Easy-To-Assemble SIPs Engineering

DADU Shell Kits

Build a Prefab ADU With Urban Cottage

Now for the fun part! Once you’ve purchased one of our DADU plans and obtained a permit, you can begin the construction of your prefab ADU.

Purchase a Shell Kit

The architectural plan you purchase will determine which shell kit you purchase; each shell kit correlates with one of the pre-approved plans and includes all of the pieces necessary to construct the specific backyard cottage. 

Shell kit prices range from $29,000 – $54,000 depending on the size of the unit and the finishes you choose to include. Contact Urban Cottage by calling (206) 617-4455 or submitting the form below for your free consultation.

Build or Contract Out Construction

Outside of the concrete for the foundation, our shell kits comprise all the parts necessary to complete the building envelope construction of our pre-approved drawings, delivered in phases right to your driveway. Once you’ve purchased one of our shell kits, our team will work with you to establish a delivery schedule that accommodates your preferred pace of construction.

The construction phases include:

Foundation –

We provide the concrete forms, connection hardware, and support beams.

Shell –

We deliver a set number of structural insulated panels (SIPs) to make up the unit’s exterior floor, walls and roof. These panels are all cut digitally to the specific size and shape of your project, carefully manufactured to allow for easy distribution and construction by hand — no mechanical lifts required!

The number of panels you receive depends on the configuration and size of the unit. Much like “assembly required” furniture, SIPs are a unique system of interlocking panels that fasten together in an easy-to-follow sequence. Picture the pieces of an IKEA cabinet that you’re going to assemble — only these are cottage-sized!

Interior Wall Framing –

Similar to the exterior shell, the interior wall framing comes pre-cut and labeled to indicate the placement of each board. Uniquely cut to be positioned with the others, adjoining boards are marked for where they attach — just line up the marks and nail the pieces together!

Framing packages are bundled by wall section to reduce mistakes and mix-ups while assembling. Whether you’ve hired a contractor or you’re doing the building yourself, our framing system ensures faster assembly, fewer mistakes, and less material waste than traditional stick-frame construction.

Roofing, Doors, & Windows –

Once the shell is constructed, you’ll receive the doors, windows, and temporary roofing. These parts will not only protect the shell from weather, but will also begin to make the unit feel functional and homey.

Siding & Optional Add-ons –

We can also provide pre-cut siding and add-on architectural accessories, such as decorative rafters, brackets, and gable pediments, to complete and stylize the exterior.

Exterior Deck –

Lastly, we can provide a standard-size exterior deck package. It’s a large 12’ x 12’ raised area to extend your usable exterior living space. 

Our Shell Kits

Our shell kits have been designed with construction in mind. Once the foundation is laid, there is no heavy machinery required — meaning, the units can be assembled with only hand tools. Additionally, the SIPs that make up the shell and roof of the unit are liftable by a team of just 2–3 people. Depending on your skill level and the complexity of your lot, it is entirely possible to assemble one of our shell kits on your own.

For complicated lots or tight timelines, however, we recommend hiring one of our referred construction companies to do the work for you. They are familiar with the process of building Urban Cottage DADUs and can typically construct the unit quicker than other contractors. Additionally, they manage the delivery schedule, coordinating with us directly to ensure each package is delivered when needed. Hiring one of our referred professionals means you’ll be in your backyard cottage in no time at all!

Why Choose to Build With Urban Cottage?


Our cottages are compact, efficient and hand-buildable. All of these factors help us keep the cost down for you. We also buy the building components in volume and can pass those savings on to you!


While we have four set plans available for purchase, each plan can be phased up in size if you decide you’d like to expand. Start with our studio model, then add on additional bedrooms in the future — we can help you plan the location of your cottage to make it possible.

Opportunity for DIY

Our panelized system comes with full installation instructions and can easily be assembled by you and a few of your friends. No special tools are required and we provide you with all the pieces. If you can put together a chest of drawers, you can put together one of our cottages. Let us show you how!

SIPs Construction

We can deliver the installation packages on a schedule that works for you. You may choose to hire a crew to complete the project in just a few weeks; alternatively, you may decide to take your time, putting the pieces together as time and funding allow. No matter the pace, we are here to support you!

All our cottages are built with structural insulated panels (SIPs). This system not only simplifies construction, it also provides a super insulated and soundproof living space.

SIPs allow for more insulation inside a thinner wall, granting an additional 12 square feet of livable space inside your base unit (24 square feet & 48 square feet in the one- and two-bedroom, respectively) than with standard framed walls. And, to top it off, SIPs are environmentally friendly.


We can deliver the installation packages on a schedule that works for you. You may choose to hire a crew to complete the project in just a few weeks; alternatively, you may decide to take your time, putting the pieces together as time and funding allow. No matter the pace, we are here to support you!


To ensure the look of your cottage complements the homes in your neighborhood, you can choose from a variety of roofing and exterior design options. Get the cost benefits of a production-oriented cottage while retaining the ability to easily and inexpensively customize it to fit your yard and design goals!

Interested In Purchasing A Drawing Plan? Let's Get Started!

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