Building an ADU/Back Yard Cottage Part 1
I’m a homeowner building a backyard cottage/ADU here in Somerville, and I thought I’d share my costs and experience along the way and hopefully answer some questions for anyone considering doing the same.
Somerville already had accessory dwelling units (ADUs) when it overhauled its zoning in 2019, but it calls them “backyard cottages.” Backyard cottages have somewhat more stringent zoning requirements, but in theory you can build up to ~1,500 square feet if you meet all of the setback and other requirements. The state-protected ADU law allows up to 900 square feet with more relaxed requirements. In theory, under state law, you could build both if you have enough room on your lot, although the city is working to close that loophole.
I’m building a ~1,500-square-foot, 3-bedroom, 2.5-bathroom backyard cottage for my aging parents. I expect the final cost to land somewhere around $400k–$500k and about 3-4 months to complete. On average you'd pay a GC 20%-25% to manage this project, in theory by taking on another full time job that is what I am saving. The market value of these cottages are about $1.3mm here: https://www.zillow.com/homedetails/16-Hamlet-St-16-Somerville-MA-02143/461573621_zpid/ https://www.zillow.com/homedetails/192-Washington-St-R-Somerville-MA-02143/461740757_zpid/
Some of my thoughts so far:
The permitting process is brutal. I started this process in January and finally got the permit to pour my foundation only last month. Somerville has a two-step process where you have to pour the foundation before you can get the building permit.
The permitting process here is extremely long and arduous, with a lot of red tape, a crazy amount of paperwork, and understaffed departments. My mother is a GC out in the Midwest, and she estimates this entire process would have taken her about a month there.
The design requirements can be overly restrictive. The design standards here can feel very subjective and overly controlling. For example, the acceptable roof designs are fairly limited, which is why you tend to see so many backyard cottages designed with cross-gables like the listings above. They are accepting feed back on it as they are looking to change it due to a group of citizens submitting their own zoning amendments to shring how big you can build an backyard cottage. https://www.facebook.com/BenForWard3Somerville/posts/somerville-was-an-early-adopter-of-the-backyard-cottage-aka-accessory-dwelling-u/1512607274197644/
The electrical requirements are another example. I have to pay Eversource roughly $12k to trench from across the street to my house, and then pay another contractor to trench and install conduit from there to the rear of my property. There’s nothing physically preventing me from keeping the existing aerial electrical connection to my house and running a line through my open basement to the rear of the property, which would save me roughly 75% of the cost.
Finding contractors willing to work in Somerville has been difficult. There is no shortage of contractors in Massachusetts. There is, however, a shortage of contractors who want to work in Somerville. The city has a reputation for being difficult to work in, and I’ve found that reputation to be mostly true especially if you aren’t already familiar with the process.
You can find plenty of threads here on Reddit and in local Facebook groups from people expressing similar frustrations. Once you get past that hurdle, sorting through the contractors who are willing to work here and finding the good ones has been another challenge.
Financing: I’m funding the project with a HELOC on my house. In the end, building the ADU made more financial sense for me than selling my house and buying a new one. Given current interest rates, buying a comparable-size house elsewhere would have meant paying roughly 2–3x my current mortgage.
Massachusetts also has 0% interest loans available for ADU construction, although there are income limits. For Eastern Massachusetts, the limit is around $250k. (https://www.masshousing.com/en/home-ownership/homeowners/adu)
They are digging the hole for the foundation and I will update as my project progresses.
| Item | Budget | Actual | Under/(Over) |
|---|---|---|---|
| Survey | $2,000 | $1,850 | +$150 |
| Permit fee | $1,000 | $600 | +$400 |
| Civil Engineering | $5,000 | $3,600 | +$1,400 |
| HERS Rater | $2,000 | $1,850 | +$150 |
| Architect | $25,000 | $30,000 | -$5,000 |
| Sewer Video & Jetting | $0 | $700 | -$700 |
| Foundation Permit | $500 | $580 | -$80 |
| Lumber Order | $12,000 | $12,140 | -$140 |
| Excavation | $15,000 | $20,000 | -$5,000 |
| Total | $62,500 | $71,320 | -$8,820 |