ADU Exterior Design Guide

An accessory dwelling unit (ADU) is an additional living space that shares the same property lot with the primary residence. Such buildings, also known as granny flats, in-law units, guest houses, and backyard cottages, can be very different: an attached ADU, a detached ADU, a completely new construction or an already-existing structure (for example, an existing garage). There’s a huge variety of open concept layouts for any taste.

Many experts are sure that ADUs are a great way to increase California’s housing supply. Some of them think that these construction projects can even solve the problem of housing shortages completely. An ADU can significantly raise your property value. Often, people use it to house their family members, such as elderly parents. Another common ADU use is rental income.

Careful planning of an ADU’s aesthetic appeal is super important — especially if you’re going to rent it out. For many people, the first look is enough to decide whether they’ll live in the house or seek another one. So, it’s vital to make it as attractive as possible and create a pleasant, inviting atmosphere. This article is a step-by-step guide on how to do it.

Blending ADU’s Exterior with the Main House

Your accessory dwelling unit and primary home may be separate structures, but they still should harmonize with each other — even if it’s a detached ADU. Their architectural features and color palettes need to look good together. Also, the ADU’s exterior should match your surroundings. This is easier to accomplish with a “stick-built” (custom) ADU but much harder with a prefab one. Since such ADUs are partially ready-made, their design is usually not so flexible. However, you can still alter it to some degree.

There are three types of integration of an ADU with the main home:

1. Complementary. Colors and materials look similar, but they’re not the same. The buildings are not identical, yet their exteriors are cohesive. Such an option is the most inexpensive. It’s perfect for places that don’t have strict design regulations. Owner involvement is minimal and usually comes down to choosing finishes;
2. HOA-level. In this case, the main goal is to meet the HOA standards, which makes the resemblance much closer. There’s way more similarity in materials, color palettes, and even most details. But there also may be some small differences — especially if the main house is old. The price of such an ADU project, just as the owner involvement, is typically moderate;
3. Seamless. Here, the likeness is almost complete. Your project team will have to do very meticulous work copying the unique features of your existing home. This includes searching for the same materials. Of course, this kind of integration is not cheap. Usually, it’s 10-15% more expensive than a typical ADU design. Owner involvement is also very high.

Main ADU Project Exterior Styles

Now, let’s look at the most popular styles of accessory dwelling unit exteriors.

Modern

This architectural style is the most beloved one in many places in California. It’s sleek, minimalistic, versatile, and functional. Its large windows and open floor plans give a feeling of lightness and relaxation. Roofs are typically flat or have low slopes. The main materials used in this style are stucco, metal, glass, asphalt (for shingles), and fiber cement (for board siding).

Mediterranean

The distinctive characteristics of this aesthetic are stucco walls, tiled roofs, and dark-colored windows and doors. Moreover, it often involves beautiful decorative tiles, various stonework, and details made of wrought iron. Colors are often bright. All of this makes the Mediterranean style truly elegant and timeless.

Craftsman

The craftsman style originates from the Arts and Crafts movement. It’s rather simple but uses intricate details and superb-quality materials such as brick, stone, and wood. This style feels warm and nostalgic and combines functionality with comfort. Its main features are deep colors, decorative braces, exposed roof rafters, and overhanging eaves. Windows are contrasting and have several panes. Also, typically, there are square-shaped columns supporting the prominent front porch.

Cottage

The cottage aesthetic is very pretty, charming, and cozy — no wonder so many people love it. It has many unique features, such as decorative trimwork, wooden siding, light pastel colors, boxes with flowers, and covered porches. Doors can be Dutch-style or classic swinging ones.

Farmhouse

This style is very simple yet has its own charm. Its distinctive characteristics are big covered porches, batten and board siding, and roofs made of metal. The main colors are neutral but often with bright accents (for instance, a red door).

Siding Types

Siding is crucial for any ADU. It’s a key part of its appearance and durability. Which ADU siding types are the most popular? Let’s find out.

