A short while back I inquired about building a shed for a future workshop and had some excellent help; I've been off the board for the last couple weeks learning everything I can and working to make some of that green to pay for the shed.
I've run into a possible problem with the design of the roof for my shed. The plans I had originally obtained were for a 12' wide shed and I have changed that to 16'. I've also upgraded everything from 2x4 to 2x6 construction for better insulation. The original plans called for the roof to be started with gable ends and a 4/12 pitch. The diagrams appear to have the 2 by whatever you use laying on the flat for the gable ends and being braced much like the walls (2x6 @ 24" OC). Then the rafters will work inward 18" from the front gable because I want a 6" overhang all around. Lookout rafters will be used to get the 6" from the gables. A ridge pole will run the length of the shed (24') for the rafters to attach to. I plan on using a 2x8 for the ridge pole. The rafters are to have birds mouth's cut where they will rest on the top of the side walls and leave the appropriate overhang. The ceiling joists are to be connected to the rafters, not the tops of the walls. See the picture at the bottom.
Here are my concerns:
1) Is the gable acceptable to be built like this (2x6's laying on the flat)? I have seen both methods (standing & lying) used.
2) Do I need a truss construction that involves more bracing and load carrying members since I change the width from 12' to 16'? There's never snow here so that's no concern, but wind is for sure!.
And a last off-topic question regarding headers for the walls, should I use 2x6 or 2x8's?
The windows header width = 3'- 9 1/8"
The doors header width = 5'- 6 1/4"
Let me know if there's anything else you need to know to help with answering the questions I've posed. Thanks for looking!
First thing you need to do is check with your building department to see if spans are determined by deflection or by bending. For a Group 1 roof ( assumed dead load of 2.5lbs per square foot), live loading at 20lbs. (which is a minimum load roof); max clear span for 2 x 6 on 12" centers is 12' 9" if span is limited by deflection, 11' 8" if on 16" centers. However, spans limited by bending, you'd be okay, providing you don't put in a ceiling. You could clear span up to 19' 4" on 12" centers, 16' 11" on 16" centers.
For the ridge board I'd go with 1 x 8, much easier to handle as it's purpose is really only to provide a surface to hold the rafters in place as they are set. Tip; lay out the ridge board when you lay out the top plate for your rafters.
As to your other questions, it's standard practice for the gable ends to be laid on the flat, then sheathed before they are set. If wind is a concern collar ties could be used on at least every other rafter (again, check what's code) these are placed in the upper third, though they are used mostly to offset the outward loading to the walls, they also help keep the ridge line straight over time. Main thing for wind loading is at each gable end a wind brace should be set. This can be a 2 x 4 nailed at the peak to a joist, usually at a 45º angle. Rat runs may also be required, these are 2 x 4s runing the length of the building nailed to the rafters. Again, check what's code.
Headers are also dictated by code but, I'd guess that 2 x 6 doubled up with half inch thick ply spacers would be good to go on that 5' span, certainly the 3' one. Hope this helps.
Before you invest too much time into researching codes and designing a roof, have you checked into pre-fab roof trusses? A 16' foot width is a very common span and the local code requirements are normally met by the trusses stocked locally. Add to that the fact that you'll have one tenth the time involved in construction, and trusses installed on hurricane plates (as opposed to birdmouthing) become very attractive. I have installed 26' foot trusses with two foot eves alone, using only three different length prop poles.
And please be sure to think it thru if you choose to stick frame your roof. As drawn, Im having trouble figuring how those tiny eves will be enclosed to prevent bird, rodent, and insect entry while still allowing ventilation. Also I see in your drawing you dont appear to be designing for a double top plate at the walls, which is something Id highly recommend and may be required by code.
In my most humble opinion, building a simple gable roof using trusses boarders on a "no brainer".
I agree, checking code is a total waste of time; wait until all the material is bought. Then when he submitts his plans for the permit: "NO GO!!!" :+
Dunno if I'd go so far as attributing the use of trusses as a "no brainer", particularly if that space is to be used for storage...Definetly needs a top plate and the joists setting on that, though. :7
The six inch soffit at the eaves is no biggie, that's what continuous soffit vents are for...very common.
OK, based on what Danford C Jennings said I should be OK if I use the 2x6's for the rafters at 24" OC because they are a length of just over 8'-9". I do not plan on using the attic area for storage of any type. The only weight that will be applied is drywall or ply sheeting so I can insulate the attic and shop lights (florescent) will be hung from them. I assume I'll still be OK with this extra weight?
ImNo_1, I have wondered about getting pre-built trusses and will look into some suppliers. A quick question - just look them up in the book or should I rely on another method for finding good local suppliers of trusses? Regarding the top plates, I do have it set up for a 2nd top plate to be applied, it's just not shown in the CAD drawing I posted, missed it because I was in a hurry. If I understand what you're saying about the eves - should I increase the overhang to provide an easier closing of them or does Danford C Jennings correctly state that I can use the vented soffits? That is what is called for in my plans also, but if it will be difficult I'd much rather just leave the overhang a little longer to ease any frustrations. And, if I understand correctly the ceiling joists arranged the way shown in the picture will be OK for my uses?
Lastly, I will be checking into our local codes and etc. to make sure everything is OK before I purchase. Just looking for the final drafts here before I feel comfortable with what I'll ask/present for inspection and permits.
The info I supplied in regards to loading apply to 12 and 16 inch centers, both for rafters and joists. Since you are planning on sheetrock ceilings, loading by deflection would be used and, thus, 2 x 6 celing joists won't fly.
I'll reiterate that continuous vent soffits are very common and a six inch overhang won't cause you problems. The joists, as shown in your drawing, are not correct, they are toenailed to the top plate and face nailed to the rafter/truss.
FYI, the info I provided came from Architectral Graphic Standards and I'd be more than happy to provide you with a drawing of the soffit with continuous vent from the same source when I get home from work this afternoon.
I didnt intend to get into a item by item debate with any forum member regarding roof construction methods, but only to point out to you that there are other methods than the only reply posted previous to mine, and to offer my opinion based on my experience.
Apparently Dan has some experience with a local box store selling trusses which dont conform to local codes, (I do not) but that doesnt surprise me if he waits until after the materials are on site to apply for the permits as he suggests. And how my statement "Before you invest too much time into researching codes and designing a roof" got turned into "checking code is a total waste of time", I cant begin to fathom.
The orange box (and most others round here) stock common span trusses in the store, and typically any small lumberyard has a truss supplier which can provide trusses and the applicable engineering data, so your yellow pages can be a guide to truss sources.
Many gable roofs are built without any eve or rake at all, but for weather protection and asthetics, I prefer larger eves and rakes. (In hindsight, I wish I had built my shop with a tapered rake over the overhead door) Dan is right, you can enclose those soffits with vented aluminum material, I just dont care for cutting little five inch pieces of it and I dont think it looks good.
While not overlooking the basic building practises of level, plumb, and square, my opinion is compared to stick framing a roof , trusses make roofs a no brainer and a lot less work, which is what makes them a marketable product.
Because your here asking about this, I assume (and maybe incorrectly) that you have little or no experience building this sort of structure. My only intent here is to try to assist you build a structure that will outlast you or I, in the most efficient manner possible. Sadly, if you'd like to hear more from me regarding this I would request you send a private message or email. I see sarcasm as only the first step down the road to the personal attacks I have seen in the past and will not be replying to this thread in the future.
Note: the first two pictures, top to bottom, show the sample woods I bought to match: mahogany, walnut, oak, the bottom is the side of the table. The remaining 3 pictures are of the wood in question...