24x32 A-Frame build Northern Sierras

Started by black_edelweiss, August 05, 2016, 11:54:54 AM

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Quite welcome, keeps my thunker working.
In the beam equations (which model breaking tests) depth is squared where width is used straight. Deeper builds strength much faster. The 8x8 with a 4 ply girder will certainly work. Unless you live heavy the 6x6 and 3 ply 2x10 works. You can also move up to dougfir, stronger and stiffer than SPF, and then there is stepping up to 2x12's. If you use 2 layers of 1/2" ply in the build up, then run a 2x6 cleat up opposite sides of the post for a couple of feet and onto the girder it will connect those two well.

You are running fast, think way out ahead of the ball and feel free to ask if you see something.


Im having a hard time finding a triple 2x10 girder hanger for the CMU wall. It seems all of the hangers are for engineered lumber or large timbers and only go as high as a double 2x10 or double 2x12....https://www.strongtie.com/topflangemasonryhangers_masonryhangers/wm-wmi-wmu_productgroup_wcc/p/wm.wmi.wmu

Does anyone have any ideas for this? I've been speaking to an Ace hardware owner and he says it may be possible to have a hanger custom made? Any ideas?


For a dropped girder I've usually gone into a pocket in the foundation wall. Rest on steel or a treated plate and allow airspace around and on the end of the wood. Will this work in your situation?


Thats probably what i should have done but figured a masonry hanger would be fairly easy to acquire for triple 2x10....seems like the local hardware store is certain they can get one ordered now at least so hopefully that works out...filled all the cores finally, took 300 bags of concrete, way more than i had anticipated.

Was going to use some heavy duty column caps but they were over $120 each to hold a triple 2x10...not sure why they were so expensive, so going to have to go with the lighter double piece post beam connectors....as for building the triple 2x beam, do i need wood glue or is there a specific nailing pattern i should use?


If not a welding shop can fabricate them. This is what I meant about getting your head way out in front of the work, it is difficult but keeps things moving better if you can do it. I used to be able to do that  :D. You can also raise the girder up onto the sill creating a flush girder and then hang the joists on the sides in hangers. This can cause plumbing issues if it needs to cross that zone and stay high.

The code nailing pattern for a girder is 32" oc top and bottom edges, staggered. I do top, middle and bottom rows about 12" on center, they look like a 45 degree angle across the face. For a dropped girder you are really just holding the parts in alignment, the joists rest on top of the girder and load them fairly uniformly. With a flush girder the joists are hanging on the outer plies and the nails provide the load sharing through to the inner plies, a better connection between plies is needed. I go ahead and stitch them together well either way. Glue does not make a beam stronger but does make it stiffer... if you get the plies drawn up tightly together.

If you are 2 piecing the rafters. The lower rafter piece can also support the second floor joist on its level top cut and the upper rafter piece passes by for several feet giving good lap. I would at least assemble the rafters on the deck into one piece to make sure they are nailed together in a straight line. You could assemble the entire rafter couple and joist into a tilt up frame.


Other ways to support a dropped girder... A steel post, either a solid "BOCA" post or a 3" min diameter schedule 40 pipe onto the footing with flat plates on each end (avoid telescoping posts) or a concrete pilaster. If you go that route it should be connected to the wall with some rebar, lag shields or similar between wall and pilaster. You'll probably need to expand the footing to do that one. Just more thoughts.


Thanks again for the info. Your idea of putting the girder on top of the sill plate seems like a good idea and im a bit doubtful ace hardware will pull through on the CMU hanger which isnt supposed to get here until Friday. Went with the diamond shaped 2x8x2 concrete squares you suggested. Glad to be done with concrete, that stuff really messes up your skin after prolonged exposure.

Heres what im going for on the rafters and upstairs floor joists... planning on assembling an entire rafter on the deck, making sure everything is good, and then using it as a template for the others. I'll build the lower half and raise it up in one piece (hopefully) and support it with a couple 2x4's until i have enough up to start the roof decking and upstairs floor to hold them together. Only half of the rafters will have floor joists as im going for an open loft/bedroom design to open everything up. All rafters will have 2x10 collars and plywood gussets to bring the rafters together. Pondering how much strength will be lost by not using the upper floor joists in half the structure...what do you think...the area does get a lot of snow, and will likely be piling up beyond the block wall...


