Author Topic: My first pass 12'x14' A-Frame design  (Read 8370 times)

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Offline Adam Roby

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My first pass 12'x14' A-Frame design
« on: June 11, 2013, 01:44:22 PM »
This is my first pass design of an A-Frame cabin, which will serve as a temporary shelter until I can save enough money for a larger cabin.  The overall dimensions are 12' wide, 14' deep with a height or around 12'.  The idea of having it 14' deep was to add a design aspect with the roof but it is probably a waste of space, and for similar money I can go a full 12'x16'.  Anyways, this is the first design, there will no doubt be a few more before the plan goes into action.

Here are the various build steps: (Can be printed on Letter paper in Landscape mode)

"Foundation" - Blocks, the green beams are pressure treated and the yellow or conventional.  Might go with all PT, this design was meant for keeping costs down as much as possible.





Knee Wall - on each side. The colored beams are part of this step, grey parts are from a previous step.



The Back Wall - This design has 3 windows that are 18"x30" (only ones I found on Home Depot site.  The white members are ones that will be added in a next step.





The Face Wall - Notice the two beams that go between the roof trusses.  The lower one is at 8' and is just structural, the upper one is at 10' and will be closed off at that point to add an attic space.  There will be a vent in front and back and soffits on the bottoms of the roof beams to allow for ventilation.



Trying to optimize the wood as much as possible.



Roof Framing - Trying to add some flare to the design by having a slanting roof line.  (Wide up top and narrowing towards the bottom)





Here is the cost breakdown.  I was planning on putting on either a vinyl siding with shingles, or wood siding with a metal roof.  For fun, this breakdown is using none of those options rather 3/4" Pressure Treated Plywood (finished product).  This was an idea from a friend of mine, doubt I would go for it but did the cost analysis based on that.

Code: [Select]
Foundation / Flooring Base Each Sub-Ttl Total

10 pcs  18"x18" Patio Stones    $ 5.25/ea       $52.50 = $  52.50
10 pcs  4-Way Dek Block $ 5.49/ea $54.90 = $ 107.40
 2 pcs  PT 2"x6"x16'  (cut to 14') $14.91/ea $29.82 = $ 137.22
 3 pcs PT 2"x6"x12'  (cut 3" off) $11.19/ea $33.57 = $ 170.79
10 pcs STD 2"x6"x12' (cut 3" off) $ 7.75/ea    $77.50 = $ 248.29
22 pcs  2"x6" Joist Hanger  $ 0.97/ea $21.34 = $ 269.63
 2 pcs  Double 2"x6" Joist Hanger    $ 2.16/ea $ 4.32 = $ 273.95
52 pcs  8x2-1/2" deck screws $ 0.10/ea $ 5.20 = $ 279.15
96 pcs  8x1-1/4" deck screws $ 0.05/ea $ 4.80 = $ 283.95



Floor Sheathing

  6 pcs 4'x8'x5/8" OSB $23.45/ea $140.70 = $ 424.65
210 pcs 8x1-1/4" deck screws $ 0.05/ea $ 10.50 = $ 435.15



Knee Wall Framing

  6 pcs 2"x4"x16'  (cut to 14') $ 6.65/ea $ 39.90 = $ 475.05
 12 pcs 2"x4"x8' $ 2.88/ea $ 34.56 = $ 509.61
192 pcs 8x 2-1/2" deck screws $ 0.10/ea $ 19.20 = $ 528.81


Knee Wall Sheathing (Experimental Design)

  4 pcs PT 2'x4'x5/8" Plywood $48.17/ea $192.68 = $ 721.49
130 pcs 8x 1-1/4" deck screws $ 0.05/ea $  6.50 = $ 727.99


Face Wall Framing

  2 pcs 2"x4"x12' $ 4.99/ea $  9.98 = $ 737.97
 12 pcs 2"x4"x10' $ 4.07/ea $ 48.84 = $ 786.81
 28 pcs 2"x4"x8' $ 2.88/ea $ 80.64 = $ 867.45
  4 pcs 2"x6"x8' $ 4.65/ea $ 18.60 = $ 886.05
140 pcs 8x 2-1/2" deck screws $ 0.10/ea $ 14.00 = $ 900.05


Face Wall Sheathing

  3 pcs PT 2'x4'x5/8" Plywood $48.17/ea $ 144.51 = $1044.56
130 pcs 8x 1-1/4" deck screws $ 0.05/ea $   6.50 = $1051.06


