My basement is just bare foundation walls and concrete floor slab.
How do I turn it into a room with walls, ceiling, and flooring?
Here are the basic steps for turning a basement into a comfortable room.
Most importantly, ensure that the basement will be as dry as possible by
taking the following steps:
- Slope the ground around the house away from the foundation, so water
- Make sure downspouts carry water well away from the house.
- If still having basement water problems, dig a ditch around the house
down to the footing and install drainpipes, sloped to carry water away.
- Coat the foundation exterior with waterproofing material before filling
in the ditch again. For concrete that has not been treated or waterproofed before, one of
the best treatments is Xypex (www.xypex.com).
Applied inside or outside, it penetrates the concrete 12 inches or more as it
expands and seals pores.
Inside, as extra precaution against flooding, install a drainage ditch
next to the foundation wall. Direct the ditch to a sump and sump pump at the low end of the
- Some homeowners attach furring strips (1-by-3 lengths of wood) to the
concrete foundation walls and then attach drywall to that. That's the hard way. The easier way is
to build a 2-by-4 stud wall on the basement floor and then raise it into place.
- Use pressure-treated wood for the sole (bottom) plate. Build the wall
with just a top plate, not adding a cap (double top) plate at this time. That way, when you raise
the wall, it will clear the ceiling joists. After the wall is up, install the cap plate.
Carefully measure the stud lengths and plate thicknesses in advance so all will fit exactly.
- Space the wall out 3 or 4 inches from the foundation wall. Once the wall
is up, slip the cap plate in place between the top plate and the bottom of a floor joist. It
should fit just snugly enough to hold the wall in place. Plumb and align the wall at this time.
- To anchor the wall at the top, drive decking screws up through the top
plate and the cap plate into a ceiling joist.
- To anchor the sole plate to the floor, buy or rent a Hilti powder-actuated
fastener to shoot hardened nails through the plate into the concrete slab. You can also glue the
sole plate to the floor.
- While the studs and ceiling joists are exposed, drill holes for all
wiring, pull the wire through, and connect all outlets and switches.
- Do the same in the floor joists and install all lighting boxes.
- Box in and drywall any exposed pipe, ducts, and other obstacles that you
cannot move. Alternatively, leave all ducts and piping exposed and paint them bright colors, as
if part of the basement decor.
- You must meet minimum ceiling height requirements. Ask your local building
inspector what they are. If a pipe or girder is too low, you may have to build a wall around it.
Turn the space into a closet.
- Install drywall on the ceiling.
- If you want to minimize noise coming through the floor from above or
below, install two layers of drywall. After the first layer is up, run aluminum resilient channel
strips (available at drywall outlets) perpendicular to the joists. Then hang a second layer of
drywall from the channel, with screws going only into the channel, not the joists. That way,
sound won't travel through the screw to the floor above. The 3/4-inch dead air space between the
two layers will significantly reduce sound transmission.
- Place batt insulation in the stud walls, with the vapor retarder
facing the warm side of the room.
- If your basement is going to be heated, you don't need
insulation between the floor joists; let the warm basement air help heat the floor above.
- Do not cover the exposed foundation wall with a plastic vapor barrier
thinking this will stop moisture in the concrete from moving into the room. The moisture will
only condense on the plastic and run onto the floor. Similarly, do not staple plastic over the
stud wall. Moisture vapor has to pass through the wall.
- If your basement is too humid, use a dehumidifier to remove water vapor.
Some moisture will inevitably either collect on the concrete floor or work its way through the
floor from the ground underneath. To prevent moisture from subsequently working its way into your
finished floor, cover the slab with 6-mils. plastic sheeting and tape down all seams.
Over the plastic, lay sleepers, which are 1-by-4s or 2-by-4s that are spaced apart 16 inches on
center (from center of one board to center of next). Instead of nailing them down, cut them to
fit snugly between the walls. Place spacers every 3 or 4 feet between the sleepers to keep them
aligned. Over the sleepers, lay down 5/8-inch plywood subfloor. Use drywall screws to attach
plywood to sleepers.
- Ceramic tile: Tile flooring can be laid directly on a slab, if the surface
is smooth and dry.
- Vinyl tile: You can also lay this directly on the concrete, but it will be
a hard and possibly cold floor. Any moisture will pop it loose. It is preferable to lay it on a
- Carpeting: This too can be glued directly to a slab, but putting it on a
subfloor is better.
- Laminated wood: It can be "floated" on the concrete floor by first putting
down the plastic sheeting, then laying the laminate so it ends up wedged in place between the
sole plates of the surrounding stud wall.
- Hardwood floor: This type of flooring must be placed on plywood subfloor
as described above because it is most susceptible to expansion and contraction from moisture and
I want to build some bedrooms in my basement. Are windows required?
Absolutely. If there is a fire, people have to get out quickly. The code requires that at a
minimum the bottom of the window be no more than 44 inches from the floor and that the actual opening be a
minimum of 20 inches wide and 24 inches high. Larger is better, not only to make escape easier but also to
allow firefighters packing tools and breathing equipment to enter the area quickly.
The crawlspace under my house smells like mold, and the ground is wet for much of the year. How can
I fix this?
