Turning a Basement Into an ADU in Puyallup: 2026 Guide

More Puyallup families are asking us the same question: can the basement become its own small home? Maybe it is for a parent who wants to live close but not in the spare room, a grown kid saving for a down payment, or rental income that helps carry the mortgage. In most cases the answer is yes, and the rules have moved in homeowners' favor. Here is what we walk people through before anyone picks up a hammer.

What changed in Washington ADU law

In 2023 the Legislature passed House Bill 1337, which requires cities planning under the Growth Management Act to allow accessory dwelling units in their urban areas. The headline points: cities must allow up to two ADUs on a lot where a single-family home is allowed, they cannot require the owner to live on the property, and they must allow ADUs created by converting existing space, which is exactly what a basement conversion is. The bill text and reports are on the Washington State Legislature's site.

Puyallup brought its code in line with the state law through Ordinance No. 3324, which amended the Puyallup Municipal Code's building, utility and zoning titles. We are not going to quote size limits or parking rules here, because those details live in the current code and can change. Before we design, we check the current PMC Title 20 rules for your address with the City of Puyallup Planning Division; you can ask the same office about your property.

One local wrinkle: some South Hill addresses sit in unincorporated Pierce County rather than the city. Different jurisdiction, different code. We confirm which one you are in first, because it shapes everything after.

Which Puyallup basements make good ADUs

Puyallup's housing stock splits into two kinds of basement, and they lead to very different projects.

South Hill daylight basements

Much of South Hill, in neighborhoods like Gem Heights and Sunrise, was built from the 1980s through the 2000s, and the sloped lots gave a lot of those homes daylight lower levels. These are often the best candidates. One wall is at or near grade, so you can usually get a real entry door, decent windows and a bedroom that feels like a bedroom rather than a bunker. Ceiling heights from that era are typically workable, and the mechanical systems are newer.

Valley homes near downtown

Near downtown and the fairgrounds the homes are older, Craftsman cottages and postwar houses on grid streets, and their basements are more of a mixed bag. Some have low ceilings, partial foundations or old cellars. Valley properties can also involve floodplain considerations and a higher water table, so moisture is the first thing we look at. A basement that gets damp every winter is not ready to be a home until the water problem is solved.

The five things that decide whether it works

• A separate entrance. An ADU needs its own way in. On a daylight basement that is often an existing slider or a new door on the low side. On a full basement it can mean an exterior stair well, which adds real cost.
• Egress and light. Sleeping rooms typically need an egress window sized for escape, plus working smoke and carbon monoxide alarms. Cutting a new egress window into a concrete wall is common work, but it has to be planned with drainage in mind.
• Ceiling height. Ducts, beams and drain lines tend to hang low in basements. We measure early, because rerouting them is easier on paper than mid-framing.
• Sound and fire separation. Two households under one roof need a ceiling that keeps footsteps and smoke where they belong. Expect insulation, resilient channel or extra drywall layers, and solid doors between units.
• Plumbing and power. A kitchen and a full bath need drains that can reach the sewer line, sometimes with an ejector pump if fixtures sit below it. The electrical panel often needs an upgrade to carry a second kitchen, a dryer and heat.

Designing a small kitchen that works

The kitchen is where basement ADUs most often feel like an afterthought: a two-burner cooktop jammed next to the water heater. It does not have to be that way. A short run of full-depth cabinets, a 24-inch range, a proper vented hood and a sink under good light will cook real meals. We put the same care into a small layout that we put into a big one, like the walk-in scullery we tucked into the Harrington kitchen in Puyallup so the main room stayed calm. In an ADU, that thinking shows up as a pantry wall or a laundry closet that hides the clutter.

Because we design in 3D before we build, you can walk through the unit, check where the furniture goes and see whether the bedroom window actually lets in light before any of it is real.

What a basement ADU typically costs

We are careful with numbers, so here is the range we already share for basement remodeling in Puyallup: basement finishing typically runs $60,000 to $120,000 for open recreation and media space, and $120,000 to $200,000 or more when it adds bedrooms, full bathrooms, kitchenettes or separate-entrance suites. A true ADU sits in that second range. Where yours lands depends on the entrance, how much plumbing has to move, whether the panel needs replacing, and the finish level you choose.

That is often about half the cost per square foot of building an addition, which is why a basement is usually the most affordable place to create a second unit if the space is there.

Permits and timeline

A basement ADU typically needs a building permit plus electrical and plumbing permits, and the city reviews it as a dwelling unit, not just finished space. Our part is to draw a complete plan set, submit it, answer review comments and schedule inspections, so the paperwork stays off your plate. We will not promise a permit timeline, because review times vary with the city's workload; the City of Puyallup's development services staff can tell you what they are seeing now.

Once permits are issued, construction for a basement conversion usually moves faster than an addition because the structure, roof and foundation already exist. The schedule depends mostly on how much has to change underground and in the walls.

Where to start

If you are curious whether your basement can become an ADU, the first step is a visit. We look at the entrance options, ceiling heights, moisture, the panel and the sewer line, and we tell you plainly whether it is a good candidate. For a sense of the full scope of lower-level work we do, see our basement remodeling services.

When you are ready, request a free consultation and we will come out, measure, and give you an honest read on what your basement can be.