Back Wall Framing

  6 pcs 2"x4"x12' $ 4.99/ea $  29.94 = $1081.00
  6 pcs 2"x4"x10' $ 4.07/ea $  24.42 = $1105.42
 30 pcs 2"x4"x8' $ 2.88/ea $  86.40 = $1191.82
  4 pcs 2"x6"x8' $ 4.65/ea $  18.60 = $1210.42
196 pcs 8x 2-1/2" deck screws $ 0.10/ea $  19.60 = $1230.02


Back Wall Sheathing

  4 pcs PT 2'x4'x5/8" Plywood $48.17/ea $ 192.68 = $1422.7
140 pcs 8x 1-1/4" deck screws $ 0.05/ea $   7.00 = $1429.7


Roof Framing

  3 pcs 2"x4"x16' $ 6.65/ea $  19.95 = $1449.65
 28 pcs 2"x4"x12' $ 4.99/ea $ 139.72 = $1589.37
164 pcs 8x 2-1/2" deck screws $ 0.10/ea $  16.40 = $1605.77


Roof Sheathing

 12 pcs PT 2'x4'x5/8" Plywood $48.17/ea $ 578.04 = $2183.81
288 pcs 8x 1-1/4" deck screws $ 0.05/ea $  14.40 = $2198.21


1 32" Door with window/screen $159.00/ea $ 159.00 = $2357.21
5 18"x30" windows $89.00/ea $ 445.00 = $2802.21


Again, this is a first design, and there will no doubt be many changes.  All advice is welcome and appreciated.  As you can see I have not designed the soffit area yet, so that is one point I need to consider and play with.  Also, the exterior siding and roofing is a concern, need to keep cost down as much as possible since this is just a temporary shelter and will become a shed later on, so it can't take too much funding away from the real project. 

What I have learned already from this first draft is that 1) this small design is still too large.  I need to either scale it back and make something smaller like a 10'x10' to save money or scale it up and just do the larger 16'x24' cabin which was my original plan.  I need to seriously think about exterior finishes as well, keeping the building protected from the elements while still not looking too residential, but at the same time not spending a fortune.  Also, all of my prices are based on the Canadian Home depot prices... and I noticed that Lowes has much cheaper materials, so the next plan will have US prices.

Offline itpdk9

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Re: My first pass 12'x14' A-Frame design
« Reply #1 on: June 11, 2013, 04:59:25 PM »
I am no expert but at a quick glance I would turn your sheething for the roof the other way, it will provide more support as one sheet will hit more rafters horizontally.  Im sure you will get a lot of ideas here too.  Just figured I would throw my 2 cents.  Good luck!

Offline rick91351

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Re: My first pass 12'x14' A-Frame design
« Reply #2 on: June 11, 2013, 06:08:16 PM »
I would make a more substantial pier and post foundation or best yet a footing and wall foundation.

 
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Offline old_guy

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Re: My first pass 12'x14' A-Frame design
« Reply #3 on: June 12, 2013, 02:11:29 PM »
My uneducated opinion, take it for what it is worth.

The 14' header joists are essentially the beams for your cabin's foundation, and must be sized accordingly.  They should certainly be doubled (or more), then check the tables to determine the allowable span between the foundation blocks.

You are using a ridge beam to carry half the roof load and prevent outward thrust on the walls.  That beam must also be sized to carry the load, and the end wall framing should carry that load directly down to foundation blocks.  Those end floor joists should probably also be doubled, to prevent crushing as they pass the ridge beam load down to the foundation blocks. 

The rafters in your drawing look as if they are cut to support the ridge beam.  The beam is actually holding up the rafters.  There is a stickied discussion of proper rafter hanging with a ridge beam.

Now I will sit back and read the responses, and learn from the people who truly know this stuff.

Offline MountainDon

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Re: My first pass 12'x14' A-Frame design
« Reply #4 on: June 13, 2013, 04:38:11 PM »
Some of this has been noted by others... just to reinforce...

The 2x in the floor plan that runs down the side over the 4 blocks in a row may be inadequate. Best practise is to use a doubled up pair of 2x's or more on larger structures). This is especially true if the floor joists are to be hung inside the 'beams'.

The sub-flooring panels should have their long dimension run across the joists. Same as for the roof sheathing panels; they should be laid with long dimension across the rafters.

Foundation: simple blocks sitting on grade is asking for frost heave movement. Deep, below frost level, piers can solve that problem but piers are not the most stable foundation in many soil types and climates.

I see screws listed on the plans (walls section) Use nails, ring shank are great. Screws are mostly not rated for structural purposes. Mostly as there are some that are structural, but the common screws from the hardware store, big blue and orange are not. Common deck screws are brittle and can break under shear loads.

