Need advice on building an A-Frame house

[black_edelweiss]

Finally got land and now planning to build a house. I'm strongly leaning towards and A-frame style house, but unfortunately there are only a handful of blogs, journals and plans available online. The design is very simple but there are a lot of details I'm not sure of.

The area my house will be built gets a lot of snow and has a roof snow load of 150. For the main 'A' rafters i'm planning on using 2x12's, but not entirely sure that will be enough, how can i know for sure if i need to go heavier?

I figure an entire 'A' made of two 2x12x24 with the loft rafter attached will be far too heavy to handle, so i'm planning on building a lower and upper section, the lower section being assembled past the loft rafter so i can then use the loft as a scaffold to attach the upper portion in the same way this guy attached his.... Will this method weaken the rafters? Will it be okay with the amount of snow we get? A couple years ago there was 16ft on the ground at one time, so i want to be 100% it will be strong enough.

What is the best method to attach the bottoms of the 'A' to the foundation sill? Are there ties i can use for this? Im not seeing how other people have attached theirs.

For the very top of the 'A' where the boards connect, should i just use mending plates to attach them together or is there a better way to do that?

The foundation will be concrete piers set using 24" sonotubes buried 4ft deep and sticking out of the ground about 4ft and reinforced with 3 pieces rebar. I'm planning on using 8x8 pressure treated lumber for the beam foundations, and the concrete piers will have 8x8 strong ties concreted into the piers attached to a rebar cage to hold the beams in place. Will 8x8 suffice for this? I've seen some people attaching 3-4 2x12's to each other for their beams, what would be strongest?

For underneath the sub floor, how can i insulate the pipes entering an leaving my house so that they do not freeze? Since the house will be up off the ground, it seems the pipes being exposed like that would create problems in the winter.

Thanks for any help you can give.

[Don_P]

Seeing the post title and that pic pop up my first thought was "too late to ask questions now". Glad that isn't you.
Yes that weakened it.
Need some dimensions/rough sketch to determine member dimensions.
The floor joists tie to the rafters to restrain thrust, various ties can secure the assembly down.
The peak can be gusseted with ply or framed to a ridgeboard.
With that snow load and piers, you need an engineer... that's nuts.
When the engineer is done it won't be open under there, then protecting the plumbing is easy.

Or avoid the engineer and put that money into a prescriptive foundation...

[black_edelweiss]

What do you mean a prescriptive foundation? What do you think about connecting the 'A' frame rafters in sections using these http://batmetalwork.com/cms/cms.jsp?menu_id=7938&prodref=SPL98

[black_edelweiss]

Bump?

[MountainDon]

Prescriptive foundation... The building codes used in most of the USA are based on the IRC.   In the IRC there are methods prescribed for building, that when followed do not require any further approvals from engineers. There are a few different foundation methods that meet the requirements in Chapter 4.


The plates you referenced would likely need to be approved by an engineer licensed to practice in your state. That company is located in Ireland. Their products have most likely never been submitted for approval in the USA.  A product that is approved should have at the very least, an ICC-ES report available. That's a report of tests carried out and results as to the performance. An engineers stamp of approval can easily cost more than doing the task with other already approved materials / methods.


You may be able to find the ground snow loads for the area you wish to build in on this site.

[Don_P]

 

Bump?

I was bumping a bobcat into a mountain 

I'd make the rafters continuous from main floor joist to peak. I joists would be one way to get long, light, and deep rafters. They would also do the engineering for their part as part of the service of the sale. They would probably want to design it using I joists for rafters and both floors. That could be explored at the contractors desk at the building supply.

[MushCreek]

A-frames are really cool, but there are reasons that they are a fad that came and went rather quickly. The biggest problem is that there are only two walls to put windows and doors on. You can put them on the 'roof' sides, but by the time you get done framing and waterproofing them, you might as well build more conventional construction. Geodesic domes have some of the same drawbacks and problems.