Concrete is rough on your hands. A beekeeper friend heats beeswax and mineral oil to make an salve that works pretty well, bag balm is another good one for healing it up but basically the best thing I've found is distance, always glad to be done with that phase. Shoot, I've got another round of it coming up, when I come down off the shiny metal tanning salon, porch piers  :P

I'd just be guessing on whether that is a good plan to 2 piece the rafters. Where the break occurs at floor level I'm not too concerned, the rafter is pretty much the same as a wall up to a floor and then another wall up to the peak. Where the rafter is spliced in span like in the picture, well, you're splicing a beam in span. That is something I have never done and you have snow loads to beat the band. I don't agree with his splice point where he has floor joists, he's missed an opportunity to support the joists on something other than nails and he's got a splice in air. If there isn't a floor joist and you have to splice in span then I can see the thinking, he's moved the splice up as far as possible out of the load and maximum bending moment. I would make that lap as long as possible and nail it very well, drop the collar as far as possible. I suspect what will happen over time is the roof at the lofted end will stay flat and the clear section will sag in to some extent. You're the guinea pig, use deep rafters, lots of nails and long laps. Shooting through and clinching the nails gives them a good bit more shear strength. If there is a roof where it will work this is it, we don't want some armchair quarterback reading this to use that logic on a lower pitch.

A tji would be one piece and they would do the engineering, it may be cheaper than long laps and would sure be lighter to handle, likely faster. I'm not sure how they would handle the loft floor but that's what they get trained to do. Anyway just putting that out there.

Notice how the snow is piling up on those side sheds in the snow pic. It is keeping snow up on the roof and really loading the sheds, load and leak, forget that!


Sunday morning armchair quarterback here.  ???   I've looked at this for my cabin with half-loft design.  The code solution for an open ceiling area is to have ties on every other rafter.  No floor, just a 2x running across every 4 feet.  That often isn't very pretty and probably is never what a builder/designer is envisioning.  The problem that they are typically addressing is withstanding the outward thrust of the roof rafters  exerted on the top plate.  Thus the rafter ties are in tension.  Some builders opt to replace the sawn lumber tie with a steel cable to have the same effect.  Again, not pretty but I imagine it's much less obtrusive visually.  In my case I am opting for a structural ridge to take the lateral thrust out of the equation.

All of the above applies when the wall and rafter are separate.  With the A-frame it's obviously different.  With potentially large snow loads and perhaps wind too, is it more of an issue of preventing inward buckling rather than outward bowing?  The solution would need to improve the resistance against downward/inward loads, and short of putting in a floor the answer is probably to stiffen the rafter.  All the methods of stiffening a beam would apply: going deeper, wider, or improving the material properties of the beam.

Edit: forgot to mention reducing rafter spacing too, doh!
My cabin build thread: Alaskan remote 16x28 1.5 story


Recheck that... I believe the callout is rafter ties across every rafter couple, collar ties at every other.

An A frame is tied by the floor... although we drifted a bit outside of the prescriptive connection. I'm not worried at this pitch, again as the pitch lowers thrust increases and the connection becomes more critical.

I am mostly concerned with bending rather than outward thrust. I was going to do a math exercise but decided not to... you might enjoy it though. AWC's DA6, find  the equations for a simple beam, load increasing toward one end, figure out where the splice is going to be and use the equation for finding bending moment anywhere along the beam, figure it for the splice point in the open area. I'm not going to pretend to engineer it. You're going to be guessing some variables, just a thought exercise.


Quote from: Don_P on August 29, 2016, 07:39:31 PM
Recheck that... I believe the callout is rafter ties across every rafter couple, collar ties at every other.


You are correct sir!  No mention of rafter ties anywhere but at each rafter.  Collar ties no further apart than 4' on center.
My cabin build thread: Alaskan remote 16x28 1.5 story


That used to be different, in the past you would have been correct. The reason for the changes... look at the heeljoint table at the end of the rafter span tables and look down to the lower pitches. The connection requirement can get out of hand. We do not have that issue here but they have to draw the prescriptive line somewhere. When I started we were coming off the ranch/ Wright design era with 4/12's being the norm, high potential thrust loads and open ceilings. People were doubling up the ties on every other rafter or wider and those connections were in distress. That's just background info, we're typically steeper nowadays and we certainly are are here so you are not wrong. My Dad had easier walking roofs most of the time than I've had. This is probably pm stuff to avoid confusing the issue at hand ;)

Off to be a concreature, what I heard her say was "pour guy"  :D


The home depot wood delivery was delayed until this Saturday, and time is of the essence, so i drove 1.5 hrs to the nearest home depot yesterday and picked up x40 2x10x16. I picked them up for about $16 bucks a pop versus buying locally at $25 each! I would not load that much wood in my 2005 f250 again, as it was hanging out about 6ft with my rear shocks maxed out, and unstable despite being tied down as best i could.

