ADUs on Middleton Properties: Income Potential and Rules

Adding a small home on your property can open new options. An accessory dwelling unit, or ADU, is a second place to live on the same lot. People use ADUs for long‑term rent, a guest suite, an in‑law home, or a quiet office. In Middleton, the city code gives a clear path for a detached second unit if your lot meets specific rules. In this guide, you will learn the local rules, permit steps, realistic costs, and income math. You will also see sample numbers for rent and cash flow, plus a step‑by‑step checklist to move forward with confidence.

What is an ADU? Types & Common Configurations

ADUs come in three main types:

• Attached conversion, like a garage or basement turned into a separate unit.
• Detached backyard cottage, also called a second dwelling on the lot.
• Internal suite, a separate space within the existing home with its own entrance.

Layouts range from studio to 1‑bedroom. Typical features include a kitchenette, bathroom, safe egress, and a private entry. Size and type affect complexity and cost. A simple internal conversion may be cheaper and faster. A detached unit offers more privacy but needs full utilities, parking, and a foundation. In Middleton, a detached option must fit the city’s second‑unit rules, including a 1,000 sq ft cap and shared driveway.

Why Consider an ADU in Middleton? Income, Flexibility, and Value

An ADU can help your property work harder. For many owners, the main draw is steady rental income. You can rent long‑term to a local tenant. Or, if allowed by your HOA and city rules, you might consider mid‑term rentals for traveling nurses or project workers. ADUs also help with life changes. Think multigenerational living, a caregiver on site, or a separate office that protects your quiet time.

For resale, a legal, well‑built ADU can widen your buyer pool. Families may want the extra space. Investors like the income stream. In Middleton, lot size, driveway access, and parking matter. So does distance to services, schools, and commuter routes. Before you plan, check your lot’s size, utilities, and parking potential. These items often make or break feasibility.

Local Rules & Permitting: Middleton and Canyon County Checklist

Middleton’s municipal code does not use the term “ADU” often. Instead, it allows a “second dwelling unit” under a clear set of rules. Start here.

1. Confirm your jurisdiction

• Is your property inside the City of Middleton or in unincorporated Canyon County? If inside city limits, you will work with the City of Middleton Planning and Building. If outside, check with Canyon County. City owners submit permits through the city’s online portal. See Middleton’s permit page and contacts in the city’s permit resources.

2. Understand Middleton’s second‑dwelling rule

• The city’s zoning table allows a second dwelling unit on lots that meet several conditions: at least 14,000 square feet, the new unit is detached, it uses the same driveway and address, utilities connect through the primary residence, and the unit does not exceed 1,000 square feet. See the city code table and notes here: Middleton Municipal Code, Zoning Table.

3. Accessory structure and permit triggers

• Any detached structure over 200 square feet requires a building permit. That includes most detached ADUs. Accessory structures must meet setbacks, and larger structures must align with material and appearance standards. Read the city’s accessory‑structure rules here: Accessory Structures and Permits.

4. Parking and access

• Middleton requires 3 off‑street parking spaces per dwelling unit. Plan for driveway or pad work if your site does not meet this. Parking rules are here: Off‑Street Parking Standards.

5. Utilities, water, and sewer

• Residences on lots under 2 acres must connect to city water and sewer if the system is within 1,000 feet. Lots 2 acres or larger may use well and septic unless public service is within 1,000 feet. This decision can drive your budget and schedule. Review the utility notes in the zoning section: Zoning Table and Notes.

6. Impact fees and timing of payment

• Middleton charges impact fees on new dwelling units. Fees are paid before permit issuance. The Parks impact fee example in the code lists Single Family Residential at 2,313 dollars per EDU and Multifamily at 2,361 dollars per EDU. Get current rates from city staff. Read the impact fee chapter here: Impact Fees.

7. Fire district review

• The local fire agency is the Middleton Rural Fire District, also called MidStar Fire. Early coordination helps you plan access, hydrant needs, and turning radii that may shape your site layout. See MidStar info here: MidStar Fire.

8. Building permits and inspections

• A detached ADU needs building, electrical, mechanical, and plumbing permits. Expect plan review, then staged inspections for foundation, rough‑in, and final. Submissions are handled through the city’s online system.

9. HOA and short‑term rental rules

• Idaho’s 2023 law, HB 166, limits an HOA’s ability to fully ban some internal ADUs, but it does not override city zoning for detached units. Always read your CC&Rs and get written confirmation from the HOA.

