The Seattle Building Code generally requires a 7′ ceiling height in all occupied rooms. Our basement is 6’9.5″ from concrete slab to bottom of joists.

However, Director’s Rule 23-2008 provides:

B. Buildings in existence prior to October 17, 1979 may be remodeled to create new dwelling units, or existing dwelling units within such buildings may be enlarged, with minimum ceiling heights of 6 feet 4 inches, provided:

1. The use (dwelling unit) could have been lawfully established either by construction or by conversion under the Land Use Code in effect at the time it can be proved that the use first existed. This means that the Land Use Code development standards in effect at the time, such as those requiring setbacks from property lines, must also be met if the use is to be established now. Further, if discretionary approval, such as a conditional use permit or variance, would have been required for establishment of the use at the time, written proof of such approval must be submitted.

2. The use shall meet minimum standards for habitable dwellings in the Seattle Housing and Building Maintenance Code in effect at the time of the application, including standards for minimum size requirements and egress windows where applicable.

3. Except as specified herein, the use shall meet minimum applicable Building Code standards as set forth in Chapter 34 of the SBC.

4. New basement and sleeping rooms shall have a window or door for emergency escape or rescue consistent with the requirements of the Seattle Residential Code or the Seattle Building Code.

5. Projections below the ceiling, including but not limited to beams, pipes, and ducts, shall not reduce the headroom to less than 6 feet 4 inches.

6. In areas with sloping ceilings, the minimum ceiling height in at least 50% of the space must be 6 feet 4 inches (not the 7 feet minimum cited in the Seattle Residential Code), and no portion shall be less than 5 feet in height.

7. For additions or alterations that change the existing building envelope:

a. When new rooms or areas are created by raising a portion of the roof, this Rule may be applied, provided that over the life of the structure, the aggregate area of such rooms or area does not exceed 50% of the area of the new rooms or area.

b. When new rooms or areas are created by excavating below grade, this Rule may be applied, provided that:

• The 6 foot 4 inch minimum ceiling height cannot be increased without modifications to the existing footings; and

• Any modifications to the existing footings are proposed for purposes other than to accommodate the 6 foot 4 inch minimum ceiling height; and

• Any modifications do not reduce the structural integrity of the foundation wall.

8. Where the existing building envelope is not changed, new rooms or areas meeting the requirements of this Rule may be created without the restrictions of 7a or 7b above.

9. The exit door from a dwelling unit shall be no less than 6 feet 2 inches in height.

10. This Rule does not apply to spaces that are not ordinarily occupied, such as storage areas and mechanical rooms, since ceiling height in these areas is not regulated by the Building Code.

11. Requirements for additions in other codes, including but not limited to the Seattle Energy Code and the Seattle Mechanical Code, shall be met.

[emphasis added]

So, assuming 5/8″ drywall on the ceilings and 7/8″ flooring, that leaves a finished ceiling height of 6’6″. As long as no ducts, soffits, etc., hang down more than two inches, we’re in luck — we can remodel our basement into “habitable” space. Now just to figure out how to reconfigure the walls and mechanicals to squeeze a reasonable bedroom and bathroom in…