Stucco

In California, stucco ADU siding with a light sandy finish is very widespread. It looks clean and smooth, but also textured, which gives it a fascinating appearance. Also, such stucco is very durable, which makes it a great variant for the Californian arid climate. And moreover, you can easily paint on this surface, customizing it as you wish!

Additionally, there’s a special kind of stucco called Santa Barbara stucco. This several-layered material has a super smooth texture that looks very sophisticated and elegant. This finish is commonplace in such aesthetics as Spanish, Colonial Spanish, and Mediterranean. You can also paint it with any color, just like regular stucco.

Lap/Clapboard Siding

Another commonplace siding type is clapboard siding, also called lap siding. It consists of fiber cement, but looks like wood. It’s extremely durable and easy to maintain. Unlike traditional wood, this siding doesn’t rot, is pest- and fire-resistant. All of this makes it very popular and highly-demanded. Also, it has a wide color assortment, and you can place it in both vertical and horizontal positions. This opens truly endless possibilities for designer creativity.

Batten and Board

This siding type is a classic variant for accessory dwelling units. It goes especially well with cottage and farmhouse-style buildings. This siding is a combination of wide, vertically-placed boards and narrow strips called battens. Battens are necessary for covering the board seams. If this siding consists of fiber cement, it has the same advantages as the previous one. And it’s also easy to paint on.

Roof Variants

Another irreplaceable element of the ADU design is the roof. It also has to blend in with the primary residence and all its surroundings.

Let’s review the primary roof types for accessory dwelling units:

• Gable. The most widespread kind of roofs. It has two slopes and a ridge between them;
• Hip. This roof has four slopes that meet at one point. Hip roofs are stable and elegant-looking at the same time, which makes them also quite popular;
• Shed. A roof with only one slope. Its sleek appearance makes it perfect for a minimalistic or modern ADU design project;
• Flat. A level roof without any slopes. It looks quite sleek and minimalistic, too. Such a roof is an ideal option for those who want to place various amenities on the rooftop.

Roof Building Techniques

After you’ve selected the style, you’ll need to choose the construction method for the roof.

In the accessory dwelling units (ADUs) sphere, there are mainly two of them:

1. Trusses. Ready-made structural elements that are effective and inexpensive are thus very popular. They help to install various utilities (such as HVAC systems, wiring, and plumbing) far more easily and conveniently. Their largest drawback is that they make the slopes a bit steeper and the ceiling lower, but it isn’t very noticeable;
2. Hand-framing. The roof will be created manually, right on the building site. This method gives more customization possibilities and also allows for a higher ceiling. However, the construction process could be much faster and more efficient. With a hand-framed roof, you can drill the wiring and plumbing through the frame, hiding them in the ceiling. However, bigger systems such as HVAC need a special boxed-out part of the ceiling (usually called a soffit).

Roofing Options

The importance of roofing is immense. It serves as a protection from sun and rain, and also as a big part of the house design. So, you’ll need to choose it super carefully.

Let’s look at the best roofing types for ADUs:

• Asphalt shingles. A popular and relatively cheap roofing type with a large assortment of variants. For instance, there are shingles that look like slate tiles or wooden shakes. This roofing has plenty of advantages. It’s durable, low-maintenance, simple to install, and not heavy;
• Terra cotta tiles. A popular variant in Spanish and Mediterranean styles. Such tiles consist of natural clay fired at a super hot temperature. It makes them durable and resistant to elements, and their unique reddish-brown hue makes them especially beautiful;
• Metal roofing. Nowadays, its popularity is growing, and unsurprisingly — it’s reliable, energy-efficient, and requires little-to-no maintenance. Also, its assortment is extremely large. Metal roofing has a sleek, minimalistic look, which makes it great for modern-style ADUs.

