I’m constructing a 12′ by 20′ utility building to house lawn care equipment and other miscellaneous items. The roof will have a 5/12 pitch and I’m getting engineered trusses from a local company. Each side of the roof will be about 7’8″ from peak to lower edge. The trusses are on 24″ centers. For simplicity, I’d like to cut a full sheet of decking to the length needed to fit from edge to peak. I’ll be using 5/8″x4’x8′ CDX for the decking.
I know that on larger structures, the sheets of decking need to be staggered for added strength. For a small building like mine, I would have a lot of unnecessary joints if I make the additional cuts to be able to create a staggered layout. If I lay the sheets of decking lengthwise from edge to peak, will it be a code violation?
Thanks in advance for your input.
Bill Arnold
Edited 3/27/2008 9:03 am ET by BArnold
Edited 3/27/2008 9:04 am ET by BArnold
Replies
(2) 4x8 pcs of plywood layed next to eachother is still 8'x8' no matter how you look at it.
Laying the plywood horizontal on the roof or verticle makes virtualy no difference in waist for your roof.
We have always staggered the joints and i dont think i would ever question doing it different.
I suppose you could ask your inspecter as he/she would have the final say .Thats assuming you need an inspection. here where i live anything over 200sqf needs a blessing from the city/county.
Span ratings for ply wood are based on the face ply being perpendicular to the supporting framing members when being used as floor and roof sheathing.
Face ply running parallel with the support members is not a code approved method of installation.
Face ply running parallel with the support members is not a code approved method of installation.
This is not always the case.
For corner shear panels on walls, for instance, code requires that plywood be intalled vertically from plate to plate.
Since 5/8 sheathing-rated CDX is rated for a 40" span, you can certainly use it to span 24" with face grain parallel to framing.
However, this will reduce the effectiveness of edge nailing, particularly if you use the recommended 1/8" spacing between sheets.
You won't have any more waste running the sheets perpendicular to framing, and you'll have a stronger roof system. It's also easier to install perpendicular from the bottom up.
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""...when being used as floor and roof sheathing.""
They can't get your Goat if you don't tell them where it is hidden.
This is note # 2 from table 503.2.1.1a of the codes here. Table is for allowable spans and loads for plywood and wood structural panels for roof and subfloor sheathing and combination underlayments. "Panels continuous over two or more spans long dimension perpendicular to supports."
They can't get your Goat if you don't tell them where it is hidden.
Hey Dove,When I was researching the correct way to form up a poured concrete foundation, i downloaded some info that said the plywood stacked 4 wide by 8 high was 33% stronger than 8 wide by 4 high. Seems the whalers would be perpendicular either way. In other words, 4x4 next to 4x4 piece of ply is stronger than 4x8.
I am not certain I am understanding you. Can you remember where you saw that info?
They can't get your Goat if you don't tell them where it is hidden.
I think I have the papers somewhere, I'll look for them and post the website tomorrow.
I would have a lot of unnecessary joints if I make the additional cuts to be able to create a staggered layout.
Actually....the "unecessary joints" would be those that ran almost eight full feet if you don't run them perpendicular and staggered. Think how weak those joints from eave to ridge will be landing on individual rafters.
J. D. Reynolds
Home Improvements
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Plywood has an axis of strength. You need to run it perpendicular to the framing so it does not sage between trusses.
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I will echo that there is no advantage and maybe a disadvantage to running roof plywood vertically. Your trusses better be plumb, level and square because you will have to catch a seam for 8 feet. Not as hard if you are only supporting 4' of seam on the end of a panel.
The first row is the hardest row of sheathing to apply because you don't have another row below to rest it on--usually we pull it to a chalk line marking the top edge. The second row is duck soup because you just flop the sheets up there and they rest on the lower row (with nails for spacers) and you have someplace to stand and work. Running them horizontally, every sheet you put up there is going to be a first row sheet.
There is no additional waste running the sheets horizontally. If your roof is 20', you will use two full sheets and one half sheet for a run. Then you can take that half sheet to start your next run and add two fulls.
With your method, you have to cut all 10 sheets. You would cross cut 2 sheets, and rip 5.
Thanks to all who responded.The "axis of strength" explanation along with the issue of alignment with trusses for an 8-foot length convinced me to use a horizontal alignment. I attached drawings of the roof deck layout using both methods. I'm scheduled to start placing the roof trusses today (Friday).
Bill Arnold
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
You are wasting a good 24" piece on every run. Instead of starting with the half sheet, start the second row with the 2' drop from the first row. Always start the next row with the drop. At the end of the job, you will only have one drop left. Bob's next test date: 12/10/07
I should have attached the drawing of the roof trusses and gable overhang. The trusses are on 24" centers starting at the center of the building. There is a one-foot overhang from each gable.Bill Arnold
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
I would need only 11 pcs. There would not be any drops with that layout. Save the owls! Bob's next test date: 12/10/07
OK, please show me how you can do that. I'd be concerned about using pieces as narrow as 1' on the overhang.
Bill Arnold
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
I'd use pieces 1' on the overhang. I wouldn't use two pieces in a row and if the overhang needed more support, I might add a few blocks. Personally, I rarely build with 12' overhangs on the gables. I don't like that look. The most I do is 8" so that worry never enters my mind, unless I'm actually building a 12" overhang. I will concede that you are probably better off avoiding the 12" pieces on the overhang even though the overhang is very, very short and if it is framed correctly, the subfascia will easily carry it and the top peaks can't fall because they hold each other up. I'd probably use the 12" pieces without incident and without losing any sleep. Bob's next test date: 12/10/07
Jim,Thanks for your patience and your explanation. I still consider myself a novice at most carpentry matters. Although I've built a few things over the years, I brought in a professional crew to do the roof. On this small project, I was planning to do the roof myself.
Bill Arnold
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
I understand that BArnold and don't mind discussing this with you. For you, the extra cost of one or two pieces of any stock will not matter and the main thing is to make your job easy and uncomplicated. Adding those smaller cutoffs could trigger a small problem if you don't know what to look for to ensure a stable installation. For me, saving a sheet of material becomes a daily part of my life. If I save on sheet every day of my career and work 40 year, 6 days a week and 50 weeks a year....I save 12,000 sheets of plywood. Additionally, that saving mentality will also save significant amounts of other stock. I dedicated myself to using every stick of lumber wisely more than 30 years ago and some things are simply part of my fabric now. That doesn't mean you are wrong. In fact, if you lay the pieces in the way you are thinking, you might end up with some nice drops to use on your work bench or shelving. Bob's next test date: 12/10/07
Hey Bill, looks like you fell asleep in your shop cam. :)
Yeah, I guess it does! One of the first things I did after buying this place was to expand the shop building to have a nice place to build furniture and boxes. The only "woodworking" I've done in months is felling a bunch of trees and clearing a jungle along our back property line. Then, I put in 170' of split-rail fence before starting on my utility building. Sheesh!
Bill Arnold
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
for instance, 5-ply has three veneers running lengthwise, and two running crosswise.
k