts in 2110 days


#8 posted 09-25-2009 11:41 PM

All, Thanks for the feedback, I got some thinking & research to do.

Dan, when you suggest to “double-up”, are you talking complete additional trusses or re-inforcement of some type? I have 4/12 pitch. Based on a couple places I looked the snow load for central Ohio seems to be 30 lbs.sq.ft.

As always, anybody & everybody, feel free to jump in!

-- Sawdust looks better in the garage than cars, explain that to your wife!

View Dan Lyke's profile

Dan Lyke

1485 posts in 2814 days


#9 posted 09-26-2009 03:30 AM

I was thinking sistering additional joists along-side the existing horizontal pieces of the truss. So far as I can tell from my various looking about at engineering for a roof load of on the order of 140lbs/sq.ft. (a living roof, so gravel + soil + water load in soil), your walls are almost certainly strong enough, so if you just slap some more 2xWhatevers across that span, you can put the load on them. I haven’t run this back through the span calculators, but this may be as easy as slap additional wood along-side the trusses and screw them together.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/User:DanLyke

View doyoulikegumwood's profile

doyoulikegumwood

384 posts in 2682 days


#10 posted 09-26-2009 03:52 AM

cb, dan is on the right trax here this is what was suggested to me by a truss manufacturer on a garage i helped a friend out with the trusses are designed for light storage its cya on the manufacturers part. but if you want to use it for what your doing i was told to add a joist at the dead center of each truss thus the joists were then 8” on center the gentlemen i talked to seemed to feel no verticals were needed, but i have to say when spanning 20 feet i don’t see how i could avoid adding them i hope this helps. with boxing it in i think you will be just fine on load rating

-- I buy tools so i can make more money,so ican buy more tools so I can work more, to make more money, so I can buy more tool, so I can work more

View TopamaxSurvivor's profile

TopamaxSurvivor

14873 posts in 2365 days


#11 posted 09-26-2009 04:24 AM

Trusses in our house are 2×4. Are yiou adding 20 foot 2×4 joists?

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View MedicKen's profile

MedicKen

1599 posts in 2152 days


#12 posted 09-26-2009 04:46 AM

Is the shop space heated/cooled? I am guessing that the attic space is not heated or cooled. You might be setting yourself up for a mold issue in the plywood/insulation “sandwich”. You might consider putting a vapor barrier up as well. Plastic sheeting might go a long way in helpig to keep mold under raps.

-- My job is to give my kids things to discuss with their therapist....medic20447@gmail.com

View bandman's profile

bandman

79 posts in 2079 days


#13 posted 09-26-2009 06:25 AM

If you’re putting additional weight on your roof trusses, I would recommend no more than 10 psf without
confirming it with the truss design from the house. An additional way you could get storrage capacity
on your ceiling would be to consider running TJI combination joists the entire span of the trusses from
wall to wall where you want to store things. I’ve seen guys to t his in Wisconisn for additional storage
capacity in their roof system. The joist can clear span between bearing walls to add capacity for storage.

Watch for any excessive deflection, cracking, or distortion of the truss members. The bottom chord is especially critical in the truss as it is the tension chord. You definitely don’t want to cut or compromise the bottom chord in any manner on your trusses.

I see your located in ohio, the best route to be sure would be to have a professional engineer in ohio take a quick look at it for you as well. Code regulations vary from state to state with snow and wind loading depending on geographic area and weather conditions.

-- Phil

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