We built our regular old house out in the woods, and every room has windows on at least two walls. It's so nice having all of those windows for light, view, and ventilation. I recommend spending some time in an A-frame before committing to build one.

[black_edelweiss]

I was bumping a bobcat into a mountain 

I'd make the rafters continuous from main floor joist to peak. I joists would be one way to get long, light, and deep rafters. They would also do the engineering for their part as part of the service of the sale. They would probably want to design it using I joists for rafters and both floors. That could be explored at the contractors desk at the building supply.

Thanks for the input, definitely going with I joists after reading about them.

For the foundation, i'm now planning on building a typical 3ft deep footer w/rebar and building a 7-8ft high stem wall out of cinder blocks. Since my structure is going to be 24x32, i wonder how manageable this would be by myself and a friend or two if i have all summer and can put all my time into it...would like to have a ground level floor, and the house built higher up off the ground for extra space and to avoid my house getting completely buried in snow. A lot of houses built in heavy snow areas are built this way for exactly that reason. All i would need to do for the foundation after the wall is built would be to build 4 piers to support the center beam. I was originally going to pour these using sonotubes 8ft tall but now im thinking something along the lines of a basic 2ft tall concrete pier with an 8x8 post attached to the base to create more space for the ground level floor...what do you think?

[Adam Roby]

I also started off planning an A-frame... but once I actually started drawing up the plans and saw just how little usable space there was, I changed my idea.  Maybe use a 3D tool like sketchup and mock up the building, then place people all over the place to see where you can actually stand, where appliances and stairs might go, it quickly gets confusing and a lot of space is wasted.  If you like it still then by all means go for it, but the 3D tools will really give you a good idea of what to expect.

[black_edelweiss]

I also started off planning an A-frame... but once I actually started drawing up the plans and saw just how little usable space there was, I changed my idea.  Maybe use a 3D tool like sketchup and mock up the building, then place people all over the place to see where you can actually stand, where appliances and stairs might go, it quickly gets confusing and a lot of space is wasted.  If you like it still then by all means go for it, but the 3D tools will really give you a good idea of what to expect.

Thanks for the input...Its just going to be my wife and I...originally we planned on building a 750sqft post beam cabin, but went with the A frame after researching snow loads in the area and coming across this build journal....http://countryplans.com/smf/index.php?topic=9259.0. Down the road we will consider building an add on, but for now we are satisfied with the idea of building an 8ft stem wall and having all that extra space along with the main housing area.

[Don_P]

It could work... if you are in a seismic zone read up on those foundation requirements in chapter 4 of Mt Don's IRC link below. Actually study that carefully either way.

Hard to say, if you are, or can be, productive with the time it would be dried in... then there's Murphy, we live in a world of monkey wrenches 

[JRR]

An A-frame probably cannot be improved on for wind and seismic events.   Hard to beat a triangle for strength.  I have seen churches that use a form of a-frame and yet have short walls that afford more entry and light portals.  If I were to build an a-frame, I think I would employ this scheme.  It would have to be scaled down for house-use, but the idea of allowing the roof framing extend to the ground, or ground-supports ... while the roof does not extend to the ground.  For an example, one could take a pedestrian view on Google maps at 6154 Reynolds Rd., Morrow GA.  Here is an effort at a link:
https://www.google.com/maps/@33.588384,-84.3400123,3a,75y,196h,90t/data=!3m7!1e1!3m5!1sMa4BpOzyHuit3TSSEEngZA!2e0!6s%2F%2Fgeo0.ggpht.com%2Fcbk%3Fpanoid%3DMa4BpOzyHuit3TSSEEngZA%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D196.02521%26pitch%3D0!7i13312!8i6656?hl=en

[Don_P]

That is using another type of framing system. Glulam beams (in white) with heavy timber planking spanning across those beams. Usually a wrap and strap roof from there up... although it could also be done with glulams and Sips. I'd love a pic of that rafter foot if you live nearby, check for rot, these are notorious there. This is neat but needs a hired engineer and the materials are not cheap. My Dad used this type of roof on his houses in the 60's-80's, I do like it. For 150 psf snow, I'm doubting it would be affordable. BTW this is more than double the max design loads in the codebook, this is really engineer territory for everything. To get an idea, a 1000 square foot area of snow would weigh as much as 2 fully loaded tractor trailers.