10. Property taxes and assessment

• Adding a dwelling increases assessed value. Ask the county assessor how a permitted second unit may affect property tax and when changes apply.

Practical tip checklist

• Site plan with measured setbacks and parking layout.
• Utility map showing current water, sewer, power, and gas.
• Preliminary floor plan and elevations.
• Written confirmation from utilities on capacity and connection points.
• Fire access notes and driveway width, slope, and surface.
• Contractor license and insurance, plus references.
• City fee estimate for permits and impact fees.

Costs, Financing & Return — Build a Realistic Budget

Your budget has three layers: hard costs, soft costs, and a reserve.

Hard construction costs

• Detached cottage: plan for foundation, framing, roof, windows, insulation, HVAC, full bath, and a small kitchen. Finishes and site work drive the spread.
• Attached conversion: less foundation work, but you still need egress, insulation, sound control, and separate mechanicals.

Soft costs

• Design and engineering, permit and plan review fees, impact fees per dwelling EDU, and utility connection or tap fees if required. Middleton’s code states impact fees must be paid before permits for dwelling units are issued. See the local reference: Impact Fees.

Utility and site items often missed

• Electrical panel upgrade to support a new range and HVAC.
• Sewer lateral extension and cleanouts, or septic capacity review if on well and septic where allowed.
• Driveway widening or a new parking pad to meet the 3‑space rule. See parking standards: Parking.

Operating expenses and reserves

• A quick screen is the 50 percent rule. Expect around half of gross rent to go to expenses like management, vacancy, repairs, insurance, taxes, and reserves before mortgage or financing. For a deeper line‑item view, many investors use a breakdown like property management at 8 to 10 percent, vacancy at 5 to 8 percent, plus maintenance, insurance, taxes, and capital reserves. See an overview here: BiggerPockets expense guide.

Financing options

• Cash or savings for speed.
• HELOC or home equity loan for lower rates and flexible draws.
• Construction loan that converts to a fixed mortgage.
• Renovation mortgages or investor partnerships if you prefer to share cost and risk.

Simple ROI framework

1. Estimate market rent using current Middleton comps. Zillow’s Middleton dashboard shows an average rent near 1,995 dollars for all types. Zumper reported a median near 1,375 dollars. HUD’s Boise Metro 2‑bedroom FMR is 1,838 dollars. Use a conservative number for a 1‑bed ADU, roughly 1,200 to 1,900 dollars per month based on size and finish. Sources: Zillow Middleton, Zumper, HUD FMR Boise Metro.
2. Subtract operating expenses. Using the 50 percent rule, 1,200 dollars rent yields about 600 dollars NOI per month before financing. At 1,800 dollars rent, NOI is about 900 dollars per month.
3. Subtract financing costs. Use your loan amount, rate, and term to get the monthly payment.
4. Compute cash flow and payback. Cash flow equals NOI minus financing. Simple payback is total project cost divided by annual cash flow.

Tip: Keep a 10 to 15 percent contingency for surprises. Also, budget time. Impact fees, plan review, and utility work often set the timeline in Middleton.

Design & Construction Considerations

Conversion vs new build

• Conversion can be faster and less costly. You already have walls and a roof. But you must meet fire, egress, and sound rules, and some layouts are awkward.
• New detached units add privacy and value, but they need a foundation, full utilities, and site work. In Middleton, they must share the driveway and connect utilities through the primary residence per the second‑unit rule. See the rule here: Zoning Table and Notes.

Space and systems

• Use efficient layouts: one bed with open living, smart storage, and good natural light. Add soundproofing between units. Decide on separate HVAC or a dedicated mini split. Separate power or water meters can help with tenant billing, but many owners keep one meter and include utilities in rent.

Accessibility and future‑proofing

• No‑step entries, wider doors, and a walk‑in shower will widen your renter pool and support aging family.

Contractor selection

• Verify license and insurance, check references, and get fixed bids with a clear scope, schedule, and allowances.

Income Scenarios & Localized Examples

Use current local comps and your final design to set rent. Here are three Middleton‑based sketches to frame expectations.

Scenario 1: Attached studio conversion, conservative

• Rent: 1,200 dollars per month
• Vacancy reserve at 6 percent: 72 dollars
• Management at 8 percent: 96 dollars
• Other operating and reserves: 432 dollars
• Estimated NOI before loan: 600 dollars per month
• If financed at 100,000 dollars, 7.25 percent, 30 years, payment is about 682 dollars. Net cash flow is about negative 82 dollars per month. Annual cash flow is negative 984 dollars. Simple payback is not met from rent alone. Value and flexibility may still justify the project.