First, you need good cross ventilation under the house so air will circulate freely. Stagnant air is
holding moisture, creating condensation, mold, and potentially serious wood rot problems. Check that
all vents are unobstructed. Repair any torn vent screens so animals don't move into the crawl space.
If you don't have sufficient vents, you should add more.
Second, cover the ground with black plastic sheeting. This will trap and hold the ground moisture
under it instead of allowing it to rise to the floor joists. Tape or weight all overlapped joints
down, including along the foundation, so no gaps exist.
I have standing water in my crawl space. How can I get rid of it?
The best solution is to prevent water from getting under the house in the first place. That's because
moisture causes problems with wood, and water may excessively soften the ground around the
foundation. To keep water out, dig ditches around the high sides of the house down to the footings.
Install gravel and drain lines. Slope the lines about 2 inches per 10 feet to carry water away from
the house. Direct the water to a natural drainage, to the street, or to a French drain in the yard.
Before you backfill, place waterproof membranes against the foundation wall. Of course, make sure
that water from downspouts is directed well away from the house at all times.
A sump pump is another answer. The best choice is a completely submersible pump with a float arm that
activates the pump as water rises to a certain height in the sump. But buy the sump pump first,
available at home supply centers. The size of the sump, which is the hole that collects the water,
will be determined by the size and type of sump pump you have.
Dig the sump at the low end of the crawl space (or basement), where most of the water collects. One
easy way to do this is to buy a plastic bucket large enough to readily hold the pump and not block
the arm movement, which must float free. Drill holes all around the bucket's sides and bottom, and
set it on some pea gravel in an appropriately sized hole. Backfill around the bucket with pea gravel
also. If necessary, do some ditching in the crawl space to direct water to the sump.
Since the pump needs electrical power, an outlet protected by a ground-fault circuit interrupter is
needed nearby. Finally, attach PVC piping to the pump to carry the water out of the crawl space to
the storm drains, a natural drainage away from the house, or a French drain in the yard.
How can I waterproof my basement walls?
In new house construction, be sure there are drains installed at footing level, sloped between 1
and 2 inches per 10 feet, to direct water away from the house. As you backfill the trench, apply
waterproof membranes to the foundation wall.
In an existing house, you can still dig drainage ditches and install waterproofing membranes or
chemicals as above. To waterproof from the inside, apply a coating of Xypex
which will penetrate up to 12 inches of
previously untreated concrete. If other waterproofing chemicals have been previously applied, it
will be less effective. Once Xypex penetrates, it expands and seals the concrete pores. It was
designed originally to work from the inside out on foundation walls, but works equally well from the
While chemicals will help block water movement through concrete, they do not stop the hydrostatic
pressure of groundwater, which is constantly pushing against the foundation wall. Installing
perimeter drain lines relieves that pressure.
I have concrete blocks for my basement wall and I don't want to
bother putting drywall over them. What else can I do?
First, seal the block to keep out moisture, then consider quick coverings such as paint, drywall
plaster, stucco, or Z-brick.
There's a post in the middle of my basement that supports the floor joists above. Can I get rid of the post somehow?
Such posts usually support a beam that runs beneath the midpoint of the joist span to prevent
sagging. The post can be removed only if a new and stronger beam is installed. The new beam must be
designed to carry the weight of the floor above over a greater span. To determine the beam's required
size and span limit, you should ask a structural engineer to calculate the load requirements. Wood
glue-lams (laminated beams) are widely used for such purposes but are deep, often interfering with
headroom. An alternative is a steel I-beam, which can then be boxed in to hide it.
Water fills up in my basement window wells and then runs inside. Help!
You need drains in the wells. Either the soil won't drain or the groundwater level is so high that
there is no place for water to flow. In either case, dig a drainage ditch underneath the window well
and install drainpipes that are sloped to carry the water away from the house. Clean out the well at
least 6 inches below the window level and backfill with small gravel to within 3 inches of the window
ledge. Caulk any cracks or openings around the window. Make sure downspouts carry water several feet
away from the house.
What can I do about all the humidity in my basement?
First, install a dehumidifier. Second, consider a thermostatically controlled fan to blow moist air
out. But there are other problems to look for at the same time. One homeowner wrote Message Boards
that he did not have a water leakage problem, just a major humidity problem. In looking for the
problem, he removed some sheetrock near the ceiling/wall junction in the basement and discovered
there were no blocking, no caulking, and no insulation at the rim joist area. He could feel a draft
of moist air rising through the concrete blocks and entering the house, pushing humidity up.
Poor attic insulation made the situation even worse. When the central heat system was on, the warm
air rose into the attic. This airflow in turn drew air from the rest of the house, including moist
air from the uninsulated area by the basement rim joist. Air rising into the attic worked like a
vacuum pump to suck air from everywhere, including the outside. He corrected the problem by updating
the attic insulation and caulking and insulating all cracks around the rim joist and basement walls.
I want to put down some flooring in my basement, but the concrete
surface is rough and not too level.
You can purchase self-leveling mortar at home supply centers. The mortar is mixed with water and
then spread with a squeegee-like tool that has adjustable nubs on one edge to smooth and level the
mortar. Spread the mortar over the floor, work it back and forth as it levels itself, and then let
Another way is to lay down 1-by-4 or 2-by-4 sleepers on the slab, then put down a plywood subfloor
on the sleepers.
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