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30063030223357
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# Posted: 8 May 2013 12:16am
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Just got started on my 16x20' cabin. Have (13) 6x6 post on top of cement, with 2x12" around the sides and 2x8 floor joist supported by (2) 2x8 supports under the center of the joist. Just have some 20p nails and 3 1/2" screws through the 2x12 for now. Thinking 1/2' bolts through the 2x12 and 6x6 pillars will support the weight of the cabin. Any thoughts or suggestions? Will also bolt the center supports. Just want to make sure it will support the weight.
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ICC
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# Posted: 8 May 2013 10:33am
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Quoting: 30063030223357 Any thoughts or suggestions?
is this from a purchased plan set?
i ask because the bolts through the 2x12 and 6x6 are maybe stronger than the 2x12 itself. it looks like five posts down each 20 ft side, is that right? about 5 ft apart? it would have been better to notch the 6x6 and place 2 - 2x8 down each 20 ft side in the notched out part and then use bolts through to hold the 2x8 tight against the post. then the 2x8 would be sitting on a solid support not hanging on bolts or nails.
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creeky
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# Posted: 8 May 2013 10:57am
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did you use any kind of simpsons joist hanger or other hardware?
You can block the joists too. Put a 2x6 scrap piece under the joist and nail/screw/bolt to the post. It's a common technique I believe.
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30063030223357
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# Posted: 8 May 2013 12:05pm
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This is my own plan. Yes five post down each side and three in the middle. Didn't use any hardware, but i am going to put scrap pieces under the joist. The more i think about this, once the floor is down and walls are up, the weight is actually going to be resting on top of the 6x6 post. But i'm still going to bolt to the post.
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ICC
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# Posted: 8 May 2013 01:00pm
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Quoting: 30063030223357 once the floor is down and walls are up, the weight is actually going to be resting on top of the 6x6 post.
yes and no. yes at the post. no in between. in between posts the wall will be bearing on the 2x12 and the edge of the flooring. the flooring will be transferring weight thru the joists to the 2x12.
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ICC
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# Posted: 8 May 2013 01:14pm - Edited by: ICC
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these could be used to help support the 2x12's
DJT14Z better than just bolts through the post and 2x12. these supply spport at the bottom edge but still reply on fasteners to carry the weight from the 2x12 to the post. still not ideal but better.
through bolts and large washers will help resist twisting or outwards forces much better than nails
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ICC
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# Posted: 8 May 2013 01:32pm
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2x8 joist hangers nailed to the 2x12 will be superior to nailing thru the 2x12 into the joist ends. nailed into the ends places the load on the nails and can eventually cause failure as the wood dries and maybe splits where the nail is.
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bldginsp
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# Posted: 8 May 2013 03:11pm - Edited by: bldginsp
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I heartily agree with ICC that you need to get direct support under your rim joists (2x12) All the wall and roof weight will be on these, or that which does not go to the posts. Get a good snow load on it and those rims will push down, even with bolts. Nothing like good old compressive strength to take a dead load, rather than anything in shear.
I would consider gluing and screwing blocks on the 6x6 posts under the 2x12. Goop it up with polyurethane glue and screw down tightly.
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ICC
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# Posted: 8 May 2013 06:24pm
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when polyurethane glues were introduced I was one of many who thought this latest feat of technology was great. I used them for a few tasks and my worst complaint was that they were very messy.
years later I came across a Fine Woodworking article that was eye opening. The article can be found here, but be warned you have to be a member. if not you can sign up for a free 14 day trial.
if you are like me and hate things you have to register to see here's the short story.
they tested 6 glues, regular pva (std carpenter glue0 type 1 pva (waterproof), slo set epoxy, liquid hide glue and hot hide glue and the famous polyurethane featuring a picture of a tough animal.
three types of wood were tested. they are not your typical construction wood but wood usually reserved for furniture, maple, oak and ipe. they tested using a bridle joint, also known as an open mortise-andtenon
joint, because it has no mechanical strength and instead
relies entirely on the glue bond. they made tight, normal and loose fitting joints.
