Estimated ADU Cost
Construction:
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Contingency:
Permits + Fees:
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Total Estimate
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*Estimated cost only. Final pricing requires a site review and design details.
General Project Information
Layout + Floorplan
Utilities + Fees
ADU COST CALCULATOR
What Impacts ADU Costs?
ADU Type
Attached ADU
Connects to your existing home. Keeps costs low by reusing utilities and structure where possible.
Detatched ADU (+15% - 30% Cost)
Higher cost since it needs its own foundation, framing, and utility runs. Offers more flexibility but adds work across every trade.
Garage / Basement Conversion
Finishing a basement ADU is usually 5–15% more than a garage conversion for moisture control, stairs, and egress work.
Layout Style
Studio Layout
Simple, unified living layout with baseline costs.
Separate Bedroom(s)
Adding a separate bedroom usually runs 10–20% more than a studio for extra walls, doors, and finishes.
Half-Bath vs Full Bath
A half bath usually includes only a toilet and sink. A full bath adds a shower or tub, more plumbing, more waterproofing, and heavier tile work. This can increase costs by 10% - 20%.
Finish Level
Basic / Budget
Entry-level finishes. Simple cabinets, laminate or LVP flooring, standard bath fixtures, basic tile or fiberglass shower units. Lowest material cost and fastest install.
Mid-Range
Better cabinets with soft-close hardware, upgraded LVP or mid-grade tile, improved lighting, quartz or similar countertops. Adds quality without going custom.
High-End / Premium / Luxury
All custom or near-custom selections. Includes upgraded cabinetry, niche work like premium tile, custom built-ins, etc. Increases prices by up to 60% based on finish and fixture choices.
Kitchen + Utility Features
Kitchenette
Compact cabinetry, small appliance setups, and limited plumbing. Lowest cost.
Full Kitchen
More cabinets, full-size appliances, expanded countertop area, and additional plumbing and electrical circuits. Can increase costs by ~15% - 30%.
Why Kitchens + Baths Heavily Control ADU Costs
Kitchens and baths drive the largest mechanical and finish costs in ADUs. Upgrading either raises plumbing, electrical, and finish labor simultaneously, creating the biggest jumps inside small square footage.
Other ADU Guides
ADU Cost FAQs
How accurate is an ADU cost calculator?
An ADU cost calculator provides a realistic planning range based on common construction scenarios in Connecticut. It is not a formal quote. Final pricing depends on site conditions, design details, permits, utilities, and finish selections that are reviewed during the planning phase.
What is the average cost to build an ADU in Connecticut?
Most ADUs in Connecticut range from $150,000 to $350,000, depending on size, layout, structure type, and finishes. Detached ADUs and higher-end finishes typically fall on the upper end of that range.
Why do ADUs cost more in Connecticut than national averages?
Construction costs in Connecticut are higher due to stricter building codes, permit requirements, utility upgrades, labor costs, and site-specific conditions. Older homes, tight lots, and zoning requirements can also increase overall ADU pricing.
Does this estimate include permits and professional fees?
The calculator includes typical allowances for permits and soft costs, but actual permit fees and professional services vary by town. Final numbers are confirmed after reviewing local requirements and project scope.
Is a garage conversion cheaper than building a new ADU?
Yes, garage conversions are often the most cost-effective ADU option because the structure already exists. However, costs can increase if major upgrades are needed for insulation, utilities, ceiling height, or code compliance.
What factors increase ADU costs the most?
The biggest cost drivers in ADU construction are:
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Kitchens and bathrooms
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Finish level and material selections
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Detached structures requiring new foundations
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Utility upgrades and site conditions
Even small upgrades can significantly affect pricing in compact ADU layouts.
Is an ADU cheaper than a home addition?
In many cases, yes. ADUs can be more cost-efficient than large home additions, especially when converting existing space. However, detached ADUs with full kitchens and bathrooms can approach the cost of an addition depending on scope and finishes.
Can I lower my ADU construction costs?
Costs can often be reduced by choosing a simpler layout, limiting square footage, selecting mid-range finishes, and minimizing structural changes. A clear design plan early in the process helps avoid costly revisions later.
When does pricing become a fixed quote?
Pricing becomes fixed after an on-site evaluation, design review, and confirmation of zoning and utility requirements. At that point, a detailed proposal is provided outlining the full scope and cost of the project.