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Tarmetto
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# Posted: 8 Jun 2015 19:18
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Been working on our pre-cabin build, which basically includes setting up our camper, adding a deck, and building a bathhouse/laundry building to get us by until we start the cabin.
I have framed in the floor joists for a 20 x 12 bathhouse/laundry, and I'd like to include a covered deck making the gable roof 20 long by 17+ wide using rafters. 4' cantilever over the porch, 1' overhang at the back.
Need advice on rafter details for a DIY by myself.
Location is southern upstate SC where snow load is minimal, and I'll probably go with sheathing and a shingle roof at 4/12 pitch.
Any advice?
Also, the floor joist framing consists of perimeter 2 x 10 treated lumber, internals are untreated 2 x 10 YP. Framing is on 6 x 6 treated pilings at 2'-4' above ground. I plan to insulate, and skin the bottom of the joists with 1/4" luan that I will saturate with thinned epoxy resin to make it critter proof. Sound like a good idea?
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Tarmetto
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# Posted: 8 Jun 2015 19:24
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Here's a couple of pics of the progress. The camper and it's deck will form an "L" with the bathhouse/laundry. The "funky" little framing where the joists tie to the deck is where a metal framed RV cover will rest.
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toyota_mdt_tech
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# Posted: 8 Jun 2015 21:02
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Are those piers holding up the rim joist? I cant tell from the picture.
At 17 feet wide, a non load bearign ridge, a 2X6 at 16" centers I think would be fine. I suspect you could to 2X8 at 24" centers, more insulation.
Easiest way to build all your rafters at once and have them all fit perfectly is to rough out one rafter as close to the pitch you want. Then build another identical to it. Set them up on the end wall or gable end wall. Let the ends hit each other. Nail them down temp on the top wall plate. Do the same for the other gable end, let the ends of each rafter come together to find center. Then slide in ridge board, load bearing or not, it will be perfectly centered (it finds its own center) now look to see if your angle cut it perfect, if not, adjust it. Now you still have your dimensions for your 4 rafter you built, mass produce the rest. If your structure is perfectly square, they will all nail right in place and fit perfectly. Dont forget your rafter tie (ceiling joist) and make sure they nail into the side of each rafter, 4 nails. The a collar tie will be needed every 4 feet, or every 3rd rafter at 16" OC or every other at 24" OC.
This Larry Haun has a book and loads of youtube videos. Its worth watching him and his brother build, they hand bang all nails.
https://www.youtube.com/watch?v=qdQH00055Fw
And get you a squangle too.
http://www.amazon.com/Great-Neck-Squangle-All-Purpose-Square/dp/B00FX99FJK/ref=sr_1_2 ?ie=UTF8&qid=1433811536&sr=8-2&keywords=squangle
A squangle will let you set the angle at the ridge and the part that pokes out is used to mark your seat cut (sometimes called a birdmouth) for the top of the wall. Once set, dont touch it.
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Don_P
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# Posted: 8 Jun 2015 22:34 - Edited by: Don_P
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A single rim looks like it is trying to support around 8 joists in a span, that isn't going to work.
For the rafters it could be something like the pic
For the rafter to tie connection, called the heeljoint connection in the codebook, there is a table at the end of the rafter span tables. That connection is the most highly stressed in a roof, it don't matter if Larry says 4 works, check it and put enough nails there. I'm picking, the rest of that is on the money.
Oh, the ledger in my pic is notched into the stud rather than just nailed on. If a 2x4 wall use a 1x4 if 2x6 use a 2x4 ledger. Gang notch these on the bench, leave the stud top length wild, stand the studs at each end, brace and install the ledger, then install the studs one at a time. Once you find the rafter location you can cut the top length for top plates. and install them prior to setting the rafters.
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Tarmetto
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# Posted: 9 Jun 2015 06:01 - Edited by: Tarmetto
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Quoting: toyota_mdt_tech Are those piers holding up the rim joist? I cant tell from the picture.
Yes they are, and more will be added before the subfloor goes down. I think the county calls for every 5', so I'll add a row down the center. Though this is considered a moveable "shed" and requires no framing inspection.
The rim joists are currently screwed to the piers, but I plan to add lag screws and a block under the joists, and braces on the higher end.
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Tarmetto
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# Posted: 9 Jun 2015 06:19
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Quoting: Don_P For the rafters it could be something like the pic
Thanks Don! That's exactly what I was looking for. Should be easy for me to do alone.
Would any other bracing be needed from the rafter ties to the rafters, and would 2x6 Fir at 16" OC be ok for the ties and the rafters?
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Don_P
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# Posted: 9 Jun 2015 19:42 - Edited by: Don_P
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Yes #2 dougfir 2x6 is good at 16 or 24" rafter spacing... whoop you didn't say which fir, you're good in #2 SPF as well. I checked the 20 psf live load (wind) and 30 psf snow load tables... I don't get 30 psf in the VA blue ridge so you're safe there.
I neglected to draw them, Toyota mentioned the collar tie every 4' in the upper third of rafter height, a metal strap over the ridge nailed to each rafter is also fine for that connection, this tie keeps the roof from unzipping at the ridge in high wind. Remember the pics during Andrew of roofs inflating from a blown out gable and opening up at the ridge then the two halves flying off screen, there ya go, we had to buckle up at the ridge after that. The porch cantilever is your weak link for uplift, tie it down well at the walls and at the porch carry beam.
Looked at the heeljoint table while checking the rafters, at 4/12 you need 5 nails at each rafter/ceiling joist connection @ 16" oc, 7 @ 24" oc... they are talking 16 penny commons, most of you have never held a 16 common, it is a big nail, you're probably used to 16 sinkers in hand drives, .149" dia vs .192 for a common. I typically shoot a .131 gun nail. Common rule of thumb is to pull half again for those, 8 and 10 shots in each end respectively. The lower the pitch the higher the stress at the heeljoint, that's the reason for the high nail count.
Your handle bridges 2 states, my people come from eastern NC. In the 1830 census most of them listed turpentine as their occupation, tapping the longleaf, tarheels  Long about '65 a fellow dropped a match, or several.
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Tarmetto
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# Posted: 9 Jun 2015 20:26 - Edited by: Tarmetto
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Thanks again Don. I failed to catch toyota's collar tie suggestion, thanks for pointing that out.
I'll probably have some 4x4 posts for porch supports that I can size length to support the cantilever from ground bury.
[u][/u]Quoting: Don_P Your handle bridges 2 states, my people come from eastern NC.
We live in Asheville. NC...and the getaway is in western Laurens County, SC. (opposite of the norm). This lengthens our spring and fall season at the getaway, but makes mid-summer at the getaway hotter than we're used to...LOL!
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