Scenario 2: Detached 1‑bed, typical finish

• Rent: 1,600 dollars per month
• Vacancy at 6 percent: 96 dollars
• Management at 8 percent: 128 dollars
• Other operating and reserves: 576 dollars
• Estimated NOI: 800 dollars per month
• If financed at 150,000 dollars, same terms, payment is about 1,022 dollars. Net cash flow is about negative 222 dollars per month. If total cost is 175,000 dollars and you place 25 percent down, payment drops, and cash flow can move near break‑even. Many owners target lower cost via smaller size and smart finishes.

Scenario 3: Detached premium 1‑bed near town

• Rent: 1,850 dollars per month
• Vacancy at 5 percent: 92 dollars
• Management at 8 percent: 148 dollars
• Other operating and reserves: 650 dollars
• Estimated NOI: about 960 dollars per month
• If financed at 140,000 dollars, payment is about 953 dollars. Net cash flow is roughly 7 dollars per month. With 20 to 30 percent down or a lower total cost, monthly cash flow turns positive.

Payback and sensitivity

• Simple payback equals total project cost divided by annual cash flow. If you net 3,000 dollars per year, a 90,000 dollar project has a 30‑year simple payback. A 10 percent rent change can swing NOI by about 60 to 90 dollars per month in these examples. A 10,000 dollar cost overrun adds about 45 to 70 dollars per month in debt service at today’s rates.

Note: Always confirm rents with fresh Middleton comps. Zillow’s local snapshot and HUD FMRs give guardrails. Sources: Zillow, HUD FMR, Zumper.

Pros, Risks & Resale Impact

Pros

• Steady income, more living options, and a bigger buyer pool on resale. A permitted second unit with solid finishes shows well.

Risks

• Permit delays, utility hookups, and parking upgrades can add cost. HOA limits or short‑term rental rules may change your plan. Insurance and property taxes can rise. Keep a buffer.

Resale tips

• Keep the permitted plan set, final inspection card, and photos of work. Note whether utilities are shared or metered. Share rent history, expenses, and maintenance logs. This builds buyer trust and can support value.

Next Steps & Local Resources

Quick start checklist

• Confirm if you are in city limits, then call Middleton Planning and Building.
• Pull your parcel map, survey, and any old permits.
• Sketch a site plan with parking and setbacks.
• Contact utilities to confirm connection points and fees.
• Meet with the city and MidStar Fire early.
• Get at least two licensed contractor bids and a written budget.

Ready to weigh costs, rent, and value uplift on your specific lot? Tap a local advisor who knows construction and income property math. Strategic guidance up front can save months.

Get expert help from a local who builds real pro formas and knows Middleton permits. Reach out to Strategic Realty for a no‑pressure consult. Get a free home or business valuation and consultation

FAQs

What lot size do I need for a detached ADU in Middleton?

• The city allows a “second dwelling unit” on lots at least 14,000 square feet, with a max unit size of 1,000 square feet, shared driveway and address, and utilities tied through the primary residence. See the rule here: Zoning Table and Notes.

How many parking spaces are required?

• Middleton requires 3 off‑street spaces per dwelling unit. Plan for driveway or pad work if you are short. Details: Parking Standards.

Do I need a building permit?

• Yes, any detached structure over 200 square feet needs a building permit, plus trade permits. See: Accessory Structures and Permits.

Will I owe impact fees?

• The city charges impact fees for new dwelling units and requires payment before permit issuance. Verify current amounts with the city. Reference: Impact Fees.

Do I have to connect to city water and sewer?

• Lots under 2 acres must connect if a city system is within 1,000 feet. Larger lots may use well and septic unless public service is nearby. See notes here: Zoning Table and Notes.

Can my HOA block an ADU?

• Idaho’s 2023 law, HB 166, limits HOA bans on certain internal ADUs. It does not override city zoning for detached units. Always get written HOA guidance.

What rent can I expect?

• A conservative 1‑bed ADU in Middleton often falls around 1,200 to 1,900 dollars per month, based on size and finish. Check live comps: Zillow, Zumper, and HUD FMR.

How long does permitting take?

• Timelines vary. Plan for plan review, utility coordination, possible fire review, and inspections. Starting with a complete submittal helps. Use the city’s permit process.