Home/Modular Homes by City/Stone Mills
Serving the Township of Stone Mills — Tamworth, Newburgh, Camden East, Enterprise & Yarker
Modular Homes & Garden Suites in Stone Mills, Ontario
Factory-direct modular homes and backyard garden suites for the Township of Stone Mills, the rural Lennox and Addington township north of Napanee that takes in Tamworth, Newburgh, Camden East, Centreville, Enterprise, Yarker and Erinsville. Stone Mills' Zoning By-law 2014-744 calls a garden suite a "second unit" (planners call it an ADU, an additional dwelling unit) and allows one in a separate building beside a single-detached house in every zone that permits a house. Here's what the by-law allows, what it costs, and the rules that apply.
What you can build in Stone Mills
Full modular homes — from $175,696. 29 models from 560 to 1,405 sq ft, 1–3 bedrooms — factory-built to the Ontario Building Code and set on a permanent foundation (a real, permanent house, not a “trailer”).
Backyard suites (ADUs) — from $96,244. 7 compact models built for garden-suite and in-law-suite use, sized to fit what Stone Mills's by-law allows.
All homes are CSA-certified (A277 modular / Z240MH manufactured), finished in the factory, and delivered ready for foundation and hook-up. What's the difference between modular, manufactured, and mobile? →
Find your backyard suite — 3 quick questions
We'll narrow the models that fit a typical Stone Mills backyard allowance to the ones that fit your life. No email needed.
1 · Who's it for?
2 · What layout?
3 · What size feels right? (Stone Mills lots typically allow up to 1,076 sq ft)
Stone Mills caps the building that holds the suite at 100 m² (≈1,076 sq ft) and 7 m tall, and all accessory buildings together at 10% of the lot. The lot must front on a road the Township or County maintains all year. Enter your address for the specifics. Your exact lot may allow more or less — get the real number for your address in seconds.
Check your exact Stone Mills address →Can you put a garden suite (ADU) in your Stone Mills backyard?
Yes, beside a single-detached house in the Prime Agriculture, Rural, Rural Residential, Hamlet Residential and Hamlet Mixed Use zones, on a lot that fronts on a year-round public road. One second unit per lot. The specifics, from Township of Stone Mills Zoning By-law 2014-744, §3.25 Second Unit (added by By-law 2018-909; April 28, 2026 office consolidation):
| Where it goes | Beside a single-detached house, in any zone that permits a house as the main use: Prime Agriculture (PA), Rural (RU), Rural Residential (RR), Hamlet Residential (HR) and Hamlet Mixed Use (HMX). Residential Limited Service (RLS) lots are usually on private roads, which the second-unit rule excludes. Not in the commercial, industrial, community facility, open space or environmental protection zones, and never in a boathouse. |
|---|---|
| Max size | 100 m² (≈1,076 sq ft) for the building the suite is in. All accessory buildings together, sheds and garages included, may cover no more than 10% of the lot. |
| Height | 7 m (≈23 ft), the cap for every accessory building. |
| Setbacks | Your zone’s yards for a house: 10 m (≈33 ft) rear and 5 m (≈16 ft) interior side in the PA, RU, RR, RLS and HR zones; 7.5 m (≈25 ft) rear and 3 m (≈10 ft) side in Hamlet Mixed Use. Front yard 15 m (≈49 ft) in PA and RU, 7.5 m (≈25 ft) elsewhere, and on a County Road it is measured as 13 m plus the front yard from the road’s centre line. At least 1.5 m (≈5 ft) from the house. |
| Units per lot | One second unit per lot, inside the house or in a separate building, not both. |
| Road access | The lot must be directly served by a road the Township or County maintains all year. |
| Parking | One space for the suite. |
| Servicing | Private well and septic across the township. You must show there is enough drinking water and enough septic capacity for the suite. The Township’s Building Department issues septic permits itself. |
| Water & conservation | No building or septic system within 30 m (≈98 ft) of a lake, river or wetland. Quinte Conservation covers most of the township and Cataraqui Conservation a strip along its eastern and southern edge; building in a regulated area needs that authority’s permit. |
Check your specific Stone Mills address →
Garden suite, laneway suite, in-law suite, ARU, ADU — different names for the same thing: a small, self-contained home in the backyard. New to the idea? Start with prefab garden suites for Ontario — what one costs in Stone Mills, and the models that fit →
Stone Mills's by-law is verified in our checker, so you can check if a garden suite is allowed at your Stone Mills address in about a minute.
Getting your building permit in Stone Mills
An eligible lot still needs a building permit before anything is delivered. Here's how Stone Mills's process actually works — verified against the Stone Mills building department's own pages.
