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DaJTCHA
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# Posted: 30 Jun 2012 02:35pm - Edited by: DaJTCHA
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MtnDon-
I appreciate your comments on this one...
Since reading a few construction posts and the critics of certain designs, I began wondering (and becoming paranoid) about my finished "Shed Mahal" and whether I should be worried about certain design aspects. The overall shed is 12'3" by 16" and the first floor joists and the second floor loft's joists run the 12'3" width of the structure.
Starting with the foundational supports: (9) 36" -41" holes with average circumferences of 12-18" filled with concrete and a 6" diameter cedar post. The 9 posts make three parallel supporting runs
Beams: 2X12" lumber with (2) ½" lag bolts on the (3) runs. 2X12" are lagged into the sides of the 6" posts without notches, one on each side.
First Floor: 2X8X12's layed 16" OC. The first floor's joist cantilever the edge of the 2X12" beams by 10" on either side. Decking is ¾" tongue and groove OSB.
Walls: 2X4x96" studs every 16" OC.
Loft: 2X8X12"s every 16" OC with two runs of blocking between the joists.
Loft Floor: ½" OSB.
Roof: 2X6 every 16" OC with 5/8" OSB covered in Ice guard G from owens corning and then metal roofing.
The structure is extremely rigid and I couldn't be happier of my labor of love, but the two areas of concern are the beams and the cantilever. Since the three somewhat parallel runs of beams/post are not tied to one another, I had considered running 2X12" from post to post between the runs to complete the tie-in and to under support the existing 2X12" 's that are there. As far as the cantilever...I'm at a loss on how to fix it if this is a problem!?
Three Views of The Under-Structure
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TomChum
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# Posted: 30 Jun 2012 03:28pm - Edited by: TomChum
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Not mtn Don but
My thought is that you have nothing to worry about. 12x 16 cabin with 9 posts? One story..... No worries here (from your pics)
You're worried about the posts leaning over time? Post to post stringers would look like 'strange construction' and huge boards like a 2x12 is about twice what I'd use for that. I'd make some flats with a chainsaw for the stringers. If the cabin NOT being skirted it will show and in that case I'd thru-bolt those 9 connections with 1/2" bolts and big washers - might look better and satisfy your concerns. Or just spike it with bigger nails.
Maybe you could nail 2X6s on from the bottom, flat, and add some knee braces to four corner (or 8 exterior) posts, ignoring the center post. Then it looks consistent to the current construction.
Cantilever does not appear to be any concern (in your pics) and they are braced anyway.
My opinion.
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MtnDon
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# Posted: 30 Jun 2012 03:28pm
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The cantilevered first floor joists are likely no problem. A joist may be cantilevered by an amount equal to the depth of the joist. As a 2x8 is actually7 1/4" the 10" cantilever slightly over the amount permitted without engineering. But the structure is small and probably not as heavily loaded as a regular full time residence (washers, dryers, big fridges and freezers, etc.) so it is probably fine with the 10" cantilever. That assumes the joists are one piece from one side to the other side.
The 2x12 beams lagged to the posts is another matter. When a lag screw or bolt is used like that the load on the 2x12 is concentrated on the lag screw hole. It's not the strength of the lag or bolt that is the cause for concern, but rather (a) the strength of the 2x12... will it split where the lag hole is, and (b) is the lag seated deeply enough in the cedar post to stay there, to not pull out or want to tear the grain of the wood and tilt downwards under load? The technique of bolting or lagging 2x's to posts used to be permitted for building things like decks. However too many fell down and injured people that now decks are required to inset the 2xbeam so the weight rests on a ledge or shoulder. Then the fasteners only job is to keep the 2xbeam tight against the post.
You could improve your situation some by hammering about 10 - 16D Common nails into each of the 2xbeam to post connections. Also if you were to scab onto each post lengths of 2x4 under each 2xbeam with "lots" of 16D nails that would also spread the load out over many more points. A handful of nails often provides better support than a single large diameter bolt as the point loads become smaller.
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rayyy
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# Posted: 30 Jun 2012 03:30pm
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I think your fine,DaJ.Maybe pound a few 16d galvinized deck nails through the 2x12,s into the posts to help them two lag bolts a little more.Look's pretty goodf to me.
