16x20 Cabin Design Feedback

[King Slayer]

I was hoping I could get some feedback on a cabin design I've been working on.  It's similar to this design, but would use tripled 2x8s in place of beams and 2x6s for rafters and angled studs.

Here is the plan:



I live in Southern Ohio, in an area where building codes are not enforced.  The cabin would be 16 by 20 feet.  The frost line here is about 30 inches.  My 8" concrete piers would extend below that, and rise out of the ground 16 inches.  Would using tripled 2x8s as beams be overkill for such a structure?  How many concrete piers should I have and how wide should they be, considering the cabin size and use of tripled 2x8s?

[poppy]

   To the forum KS.  You will need to slay more than kings to get this design past some on this board. 

I too am building my cabin in southern Ohio (Adams county) where building codes are pretty much ignored.   http://countryplans.com/smf/index.php?topic=7241.0 You must be somewhere removed from where I am since we don't have 30" frost depth here.  Do you have expansive clay where you are?

I wouldn't know where to start in commenting on your design.  Most of the info on the web site you referenced is in a foreign language, except for the main page and at least one video, so it's not easy to comprehend the details beyond it being an eco friendly concept.

Some on this site will discourage you from doing piers and they make excellent arguments in favor of code friendly type foundations.  You have asked some very basic questions which most of us really can't answer.  For example, how many piers to use.  That depends on your design loads and the type of soil you're dealing with, as well as the foot print at the bottom of the pier.

So I suggest you tell us what you are trying to accomplish.  An eco friendly design?  Off the grid?  Weekend retreat?  Permanent residence?  Easy for one person to build?  Cost effective or just unique design?  Etc.

There are lots of smart builders on this site and they can give you lots of good info.  Good luck.  Dale

[Carla_M]

I am NOT one of the experts on construction here, but I know a pretty or handsome dwelling when I see one.     I know that one or two of the knowledgeable guys here are more or less taking the summer off to pursue their own projects.


I have hung out here from time to time for a while and have read a lot of the posts. One thing that came to my mind when seeing the wall of glass is that an engineer may be needed to ensure that glass wall can lend needed rigidity to the frame. There is no obvious bracing to resist a sideways force. Lateral force is the term I believe.

Then I had a thought, again from reading what has been posted here before. In the drawing if we look at that frame on the left, a possible good idea might be to consider building the end as a post-framed wall. The 3 vertical columns located directly above the concrete piers would be done as a one continuous solid or laminated column from concrete footing pad below frost line up to where it connects to the roof framing. You're gong to need some other input to be certain of how that would be designed and built.

I have also read here a lot about using the information in the IRC (code). The triple laminated 2x8 beams appear to be under sized if I interpret correctly what I have read. There is a table that makes it look like the 3- 2x8 could only span 7 ft 2 inches with a 30 psf ground snow load, single floor with a beam down the center. Have a look and see if you can figure what I was looking at. Somebody else with greater and better experience can validate or perhaps invalidate what I have said there. That is for a building 20 feet wide so with the plan being only 16 feet wide the span can be increased some but I think 10 feet would be a stretch. Those numbers in the table can be interpolated. Larger members for the beam or a shorter span may be in order.

I know you said you will be building in an area that has no code enforcement. However, sometimes it is cheaper and expedient to use the box the code comes in rather than step outside the box. 

Now for the piers themselves. From what I have read a design on piers in an area that enforces a building code like the IRC, will have problems getting approved without an approval from a professional engineer licensed to practice in structural engineering. You can find plenty of discussion in a number of topics here. Basically it comes down to needing to know the qualities of the soil and then how to ensure that even if the soil becomes water saturated how will the piers resist sideways movement from forces like high winds. Piers act independently of one another. Oftentimes builders choosing piers seem to be doing so as they conceive the cost to be lower. That's not always true though.

Aesthetically I wonder about layering 2x's to make a beam or column. Hey can be strong enough but if they are to be left exposed does that look as good as if a solid timber was used?

It is pretty. I'd like to see how one goes about building it. G/L.

[King Slayer]

Thanks for the replies.  I live in a valley, the floor of which has about a foot or so of topsoil, then packed creek gravel.  Solid rock runs about 4-5 feet below the surface.  There is some clay in the area, but mainly just in the hills.  There are four buildings on my property that are 100 or more years old (my house is approaching 200), all of which have untreated log beams resting on large rocks directly on top of the ground.  They're all still standing, and are still level.

I wouldn't be building the cabin exactly as in that link (eg. glass panels).  I just like the look of the angled walls and the pergola structures coming off them.  I was thinking a timber frame structure fabricated out of tripled 2x8s could work, with 2x6s between the beams to finish the rafters and angled sides.  If I was more talented with Google Sketchup I'd do some better drawings.

I'm now thinking maybe four piers per row would be best, that would cut the span down to 5-6 feet.  Also, I'm now leaning toward using concrete blocks instead of the cylindrical tubes, like here.

Aesthetically, the tripled 2x8s aren't going to look as nice as solid beams, but they're cheaper.  I was hoping to build the shell of the cabin for around $3,000 (excluding the metal roof, windows, doors, and interior finish).  I have a lot of materials already on hand and stored in my barn, including metal roofing, flashing, roofing felt, lumber, insulation, concrete blocks, rebar, etc.