Irontown Modular · Duplex, Triplex and Fourplex

Modular Duplex, Triplex and Fourplex Buildings

A modular duplex is a factory-built building with two homes, set by crane on your foundation. It follows the same code as site-built buildings and also comes as a triplex or fourplex.

Irontown Modular is the home builder. My Cozy Outdoors, its authorized dealer, quotes your project and is your one contact from first question to keys.

Tell us about your project See finished projects See the plans

Six townhomes set in two days in San Rafael, California, by Irontown Modular. See the San Rafael Townhomes project

Does a duplex, triplex or fourplex fit your lot and plans?

These five cards help you quickly decide whether this page fits your project.

How small can your project be?

No project is too small to ask about. Irontown Modular has built a duplex and a fourplex in Salt Lake City.

Where is your building site?

Irontown builds in Arizona, California, Colorado, Idaho, Montana, Nevada, Oregon, Utah and Wyoming.

How long does the project take?

Allow about five to seven months from the Feasibility Review to the set, with local permit review additional.

Who handles site construction?

Your general contractor separately prices the foundation, utilities, access, grading, closing the seams between modules and finish work.

What happens next?

My Cozy Outdoors starts your quote conversation about modules, delivery and the crane set. You confirm lot use and density with the local planning office.

Prefab home pages by state: California · Utah · Oregon · Arizona · Colorado · Idaho · Montana · Wyoming · Nevada.

Irontown Modular builds to the International Residential Code, the same code as a site-built duplex. Your building department reviews engineered, stamped plans for the permit. It is not a HUD-code manufactured home. On its foundation, it is permanent, permitted and inspected like any other building. On this page, prefab and modular mean the same thing.

Most buyers use a construction loan that converts to a mortgage once the building is set and finished. Some lenders know modular construction less well, so talk to yours early. Irontown Modular refers lenders familiar with modular draw schedules. These are outside references, not Irontown financing. My Cozy Outdoors does not lend or promise approval.

Finished duplex and townhome projects

In San Rafael, Irontown Modular built six townhomes for a family-led investment project: 16 weeks in the factory, then a two-day set. In Salt Lake City it built a duplex and a fourplex. The Los Altos photos show the crane set and the finished stairs, baths and rooftop deck. See all commercial projects.

Finished project

San Rafael Townhomes, California

San Rafael, California

6 townhomes · 16 weeks in the factory · 2-day set

Six townhomes with a two-day set near Main Street in San Rafael.

See the San Rafael Townhomes, California photos

Finished project

Supportive Housing Duplex and Fourplex, Salt Lake City

Salt Lake City, Utah

A finished duplex and fourplex within a Salt Lake City supportive housing neighborhood.

See the Supportive Housing Duplex and Fourplex, Salt Lake City photos

Finished project

Urban Infill Multifamily, Los Altos

Los Altos, California

A finished Los Altos infill project, with photographs of the crane set.

See the Urban Infill Multifamily, Los Altos photos

Larger multi-family buildings, townhomes and apartments

The same approach serves larger multi-family housing projects. Condominiums sit above storefront space beside a river. A ski area duplex has wood siding and a stone base. Irontown Modular reports TOSA in Salt Lake City has four stories and 32 two-bedroom apartments, delivered in 12 months with 7 months on site. These pages suit you if you are planning larger developments.

Finished project

Mixed-Use Luxury Condominiums

A finished condominium building with storefront space and a setting beside the river.

See the Mixed-Use Luxury Condominiums photos

Finished project

Ski Area Community Homes

A finished ski community project with a duplex among pines.

See the Ski Area Community Homes photos

Finished project

TOSA Prep School Apartments, Salt Lake City

Salt Lake City, Utah · 2025 to 2026

4 stories · 32 two-bedroom units

A finished Salt Lake City building with 32 apartments and gathering spaces.

See the TOSA Prep School Apartments, Salt Lake City photos

Duplex and fourplex floor plans

Irontown Modular calls the Berkeley its workhorse plan for single-family, narrow lot, duplex or townhome projects, in a traditional or modern exterior style. Berkeley has 2 or 3 bedrooms and 1,275 sq ft above garages. Berkeley 2’s contemporary windows accompany shed roofs. Back-to-back fourplexes have 1,463 sq ft and one or two car garages. Ida and Rabbit rise two stories above garages. Most pages carry floor plan PDFs.

Plan

Berkeley 1 Townhome Duplex Plan

A Berkeley 1 duplex plan with bedroom and garage options.

See the Berkeley 1 Townhome Duplex Plan plan

Plan

Berkeley 1 Townhome Fourplex Plan

The Berkeley 1 fourplex plan, shown at grade and above garages.

See the Berkeley 1 Townhome Fourplex Plan plan

Plan

Berkeley 2 Townhome Duplex Plan

A Berkeley 2 duplex plan with shed-roof renderings and garage options.

See the Berkeley 2 Townhome Duplex Plan plan

Plan

Berkeley 2 Townhome Fourplex Plan

A Berkeley 2 fourplex plan with bedroom, garage and exterior choices.

See the Berkeley 2 Townhome Fourplex Plan plan

Plan

Back-to-Back Fourplex Townhome Plan

A back-to-back plan with fourplex or duplex configurations and garage choices.

See the Back-to-Back Fourplex Townhome Plan plan

Plan

Ida Townhome Plan: Two Stories over a Garage

A townhome plan with two living floors over a garage and bedroom options.

See the Ida Townhome Plan: Two Stories over a Garage plan

Plan

Rabbit Two-Bedroom Townhome Plan

A two-bedroom townhome plan with upstairs living, front decks and a garage option.

See the Rabbit Two-Bedroom Townhome Plan plan

This plan is a starting point that Irontown adapts to your site and program, with a quote provided through My Cozy Outdoors.

