How Much Does It Really Cost to Build an ADU in Massachusetts?
Accessory Dwelling Units (ADUs) are booming in Massachusetts — thanks to new state laws, rising housing demand, and homeowners looking to unlock passive income. But let’s get to the question everyone asks first:
How much does it really cost to build an ADU in Massachusetts?
The answer depends on many factors — but in this post, we’ll break it all down so you can plan with confidence.
🧱 The Real Cost Range
Here’s a general estimate of what you can expect to invest:
| ADU Type | Starting Cost |
|---|---|
| Basement Conversion | $75,000 – $125,000 |
| Garage Conversion | $90,000 – $140,000 |
| Attached ADU Addition | $130,000 – $175,000 |
| Detached Backyard Unit | $140,000 – $250,000+ |
These costs include design, permits, materials, labor, and basic interior finishes. Your final number depends on site-specific factors and personal preferences.
🔍 What Affects the Cost?
Here are the key variables that can move your price up or down:
1. Size & Layout
- A 1-bedroom ADU (400–600 sq ft) costs less than a 2-bedroom with full kitchen & bath.
- Simple rectangles are cheaper to build than L-shaped or multi-level units.
2. New Build vs. Conversion
- Converting a garage or basement is often cheaper than building a detached ADU — but only if it’s in good shape and up to code.
3. Site Conditions
- Sloped lots, rocky soil, or tight access can add excavation and foundation costs.
4. Utilities
- Tying into existing water, sewer, and electric systems can cost $10K–$30K+
- New lines or upgrades (especially for detached units) increase costs
5. Finish Quality
- Ikea vs. custom cabinetry? Quartz or laminate? Choices here can swing your budget by $10K+.
6. Permits & City Fees
- Vary by town — some municipalities charge impact fees, plan review fees, and require special inspections.
💡 What About Prefab ADUs?
Prefab (modular) ADUs offer cost and time advantages:
- Faster to install (sometimes in weeks)
- More predictable pricing
- Great for backyard placements
However, they still require:
- Site prep
- Foundation
- Utility hookups
- Crane delivery in some cases
Total cost for prefab units in MA still ranges from $135,000 to $200,000+
💳 How Do People Pay for ADUs?
At ADULink, we help clients explore:
- HELOCs (Home Equity Line of Credit)
- Cash-out refinancing
- Construction loans
- $0 down lending programs (when available)
Some towns also offer grants or incentives for building ADUs for family, caregivers, or affordable housing. We’ll help you look.
📈 Will I Get a Return on Investment?
Yes — in most cases.
You can:
- Rent it out ($1,200–$2,200/month avg)
- Increase property resale value
- Create housing for aging parents or adult children
- Use it for home office, Airbnb (where allowed), or flexible space
The ROI comes from use, income, and long-term value — not just equity.
🎯 Final Thoughts
The bottom line?
An ADU in Massachusetts can cost anywhere from $100K to $250K+, depending on your site and design — but the payoff in flexibility, value, and income can be worth it.
And with statewide ADU support and easier permits, now is the best time to explore the possibilities.
👉 Ready to Get a Personalized Estimate?
Let’s check your lot, your goals, and your budget — and we’ll give you a clear plan.
📞 [Schedule Your Free ADU Consultation]
📍 Serving Homeowners Across Massachusetts