Entrances and Patios

Another large part of the ADU design is its entrance. It greatly impacts the style of the entire building. A covered entry or a tiny, cozy patio is an amazing place to sit down and relax. It offers great protection from the weather and helps optimize space outside the house. In ADU patios, people often place cozy armchairs or tables, so they can eat, talk, or read a book there. Doesn’t it sound awesome?

Door Types

You can’t underestimate how strongly a door influences the look of an ADU. After all, it gives your guests or potential tenants the first impression of the building. Also, if the house has a neutral color palette, its door can serve as a bright accent.

Let’s look at the most popular types of ADU doors:

• Swing. A simple, typical door with hinges on one side. The most widespread ADU door type. Offers wide possibilities of customization. The range of materials is also large and includes wood, glass, metal, and others;
• Sliding glass. People often select them if they opt for the so-called “indoor-outdoor” living space feel. Such doors allow lots of natural light in and make the house interior harmoniously blend with the environment. They usually have frames made of vinyl or aluminum;
• French. Classic doors that look very sophisticated and elegant. They usually consist of fiberglass and wood, with several glass panels decorated with special grids. French doors can serve not only for entrance but also as inner doors or doors to the patio. You can paint such a door in any color to make it match your ADU design even more;
• Multifold. This inexpensive door is also great for an indoor-outdoor lifestyle. It has several folding panels. The materials of multifold doors are usually wood, aluminum, glass, and others. Customization possibilities are numerous, including glass variants, panel placements, and finishes — all of which can be very different.

Window Options

The design and color of your windows also plays a huge role in an ADU design. They greatly impact its living space feel and optimize natural light. While planning your residential construction, you need to pay very close attention to the size and locations of your windows.

Frame Colors

Minimalist and modern ADU projects usually involve large windows with simple white or black frames. The black color gives a frame a bold, sleek, and stylish appearance, while a white-colored frame looks clean and fresh. The contrast of black frames and white walls catches attention and makes an ADU look sophisticated.

Recessed Windows

A recessed window is a window situated below the wall surface. It looks stylish and unusual, and also provides some important advantages — for example, improves tenants’ privacy and lets them save more energy. Moreover, this window type is really universal and suitable for lots of different styles.

Window Grids

Grids, also called grilles and mullions, are frames that split windows up into many sections. They come in many shapes and sizes. You can find a grid for almost any ADU style – from colonial to modern. The range of materials is very diverse, too. There are metallic, vinyl, wooden, and other grids. Also, you can paint them in any color to make them fit the overall ADU design.

Railing and Decking

Railing and decking are also vital parts of an ADU construction — especially in case it’s got a raised foundation or a balcony on the second floor. Their appearance can hugely influence the building’s design, so you should select them very attentively.

Decking

Usually, materials used for decking are PVC, composite, and wood. The first two are low-maintenance and durable at the same time. You can customize decking with any colors, patterns, and finishes in accordance to your personal style.

Railing

The railing is vital for the safety of ADU balconies or raised decks. The most widespread railing materials are metal and wood, but sometimes, there can even be glass railings. Metal ones are more suitable for modern style, while wooden railings are great for traditional aesthetics (for example, cottage). In addition to that, railings can be vertical or horizontal. And, of course, it’s possible to customize them — just as the majority of other ADU elements.

Other Trimwork Elements

The aforementioned elements of accessory dwelling units (ADUs) are not the only ones. There are many others that can help you enrich its design even more. Many of them are not only decorative, but also have important functions.

Accents

Sometimes, people decorate the exterior walls of their ADUs with various decorative accents. They can give your building an interesting and unique touch, and add a nice matching detail to your design. There’s a huge assortment of such decorations. They can consist of stone, wood, fiber cement or other materials. Colors, sizes, and shapes are incredibly diverse too.

Shutters

These window elements look pretty and elegant. There are wooden, metallic, vinyl, and other shutters, suitable for different ADU styles and designs. Some shutters are functional, while others are solely decorative.

