Backyard ADU / Granny FlatPlan HG-1125
648 Sq Ft (18x36) 1 Bed 1 Bath Backyard ADU / Granny Flat Floor Plan
648
Sq Ft
1
Beds
1
Baths
18x36
Shell
Shell Est: $30,500
18' × 36' Shell • 14 Floor Plans
18' × 36' Floor Plans (648 Sq Ft Base)
Compare 14 build-ready ways to configure a 18-foot by 36-foot structure—including all-living homes, shop-house splits, and 2-story lofts.
14 Plans
14 Plans
Backyard ADU / Granny FlatPlan HG-1126
648 Sq Ft (18x36) 2 Bed 1 Bath Backyard ADU / Granny Flat Floor Plan
648
Sq Ft
2
Beds
1
Baths
18x36
Shell
Shell Est: $30,500
A-Frame CabinPlan HG-1127
936 Sq Ft (18x36) 1 Bed 1 Bath A-Frame Cabin Floor Plan with Loft
936
Sq Ft
1
Beds
1
Baths
18x36
Shell
Shell Est: $43,500
A-Frame CabinPlan HG-1128
936 Sq Ft (18x36) 2 Bed 1 Bath A-Frame Cabin Floor Plan with Loft
936
Sq Ft
2
Beds
1
Baths
18x36
Shell
Shell Est: $43,500
Modern CabinPlan HG-1129
648 Sq Ft (18x36) 1 Bed 1 Bath Modern Cabin Floor Plan
648
Sq Ft
1
Beds
1
Baths
18x36
Shell
Shell Est: $29,500
Modern CabinPlan HG-1130
648 Sq Ft (18x36) 2 Bed 1 Bath Modern Cabin Floor Plan
648
Sq Ft
2
Beds
1
Baths
18x36
Shell
Shell Est: $29,500
Modular / Prefab CottagePlan HG-1131
648 Sq Ft (18x36) 1 Bed 1 Bath Modular / Prefab Cottage Floor Plan
648
Sq Ft
1
Beds
1
Baths
18x36
Shell
Shell Est: $28,500
Modular / Prefab CottagePlan HG-1132
648 Sq Ft (18x36) 2 Bed 1 Bath Modular / Prefab Cottage Floor Plan
648
Sq Ft
2
Beds
1
Baths
18x36
Shell
Shell Est: $28,500
Tiny Home on FoundationPlan HG-1133
648 Sq Ft (18x36) 1 Bed 1 Bath Tiny Home on Foundation Floor Plan
648
Sq Ft
1
Beds
1
Baths
18x36
Shell
Shell Est: $32,000
Tiny Home on FoundationPlan HG-1134
648 Sq Ft (18x36) 2 Bed 1 Bath Tiny Home on Foundation Floor Plan
648
Sq Ft
2
Beds
1
Baths
18x36
Shell
Shell Est: $32,000
Garage with Loft / Apartment AbovePlan HG-1135
649 Sq Ft (18x36) 1 Bed 1 Bath Garage with Loft / Apartment Above Floor Plan with Apartment Above
811
Sq Ft
1
Beds
1
Baths
486
Shop SF
Shell Est: $42,000
Garage with Loft / Apartment AbovePlan HG-1136
649 Sq Ft (18x36) 1 Bed 1 Bath Garage with Loft / Apartment Above Floor Plan with Apartment Above (Drive-Through Carriage Loft + Primary Suite)
811
Sq Ft
1
Beds
1
Baths
486
Shop SF
Shell Est: $42,000
18' × 36' Build Cost Guide, Nearby Sizes & FAQs
Slab takeoff, framing span notes, and comparable footprint sizes
18' × 36' Build Cost Guide, Nearby Sizes & FAQs
Slab takeoff, framing span notes, and comparable footprint sizes
Nearby Footprint Sizes:14'×32' (448 sf)14'×36' (504 sf)14'×40' (560 sf)16'×28' (448 sf)16'×30' (480 sf)16'×32' (512 sf)16'×36' (576 sf)16'×40' (640 sf)
18' Clear-Span Truss & Slab Engineering
A 18' × 36' rectangular building envelope (648 sq ft base area, 108 linear feet of exterior wall) is one of the most cost-effective structural modules in residential construction. Because the 18-foot width can be spanned by single-piece prefabricated wood roof trusses or cold-formed steel rafters, interior walls are non-load-bearing—allowing complete flexibility between open great rooms, split bedroom wings, and drive-in garage bays.
Material Takeoff Baseline (10 Cu. Yds. Concrete / 8 Roof Squares)
Every 4-corner 18x36 layout eliminates expensive hip-and-valley roof framing and minimizes foundation form corners. Builders typically budget 10 cubic yards of 4,000-PSI concrete for the monolithic slab, 92 exterior 2x6 studs (or 14 laminated post-frame columns at 8' o.c.), and 8 squares of standing-seam or ribbed metal roofing.
How many bedrooms and bathrooms fit inside a 18x36 (648 sq ft) floor plan?
A 18' × 36' building footprint (648 sq ft base area) comfortably supports 1 to 2 bedrooms and 1 bathroom in an open-concept ADU, tiny home, or cabin configuration. Browse all 14 vetted 18x36 floor plan variations above to compare room sizes.
How much concrete and roofing material does a 18x36 building require?
A 18' × 36' footprint has 108 linear feet of exterior perimeter wall. Pouring a 4-inch monolithic concrete slab with thickened perimeter grade beams requires approximately 10 cubic yards of ready-mix concrete. A standard gable roof with 18-inch overhangs requires roughly 8 roofing squares (800 sq ft of metal or shingle coverage).
What is the average cost to build a 18x36 house or barndominium?
Across our 14 engineered 18x36 blueprints, dried-in structural shell packages range from $19,440 to $31,104, while full turnkey construction averages $139,643 depending on whether the footprint is configured as all-living space or split between living quarters and an unheated shop bay.