Backyard ADU / Granny FlatPlan HG-1108
540 Sq Ft (18x30) 1 Bed 1 Bath Backyard ADU / Granny Flat Floor Plan
540
Sq Ft
1
Beds
1
Baths
18x30
Shell
Shell Est: $25,500
18' × 30' Shell • 5 Floor Plans
18' × 30' Floor Plans (540 Sq Ft Base)
Compare 5 build-ready ways to configure a 18-foot by 30-foot structure—including all-living homes, shop-house splits, and 2-story lofts.
5 Plans
5 Plans
A-Frame CabinPlan HG-1109
780 Sq Ft (18x30) 1 Bed 1 Bath A-Frame Cabin Floor Plan with Loft
780
Sq Ft
1
Beds
1
Baths
18x30
Shell
Shell Est: $36,500
Modern CabinPlan HG-1110
540 Sq Ft (18x30) 1 Bed 1 Bath Modern Cabin Floor Plan
540
Sq Ft
1
Beds
1
Baths
18x30
Shell
Shell Est: $24,500
Modular / Prefab CottagePlan HG-1111
540 Sq Ft (18x30) 1 Bed 1 Bath Modular / Prefab Cottage Floor Plan
540
Sq Ft
1
Beds
1
Baths
18x30
Shell
Shell Est: $23,500
Tiny Home on FoundationPlan HG-1112
540 Sq Ft (18x30) 1 Bed 1 Bath Tiny Home on Foundation Floor Plan
540
Sq Ft
1
Beds
1
Baths
18x30
Shell
Shell Est: $26,500
18' × 30' Build Cost Guide, Nearby Sizes & FAQs
Slab takeoff, framing span notes, and comparable footprint sizes
18' × 30' Build Cost Guide, Nearby Sizes & FAQs
Slab takeoff, framing span notes, and comparable footprint sizes
Nearby Footprint Sizes:12'×28' (336 sf)12'×32' (384 sf)14'×24' (336 sf)14'×28' (392 sf)14'×32' (448 sf)14'×36' (504 sf)14'×40' (560 sf)16'×20' (320 sf)
18' Clear-Span Truss & Slab Engineering
A 18' × 30' rectangular building envelope (540 sq ft base area, 96 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 (9 Cu. Yds. Concrete / 7 Roof Squares)
Every 4-corner 18x30 layout eliminates expensive hip-and-valley roof framing and minimizes foundation form corners. Builders typically budget 9 cubic yards of 4,000-PSI concrete for the monolithic slab, 82 exterior 2x6 studs (or 12 laminated post-frame columns at 8' o.c.), and 7 squares of standing-seam or ribbed metal roofing.
How many bedrooms and bathrooms fit inside a 18x30 (540 sq ft) floor plan?
A 18' × 30' building footprint (540 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 5 vetted 18x30 floor plan variations above to compare room sizes.
How much concrete and roofing material does a 18x30 building require?
A 18' × 30' footprint has 96 linear feet of exterior perimeter wall. Pouring a 4-inch monolithic concrete slab with thickened perimeter grade beams requires approximately 9 cubic yards of ready-mix concrete. A standard gable roof with 18-inch overhangs requires roughly 7 roofing squares (700 sq ft of metal or shingle coverage).
What is the average cost to build a 18x30 house or barndominium?
Across our 5 engineered 18x30 blueprints, dried-in structural shell packages range from $16,200 to $25,920, while full turnkey construction averages $113,000 depending on whether the footprint is configured as all-living space or split between living quarters and an unheated shop bay.