12x16 Little House Questions

[Ralph]

I've purchased the Little House Plans package and have some questions that I hope you will be able to help me with.

I'm using the 12x18 plans but need to shorten the building to 16' to stay under 200sq ft for zoning purposes.  The wall height will be 8', roof pitch 10/12, and the roof will be constructed with a structural ridge beam to provide an open cathedral ceiling.  The project location will be my sloping back yard in central Maryland. 

Questions/Considerations:
Foundation - Planned to consist of 16" x 8" footings, 36" below soil line, with 10" concrete piers resting on the footings.  Girders will rest in Simpson brackets on the high side of the slope (the gable end) and on posts in brackets where needed on lower end.
1.  How would pier spacing differ from the 12x18 Little House plans as the length is reduced to 16"
2. I plan to add a 4x4 post centered under a double 2x8x12' rim joist to support the ridge beam. Will this work?
3. If I add two additional piers with posts (see #2), would it be worth adding a 3rd post in the middle to carry a 3rd girder?  The goal is to reduce overall height of the building by using girders that are shallower than the 4x10 girders shown on the plan. I plan to use #1 pressure treated southern yellow pine for girders and floor joists.

Walls - The gable walls will be load bearing (carrying the structural ridge beam).
1. Will 2x4 at 16" centers be adequate to frame a 13' load bearing gable wall or do I need to upgrade to 2x6?
2. When framing the four walls, does it matter which walls are the "through walls" (full length or full width of building)?

Rafter/Roof - Planned construction is 18' structural ridge beam with 2x8 rafters sitting on top of beam.  Oposing rafters will line up with each other (not overlap) and will be nailed to the beam and joined to each other with plywood gussets.  The gable overhang and wall overhangs will be 12". The roof will be plywood sheathing with asphalt shingles.
1. The local lumberyards recommend 2, 1 3/4" x 9 1/4" LVL beams sistered together to span 16' for the ridge beam. Does this sound reasonable?
2. Should the ridge beam extend 1' past the gable walls to carry fly rafters?
3. Should the rafter spacing be 16" or 24"?
4. Will the structural ridge beam as described eliminate all ceiling joists and collar ties?

Many thanks for any advice you can provide.

-Ralph

[John Raabe]

While I can't provide new engineering for such a major redesign (that should be done locally) I will give you some thoughts on your suggested design.

See the Shed and Playhouse details in the stapled booklet in your plans. That beam and joist design will get you closer to the ground and give you full span joists supported at the outside of the long walls. Support the double 2x12 with 4 piers under each beam - that will give you three spans of 5.33' each. Add an additional pier at the middle of each gable end wall to support the ridge beam. The gable end wall is not so much load bearing as it carries a point load. Double the floor joists and provide solid wood bearing (a built-up post) under the beam to the foundation. It does not need to be more that a double 2x4. Design the beam locally for your snow loads - your lumber yard's suggestion should work. Attach the top of the rafters (over the beam) with a metal strap or plywood gusset and use framing anchors to clip the roof rafters to the double wall plates. You do not need collar or rafter ties. 2x8 @ 24" o/c should be fine for rafters.

If you want an extension on the gable end see this detail from George Nash p. 188, "Do it yourself Housebuilding". There are other ways to do this.