Garage Conversions

Converting an existing single family garage into living space (bedroom, recreation room, study, etc.) requires a building permit, and may require electrical, mechanical and plumbing permits as well. 

Whether or not the conversion will be allowed depends largely on the property and if there is adequate space to replace the number of parking stalls that are being eliminated from the garage.

STEP 1 - Determine if there is adequate parking outside of your existing garage

Come to the Development Services Center and ask for a “Planner” to assist you with zoning and land use questions you might have regarding the conversion of a single family garage into living space.

The planner will be able to look up your property on our maps and review options to replace parking that is being eliminated from the garage. 

In general, most detached single family homes require a minimum of 2 off-street parking stalls.  If the Planner determines that you have adequate space for the required amount of parking spaces, and there are no other zoning or land use issues regarding the proposal, you can move on to Step 2.

STEP 2 - Determine what building code requirements need to be met

Following a conversation with a Planner in Step 1, ask for a “Plans Examiner” to assist you with questions you might have regarding building code requirements.  The plans examiner will be able to go over building code issues with you.

There are two basic areas of code to address during the conversion of a garage to living space. These are discussed below.

Fire and Life Safety Code Requirements

When converting a garage to living space, the code requires provisions for occupant health and safety, such as emergency egress from sleeping areas, smoke and carbon monoxide alarms, minimum headroom, stair rise and run, landings at stairs and doors, ventilation, lighting and heating of habitable spaces, etc. Most likely, a minimum amount of modifications will be required to convert the garage to a safe living space.

Energy Code Requirements

The Washington State Energy Code (WSEC) requires that any previously unheated space that is being converted to heated space shall fully comply with current energy code requirements such as attic insulation and venting, wall and floor insulation, and energy code compliant windows and exterior doors. 

Here are the specifics:

  •  Attic insulation: Minimum R-49 for attics (possibly R-38 for single rafter framing with no attic space). An attic access panel (minimum 22” x 30”) will be required to access the attic area.  Since the attic area will now have heated space below the ceiling, it will also need to be ventilated.
  • Wall insulation: Minimum exterior wall insulation of the heated space shall be R-21. If existing walls consist of 2x4 framing, they will need either rigid or high-density insulation, or be furred out to accommodate R-21 insulation. The existing garage door(s) will need to be removed and replaced with a framed wall that can accommodate R-21 insulation.
  • Windows and exterior doors: Fenestrations (openings in an exterior wall) shall have a maximum U-factor of 0.30. (The lower the U-factor, the greater a window or door's resistance to heat flow and the better its insulating properties.)
  • Floor insulation: The existing concrete slab serving as the garage floor does not provide adequate insulation for a heated space. Bringing the space up to current code will require modifications, and can be achieved in multiple ways. Some common solutions are listed below.
  • Provide R-10 rigid insulation on top of the slab. Flooring material could then be placed atop the rigid insulation; or
  • Install wood floor joists over the slab and add loose R-30 insulation between the slab and floor sheathing or covering; or
  • Provide R-10 insulation on the exterior of the foundation and stem wall of the garage area for a total depth of 24" (or to the top of a footing, whichever is less).

No matter how floor insulation is accomplished, thermal breaks must also be provided around the perimeter of the floor and foundation stem wall, where heated space is adjacent to unheated space 

Note: If raising of the floor occurs, code requirements for stairs, landings, doors, and headroom must still be met, along with underfloor ventilation and access where required.

  • Energy credits: When an addition of heated space is made to an existing house, a certain number of energy credits shall be obtained. There are several methods of obtaining credits, and the chosen method must be indicated on the plans. 

The required number of credits and ways of obtaining credits can be found in the WSEC, R406.2.

STEP 3 - Apply for a building permit

When applying for a permit:

  • A Site Plan shall be provided to show the location of the existing house and garage, along with showing where the required off-street new parking stalls are to be located.
  • Floor Plans with dimensions shall be provided to show how the new space will be used, indicating any new walls, windows, doors, and plumbing fixtures. Be sure to label all adjacent rooms, and show components of fire and life safety along with insulation and energy compliance.
  • Any structural alterations and framing members must be identified on the plans (window and door headers, posts, beams, shear walls, etc.).
  • Any structural calculations that have been done for structural work shall be provided.
  • Building Elevations shall be provided to show any modifications to the exterior of the space, such as new windows, exterior doors, the elimination of the garage door, etc.
  • Other building permit application requirements can be found on the Building Permit Checklist.

Apply for a permit

STEP 4 - Plan Review

Once a permit application is accepted, the typical initial review time for a garage conversion (with no other work to the rest of the house) is 2 weeks (if it qualifies for Fast Track review). Following the initial review period, the permit will be issued if no corrections to the plans are required, or a correction letter will be sent out and must be responded to prior to issuance of the permit.