Self-supporting Residential Addition Design
Budget: $30 – $250 USD
I’m planning a 14′ × 70′ addition alongside an existing manufactured home in Happy, Perry County, KY. I want to confirm my plan is OK as-is or what you’d upgrade.
What I’m building (simple version):
Independent structure (no loads on the trailer).
Foundations: concrete pads with 12″ sonotube piers and 6×6 PT posts. Local frost ≈ 24″; I’ll set footing bottoms at ≥30″ below grade. Site slopes about 2′ across the width (trailer underside ~3′–5′ off grade).
Framing – floor: 2×8 joists @ 16″ O.C. spanning about 7′ to a center beam.
Beams: 3-ply 2×10 built-up girders (two perimeter + one center), posts about 7′–8′ O.C.
Walls: 2×6 exterior @ 16″ O.C., ~9′ high. A trailer-side support wall carries the new roof to the ground (no windows here). Two 14′ return walls at the ends.
Openings: 1 exterior door and windows in each room (none on trailer side).
Roof: engineered trusses @ 24″ O.C., ~4:12 pitch, sheathed (7/16″ OSB with H-clips or your call). Provide a slip/expansion joint + flashing where new roof meets the trailer—no structural tie-in.
What I’m building (simple version):
Independent structure (no loads on the trailer).
Foundations: concrete pads with 12″ sonotube piers and 6×6 PT posts. Local frost ≈ 24″; I’ll set footing bottoms at ≥30″ below grade. Site slopes about 2′ across the width (trailer underside ~3′–5′ off grade).
Framing – floor: 2×8 joists @ 16″ O.C. spanning about 7′ to a center beam.
Beams: 3-ply 2×10 built-up girders (two perimeter + one center), posts about 7′–8′ O.C.
Walls: 2×6 exterior @ 16″ O.C., ~9′ high. A trailer-side support wall carries the new roof to the ground (no windows here). Two 14′ return walls at the ends.
Openings: 1 exterior door and windows in each room (none on trailer side).
Roof: engineered trusses @ 24″ O.C., ~4:12 pitch, sheathed (7/16″ OSB with H-clips or your call). Provide a slip/expansion joint + flashing where new roof meets the trailer—no structural tie-in.