Berkeley 1 on My Cozy Outdoors Berkeley 2 on My Cozy Outdoors Ask about a plan

Buyers building two to four homes on one lot

You may want a building entirely for tenants, a place for yourself or homes for relatives.

Rental property investors

You get two to four rental homes in one building, on one foundation, set by one crane, instead of two to four separate builds. You rent every unit.

Owner-occupants

You keep one unit as your new home and rent the others in the same building.

Relatives living next door

Your family can have two homes under one roof line, each with its own front door. Parents, adult children or other relatives can live next door.

Infill developers

You add missing middle housing on vacant or underused lots within existing neighborhoods. Irontown Modular projects in San Rafael and Los Altos show this approach.

How your duplex project goes

Allow about five to seven months from the Feasibility Review to the set. Local permit review is additional. Site readiness and permit or construction delays can move the schedule.

Feasibility ReviewIrontown Modular and My Cozy Outdoors · 1 to 2 weeksYour review covers site and route access, budget, schedule, building requirements, financing assistance, contractor support and the preconstruction agreement.
Preconstruction and permitsIrontown, your contractor and your city or county · 2 to 3 monthsIrontown prepares factory drawings and stamped plans for design and construction. Your contractor applies for the permit, and local review adds time.
Manufacturing and site preparationIrontown and your contractor · 12 to 16 weeksManufacturing happens indoors while your contractor builds the foundation, runs utilities and prepares access on site. Delivery to your site closes this stage.
Set, stitch and closeoutIrontown’s set crew and your contractor · Days to about two weeksIrontown sets the modules by crane. Your contractor completes the seams, exterior and finish work before inspections and keys.

Pricing: what moves the number

Your pricing depends on the project, so this page gives no figures. The list below shows the main drivers. The Feasibility Review gives you a whole-project budget estimate before anyone commits to construction.

Number and size of modules
Foundation type
Utilities and connection distances
Crane access and truck route
Finish level and building materials
State and local permit and impact fees

My Cozy Outdoors quotes the modules Irontown Modular builds, their delivery and the crane set. Your general contractor prices the foundation, utilities, access, grading, stitch and finish work separately. Your city or county sets permit, plan review and impact fees.

Ask for a budget estimate

Your lot: zoning, width and crane access

Your city or county decides lot use, density and setbacks. Confirm these with the local planning office before ordering. Berkeley and Ida suit narrow lots, with living space in two upper modules above garages. Module dimensions shape your layout.

Module sizes on this page

Berkeley 1 and 2 14 ft 6 in x 47 ftIda 14 ft 6 in x 43 ftRabbit 16 ft x 24 ftBack-to-back 20 ft x 32 ft 6 in

Your site needs room for a crane and a truck route that accommodates oversized loads. Before drawing begins, the Feasibility Review includes a virtual site review for crane placement and staging, plus a route review.

Ask about your lot

Set before the snow flies

Your modules are built indoors, and factory work continues through winter. Foundation work, utilities, access and the crane set depend on seasonal conditions. Irontown Modular coordinated Tenaya cabin deliveries and sets around seasonal access and weather.

Irontown Modular reports that TOSA units were never exposed to rain, snow or sun. Its mountain projects include Vail, Aspen, Jackson Hole and Montana. Count back about five to seven months plus local permit review, so a spring start aims at a fall set.

Questions about modular duplexes

What is a modular duplex?

It is one building with two homes, built as modules to the International Residential Code on stamped plans. Irontown Modular builds the modules and sets them by crane on your contractor’s foundation. A triplex holds three homes, and a fourplex holds four. The same approach also serves townhome rows and small apartment buildings.

How much does a modular duplex cost?

The number depends on the modules, foundation, utilities, site access, truck route, finishes and local fees. The Feasibility Review provides a budget estimate. My Cozy Outdoors quotes its own pricing for your project.

Can a modular home be a duplex?

Yes, you can choose a duplex, triplex or fourplex. Berkeley 1 and Berkeley 2 use the same module for two-unit and four-unit buildings. The back-to-back plan works as a fourplex with side entry or a townhome with front entry.

What is the cheapest duplex to build?

A stacked or back-to-back plan with shared walls and one foundation uses the least material and site work for the homes it holds.

Is it cheaper to build a house or get a modular?

Factory work and site work run at the same time, and the crane set takes days. This closes in your building sooner and reduces your contractor’s months on site. Irontown Modular reports San Rafael took one-third the time of local site-built construction, including 16 weeks in the factory and a two-day set.

What is the downside of buying a modular home?

Your site needs crane access and a truck route for oversized loads. Module widths shape your floor plan. Some lenders are less familiar with modular construction. The Feasibility Review covers crane placement and the route.

Do I need special zoning for a duplex?

Your city or county decides which uses and how many homes your lot allows. Confirm your proposed use and density with the local planning office before ordering.

Which states can Irontown deliver to?

Irontown Modular serves Arizona, California, Colorado, Idaho, Montana, Nevada, Oregon, Utah and Wyoming. My Cozy Outdoors has a prefab-homes page for each state.

California · Utah · Oregon · Arizona · Colorado · Idaho · Montana · Wyoming · Nevada.

Is a modular duplex a manufactured home?

No. Irontown Modular builds to the International Residential Code on stamped plans that your local building department reviews. That is the same code as a site-built duplex. Your completed building is permanent on its foundation.

Tell Us About Your Project

Prefer to talk? Call or text +1 (307) 200-8752, Monday to Saturday, 9am to 5pm PST, or email support@mycozyoutdoors.com.

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Residential projects · Modular homes · ADU plans · Photos and renderings belong to Irontown Modular, and project details are presented as Irontown published them.