The best home addition ideas solve a specific problem: not enough bedrooms, a kitchen that feels cramped, no place for a home office, or a family that needs a separate living space. Most Portland homeowners choose from a short list of proven options, including a second story, a primary suite, a kitchen bump-out, a garage conversion, or an accessory dwelling unit (ADU). This guide walks through 12 addition ideas, what each one is best for, and what Lamont Bros. sees on real Portland-area projects.
| Addition idea | Best for |
|---|---|
| Second-story addition | Adding bedrooms or a primary suite on a small lot |
| Primary suite addition | A private bedroom, bath, and closet |
| Kitchen bump-out | More counter, seating, or pantry space without a full addition |
| Garage conversion | A home office, guest room, or family room at lower disruption |
| Room over the garage | An extra bedroom or bonus room without using more yard |
| ADU or in-law suite | Multigenerational living or rental income |
| Home office addition | A quiet, separate workspace |
| Mudroom addition | Storage and a clean entry for active families |
| Sunroom | Bright, flexible living space tied to the yard |
| Bathroom addition | Homes with too few bathrooms for the bedrooms |
| Family room or bedroom addition | Growing households |
| Dormer addition | Usable headroom in an attic |
Start with the problem, not the floor plan. Lamont Bros.' free Home Addition Buyer's Guide walks through scope, budget, and design decisions before you meet with a design consultant.
A second-story addition adds bedrooms, a primary suite, or a home office without using any of your yard. It is often the right answer on a smaller Portland lot, where setbacks limit how far a house can grow outward. The existing foundation and framing must be evaluated first, which is why a thorough feasibility review comes before design. Lamont Bros.' guide to second-story additions covers what to consider before you start.
A primary suite addition gives you a bedroom, bathroom, and walk-in closet in one private wing. It is one of the most requested additions because it changes how a home lives every day. The suite can go on the ground floor, which also supports aging in place, or above an existing room.
A bump-out extends one wall of the kitchen by a few feet, enough for a breakfast nook, a larger island, or a pantry. Because it adds a small footprint and often reuses the existing roofline, it is a lower-impact way to fix a cramped kitchen. It also pairs naturally with a full kitchen remodel so the new space and the old kitchen read as one design.
Converting an attached garage into living space uses the structure you already have. Common results include a home office, guest suite, or family room. A garage conversion still needs insulation, heating, egress, and a plan for the parking you lose, but it avoids new foundation work.
If you want to keep the garage, building above it adds a bedroom or bonus room without taking yard space. The garage framing has to carry the new load, so structural review matters. Read how an addition over a garage works before you decide.
An accessory dwelling unit is a separate living space with its own kitchen, bath, and entrance. It suits multigenerational families, adult children, caregivers, or rental income. Lamont Bros. ADUs generally start around $150,000. The ADU vs. home addition comparison explains how to choose between the two.
A dedicated office addition separates work from the rest of the house with its own entrance, acoustics, and light. Good designs plan for power, data, and natural light early, because they are hard to add later. See Lamont Bros.' home office addition design ideas for layout choices.
A mudroom addition gives a busy household a place for coats, boots, and backpacks before they reach the kitchen. Built-in cubbies, a bench, and durable flooring do most of the work. Lamont Bros. explains the purpose and features in what a mudroom is and how to design one.
A sunroom adds bright, flexible space that connects to the yard, which is valuable through Portland's gray months. The key choice is whether it is a three-season room or fully insulated for year-round use. Lamont Bros.' sunroom additions guide compares costs and types.
Homes with three bedrooms and one bathroom are common in Portland, and adding a second bath is one of the most practical upgrades. The main challenge is routing plumbing to the new space. Lamont Bros. outlines the steps in how to add a bathroom addition to your house.
A ground-floor family room or bedroom addition is the classic way to grow outward. The right size depends on how the room will be used and how it connects to the existing floor plan. Lamont Bros. looks at sizing in the best size for a home addition.
A dormer pushes out part of a sloped roof to create full-height ceilings in an attic or upper floor. It is a smaller structural change than a full second story, so it works for homes where headroom is the main problem. Learn what a dormer addition is and why you might need one.
Build up when your lot is small, your setbacks are tight, or you want to keep the yard. Build out when your foundation cannot support a second story, or you want a ground-floor suite for accessibility. A second story often costs more per square foot than a single-story addition, but it avoids using any land. Lamont Bros. compares both in should I build my addition up or out.
For projects of about 500 square feet, Lamont Bros.' planning ranges are $150,000 to $250,000 for a simple addition, $300,000 to $500,000 for a standard addition, and $500,000 to $800,000 or more for a complex one. Across nine comparable Lamont Bros. addition projects, the average was about $469 per square foot, with individual projects ranging from $348 to $802 per square foot. These are early planning figures, not quotes. The home addition cost calculator gives a starting estimate for your project.
The 2025 Cost vs. Value Report found that a midrange primary suite addition cost about $170,517 nationally and recouped 32 percent at resale, while a midrange bathroom addition cost about $60,645 and recouped 53 percent. An ADU averaged about $166,406 and recouped 41 percent. These are national averages, not Lamont Bros. pricing, and the right addition is the one that solves your household's problem, not only the one with the best resale return. See the 2025 Cost vs. Value Report for the full data.
The City of Portland requires a building permit to add a room, garage, or other enclosed structure attached to a house. Zoning setbacks and lot coverage also shape how large an addition can be. Lamont Bros. explains the process in how to get remodel permits in Portland.
Portland allows one ADU on a site with a house. An ADU can be up to 75 percent of the main home's living area or 800 square feet, whichever is smaller, and the 800-square-foot cap does not apply to a basement ADU in a primary structure at least five years old. Homeowners who use the city's SDC waiver must agree not to use the ADU or house as a short-term rental for 10 years. Confirm current rules with the City of Portland's ADU page before you design.
The best additions look like the house always had them. That means matching roof pitch, siding, window style, and trim, then blending interior flooring and finishes. Lamont Bros. covers the details in how to design an addition to match your home.
Lamont Bros. is a design-build remodeling firm in West Linn, serving the Portland metro and Southwest Washington. One cohesive team handles each project from design through construction, and projects are built under fixed-price contracts after a paid design phase. That process lets homeowners see 3D renderings and floor plans before construction starts.
Lamont Bros. works with Portland-area homeowners who want a thoughtfully designed addition built by one cohesive team, from first sketch to final walkthrough. Every project begins with a conversation about how you want your home to function. Schedule a consultation to get started
Converting existing space, such as a garage or finished attic, is typically less expensive than building new square footage. A bump-out or small mudroom is usually the lowest-cost new addition, because it needs less foundation and roofing.
Lamont Bros.' planning range for a simple 500-square-foot addition is $150,000 to $250,000, while standard additions fall between $300,000 and $500,000. Final cost depends on foundation, structure, finishes, and mechanical systems.
Neither is always cheaper. A second story avoids a new foundation but requires structural upgrades, while a ground-floor addition needs a foundation and uses yard space.
Yes. The City of Portland requires a building permit to add a room or enclosed structure attached to a house.
It can, but the return varies by addition type. National Cost vs. Value data shows midrange bathroom additions recouping about 53 percent and primary suite additions about 32 percent, so the best reason to build is the improvement in how the home works for you.
Yes, if your site qualifies. Portland allows one ADU on a site with a house, and it offers a separate living space instead of an extension of the main home.