Basement finishing

What is the average cost to finish a basement?

HomeGuide puts the national average at $30 to $50 per square foot. For a 500 to 1,500 square foot basement that comes to $15,000 to $75,000.

Walls and rooms raise the price. HomeGuide prices a 1,000 square foot open plan at $30,000 to $40,000. The same space split into three rooms runs $40,000 to $50,000.

Local prices can sit above the national figures. In metro Atlanta, a typical full finish runs $45,000 to $80,000 according to one local design-build firm.

What is the proper way to finish a basement?

The proper way to finish a basement is to settle water, air quality and code limits before you design a single room. Skipping these checks is what forces new walls to come back down.

• Watch the basement through a season of heavy rain and fix gutters, grading or leaks.
• Run a radon test. The EPA says to fix a home that tests at 4 pCi/L or higher.
• Measure ceiling height under ducts and beams before you draw rooms.
• Place any bedroom on an outside wall where an egress window can go.
• Use a treated bottom plate where wood framing meets concrete.
• Keep access panels at shutoff valves, cleanouts and the sump.

What ceiling height does a finished basement need?

Under the International Residential Code, basement living space needs a ceiling height of at least 7 feet. Beams, ducts and pipes may drop to 6 feet 4 inches above the finished floor. Bathrooms and laundry rooms need 6 feet 8 inches.

Each city adopts its own edition of the code. Your contractor confirms the local number during the estimate.

A low basement can often still pass. Ducts can move into soffits along the walls to clear the middle of the room.

Can a finished basement have a legal bedroom?

A basement bedroom is legal when it has an emergency escape opening and the other sleeping room safety items. The code sets the minimum size of that opening.

HomeGuide puts an installed egress window at $2,000 to $5,000. Smoke alarms go inside each sleeping room. Carbon monoxide alarms go outside the sleeping area.

• Net clear opening of at least 5.7 square feet
• Opening at least 24 inches high and 20 inches wide
• Bottom of the opening no more than 44 inches above the floor
• A ladder or steps in any window well deeper than 44 inches

What are the common problems with finished basements?

The most common problems with finished basements trace back to moisture. Damp air feeds mold behind drywall and under carpet long before anyone sees it.

The EPA advises keeping indoor humidity below 60 percent. A dehumidifier with a drain line to the sump or a floor drain keeps the level in check without emptying buckets.

• Carpet pad laid straight on a slab that wicks moisture
• Paper-faced drywall touching the concrete floor
• Boxed-in valves that a plumber cannot reach
• Rooms with no heat or return air that stay cold
• One overhead light per room and too few outlets

When should you not finish a basement?

You should not finish a basement while water still gets in or the structure is moving. Wait and fix the cause first if any of these apply.

• Water comes through the walls or floor after heavy rain
• A radon test reads at or above 4 pCi/L and no mitigation is planned
• Foundation cracks keep widening or a wall bows inward
• The ceiling sits below code height and lowering the floor is out of budget

Does a finished basement increase property tax?

A finished basement can increase your property tax because the assessor may add the new living space to the home's value. The change can show up at the next assessment after the permit closes.

How much it rises depends on your county's rules and tax rate. Call the county assessor's office and ask how they treat finished basements.

Skipping the permit to dodge the tax is a poor trade. Unpermitted rooms can cause trouble with insurance claims and slow down a sale.