after assembly and drying they used a machine to measure the force it took to break the joints.
there were variations in strength between woods and joint tightness but the overall strengths from best to worst went like this.
best = waterproof pva (type 1)
slo set expoxy
regular pva
liquid hide (slightly better than the hot hide)
hot hide
and last, the polyurethane.
examples - type 1 pva tight or normal joint took 1840 lbs to break and the tight or normal polyurethane joint took 1400 ponds. not too bad a difference.
but when the joint was loose the type 1 pva tested at 1600 pounds while the polyurethane could only hold up to 565 pounds. !!!
my thoughts are that since many joints in construction work involve wood with some cupping and all the joints do not fit as tightly as we might like. the poly glue fails here and quite badly. i quit using poly glue for most things, especially things that don't fit tightly. that was an area it had been touted for as the glue expands to fill the spaces.
anyhow, interesting article.
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toyota_mdt_tech
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# Posted: 8 May 2013 09:22pm
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I see this often. As soon as you start adding more weight, you will shear that floor off your post and the floor will drop to the ground. The rim joist should be supported on top of your pier post, not anchored into the side of them. Then the center should have a support beam, running under the middle all the way across supported on TOP of the post/pilings to keep the joist from bouncing/flexing.
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30063030223357
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# Posted: 9 May 2013 12:52am
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The center is supported with 2x8 on each side of the center 6x6 post under the 16ft. 2x8 floor joist. So without complete renovation. what about a 2x6 piece around 18" long under each 2x12 joist fastened to the 6x6 post? I wish i had thought of notching out the post before, but this may work as well. I don't think i'll be carrying a lot of weight with a steel roof , and a high pitch.
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ICC
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# Posted: 9 May 2013 01:44am - Edited by: ICC
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anything you do is better than nothing, but anything you do at this point without changing the basic structure is a band-aid. it is difficult to say what the best band-aid will be. the DJT14Z brackets mentioned above are my choice for off the shelf remedies, have the advantage of being steel. using wood blocks has the disadvantage of placing more wooden items in a shear load situation. wood dries and cracks. under shear loading with bolts through it there is always the chance of splits and that means the support becomes more or less ineffective. it is too bad you did not ask the question before doing the construction.
even something like sections of 2x2 x 1/4" angle iron bolted to the posts and under the 2x12 would be better than wood supports added as proposed. the DTJ14Z's have the additional advantage of being bolted through the 2x12 and post to clamp the 2x12 in place preventing any outward rolling of the 2x12.
the good thing is that things like this, if they do fail, usually fail slowly. over time nothing worse than a sag here or there may occur. it is unlikely that failures in the fasteners or the wood will occur in several places at once. it is hard to predict. a small failure in one lace can cause addition stress in another and cause a domino effect. there is more than gravity and the simple weight of the building components at play here. snow weight may be a factor if applicable to the location. wind is a frequently overlooked source of building stress or movement. there may be seismic factors depending on your location.
are the 2x12's and 2x8's pressure treated? the rims and floor joists are close enough to the ground that they should be. are the posts treated? they should be. it is hard to tell from the picture as some of the new PT treatments do not have the traditional dark green color. the fasteners and hardware should be suitable for PT contact. FYI, the "Z" in the part numbers like DTJ14Z denotes suitability for contact with PT wood.
how are the posts anchored to the ground? you said " 6x6 post on top of cement". if that means what it sounds like there may be a cause for worry with high winds.
if you have questions about any of the terms please ask.
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bldginsp
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# Posted: 9 May 2013 08:15am
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ICC is right that anything at this point is a band aid.
Is this going to take a snow load? If so, I suggest you rebuild it. If not, use the band aid of your choice, but for the long run you really need to do something. Those 2x12s just wont take weight attached to the side.
Good luck!
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30063030223357
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# Posted: 9 May 2013 08:26am
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O.K. sounds like a good time to restart. What's the consensus on this. Without moving the post, I'll tear apart and notch out the post so 2x12 are resting the post and use hangers for the joist. All lumber is pressure treated except the 2x8 joist which are over two feet off the ground. This will make the cabin 3" smaller , but no problem.