[JRR]

I agree, this design is almost "off the page" to be considered for an A-frame house.  I have seen it done already in house plans, but at the moment cant find a reference on the net.  I think this particular church may be using steel for the majors, but I may be wrong.  That would be a bit of overkill, but so I think it is.  I will try to get a closer image.  If built-up or glulam wooden beams are used, there should be a water (and fire) protection included.  A bit of metal flashing would do a lot.

[Don_P]

Although with the main timbers well spaced it opens up some options. Scroll down to the photo of the A frame here;
http://www.luxustimberframes.com/frames.html

Although the tractor trailers are now sitting on that shed roof 

...at that snow load the footprint of a tractor trailer, its parking space, weighs in snow what the loaded tractor trailer did... wow.

[black_edelweiss]

Although with the main timbers well spaced it opens up some options. Scroll down to the photo of the A frame here;
http://www.luxustimberframes.com/frames.html

Although the tractor trailers are now sitting on that shed roof 

...at that snow load the footprint of a tractor trailer, its parking space, weighs in snow what the loaded tractor trailer did... wow.

Thats a gigantic A-frame!!

My project is going to start in a couple weeks and still haven't figured out the roof rafter details. I came across these plans...https://www.ag.ndsu.edu/aben-plans/5965.pdf which i really like, with some changes. In the plans it states the structure can handle 85mph winds and a fiber bending stress of 1200psi. Would 1200psi equate to a 100lb snow load?

I would have the foundation on a 8ft tall cinder block stem wall and i'd use 2x10 rafters instead of 2x6's. Having a continuous i-joist would be extremely difficult for me to transport, and this area is very isolated. It would also be extremely difficult for me to put up, as i will be doing most of this myself, so not having a continuous beam is really the most realistic option.

What do you guys think? The snow will slide right off the A-frame so i cant see why i would need to use anything bigger than 2x10's  for a 150lb roof snow load, especially since the base will be elevated 8ft, so any snow build up wont get much past the base of the roof. Maybe im wrong though. Maybe it would be better to use i-joists instead of 2x10's and splice those together? 

Thanks

[Don_P]

The allowable fiberstress multiplied by the section modulus will give the maximum allowable bending moment of the material at that dimension.
The design bending moment is compared to the allowable bending moment to check that design load is less than maximum allowable load. They are specifying the strength of wood required for that design... which I'll bet is 30psf. Fb 1200 psi relates roughly to #2 SPF lumber. I'm not going to reverse engineer their plan, you need to have an engineer review your plans, our logic and wannabees are not up to assuming on this... you need to contact an engineer prior to proceeding.

[UK4X4]

As a note referencing Don's comments above, I had 90lbs snow load for my build

roof had to be engineered and signed off
foundation needed geotechnical report and engineer to sign off the design
The plans then needed signing off to check support from the roof down to the foundations...

[flyingvan]

I'd like to build something like this someday, only with equilateral triangles 16' each side.  Downstairs would have 86" of headroom except the 'T' shape for the loft floor would be open in one section for more headroom over the entrance. 


You'd have to be really good at valley rafters though.  They'd all be the same angles though so once you got one right the rest would be easy

[black_edelweiss]

Yep, once you get one 'A' built, you can use that as a model to copy the rest of the rafters, and it would go pretty quick. I like your idea of having another A built on each side of the main one. It makes for a unique structure.

[azgreg]

You could add dormers to a "A" frame for more upstairs room.