Design and Remodel of Basement and Crawl Spaces

By Alan Ness, Principal, Ten Directions Design

Your basement is a potential resource that can become a valuable living space as part of your house. However, there are a variety of issues that you need to research, analyze and respond to.

1) Head Height. 

You may need to create a legal and/or comfortable head height in your basement. Your two options are to raise up your house, or digging down.

Raising your house is a large investment that requires a significant reason: failed water exclusion or failed structural system. You might also be involved in raising your house to redo of structural system for a future 2nd story addition, or a desire to raise your house for views.

Digging down is also a major investment because cannot undercut your foundation footings, and you must structurally stabilize the bottom of your basement walls.

2) Water proofing. 

A critical issue is excluding water from the interior of your basement. Passive drainage can be created to the interior or exterior of your basement. Mechanical systems include the sump pump.

3) Design Issues. 

As with any remodel, there are many design issues to be resolved. Here are some of the important design issues:

  1. Stairs: legal risers and treads. New definitions: Riser 7-3/4" max. and Tread 10" min. Stair headroom at nosing: 6'-8" minimum.
  2. Headroom: includes beams, ducts. Min. headroom 6'-4" for everything, if built before 1979.
  3. Egress: window wells: max sill 3'-8". Net clear 5.7 SF. Min ht 24" and min width 20".
  4. Lighting: natural and artificial. Window area to be minimum 8% of floor area.
  5. Flooring: on concrete slab there can be mold growth under flooring.
  6. Plumbing: don't be afraid... to move fixtures.

4) Attached Mother-in-law (ADU) unit. 

Here are some of the City of Seattle permit issues:

  1. Entrance - not on front of house (with exceptions)
  2. Parking - two off-street parking spaces.
  3. Headroom - again, pre 1979: 6'-8" or 6'-4" w/hard wired smoke detector.
  4. Size - max 1000 SF, except pre 1999. Must be all on one level.
  5. Owner - must be living in either unit.

These requirements can vary with different localities.

5) Earthquake proofing. 

The Seattle area is in a high-risk earthquake zone. Here are some of the critical issues. Consulting with a structural engineer or earthquake-proofing company is recommended:

  1. Connecting foundation to sill plate
  2. Connecting top of cripple wall or concrete foundation to floor above
  3. Connecting center line posts (top and bottom) and beam
  4. Shear resistance: covering cripple walls with plywood
  5. Option: Creating new walls inside of existing concrete walls.

6) Design Process. 

The Designer will assist you through the following phases of work:

  1. Preliminary Phase:
    - Evaluate your needs and goals 
    - Prepare schematic designs and options, for your approval
    - Get preliminary cost estimate. Scope - Cost - Quality "triangle".
  2. Construction Document Phase:
    -Prepare drawings and specifications. Specifications are the biggest opportunity to make your project "green". Think recycled materials/low-impact materials. Also consider: exceeding standard insulation; low-energy lighting fixtures and appliances.
  3. Permit Process:
    -Project Number - to begin. Need site plan of some sort to apply.
    -Pre-Application Site Visit Fee = $132.75 (subject to change), depending on ground disturbance.
    -Side Sewer permit. Newly transferred from Utilities to DPD.
  4. ECA (Env. Critical Area) - additional requirements and site meetings:
    1. Permit requirements: survey plus/geotech engineer report/full review plus geo review.
    2. Exemptions: is 750 SF, Proposed 300 SF.
    3. Seasonal timing: Construction is only in dry season: April 1 through October 31.
    4. Erosion control. Additional sheet from DPD with your site plan attached.