insulate and pour concrete crawl space floor

[msimerson]

info

• dirt floor covered with black plastic (moisture & radon control)
  • seams not taped
• there are two dirt levels (~30" variance)
• partially insulated duct work
• no insulation on ceiling (effectively "conditioned" space)
• concrete pad in center supporting chimney (see also has a brick chimney #19)
• unvented
• mechanical equipment is already located here (necessitating that it remain conditioned)
• plumbing is located here, mandating that it be kept warm.
• 23' x 26'

materials

• 6 yards of pea gravel
  • sky nursery: $47/yard @ 10 yards
  • pacific topsoil: $44/yard @ 10, $51.75 @ 6 (total w/tax: $340)
• 20 sheets of 2" XPS foam board insulation ($32 ea)
• 74 feet of perforated drain pipe
• 7 sheets of 3/4 plywood to build concrete forms ($23/ea)
• 6-mil polyethylene

TODO

• clear out the space (gas furnace is 80% efficient #3 gas furnace, racks, benches, concrete blocks)
• remove furnace ductwork (anticipating subsequent ductless heat pumps)
• dig out 9" of dirt all around ($400)
  • dig out 4" around chimney pad (July 4th) $200
  • dig out 6" all around (July 8th) $175
• remove the chimney (has a brick chimney #19)
• remove chimney foundation (July 8th) $175
• dig drainage channel along footings and future interior walls
• install drain pipes along footings, connected to existing drain & sump
  • filter fabric, pea gravel, drain pipe, more stone, filter fabric (a drain pipe "burrito")
• level and grade the dirt (two heights)
  • sloping (1/4" per foot) toward the drain
• install sub-slab layers
  • install drainage pad and capillary break (3-4" pea gravel) (Jul 13)
    • vented to exterior
  • insulation board on grade (Jul 18)
  • insulation board around perimeter wall
  • air/vapor/moisture barrier (polyethylene) (Jul 27)
• lay rebar (Jul 29-30)
• build forms (Aug ~10)
• pour concrete slab (Aug 16)

thoughts

• Mold, mildew, and dust mites don't colonize dry areas
• Warm dry basements:
  • attract fewer pests and insects.
  • are great for storage
• Insulating the floor above the space is a bad idea.
• Heating this space will provide a warm floor above it.
• the walls need at least R-15 (Marine Zone 4)

references

• greenbuildingadvisor: building unvented crawl space
• building science: new light in crawl spaces
• gba: fixing wet basements