Building a guest house costs $62,000 to $225,000, with an $85,000 national average, on Angi and HomeAdvisor’s matching figures (October and June 2026)23. HomeGuide breaks it down by build type: $150 to $250 per square foot custom-built — $90,000 to $150,000 for a 600-square-foot one-bedroom — against $80 to $160 per square foot for a modular unit and $20 to $200 per square foot to convert an existing structure (December 2025)1. Angi and HomeAdvisor are corporate siblings, and matching figures alone don’t establish independent corroboration — their pages match on many rows below, with HomeGuide providing the separate comparison. All figures are the latest published data from each source.
Cost by size
HomeGuide’s size table, average installed cost by build type1:
| Guest house size | Custom-built (HomeGuide) | Modular (HomeGuide) |
|---|---|---|
| 400 SF (studio) | $60,000–$100,000 | $32,000–$64,000 |
| 600 SF (1-bedroom) | $90,000–$150,000 | $48,000–$96,000 |
| 800 SF (2-bedroom) | $120,000–$200,000 | $64,000–$128,000 |
| 1,000 SF (2-bedroom) | $150,000–$250,000 | $80,000–$160,000 |
| 1,250 SF (3-bedroom) | $187,500–$312,500 | $100,000–$200,000 |
| 1,500 SF (3 beds + flex) | $225,000–$375,000 | $120,000–$240,000 |
The siblings publish an identical size table of their own — a sibling match — that diverges from HomeGuide’s on several rows: 300 SF at $45,000 to $95,000 new build against $27,000 to $53,000 prefab; 400 SF at $55,000 to $110,000 against $31,000 to $59,000; 550 SF at $80,000 to $140,000 against $40,000 to $88,000; 800 SF at $115,000 to $210,000 against $65,000 to $110,000; 1,200 SF at $170,000 to $330,000 against $89,000 to $160,000; 1,500 SF at $210,000 to $380,000 against $102,000 to $220,00023.
Cost by build type
HomeGuide’s type table, with totals for a 600-square-foot build1:
| Guest house type | Cost per sq ft (HomeGuide) | Total for 600 SF (HomeGuide) |
|---|---|---|
| Custom-built | $150–$250 | $90,000–$150,000 |
| Modular | $80–$160 | $48,000–$96,000 |
| Convert existing structure | $20–$200 | $12,000–$120,000 |
The siblings frame the per-square-foot spread at $110 to $250 depending on build type23, while HomeAdvisor puts a custom guest house at $100 to $500 per square foot — $60,000 to $300,000 for a 600-square-foot cottage — a wider published range than HomeGuide’s custom row3.
Prefab and ready-made options
HomeGuide’s ready-made table, installed1:
| Prefab unit type | Cost per sq ft installed (HomeGuide) | Installed cost for 600 SF (HomeGuide) |
|---|---|---|
| Modular guest house | $80–$160 | $48,000–$96,000 |
| Accessory dwelling unit (ADU) | $90–$160 | $54,000–$96,000 |
| Prefab tiny home | $150–$250 | $90,000–$150,000 |
| Container guest house | $120–$300 | $72,000–$180,000 |
| Prefab concrete guest home | $110–$180 | $72,000–$108,000 |
| Prefab log cabin | $100–$250 | $60,000–$150,000 |
HomeAdvisor prices ready-made kits at $5,000 to $100,000, noting permits, labor, plumbing, and electricity can add up to $10,000 or more3. On the ADU distinction: HomeGuide notes an ADU is designed for long-term use and must have a kitchen and bathroom, unlike a guest house1; Angi prices ADU new builds at $100 to $500 per square foot with most units at $40,000 to $200,000, and garage-to-ADU conversions at $95 to $360 per square foot2. See our ADU cost guide for the full breakdown.
Converting an existing structure
HomeGuide’s conversion table, installed1:
| Structure | Cost per sq ft (HomeGuide) | Installed cost for 600 SF (HomeGuide) |
|---|---|---|
| Garage conversion | $50–$200 | $30,000–$120,000 |
| Metal building guest house | $25–$80 | $15,000–$48,000 |
| Pole barn guest house | $20–$60 | $12,000–$36,000 |
HomeAdvisor prices a garage or shed conversion at $110 to $120 per square foot with most conversions at $15,000 to $30,000 — a much narrower published range than HomeGuide’s, presented as published3. A garage conversion takes 4 to 8+ weeks on HomeGuide’s figures, covering new floors, walls, windows, insulation, drywall, electrical, plumbing, and HVAC1. See our garage conversion cost guide.
Site prep and foundation
HomeGuide’s prep rows: house plans at $1,200 to $5,000 for drafting plus engineer or architect input, a land survey at $200 to $1,200, excavation at $1,500 to $10,000, grading and leveling at $1,000 to $5,000, a concrete slab foundation at $6 to $14 per square foot, a septic system at $3,500 to $8,500 when the existing one is undersized, and running utilities at $2,000 to $12,0001. The siblings diverge on foundations: Angi prices a guest house foundation at $3,500 to $16,000 while HomeAdvisor prices $5 to $37 per square foot depending on material — different published units23. HomeAdvisor adds demolition of a small structure at $2,000 to $9,000 with disposal and cleanup at $300 to $1,8003.