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bldginsp
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# Posted: 9 May 2013 08:41am
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That's the right thing to do. I'm a 'wood preservative nazi' myself, having seen a lot of rotted wood.... so I suggest you dip the cut ends of any piece of PT that is near the ground. But if the joists are more than 2 feet off the ground maybe this is not necessary.
You are wise to backtrack at this point. You don't want to build on a questionable foundation.
Hate to say it, but posts stuck in the dirt, even with concrete around them, will only last so long. But that's another story.
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toyota_mdt_tech
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# Posted: 9 May 2013 09:06am
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Quoting: 30063030223357 The center is supported with 2x8 on each side of the center 6x6 post under the 16ft. 2x8 floor joist. So without complete renovation. what about a 2x6 piece around 18" long under each 2x12 joist fastened to the 6x6 post? I wish i had thought of notching out the post before, but this may work as well. I don't think i'll be carrying a lot of weight with a steel roof , and a high pitch.
That would do it. I suspect those are 4X4 post, so a 2X4 nailed or bolted to the side of it going right to the post footers (cement pad, block etc) should do it. Do it on all parts of the post that has the rim joist, same goes for the center beam to support the joist. Make sure they are treated, not that decking, but real treatment, ie the greenish looking wood. And coat each end you cut. If you cant find it, make your own using "Jasco" wood preserve.
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toyota_mdt_tech
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# Posted: 9 May 2013 09:11am
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Quoting: bldginsp Is this going to take a snow load? If so, I suggest you rebuild it. If not, use the band aid of your choice, but for the long run you really need to do something. Those 2x12s just wont take weight attached to the side.
The best fix IMHO at this point without complete teardown would be to remove each post, do it one at a time right now before any decking is applied. Dig the post out to the concrete footers, build a form for a column, fill that hole with cement down to the footer to the grade and above inside your form to the underside of the rim joist. Do it to each post. Without decking in place, its doable, will be time consuming.
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ICC
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# Posted: 9 May 2013 10:47am
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one more suggestion. if going to the trouble of tearing back to posts on the ground change the single 2x12 'beams' for double 2x somethings. what exactly depends on what you are building.
is there an upper floor?
a loft?
is the ceiling or upper floor going to clear span the 16 foot distance?
what is the snow load?
that info will help determine the best size for the beams. example: to support a floor with center beam, a roof and ceiling two 2x8's would work for snow load up to 30 psf and a span between posts of up to 5 ft 9 inches.
two 2x8's are about 22% stronger than a single 2x12.
beams that carry loads like this are always designed by engineers to be doubled or even a solid timber, never a single piece of 2x dimensional lumber. they resist twisting torque loads from the joist connections much better.
cut the notch carefully without any overcutting in the inside corner of the notch. nail the first 2x into place. then place the second 2x and use a nail or two to hold in place while drilling through the beam and the post. Use hot dipped galv if you can find them. 1/2" , use big flat washers and do not tighten so much that the wood fibers are crushed. use lock washers or lock nuts. then place the hangers and install the joists.
the center posts and beams should be notched into one side of the center posts. my inclination would be to use the 2x12's from the outer long sides as the center support beams and use the 2x8 that are in the center beam now for something else such as doubled for the outside beam. . the center beam carries one half the total floor load. two 2x8's are going to be tested with only three posts. there may be some bounce to the floor in points between center posts? didn't run any calcs but it looks that way.
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ICC
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# Posted: 9 May 2013 10:51am
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re the PT wood. the rule is that if the lower edge is 18" or more off the ground PT is not needed. and do coat the cuts with the appropriate chemical.
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WY_mark
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# Posted: 9 May 2013 11:47am
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ICC has it pretty well covered, but this bears pointing out on it's own...
screws sometimes seem like the stronger choice than nails, but your nails have greater sheer strength than screws.
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ICC
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# Posted: 9 May 2013 12:56pm - Edited by: ICC
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right mark, lots of screws get used for the wrong reasons, the wrong applications
sometimes screws are handy as a clamp to draw 2 pieces together, then nail. other times i use large bar clamps to hold pieces before nailing.
there are also screws that have the term structural in their name or description. those are another thing altogether, but the common screws found in large numbers are brittle from the hardening used to prevent the heads from tearing out.
