A finished basement is one of the few ways to add real living space without changing the footprint of the house, and winter suits the work because it all happens indoors. The hard part is the order. Moisture, egress and radon have to be dealt with before framing and drywall cover the foundation walls. This checklist covers what to confirm first.

Moisture: Prove the Foundation Is Dry

Drywall over a damp wall becomes a mold problem. Before planning finishes, look for evidence of water:

  • White, chalky deposits on the concrete walls or slab. This is efflorescence, and it marks where water moved through the concrete and evaporated.
  • Stains, rust on nail heads or bottom plates, or a musty smell in one corner.
  • Cracks in the walls or slab with staining around them.

A simple check: tape a square of clear plastic tightly to the slab and another to a wall, and leave them for a couple of days. Moisture collecting under the plastic means vapor is coming through the concrete. It's a rough test, but it tells you whether you have a question worth putting to a professional.

Look outside too. Downspouts should discharge well away from the foundation, and the soil should slope away from the house. Plenty of basement water problems start at a gutter, and the gutter is the cheapest repair on this list.

Egress: Every Bedroom Needs a Way Out

If the plan includes a bedroom, that room needs an emergency escape and rescue opening. The International Residential Code, which Colorado cities and counties adopt with their own amendments, sets the baseline for these openings:

  • A net clear opening of at least 5.7 square feet, or 5.0 square feet at grade-floor level.
  • A clear opening at least 24 inches high and at least 20 inches wide.
  • A sill no more than 44 inches above the floor.
  • For openings below grade, a window well of at least 9 square feet with at least 36 inches of projection and width, plus a permanent ladder or steps if the well is deeper than 44 inches.

The minimum height and the minimum width together don't add up to 5.7 square feet, so a window that meets both can still be too small. Your building department has the final word on the code version in force where you live.

Cutting a new opening in a foundation wall and digging a window well are exterior jobs, and they go more smoothly before the ground freezes hard. If a bedroom is part of the plan, schedule the egress work first.

Radon: Test Before You Finish

Radon is a radioactive gas that comes from the soil and collects in the lowest levels of a house. The Colorado Department of Public Health and Environment recommends testing every home, and the EPA's action level is 4 picocuries per liter. Short-term test kits are easy to find at hardware stores and through the state's radon program.

Test before construction starts. If the house needs a mitigation system, the pipe usually runs from beneath the slab up through the house, and routing it before the walls go up is far easier than fitting it around finished drywall. If a system already exists, plan the layout so the pipe, the fan and the gauge stay accessible.

Mechanical and Layout Questions

  • Where are the furnace, water heater and electrical panel, and what clearances do they need? Gas appliances need working space and combustion air, so the mechanical room can't be squeezed.
  • Is there a sump pit or a radon suction point that has to stay accessible?
  • Will the new rooms get enough heat? Unfinished basements often have few supply registers, and a finished space may need ductwork changes.
  • Does the electrical panel have room for new circuits?
  • How much headroom is left under ducts and beams? Soffits around ductwork are common, and the height beneath them shapes where rooms can go.

Minimum ceiling heights for habitable basement rooms are set by code, with allowances for beams and ducts. Measure early and confirm the numbers with your building department before the layout is final.

Insulation and Wall Assembly

Foundation walls in a heated basement should be insulated, and the method matters because the wall has to cope with moisture coming from the concrete side. Rigid foam board against the concrete, with the stud wall built inside it, is a common approach because foam doesn't soak up water the way fiberglass batts do. Ask how the wall will be built layer by layer. Be wary of any plan that traps fiberglass between concrete and a plastic sheet, because moisture can get caught in that sandwich.

Permits

Finishing a basement almost always needs a permit, since it adds framing, electrical work and often plumbing. Permitted work is inspected before the walls close, and an unpermitted finished basement can complicate a future sale. Build the permit into the plan from the start.

Planning a lower level this winter? Read how we approach basement finishing