ADU conversion to existing building on primary home property

Portland, Maine
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ADU conversion to existing building on primary home property

Gregory McCarthyPro Member
Rental Property Investor · Portland, ME · Member since 2026 · 6 posts · 4 votes

We live in a development with no HOA, with approximately 170 lots in the neighborhood. I have a two-story, 1000 square-foot building in in the back of my primary homes property. It's currently empty and has electricity and insulated walls. It also stores our pool filter, pump and equipment for my pool. It was there when we bought the house five years ago and appears the original owner used it as a workshop. We want to turn this into a rental unit, but our we just realized our warranty deed may restrict this. It says the following:

1. These lots shall be used for single family residential purposes exclusively.

2.. No structure shall be erected on these lots except one (1) detached single family residentiai dwelling of not more than (2) stories in height, and such other building

• necessary and subsidiary to same such as a garage

3. No duplex residence, garage apartment or apartment house shall be erected or placed on these lots, and no buildings shall be altered or converted into a duplex residence, garage apartment or apartment house.

I know both our neighbors left and right have in law apartments in their basements, but they're not in a separate building. Are we dead in the water, or do we have any recourse to make this project happen? Any advice is appreciated. Thank you 

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  • Dan H.Pro Member
    Investor · Poway, CA · Member since 2015 · 7k+ posts · 8k+ votes
    7mo
    Quote from @Gregory McCarthy:

    We live in a development with no HOA, with approximately 170 lots in the neighborhood. I have a two-story, 1000 square-foot building in in the back of my primary homes property. It's currently empty and has electricity and insulated walls. It also stores our pool filter, pump and equipment for my pool. It was there when we bought the house five years ago and appears the original owner used it as a workshop. We want to turn this into a rental unit, but our we just realized our warranty deed may restrict this. It says the following:

    1. These lots shall be used for single family residential purposes exclusively.

    2.. No structure shall be erected on these lots except one (1) detached single family residentiai dwelling of not more than (2) stories in height, and such other building

    • necessary and subsidiary to same such as a garage

    3. No duplex residence, garage apartment or apartment house shall be erected or placed on these lots, and no buildings shall be altered or converted into a duplex residence, garage apartment or apartment house.

    I know both our neighbors left and right have in law apartments in their basements, but they're not in a separate building. Are we dead in the water, or do we have any recourse to make this project happen? Any advice is appreciated. Thank you 

    I do not know the rules for Portland MN so present this as something to investigate.

    in CA they passed statewide ADU laws (many - actually quite a few most years) that override virtually all laws and deed restrictions that do not allow ADUs.   The goal was to not allow communities or HOAs to decide not to allow ADUs.

    i am not a fan of state making this decision over the desire of the local community because I believe there should be places with lower density.

    in general, ADUs add significantly less value than they cost to add and this even holds for garage conversions.   However, it you extra building was built to residential space rules and was permitted, your conversion could be much less than even a garage conversions.   I still suggest you understand the value that will be added by the ADU.   In many areas ADUs add crazy low value.  In my HCOL area (median SFH is ~$1m), NAR data from Nov 2021 showed ADUs added less than $20k of value (NAR about one month ago pulled their data on pretext of it being old but I believe the data was pulled because it did not conform to the ADU narrative beneficial to NAR.   

    there are a plethora of other things to factor into any underwriting gor adding an ADU.   If you want my list for my market, PM me.

    good luck
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  • Lucas Kurtz
    Property Manager · MA · Member since 2025 · 19 posts · 16 votes
    7mo

     Just sharing perspective from the property management side in Massachusetts. Based on what you shared, the language in the deed is pretty explicit around limiting use to a single-family residence and prohibiting separate dwelling units like garage apartments or converted structures. The fact that the building already exists and was historically used as a workshop helps from a use/history standpoint, but converting it into a separate rental unit is usually where things get tricky. What we often see in similar situations is that basement in-law units sometimes slide through because they’re within the primary dwelling and not considered a second structure, whereas a detached building is viewed very differently. That said, neighbors having in-law apartments can still be relevant context, even if not directly comparable. Practically speaking, the path forward usually involves confirming whether the restriction is actively enforced, whether there’s any amendment or variance process, or whether alternative uses (home office, guest space, storage, etc.) make more sense short-term. Before spending money, it’s worth validating expectations with the town and understanding enforcement risk so you don’t invest into something that can’t be used as intended. From a management standpoint, we always recommend getting clarity first, then working backward into feasibility.

    Lucas-Howzer Property Management

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