There are most likely building codes and inspections where this project is to be located. Have ypu checked into that?  Are the codes enforced? They are not just silly rules but can help keep projects safer for the builder and occupants.

Wall sheathing should be nailed around all sides.

The rfaters as drawn look like more trouble than the worth. As drawn if you mean to have a structural ridge beam you are missing the support columns that should be at each end. A structural ridge beam must have a column or columns that extend down from the ridge beam to the earth. The columns can be designed to go around windows and doors in the end (gable) walls. As pointed out one half the roof load would be supported by the ridge beam. If a ridge beam is used the rafters must be supported by the beam. The rafters would not be notched to fit under the beam. A ridge beam deep enough to allow the abgled rafter cut full contact with the side of the beam, and nailed in, would be the usual method.

As drawn the rafters could be strong enough for expected loads (I have done no calculations) but they are probably not deep enough to allow for sufficient insulation or venting of the insulated cathedral-like ceiling. Being north of the 49th that should be a factor addressed in the design I would think.

Also as drawn, the rafters would be exerting a horizontal outward force on the wall tops. In a structure of normal wall height this would be countered by ceiling joists across the wall tops. In an A-frame like this the way to avoid those forces is to use a true ridge beam with columnar supports as mentioned. The steep roof design helps lower those forces but the height and area of the roof also increases the "sail" effect when the wind blows hard. That also raises the issue of anchoring to the ground. That anchoring effect is one of the advantages of a proper perimeter foundation.


Most commonly stocked grade #2 species of 2x6 can safely span about 9 to 10 feet maximum on 16" centers and lighter than normal house loads. The simplest solution would be to use 2x8.

The side beams could then be 2-2x8 and at the indicated spacing should be adequate.

Those are the first thoughts that come to mind as far as the structural aspects go.

Note that beams closer to the ground than 12 inches should be PT and floor joists closer to the ground than 18 inches should be PT. That's for the USA; I haven't any idea of Canada but most likely they run with similar rules.


Is there a reason you chose a modified A-frame over a more conventional wall height and roof?



 



« Last Edit: June 13, 2013, 04:58:47 PM by MountainDon »
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Offline Adam Roby

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Re: My first pass 12'x14' A-Frame design
« Reply #5 on: June 14, 2013, 02:13:44 PM »
Thanks for all the great advice.

I have always used screws simply from my deck building experiences, the nailed decks tend to fall apart.  I also see a lot of shows using screws (Holmes on Homes for example) but as you pointed out, these are construction grade screws and not deck screws as I have listed.  I will have a look at the ring shank nails, which would be a much better choice also for the reason of a lack of power so you can't charge the drills.  A hammer works as long as you have the energy left in you.  I normally always use PT lumber on any flooring system... was just trying to cut costs on this one.  Maybe not the best place to cut admittedly.

I am currently speaking with the code enforcer for the area.  Turns out he is the same for both counties I am looking at, so I will definitely wait for his approval of my ideas before moving forward on anything.

Normally when I build a shed, I use a 10" ridge beam with 6" rafters, when cut tend to line up perfectly so the entire cut is on the ridge.  This time I was thinking the extra cuts would give room for more anchoring, but I can see where it may actually weaken the beam and cause it to crack over time.  I will change that design for sure.

As for the walls falling out, for this structure it wouldn't work but for a structure will full sized walls, could you not put a beam across the entire structure and brace it to both side walls?  (Imagine a 16'x24' cabin, ridge beam runs the length of the 24', while 16' tripled up 2"x8" run across to hold the walls in?  (Could later be wrapped in some nicer wood to make it look like a solid beam).  Also, obviously a full foundation is always best, but on a tiny project the post system seems to fit better.  Would it be wiser to put less posts but with much larger dimensions, or put many posts with a smaller dimension?  For example, I would probably out a 4 foot deep, 10" diameter sonotube, with a flared bottom on the hole (as much as I can reach with the post digger ~16" base?).  Would you recommend adding 50% more holes and posts, or going with 12" sonotubes and expanding the base of the hole to some 20"?  Which gives you the most bang for the buck?  I have read on the web that a building can be roughly weighed at 60 lbs per square foot per floor.  Providing both options give the same amount of support (depending of course on the soil type etc), which option would be better.  My feeling would be the smaller posts but with more of them, so if one fails it has more backups.  But that is just an opinion.