Systems: plumbing, electrical, roofing, HVAC
The siblings match on the major systems: plumbing at $10,000+ for smaller builds and $20,000 or more for larger ones, a full electrical rough-in at about $8,000, a new roof at about $8,000 ($4 to $11 per square foot by material), and HVAC installation at $5,000 to $12,500 — sibling matches, counted once23.
Features and finishes
HomeGuide’s feature table1:
| Feature | Average installed cost (HomeGuide) | Details |
|---|---|---|
| Kitchenette | $5,000–$20,000 | Sink, microwave, small refrigerator |
| Full kitchen | $25,000–$45,000 | Full-sized appliances |
| Half-bath | $4,500–$8,000 | Toilet and sink only |
| Full bath | $18,000–$47,000 | Toilet, sink, shower/tub combo |
HomeGuide adds a matching kitchen appliance set at $2,500 to $6,800 installed, or $100 to $350 per appliance for labor alone1. The siblings publish an identical luxury-additions table — a sibling match: high-end appliances $6,000 to $13,000, heated floors $5,000 to $16,000, granite countertops $2,500 to $9,000, sauna $1,900 to $5,000, wrap-around deck $18,000 to $36,000, security system $2,000 to $7,000, custom lighting $1,500 to $8,500, luxury bathroom finishes $2,500 to $8,000, solar panels $12,000 to $25,000, and custom cabinetry $5,000 to $45,00023.
Labor
The siblings match on a general contractor fee of 15% to 25% of total project cost for a build of this scale23. Their shared hourly rates: electrician $70 to $200, plumber $50 to $200, roofer $25 to $75 per worker23. Angi adds a carpenter at $35 to $200 per hour (typically $6,000 to $12,000 total for a guest house), a painter at $3 per square foot on average, and a senior architect at $180 to $300 per hour or about 15% of project cost2. HomeAdvisor adds drafting blueprints at $800 to $2,700 and an architect at $2,200 to $11,6003.
Permits and zoning
Permit requirements are set locally and vary by municipality, so confirm with your local building department and HOA early — zoning rules can dictate square footage, setbacks, and parking13. Published permit estimates: $600 to $3,000 on both sibling pages against $500 to $2,000 on HomeGuide123. HomeGuide notes a small structure under 100 square feet may not require a permit in some areas — check locally1.
Taxes, insurance, and home value
Angi reports annual property taxes commonly rise 15% to 25% after a guest house build, and that a guest house increases home value by 20% to 40% on average while recouping 50% to 75% of its cost — Angi’s published averages across projects, not budgeting predictions for an individual property: the actual tax effect depends on your local assessor and how the structure is classified, and any value change depends on your market2. HomeGuide notes a detached guest house generally increases value, especially with a bathroom, kitchen, and laundry1. Both note insurance premiums rise and recommend discussing the build with your insurer12.
Timeline
HomeGuide puts a custom build at 4 months to a year plus planning and permitting, a modular unit at 1 to 4 months delivered and installed, and a garage conversion at 4 to 8+ weeks1.
DIY finishing
The structural, electrical, plumbing, and HVAC work belongs to licensed pros, but the siblings note finishing touches are the realistic DIY zone — Angi names painting as one of the few tasks homeowners can reasonably tackle, and both suggest DIY painting and flooring to trim labor costs23. If you’re finishing a conversion yourself, compare interior paint prices at Home Depot’s interior paint category (non-affiliate link).
Related cost guides
See ADU cost for a fully equipped second unit, garage conversion cost for the budget route, and tiny home cost for another small-footprint option.
The bottom line
On Angi and HomeAdvisor’s matching figures, budget $62,000 to $225,000 with an $85,000 national average. HomeGuide splits the paths clearly: $150 to $250 per square foot custom-built, $80 to $160 modular, and $20 to $200 for a conversion — a 600-square-foot modular guest house at $48,000 to $96,000 installed against $90,000 to $150,000 custom. Systems add up fast: plumbing $10,000+, electrical about $8,000, roofing about $8,000, and HVAC $5,000 to $12,500 on the siblings’ shared figures, with a general contractor at 15% to 25%. Permits, zoning, and taxes are the local checks that decide what you can build.
Sources (each fetched and read October 27, 2026; figures are each publisher’s latest published data):
1. HomeGuide, “How Much Does It Cost to Build a Guest House?” (December 1, 2025) — homeguide.com/costs/cost-to-build-a-guest-house
2. Angi, “How Much Does It Cost to Build a Guest House?” (updated October 23, 2026) — angi.com/articles/cost-to-build-guest-house.htm
3. HomeAdvisor, “How Much Does It Cost to Build a Guest House?” (updated June 17, 2026) — homeadvisor.com/cost/architects-and-engineers/build-a-guest-house
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