Eaves

Eaves are roof edges that protect the area near the house from the weather. But they also add visual interest to the exterior. The width and appearance of eaves vary greatly. They can be opened or boxed and have different colors and styles. Some eaves can even hide downspouts and gutters.

Gutters

Gutters are necessary functional elements of a house. They gather the water that goes down the roof during rain, after which it pours into downspouts. Thus, they protect the building from possible water damage. Gutters are very popular because they’re inexpensive, low-maintenance, and simple to integrate into the exterior design. Their most common material is metal (usually it’s steel or aluminum), but vinyl gutters exist too.

Torch-Down Roofing with Inner Drains

This roofing type is an alternative to gutters. It’s suitable for roofs with low slopes or without them at all. In such roofing, a torch adheres to several layers of special bitumen. The resulting surface is waterproof and durable. Its main element is inner drains within the roof, which lead to pipes hidden in the interior walls. These pipes end with spouts near the ground. The absence of visible gutters makes the house look clean and clutter-free. Torch-down roofing is common in minimalist buildings.

Rafter Tails

Another popular ADU decorative element. Situated under the eaves, roof rafter tails add a unique and charming look to the house exterior. The variety of their designs, shapes, and sizes is truly astounding, so it’s easy to find something that will perfectly fit your ADU exterior.

Trellises

A trellis is a structure that consists of several bars. They can be either vertical or horizontal. You can attach a trellis to a wall or install it separately. People often use it as a support for vines and other foliage. Plants are very common in ADU exterior design. They add a sense of coziness, warmth, and natural beauty to the outdoor space.

Trellises can be wooden, vinyl, metallic, and other. Their style range and customization possibilities are really huge. If you want to add trellises, do it after the finish of your entire ADU construction process, when you’re working on minor design additions.

Local Regulations and Climate Requirements

To build an ADU in California, you’ll need to ensure that your project complies with all the local building codes. It’s necessary for completing the permitting process and getting the approval during the final inspection. You’ll need to carefully read all the regulations regarding underground utilities, property lines, plumbing lines, electrical wiring, and so on.

In case your area is prone to wildfires, all your materials need to be fire-proof. Many experts recommend installing boxed eaves. This construction can protect the house from fire by covering the overhanging parts of the roof. Also, in many places, local authorities require builders to get energy efficient appliances (such as solar panels) and sustainable design elements.

With a pleasant, cozy, and harmonious design, your accessory dwelling unit will be an amazing living space for your family member or a great source of rental income!

Frequently Asked Questions — FAQ

What is a good size for an ADU?

The optimal ADU size depends on many factors — the available space on your existing property lot, your budget, local zoning regulations and building codes, intended purpose (whether you’ll build your ADU for rental income, your family members, as a guest house, or anything else) and so on.

The upper limit of ADU size in California is half the size of the main house. However, it must be at most 1,200 sq.ft. But you can maximize space inside of it with different techniques — for example, using multifunctional furniture. There are many ways of maximizing space that can help you use the most out of every square foot.

What is the best foundation for an ADU?

It depends on the landscape on which you plan to construct your ADU. For example, if the ground is level, the best variant is slab-on-grade. If it’s too uneven, the most suitable option can be a raised foundation. In some cases, people also use a hybrid type.

What are the new laws for ADU in California, 2024?

In California, there are several new laws that make an ADU building process much simpler. For example, height restrictions have softened. Maximum ADU height is now 25 ft. instead of 16 ft. The 60-day rule has become more transparent, and in case an ADU of 800 sq. ft. is going to encroach on the front setback, local authorities can approve the project. Meanwhile in the past, they always denied such applications.

How close to the property line can you build an ADU?

If you plan to construct an ADU closer than 60 ft. to your front property edge, it will require at least three ft. interior side and back yard setbacks. If this distance is 60 ft. or more, setbacks in the interior side and backyard are not necessary.