How do you apply for an ADU building permit in Stone Mills?
Through Email, mail or in person (Township of Stone Mills Development Services) (application portal ↗). The Township of Stone Mills takes building-permit applications by email to cbo@stonemills.com, or by mail or in person at the Township office, 4504 County Road 4, Centreville (613-378-2475). Send the application complete with every document: the Township says it can't save or track incomplete applications. Septic permits are issued by the same Building Department (ext. 228). Stone Mills's building-permit page ↗
- Confirm where you stand: a garden suite (the by-law's "second unit") is allowed beside a single-detached house in the Prime Agriculture, Rural, Rural Residential, Hamlet Residential and Hamlet Mixed Use zones, one per lot, on a lot directly served by a road the Township or County maintains all year (Zoning By-law 2014-744 §3.25). Check your zone on the Township's zoning schedules.
- Size and place the building: up to 100 m² (≈1,076 sq ft) and 7 m tall, with all accessory buildings together under 10% of the lot. Keep your zone's yards for a house (10 m rear and 5 m side in most zones), 1.5 m from the house, 30 m from any lake, river or wetland, and plan one extra parking space.
- Sort out water and septic first: you must show an adequate drinking-water supply and enough sewage-system capacity for the suite. Apply to the Township's Building Department for a septic permit for a new or enlarged system, and to Quinte Conservation or Cataraqui Conservation if the lot is in a regulated area.
- Have a designer with a BCIN prepare the drawings, including an HRAI heat-loss calculation and duct layout and the manufacturer's truss and joist design sheets, and submit the complete application by email to cbo@stonemills.com.
- Pay the building-permit fee when it's issued (cash, debit, cheque or online by credit card with your application number), then book inspections as the work goes. The Electrical Safety Authority inspects the wiring separately.
What does an ADU permit application in Stone Mills need?
- Township of Stone Mills Building Permit Application form, with the designer's BCIN information
- Site plan showing the lot lines, the house, every existing accessory building (for the 10%-of-lot cap), the suite's setbacks, the well, the septic system, any water body within 30 m, the driveway and the extra parking space
- Construction drawings to the Township's Part 9 Building Plans Checklist: foundations, framing, the manufacturer's stamped truss and engineered-joist sheets, insulation (SB-12), plumbing, and an HRAI-certified heat-loss calculation and duct layout
- A septic permit application, or a performance review of the existing system, showing the suite can be served
- Authorization for an agent, if someone other than the owner applies
How much does an ADU building permit cost in Stone Mills?
Estimate for a ~600 sq ft (≈56 m²) detached suite under Stone Mills' Fees and Charges By-law 2024-1237: the building-permit fee is 1.1% of the value of the work, and the Township values a permanent dwelling at no less than $140 per sq ft, so expect at least about $924, plus a plumbing permit of $50 and $10 per fixture. A new septic system adds $950. These are estimates: the CBO can have an under-valued application independently reviewed, and fees are re-set by by-law, so confirm current figures with the Building Department (613-378-2475).
| Building permit | 1.1% of the reported or estimated value of the work, minimum $100 (By-law 2024-1237, Schedule D). The minimum value for a permanent dwelling is $140 per sq ft, so a 600 sq ft suite ≈ $924 and the 1,076 sq ft maximum ≈ $1,657, or more if your actual cost is higher. |
|---|---|
| Plumbing permit | $50 plus $10 per new plumbing fixture |
| Septic (Township of Stone Mills) | $950 for a Class 2 to 5 septic permit; $250 for a performance review of an existing system for a renovation, addition or garage. Ask the Building Department which applies to a suite tied into your existing system. |
| Occupancy permit | $100 |
| Entrance permit | Only if the suite needs a new or wider driveway: $200 plus a $1,000 refundable performance bond for a Township road. A County Road entrance needs a permit from the County of Lennox and Addington (613-354-4883). |
A qualifying additional residential unit is exempt from development charges under the Development Charges Act (s. 2(3.1)–(3.3)), which since June 8, 2023 covers one unit in a building ancillary to a house on any parcel. Stone Mills' development-charge pamphlet (By-law 2024-1276, January 2026) also lists buildings ancillary to a residential use among its exemptions. Check any quoted charge against the Act before you budget.
How long does an ADU building permit take in Stone Mills?
Ontario's Building Code requires a decision on a complete house-class application within 10 business days. The Ontario Building Code gives a house-class permit 10 business days from a complete application. A septic permit and any conservation-authority permission come before the building permit, so start those first, and send the application complete: the Township doesn't hold incomplete ones.
Registration: We found no second-unit registration by-law or fee in the Township's fees by-law. Ask the Building Department (613-378-2475) whether your unit needs anything registered.