I decided to try an A-Frame design for a couple of reasons.  For one, if you build a full wall then you need to build some scaffolding to get access to the roof.  With the A-Frame design, you can simply lie a latter against the roof from the ground and work like that.  Secondly, I thought it could cut down the costs enough to make it worth while.  Now that I am looking at a first design, I can see that the usable room inside is greatly reduced and it might not be the best option (same square footage but less space).

One more little question... have any of you built a home-made septic system or well?  Is it still feasible or legal to do anywhere in America?

Thanks a ton, next plan is on it's way encapsulating all of the feedback. 

Offline UK4X4

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Re: My first pass 12'x14' A-Frame design
« Reply #6 on: June 15, 2013, 06:43:41 PM »
Things to add

Canada- guess it might Snow- so your local snow load needs to be concidered in the design

Frost depth - another major

Soil type- yet another

These 3 factors effect the whole construction- from the roof down and the foundation up !

It all needs to be designed for your region -weather and soil

Cost is always an issue- but a failed structure is worthless !

I did similar to you started from a simple structure and design-looking for ease of build and cost effectivenes

Then with time and investigation and an awfull lot of help from here- I had to start again - concidering all these major variables- which affected the whole design.




Offline tommytebco

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Re: My first pass 12'x14' A-Frame design
« Reply #7 on: June 16, 2013, 01:34:49 AM »
Eagle  SJ documented his installation of a "home made" septic system on his property. A year or so later, it is still working well for a family of three (going on four) . Search user "EaglesSJ" and "septic" for topic.

He referenced this link
http://www.wikihow.com/Construct-a-Small-Septic-System

Offline cholland

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Re: My first pass 12'x14' A-Frame design
« Reply #8 on: June 16, 2013, 07:03:06 PM »
I built an 8x12 shed a few months back, based on the free plans on the tinyhousedesign.com site. It would make a solid small starter cabin. 8' walls and with a 12/12 roof, you can put a decent loft in. With a couple of roof jacks and a 2x10 you can easy finish up the roof.
I put mine on a couple of 4x6 skids, three piers each. I don't really have a frost issue, and this way I can move it if I want to.

If I were needing a small camp cabin, I would build another one of these. It was relatively simple and quick. Code wise, you probably couldn't live in it.

Offline Adam Roby

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Re: My first pass 12'x14' A-Frame design
« Reply #9 on: June 17, 2013, 03:49:35 PM »
I also built an 8x12 with loft a few years back, and the loft is probably big enough for a queen mattress so it is an option. 

Is there any reason why we should not make a post from 2"x6" PT lumber as opposed to a 4"x4" or 6"x6" post?  It seems it wouild make sense with respect to fastening the main beam down without the need for any strong ties, and without needing to cut a post to fit the beam properly.  I am trying to think of ways to reduce cutting since I will not have power, all hand tools.


Offline cholland

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Re: My first pass 12'x14' A-Frame design
« Reply #10 on: June 19, 2013, 05:38:12 PM »
That same topic was in another thread not long ago. A post is just a beam in a vertical position, so there is no reason it shouldn't work. At minimum I would follow the same fastener requirements used in a beam. I might even add a few bolts, if it isn't all nailed to siding, to make sure the individual 2x's don't separate, just nails might pull out a bit.
It's basically the same thing one does when framing a large window or door where double jack studs are needed.

As for reducing cutting it might be a little faster. But with some good wood chisels, and the other hand tools your already going to have. It's not to hard to notch a beam in a similar way. I actually find it enjoyable and relaxing.

Offline JRR

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Re: My first pass 12'x14' A-Frame design
« Reply #11 on: June 20, 2013, 04:23:17 AM »
I'm not an expert, but I think an "A-frame" typically has the roof rafters extend all the way to the foundation/ground.  But I like the shape you have chosen better than the A-frame.  Better utilization of space.

Rather than all those individual footings that you show, I would prefer three continuous footings, front-to-back, both sides and the middle.  Would be easier, for me, to manage three footing ditches than the individual square footings.  Easier to manage elevations, at any rate.  Then add three short-height foundation walls, front-to-back, formed of block or stone.  This way the floor joists get middle support and you can get away with smaller-section joists.  A full perimeter footing would be better yet ... even if you did not install a wrap-around perimeter wall.

I think the roof would look better left "square" ... but that's just me.  And it would be easier to cover/shingle.

Offline JRR

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Re: My first pass 12'x14' A-Frame design
« Reply #12 on: June 20, 2013, 04:36:49 AM »
BTW, I like to use "purlins", not just roof-sheathing, atop rafters.  Yes, it cost a little more in materials and labor ... but it adds stiffness to the roof ... makes 4' spacing more feasible ... and makes roof-overhangs easier to fabricate and manage.  And they are very useful if metal roofing is chosen.

