ADU and DADU Construction Materials in Western Washington
Foundation materials, structural hardware, and the subcontractors to put it all together. One supplier for your backyard cottage, garage conversion, or basement unit.
Get A QuoteMore ADUs Are Coming. Build Them Right.
Washington changed the rules. Under HB 1337, most cities and counties inside urban growth areas now have to allow two ADUs per residential lot. Attached, detached, or one of each. Units can be at least 1,000 square feet, and most owner-occupancy requirements are gone.
That means more backyard cottages going up across the Puget Sound region. Every one needs a solid foundation, a complete load path, and a crew that knows the work. That's where we come in.
ADU Projects We Supply:
- Detached ADUs (DADUs): Standalone backyard cottages on new slab or stem wall foundations
- Garage Conversions: Existing structures upgraded to meet code for living space
- Basement Units: Below-grade apartments that need egress and moisture control
- Above-Garage Units: Second-story builds that put real loads on the framing below
- Attached ADUs: New units tied into the main house
Foundation Materials for ADU and DADU Builds
A small footprint doesn't mean a small foundation job. Our soils hold water and our region is seismic. Your foundation has to handle both.
Concrete and Rebar:
- Fabricated Rebar: Cut and bent to your plans so your crew isn't doing it on site
- Concrete Accessories: Forming supplies, chairs, ties, and expansion joint for a clean pour
- Insulated Concrete Forms: ICF blocks for energy-efficient stem walls and basement walls
Moisture and Drainage:
- Vapor Barriers: Under-slab protection that keeps ground moisture out of the living space
- NDS Drainage: Footing drains, downspout connections, and yard runoff control
- Egress Window Wells: Code-compliant escape and natural light for basement ADUs
Simpson Strong-Tie Hardware for a Complete Load Path
Inspectors look hard at ADU connections. We stock the Simpson Strong-Tie connectors that tie a DADU together from roof to foundation.
Hardware for ADU Framing:
- Anchors and Hold-Downs: Resist uplift and overturning in wind and seismic events
- Joist Hangers: Code-listed connections for floor and roof framing
- Straps and Ties: A continuous load path from rafters to sill plate
- Post Bases and Caps: For covered entries, porches, and decks
- Retrofit Hardware: Seismic retrofit products for garage conversions on older foundations
A Subcontractor Network That Shows Up
Materials are half the job. Finding good trades is the other half. We've worked with Western Washington contractors for decades, and we know who does solid work.
Trades We Can Connect You With:
- Excavation and site prep
- Foundation and concrete crews
- Rebar placement
- Framing
- Drainage and waterproofing
Tell us what you're building. We'll point you to the right people and keep materials moving to the jobsite.
Who We Work With
- Homeowners: Planning a backyard cottage or conversion
- General Contractors: Adding ADUs to their project list
- ADU Builders: Design-build firms running multiple units a year
- Architects and Engineers: Specifying foundation and connector products
- Developers: Adding units to infill lots
Planning an ADU? Start Here.
Rules still vary by city, even under the new state law. Check with your local planning department first. The Washington State Department of Commerce publishes free guides covering zoning, permits, financing, and selling an ADU separately.
Free ADU Guides:
ADU Landowner Checklist Separate Sale of ADUs Fact Sheet WA State ADU RulesAlready have plans? Send them over. We'll run a material takeoff and quote the job.
ADU and DADU Questions
What's the difference between an ADU and a DADU?
ADU is the umbrella term for any secondary unit on a residential lot. A DADU is a detached ADU, a standalone building separate from the main house.
How many ADUs can I build on my lot?
Most residential lots inside Washington urban growth areas can have two. Size, height, and setback rules still come from your city or county, so confirm locally.
What kind of foundation does a DADU need?
Most use a slab-on-grade or a stem wall with a crawl space. Your engineer and local code make the call. We supply rebar, forming accessories, vapor barrier, and anchors for either.
Do you deliver to residential job sites?
Yes. We deliver from our Marysville and Pacific locations. Call the yard closest to your project to schedule.
Can you recommend contractors for my ADU?
Yes. We can connect you with foundation, framing, and site prep crews we've worked with for years.
Ready to price out your ADU? Send us your plans and we'll put together a quote.
Get A Quote