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MtnDon
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# Posted: 30 Jun 2012 03:48pm - Edited by: MtnDon
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AWC Connection calculator
Easy enough to use. Where it asks for Main Member it means the post, in your case. Where is refers to Side Member that is the 2x12 beam. Notice the calculator takes length of bolts/lags into account as well. It will advise when the fasteners are too short of the main member not thick enough. Depending on wood species and fastener lengths 3 or 4 - 16 D common nails can be stronger than a single 1/2 inch lag.
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MtnDon
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# Posted: 30 Jun 2012 04:05pm
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As for lateral bracing, that would make things remain solid in the event the ground gets soaked. You don't mention your soil type, but many soils offer very little lateral resistance once soggy with water. If that's the case the piers can begin to move, either down or rotating (tilting) to one side. If there are solid footers under each pier then bracing can help prevent lateral pier movements.
Note to readers and future builders....
A 6x6 makes a superior pier.
Notching and making a ledge for both 2xbeams to sit on on the same side of the post is better than having a 2xbeam on each side of the pier.
It's always a heck of a lot more difficult to strengthen things like this after the fact. I'm working on one myself right now.
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OwenChristensen
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# Posted: 30 Jun 2012 05:09pm
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Yeah, like they said, the only real issue is not having the weight of the cabin on top of the posts. You might have the cabin push down and a post through the floor.
I think you could put a dogeared scab of 2x8 under each stringer and aboout three bolts all the way thru to another one on the other side of the post.
I'll bet you wish you had cut the floor joists off to 11'-9''.
Owen
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DaJTCHA
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# Posted: 30 Jun 2012 06:01pm - Edited by: DaJTCHA
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I should have correctly said...I used 1/2" carriage bolts, washers, lock nuts through the entire post and (2) 2X12" beams on either side. I said lag bolts, in fact they are carriage bolts.
I like the idea of the scabs bolted into the 6" post underneath the 2X12's to support them a bit more. I have a box of lag bolts (correct this time) with washers that I could screw the scabs to the post with. Do you think that 3 lags for every scab under every post to beam point would be the ticket.
I should also clarify that the photos I've included do not include the 1/2" carriage bolts as they arrived after I filmed the video that those photos were screen snapped from.
Please comment with this new information and I appreciate your time!
LOL! Yes, I wish I would have better thought out the 12'3" width measurement, but in the end...we got more space out of the error. Its my story and I'm sticking to it! LOL!
D
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MtnDon
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# Posted: 30 Jun 2012 06:15pm
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Personally I'd use 16D common nails and not the lag screws, but that's an individual choice.
Re the 1/2" carriage bolts. They have the advantage over a lag screw that they will not pull out when installed with washers. However a 1/2" carriage bolt does not have the same shear strength as a 1/2" bolt , like a machine bolt. reason? Carriage bolts almost always have the shanks threaded full length. That reduces the effective diameter to about 3/8 inch, more or less. A machine bolt only has threads at the end where the nut will go. Plus a machine bolt can have a washer under the head whereas a carriage bolt can not. Those reasons are why you will never find a carriage bolt referenced as suitable for construction under any building codes.
Another good choice for fasteners are the engineered screws such as the LedgerLok and HeadLok varieties. There are others as well.
It should also be noted that bolts, etc. should not be tightened to the point where the wood fibers are crushed. Very large washers can help prevent that.
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toyota_mdt_tech
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# Posted: 30 Jun 2012 09:36pm - Edited by: toyota_mdt_tech
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I'd say from your specs and runs, everything is built to specs, loft and roof are overbuilt (which is perfectly fine) but you will need collar ties on the rafters every 4 feet? This could be part of the framing for the flat ceiling? Are the rafters tied to the loft joist? If so, you are plenty golden dude IMHO
I'd say lagging those joist hangers to the post is a MUST though or add a load bearing board under the beams supporting the floor joist. (reffering to your foundation piers and beams) I think I would of set the beam on top of the post. But easy fix. I'd attach blocking on each side of the round post to the concrete footer to support the beam the floor joist are on.
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DaJTCHA
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# Posted: 2 Jul 2012 09:56pm
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I still have to get around to putting in the collar ties. The roof is a salt box with the angle of the 11'6" deck to the 8' short deck sitting at 87 degrees. I ask MtnDon about this a while ago and decided I'd tie them together, but haven't got around to it yet.
I was able to measure the posts today and each side has a 4" wide flat spot on it (They aren't perfectly round), so nailing a scab to it and getting to the sit flat to the underside of the 2X12" beam above it that it'll support will work perfect.
I may just pick up a box of those engineered screws that MtnDon mentioned as well.
Thanks guys!
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