Worth knowing before you apply
- The fee is a percentage of the work's value, not of floor area: the Township's minimum values are $140 per sq ft for a permanent dwelling and $100 per sq ft for a seasonal one, and the Chief Building Official can have a low valuation independently reviewed at your cost.
- The suite must be directly served by a year-round, publicly maintained road. A lot on a private lane or a seasonal road doesn't qualify as of right.
- The 10%-of-lot cap counts every accessory building on the lot, sheds and garages included.
- On a County Road the front setback is measured from the centre line: 13 m plus your zone's front yard.
- Electrical is a separate permit and inspection through the Electrical Safety Authority (1-877-372-7233).
Fees and timelines are estimates from Stone Mills's published schedules, verified October 31, 2026. Rates and processes change — always confirm current requirements with the building department before you apply.
A garden suite on a well and septic in Stone Mills
Can I add a garden suite on a septic system in Stone Mills?
Yes, if your septic system can carry the house and the suite together. A garden suite with a kitchen and bathroom adds a new source of sewage, so a qualified septic designer checks the combined load before you order. If the system has room, the suite can connect to it; if not, it may need to be altered, expanded or replaced.
In Stone Mills: The septic check has to be in writing (a septic capacity letter) before the building permit is issued.
Who approves septic systems in Stone Mills?
The Township of Stone Mills approves septic systems itself, so the septic review and the building permit both go through the municipality.
Township of Stone Mills: septic permits ↗ · 613-378-2475 ext. 228 · CBO@stonemills.com
What to gather, and why even a small suite needs the check: our guide to garden suites on a septic system →
From Township of Stone Mills’s own page, checked October 31, 2026. Confirm with them before you apply.
Grants & financing in Stone Mills
Development charges — exempt for a qualifying garden suite — Stone Mills charges development charges on a new house under By-law 2024-1276, but the Development Charges Act exempts one unit in a building ancillary to a house, on any lot, and the Township's own pamphlet lists buildings ancillary to a residential use among its exemptions. A qualifying garden suite should owe none; check any quoted charge against the Act before you budget.
See every program → Ontario ADU Grants Directory
A modular or prefab home on a permanent foundation is financed like any house. CMHC Prefab Plus allows an insured mortgage with as little as 5% down on the first $500,000, with construction funds released in stages. How modular home financing works →
Thinking of the suite as a rental? Run the numbers →
Stone Mills modular homes — FAQ
Can you build a garden suite in Stone Mills?
Yes. Stone Mills' Zoning By-law 2014-744 (§3.25) allows one "second unit", a garden suite, in a separate building beside a single-detached house in any zone that permits a house: Prime Agriculture, Rural, Rural Residential, Hamlet Residential and Hamlet Mixed Use. The lot must front on a road the Township or County maintains all year, and there can be only one second unit per lot.
How big can a garden suite be in Stone Mills?
The building the suite is in can be up to 100 m² (≈1,076 sq ft) and 7 m (≈23 ft) tall. All accessory buildings on the lot together can't cover more than 10% of it, which only matters on a small hamlet lot. The suite meets your zone's yards for a house: 10 m from the rear lot line and 5 m from an interior side lot line in most zones.
Can you build a garden suite on a well and septic in Stone Mills?
Yes. Almost all of Stone Mills is on private wells and septic systems. You must show there is enough drinking water and enough capacity in the sewage system for the suite, and the Township's Building Department issues the septic permit itself (613-378-2475 ext. 228). No septic system can be within 30 m of a lake, river or wetland.
Can you put a modular home in Stone Mills, Ontario?
A CSA A277 modular home set on a permanent foundation fits the by-law's definition of a single-detached dwelling. The by-law excludes a "mobile home", meaning a home designed to be made mobile, and no zone lists one, so a CSA Z240 home built on a transport frame needs the Township's confirmation before you order. Building permits are applied for by email to the Chief Building Official (cbo@stonemills.com).
How much does a modular home or backyard suite cost in Stone Mills?
Modular home models start at $175,696 and run to about $338,000 for the largest layouts; backyard ADU models start at $96,244. Site work, foundation, delivery, and permits are additional.
Can I get a mortgage on a modular home in Stone Mills?
Yes — on a permanent foundation it is financed as real property, including via CMHC Prefab Plus (5% down on the first $500,000).
Local rules summarized from Township of Stone Mills Zoning By-law 2014-744, §3.25 Second Unit (added by By-law 2018-909; April 28, 2026 office consolidation); verified by Modular Homes 400 and reviewed by James Clarke, REALTOR®. Always confirm current requirements with the municipality before you build.