'lok' series screws by fastenmaster are one of the great structural rated screws, plus they use a torx drive head that does not slip unlike philips. they are better than the regular lad screws, imo. there are also other brands. the 'lok' series come in different varieties for different uses.
one big difference between the run of the mill screw and a structural screw is you can find all kinds of strength data for the structural but you can not find that for other screws.
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30063030223357
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# Posted: 9 May 2013 11:54pm
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ICC are saying notch for one 2X and nail the second on the outside, or notch for both to set on the post? And, two 2X on all four sides. Or just the sides holding the floor joist? And how do i do the corner post?
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ICC
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# Posted: 10 May 2013 12:36am - Edited by: ICC
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down the long side notch the 6x6 for two 2x so they both have a ledge to sit on. google 'AWC DCA6-09 Prescriptive Deck Guide' that's guide meant for deck construction and not a whole building but the post design is what i mean. the tables in there are not meant for a building, only a deck
if you are using a regular gable roof with ridge running the 20 ft direction the beams down the long sides carry the bulk of the weight, the side walls and roof loads plus 1/4 of the floor load (each side) the 16 ft ends only carry the weight of the wall materials. you can get away with a single 2x at the ends. that's for a reg gable roof with a simple ridge board in the roof, all the loads going onto the long side walls.
you could cut that end 16 ft joist down to fit between the posts. you could use concealed flange hangers at the ends (simpson LUC series)
 nail into the posts with 16D nails.
http://www.strongtie.com/products/connectors/luc-lu-u-hu-huc.asp#
you could also place the floor joists on top of the doubled side beams and not need the joist hangers at all. that does raise the floor some, maybe good, maybe not. personal choice. when i do that i use H1 hurricane ties to aid in positioning the joists. toe nail into the beams well.
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toyota_mdt_tech
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# Posted: 10 May 2013 12:52am
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And if you use any hangers, get a air powered palm nailer. If I didnt have this doing mine, I'd just quit. I have the Bostich 50 and 100 model. Makes nailing in those special hanger nails (with the "10" on the head) a snap. You could use it to build the entire cabin too. May not be quite as fast, but a lifesaver.
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Josie
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# Posted: 18 Jul 2017 08:10pm
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Is it feasible or O.K to put down a cement floor in the mountains. I'm trying to cut cost.
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toyota_mdt_tech
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# Posted: 18 Jul 2017 08:48pm
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Slab foundations are used all the time, it still requires a footer over the wall location, its just a deep channel around the perimeter of the slab is all. I would suspect good drainage gravel under it, pack it well, add vapor barriers, and you can insulate it also. If its real cold, the gravel may prevent frost heaving too. There is a way of doing this if this is the route you want to go.
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Josie
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# Posted: 19 Jul 2017 01:25am
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Thank you...
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neckless
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# Posted: 20 Jul 2017 07:01am
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are u goin to park a d8 in there....lol
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DCRUMRINE
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# Posted: 17 Nov 2017 12:44am
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30063030223357
All your 6x6s should have been notched an 1inch and a half so your boards rest on the notch and wont shear the bolts. Like someone mentioned you can take ground contact pressure treated 2x6s and cut them the length from the top of your cement pad to the bottom of the board and bolts those through your 6x6s. This will stop the down force from shearing the mechanical fastners from shearing. The brackets someine posted earlier is not a very good fix at all. If ya didnt notch the post to fit the 2 xs than the method of a 2x from the bottom of the rim joist to the top of the cement pad is the best fix....... To get a better idea of seeing what i am talking about google pole barn construction and see how the do the top 2x12 headers that the rafters sit on. This will give you a visual of whatf i am talking about the notched post.
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toyota_mdt_tech
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# Posted: 2 Jul 2018 06:27pm
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So what did we come up with on the correct fix or patch? A sistered 2X under rim joist to pad would be the ticket at this stage.
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