Preparing for Sammamish ADU and home addition building permits is easier when the household first defines who the new space serves. An independent dwelling for long-term occupancy raises different layout, privacy, utility, and parking questions from a bedroom wing, home office, or expanded family room.
The next step is property research. The design has to fit the parcel, the existing house, access for construction, and the systems that will serve the new area. A generic floor plan should not lead those decisions.
Write the use story before choosing a configuration
Describe sleeping, cooking, bathing, storage, laundry, work, outdoor access, and privacy needs. Note whether occupants need a step-free route, separate entrance, acoustic separation, or a direct connection to the main house.
A discussion with a Sammamish addition and ADU builder can compare attached, detached, converted, and expanded-house options against that use story. The best configuration is the one that fits both the household and the site.
Research the parcel before refining elevations
Collect available surveys, recorded documents, utility information, septic or sewer records where applicable, and plans for the existing house. Identify lot dimensions, slopes, easements, critical areas, trees, access, and known drainage features.
The City of Sammamish’s current ADU information describes allowed configurations and development standards. Use City guidance and property-specific review to confirm what applies rather than relying on a design copied from another parcel.
Compare an attachment with a separate structure
An attached space may share walls, roof connections, utilities, and circulation with the house. A detached ADU can create clearer independence but introduces its own foundation, envelope, service routes, and path across the property.
Draw both the daily route and the construction route. Consider privacy between entrances and windows, outdoor space, trash and recycling, emergency access, deliveries, and the way residents reach vehicles during wet or dark weather.
Make access visible on the site plan
Show gates, driveway width, slopes, retaining conditions, overhead constraints, staging, material storage, equipment paths, and the route for soil or demolition debris. A design can fit geometrically while remaining difficult to build.
Decide how existing landscaping, fences, paving, and occupied areas will be protected. If temporary access crosses an area that must be restored, include that restoration in the scope and budget.
Trace every utility from source to fixture
Map water, sanitary service, electrical capacity, heating and cooling, ventilation, communications, and any fuel source. Determine where connections are feasible and what parts of the existing home or yard must be opened to reach them.
The guide to Sammamish ADU and addition cost explains why a compact building can still carry substantial site and utility work. Resolve these routes before treating the floor area as the main budget variable.
Record the changes required inside the original home
An attached unit or addition may need a new opening, altered hallway, relocated window, upgraded panel, utility route, or fire and acoustic separation. A detached ADU can still affect the house where services originate or controls are located.
Mark these enabling tasks on the existing floor plan and include finish repair around them. Flooring, drywall texture, trim, paint, cabinets, and landscaping may extend the practical scope well beyond the outline of the new construction. Identify which rooms must be emptied or taken out of service so the household plan reflects the true impact. Record how each affected area will be restored after the connection or service work is complete.
Design drainage with the building footprint
New roof area, paving, excavation, and grading can change how water moves across the property. Coordinate finished floors, thresholds, foundations, roof drainage, walkways, and landscaping rather than treating stormwater as a note added after the plan is fixed.
Photograph existing drainage patterns during wet conditions if practical. A site plan should show how the new work relates to the house and neighboring properties, while the project team confirms the current requirements for the parcel.
Integrate life safety without compromising daily use
Address emergency escape, alarms, separation, heating, ventilation, stairs, guards, and the path to the exterior as coordinated design elements. A safe route should also feel intuitive to residents and visitors.
If aging family members or guests may use the space, review door widths, bathroom clearances, reachable storage, lighting, and step-free possibilities early. Retrofitting those relationships after structural and plumbing decisions is far more limiting.
Build a complete and consistent submittal set
Site, floor, roof, elevation, structural, energy, utility, and other required information should describe one design. Give every sheet a revision date and maintain a record of review comments and responses.
Selections with construction consequences—windows, exterior doors, mechanical equipment, water heaters, plumbing fixtures, and major appliances—should be coordinated before their requirements are embedded in different drawings.
Sequence inspections and household disruption
Identify work that must remain visible for review and the points when the existing home loses access, weather protection, or utility service. Plan temporary barriers and safe routes before excavation or demolition begins.
The article on Sammamish whole-home planning can help if the addition also changes the kitchen, entry, or family spaces. When the use, site constraints, and utility concept are documented, share them through a Sammamish addition estimate request.