Converting an Attic to Living Space

Click here to open a PDF version of this tip sheet

Things to consider when converting an attic to living space:

• All work must comply with the most recently adopted City construction codes. This tipsheet is specific to one and two family dwellings under the International Residential Code (IRC), Washington State Energy Code (WSEC), City Existing Building Code Appendix J, and other codes as applicable.
• Ceiling height minimum is 6’8” from finished floor to ceiling. A habitable room must be at least 70 square feet with a minimum horizontal dimension of 7 feet. No part of the room less than 5 feet in height may be considered in the calculation.
• Inadequate ceiling height: If the attic does not meet the required ceiling height and raising the roof or reframing dormers to accommodate additional ceiling height may be an option, but will require more plans showing compliance with land use and building code requirements.
• Ceiling joists directly below the attic are often not designed to support furniture and living space above. The plans must show the size, the spacing, and the length of these members between supports meeting current code.
• Internal stairs are required to connect the lower floor(s) to the new habitable space. If there are existing stairs, the risers cannot exceed 8”and the treads cannot be less than 9”. The tread depth and the rise heights must be consistent to within a 3/8” tolerance. The minimum headroom must be 6’ 8” measured from the nose of each tread. The width of the stairway may not be less than 32”. The stair must have at least one handrail. Light switches and landings are required at the top and bottom of the stairs. New stairs must meet tread maximum rise of 7.75” and minimum run of 10” and other standards not identified here.
• Smoke Alarms – There must be at least one smoke alarm in the basement that is interconnected with the main floor alarm. If there are bedrooms, then provide an alarm in each bedroom and one outside the bedroom(s) in a common location.

• Carbon Monoxide Alarms – There must be at least one carbon monoxide alarm that is interconnected with the main floor alarm. It must be in the hallway/common area outside the bedroom(s), and in bedrooms with gas fixtures.
• Egress – Any bedroom and habitable attic must have an emergency egress opening. If you are creating a bedroom, the egress window or door must be within the bedroom itself. Egress windows shall provide 5.7 square feet of openable area, with a minimum openable width of 20” and a minimum openable height to 24”.
• Window Fall Protection is required where the bottom of the clear opening of an operable window opening is located less than 24 inches above the finished floor and greater than 72 inches above the finished grade or other surface below on the exterior of the building, the operable window shall comply with one of the following:
1. Operable window openings will not allow a 4- inch-diameter sphere to pass through where the openings are in their largest opened position.
2. Operable windows are provided with window opening control devices or fall prevention devices that comply with ASTM F2090.
Fall protection shall not limit emergency escape and rescue net clear opening area after operation to release the fall prevention device.

• Energy Code requires newly heated spaced meeting fuel normalization and additional energy credit requirements that must be accurately reflect in plans, details, and any additional forms. Windows and doors typically must meet 0.30 U-value or less.
• Heating source for the habitable areas and all bedrooms must be clearly identified on the plans. Heating ducts must not project below 6’4” and not be located at a walking area or in-line with access hallways
• Insulation – New habitable area must be insulated per Washington State Energy Code. Typically this will consist of R-60 in attics and single joisted vaulted ceiling portions to R-38. Additionally, a 1” airspace must be provided above the insulation, ventilated at the top and bottom. Often times the existing rafters must be furred down to accommodate the insulation and ventilation, a process which often reduces ceiling height. Knee walls must be R20 with R5 continuous rigid insulation or meet WSEC alternative UA calculations.
• Exhaust Fans must be identified on plans for bathrooms and toilet rooms as applicable. Include locations and proper exhaust rates per IRC M1503 and associated Washington State Amendments.
• Plumbing fixtures layout must be shown in section view with sloped ceilings to verify proper ceiling heights at fixture clearance areas per IRC R307.1 and associated figures. Upper floor plumbing often results in the need to install drop ceilings in the level below to avoid excessive cutting and notching of existing attic floor joists. This must be detailed on the plans if proposed and will result in a field revision needing to change during construction.
• If proposing an Accessory Dwelling Unit (ADU) then additional plan and code requirements will apply and must be addressed with the permit submittal. Contact Planning and Development Services for more information about this scenario.

• Plans must show in detail that the work will comply with code. Plans must be indelible, reproducible, to scale, with two lines for walls, and 3 lines for windows, and doors locations clearly identified. Common plans include:
• Scope of work document describing all the proposed work with cost of materials and labor.
• Floor plans with plumbing and mechanical fixture locations and clearances, stairs and access points tied into the downstairs heated area, emergency escape, smoke and carbon monoxide alarms, heating, clearly identified heated and unheated areas.
• Details for existing internal connection and stairs showing ceiling height, rise and run, and handrail call-outs.
• Section view at plumbing fixtures to clearly show ceiling height compliance when at a sloped ceiling.
• Section view of attic area with furred out ceilings, ceiling height, insulation details, window opening sizing, floor joist framing size, spacing with spans and support.
• Site plan showing property line distances from structure with adequate emergency escape pathways to public way.
• Framing modifications require additional before and after top view framing details for roof, floor and any other modifications. Engineered design is required if not meeting prescriptive requirements of the IRC.
• Completed WSEC compliance information.