Structure 20by30 1-1/2story plans.

[lelodge]

Hi all,

I'm in the planning stage to build a 20by36 1-1/2 story cabin with two full length porches on concrete columns in a higher snow load area.

My general idea is to overbuild everything and spend a little more time and money doing this by...

1) spacing the columns 6' apart. (Shorter span which works for the cabin length)
2) using 4*(2by12) build up beams (as per John's plans)
3) buying engineered roof trusses designed for the snow load in the area.
4) possibly spacing the trusses closer together 16o/c instead of the 24".

Any other ideas?

One concern I have is having a full length porch (36ft) along a wall with a lot of wide span windows and ranch slider door? (Ie less full length 2by6s) Their is currently no interior perpendicular walls planned for that wall either. Are horizontal loads on walls a concern when adding porches? I'm planning 12foot high walls and full floor loft.

Thanks

[John Raabe]

First off you might want to have a review by a local engineer for these changes and any necessary visits to the building department.

Strong bracing on the pier to beam connections is advised, especially as piers get taller.

Your idea of cutting down the spans on the foundation beams seems reasonable for the extra porch and snow load. The roof trusses are also a good idea. The truss company can determine the spacing of the trusses (usually 24").

Are you going to do a ledger in the 12' tall 2x6 wall for the loft floor? What will be the ceiling height and will the loft be full length? If so, I would suggest using the full sized U-shaped stair in the booklet rather than the steeper cottage stair. The loft floor ties the two long walls together and properly sized headers (Sht 2 has headers up to 8' span) will handle the openings. You generally don't want an unbraced wall to be more than 10' tall. If you are planning a cathedral area you should provide some cross tie beams (perhaps every 4') to tie and stabilize the side walls.

[Don_P]

 
Some things to consider after reading your post. I agree with John that an engineer is needed.  A pier foundation is non code unless designed by an engineer, as generally seen they are underbuilds. A continuous perimeter foundation is code minimum without professional design.

With a wall full of windows loaded by 2 roofs and a floor, the window and door jacks are delivering sizeable concentrated loads to the main floor rim. If that rim is on a girder rather than a continuous foundation wall those point loads, the main floor and the porch floor loads all need to be considered in the girder design, a point load at midspan delivers twice the bending moment compared to a uniformly distributed load... part of the reason for either continuous foundation support or a design pro. Horizontal loads being delivered to the foundation from above are another good reason for an RDP.

Trusses can be designed for 16 or 24" spacing, they can also be designed for heavier or lighter loads in either case, you can have a truss at 2' spacing that is stronger than a truss at 16" spacing all depending on the design of the trusses, for instance using either higher grade or larger dimension lumber.

[lelodge]

Thank you both for the quick replies. I'm learning all the time!

I plan on using a Simpson connector CB5-6 which are 6" wide (most are 5-1/2") the columns would go at least 4 feet underground no more than a few feet above ground. The crawl space/stem wall options just to many $$$.

We're planning a full second floor loft (4' joists and TnG) resting on a ledger with an 8' ceiling on the main floor and 3' walls in the loft. I see now how the full loft floor makes things stronger.

John we're in a none coded area so I'm thinking of staying with the steeper stairs exactly as in the plans to save floor space. We messed around with fitting the stairs into the floor plan for along time!

Don thanks for mentioning the point loading I'll review my window and doors with that in mind.

I have a different question on windows. If you want high/tall windows can you stop the ledger and hang a joist off a higher window header or how is that best done?

Thanks again

[Don_P]

a higher snow load area.
My general idea is to overbuild everything and spend a little more time and money doing this by...

Remember the chain of parts you are building is only as strong as the weakest link. Overbuilding one element and ignoring another doesn't make the structure any stronger than the weakest element. I'm helping side an ill thought out bank barn that will probably be quite intact when the foundation fails and it lands on the ground.

The soils are of unknown resisitance and the depth/height/diameter of the pier is arbitrary. The Simpson connector is not rated for lateral loads, from the catalog;

Post bases do not provide adequate resistance to prevent members from rotating about the base

Have you considered a PWF, permanent wood foundation? You'll pick up resistance to horizontal loads and continuous uniform bearing capacity. The footing is a gravel trench and the walls of the foundation are treated wood, all DIY friendly. Using the funds that would have gone into concrete, extra piers, simpson post bases, heavier girders, extra trusses and unneccessarily overbuilding other elements would go a long way towards offsetting the cost of bringing this element up into adequate strength range. The point load and girder overload scenarios begin to fade as continuous uniformly bearing support walls are provided under the main floor.

[lelodge]

Thanks for the Suggestions. The PWF is interesting as a money saver. I think, aesthetically if nothing else, concrete is my preference though.

I'm pricing a concrete stem wall now. Being more than an hour from town and with 4-5 foot frost line the excavation and concrete will be expensive. We already have a tractor for auger work so the piers with an engineer review is still an option.

Thanks again.

[astidham]

a PWF sounds like it would be a good option for you.
if you decide to go with piers, it probably wont be long before you wished you didnt.
I went with piers on my cabin, now I am planning a concrete pour around the cabin, so I can build a small stud wall up to the beams.
with a PWF, you will have a better racking resilient structure.