Offline Adam Roby

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Re: My first pass 12'x14' A-Frame design
« Reply #13 on: June 21, 2013, 02:35:05 PM »
I had commented that I was interested in an A-Frame and someone mentioned that a 4' knee wall would provide more room, so my first plan had that.  The individual footings were simply because I have a 4 foot deep frost line, and I will be digging this all by hand, so a ditch would take me forever to do by hand.  I did a shed years back that simply sat on blocks... well, I dug about 1 foot and put some crushed stone, compacted down.  8 years later and it is still rock solid and hasn't sunk in the least.  Funny thing is that it's all clay there... not too much weight at 12'x8' but I stored my 600lb motorcycle in there 4 months a year.

I am not sold on the pulins.  In my eyes, the purlin has a small area to screw or nail to the rafters.  Then you screw or nail the plywood to the purlins, but only the small pivot points where they purlin is connected to the rafter is giving any strength.  I figured, fasten the plywood to the rafters (no give in the plywood) stiffens it all up... then *maybe* the purlins could go across just to make the overhangs easier.  Not sure, maybe my logic is flawed.

This design made me rethink the whole thing.  I am thinking a 12x16 with 10' walls and a loft area, or go big and do a 16'x24'.  Going up next week to see the lot, hope it is still there by the time I get there.  Just waiting for my passport to come in to cross the border.

Offline MountainDon

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Re: My first pass 12'x14' A-Frame design
« Reply #14 on: June 21, 2013, 03:10:18 PM »
Re: roof.... purlins are not as good as a sheathed roof; read that as not making as rigid a roof. A fully sheathed roof, osb or plywood, forms a diaphragm that makes the entire roof plane extremely resistant to deforming. The same thing at work that makes a wall rigid when it is sheathed and nailed with structural panels.

Purlins laid across the rafters at right angles, do not form a rigid structure. Try it with popsicle sticks or tongue depressors and pins. The rectangular shape of the roof or wall can be pushed into parallelogram shapes with relative ease.

Add to that another factor that is very important in a habitable space is that he underside of the metal roof on purlins will have moisture condensing and then dripping where you do not want it. Maybe purlins can work for a barn or machine shed? There still is the possible condensation issue though.

Last year we built a small pole barn or shed. Before the roof was sheathed I could make the whole structure wiggle and shake. I installed girts around the wall perimeters; 2x4's nailed to the poles. That hardly made any difference to the rigidity. After installing two 4x8 osb panels across the rear wall and two on one end wall the increased rigidity was amazing. After the roof was sheathed with osb, again there was a marked increase in wall rigidity. I challenge anyone to come up with a similar degree of resistance to deformation with purlins and regular ribbed panel roofing metal.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline Adam Roby

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Re: My first pass 12'x14' A-Frame design
« Reply #15 on: June 24, 2013, 04:58:46 PM »
I am rethinking the 12x16 plan.  It is small, but does have a lot of potential, especially seeing all of the success other builders have had.  I am wondering if you could build a bump out on two adjoining sides, not a bay window but to the floor, up maybe 6'... the basic premise not to change the basic roof, have 10' walls, and small jut out roof for each "bay" window section. 

Hard to explain, maybe this floorplan would show it better.


This is my first attempt at SketchUp, so forgive the missing parts.  It's just an idea of how I would brace these bump outs.  The final plan would be to have the kitchen table in this section, all windows around, would really open it up and make it feel big.


Too bad I only have 400 minutes of trial with that software.

Offline JRR

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Re: My first pass 12'x14' A-Frame design
« Reply #16 on: June 24, 2013, 05:15:30 PM »
I should have written more detail.  I like purlins added atop regular sheathing.  I.E., the plywood against the rafters ... the purlins glued onto the plywood, nailed/screwed through to the rafters.

Purlins IN ADDITION to sheathing!  That's what I meant, but used poor wording.
« Last Edit: June 25, 2013, 03:05:05 AM by JRR »

Offline Adam Roby

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Re: My first pass 12'x14' A-Frame design
« Reply #17 on: June 26, 2013, 02:06:08 PM »
I worked on this idea a bit more today.  It would cost a bit on windows but I really like the look.  Thoughts?

Outside View


Inside View


I still haven't mastered this tool, so some extra lines and such exist.  The straight 45 degree wall would probably be flat on the inside.  The outer walls are 10' tall (for the loft) and this part is open, so the window section goes up to 8', so a small "hip?" roof over each bay section.

Will keep working the idea to see any pitfalls.  Has anyone ever done this before?

 

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