The 20ft shipping container finally got dropped off, and the driver was a bit pissed as he muttered "This is not a normal delivery"...luckily he only got one flat. Paid $2640 for that container but had no choice as we need a dry storage area for moving our crap out next week. Considering the entire wood order for the A-frame was $3900, i could have built one hellavu storage shed. Luckily a friend managed to borrow a bobcat mini excavator and dug the garage out and cleared a lot of stumps/manzanita and improved the road...impressive little machine!

Got the 6x6's posts setup in one day, along with the sill plates and girder, put the double 2x10 rim joists up in another day, and just finished half the floor joists today...goes a bit quicker when working with wood versus concrete, and my wife has been able to help a lot lately. The remaining floor joists will be put up tomorrow (if i can buy the 2x10x12's locally) and hopefully i'll be ready to put the OSB over the joists by saturday when the delivery arrives...still have to drive in x170 2x10x16s and a lot of OSB, so not sure how long that will take.

Some of these 2x10x16s are extremely heavy and wet. Seems like the wet ones weigh twice as much as the semi dry boards. If the home depot delivery has a lot of wet boards, i dont see how i could get the rafters up without letting them dry for several days first.


Just seeing that stack of concrete bags makes me tired.   ;)

Just because something has been done and has not failed, doesn't mean it is good design.


Amen to that. It's looking good though.
Double check the center girder, I think it needs to be a triple;
Look at table 502.5(2)

It is possible to do a wheelie and dump the entire load in the road... or so I've heard  :D Borrow a trailer if you can, it'll save the truck and haul lots more.


Most of this work is hauling the materials in...i'd be happy if they dropped it off within 3 miles. Anyway, maybe its just the pic but the center girder is a triple 2x10...all doug fir.



Lookin real good.

Did you use line blocks to run the string for the posts? Man those have been my favorite tool, carpenters are missing out. Way better than nailing off 8d's and winding string around them to try to get em tight.

Some of my lumber got wet, or was delivered wet and it sure does make a difference in lifting. I've got about 12 or 16 rafters left for my roof. This has been one job that I stop before I am tired because walking a 2x6 plate at 20' up I don't want to trip.

Lifting both rafters together, it might be tough to get proper leverage. Putting up a ridge board would be tricky and would require scaffolding or getting creative with triangles.


For scaffolding, if you don't have access to metal scaffold, I build a pair of light "walls" to the height needed with a diagonal across them to brace, stand and spread them apart, these are the "ends" a top and bottom horizontal 2x across each side and an X at each side to form a rigid box then some 2x's  laid across and a couple of sheets of ply on top for a floor. Keep it light enough to drag as you work.


Nathan- Yea i used the block string....started to unwind the string and then thought what the hell am i doing, these will work perfect.

Checked out your build, man that has to be a bit nerve racking putting rafters that high up. Thats the last beast i have to slay and i'm not looking forward to it...good luck to you!!!

Thanks Don_P...i'm thinking i will probably have to put together something like that. The 2x10's have almost all been sopping wet, heavy as hell. Home depot changed the schedule again...wont have the x170 2x10x16 until Wednesday...said they're going to at least drop off the OSB tomorrow (hopefully) so i can finish the floor...will probably spend the next four days moving my junk out of my current house and building a front porch with stairs so i can get the materials up past the CMU wall easier. Something i would have to do shortly anyhow. Thinking i'll use four 6x6's spread ~8ft apart and run 2x10x12s out to the tops of the posts from the rim joist via joist hanger every 16" and connect them into another set of 2x10s running over the tops of the 6x6s. I'll use 2x12's for the stairs, and connect the 6x6 to the 2x10 with a post cap.


Quote from: MountainDon on September 01, 2016, 11:41:59 PM
Just seeing that stack of concrete bags makes me tired.   ;)

My back hurts just looking at them.


Been a while since i have updated. Using a phone to post this which is rather difficult. Been living in a wall tent since sept 13. Have to go pick up windows and a door and i can begin framing it in. Waiting for metal roofing wood stove insulation siding and stove pipe to arrive. Wood stove weighs 500lbs. Do i need to reinforce the floor joists below the stove??Also does anyone have any idea on the roof flashing for where the stove pipe goes through the roof to make it so water doesnt get through? Ill be using 12ft of triple wall insulatrd chimney pipe the whole way through so not too concerned about heat.


This whole journey of yours just impresses the hell out of us here  [cool]
How far did you get? The roof on yet ---  and stove in and working?
Keep us updated .... ;)



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