Basement Finishing: How to Finish, Frame, and Insulate a Basement (DIY)
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How to Finish, Frame, and Insulate a
Basement
With special framing and insulating techniques, your
basement can be as comfortable as any other room in
your home. Find out more about insulating basement
walls and framing basement walls here.
Family Handyman
Project step-by-step (21)
Step 1
Submit Building Plans
Make a scale drawing of your plans to submit to your local building
inspections department.
Note: Your plan should include wall dimensions, window and door
sizes, and each room's purpose (e.g., family, bedroom, etc.) along
with any special features like fireplaces. Some rooms may require
large windows, called "egress" windows, for fire safety. Ask your
building inspector if you need them. Also measure the future
finished ceiling height and low-hanging pipes or ducts that'll lower
headroom.
Sketch the details of the exterior wall construction you intend to use as
we show in this article.
Pro tip: If you're uncertain about the best use of space, hire an
architect to help with the design.
If you choose to do your own electrical work, draw up and submit that
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plan as well.
With your plan and permit in hand, clear everything out of the
basement and you're ready to go.
Pro tip: Walk around the basement with caulk and cans of spray
foam and plug every gap you can find between framing and
masonry and around pipes or wires that penetrate the rim joist or
exterior walls. This is your last chance to seal air leaks from the
inside.
Step 2
Resolve Any Dampness Issues
To tell if walls are damp from exterior water or just condensation from humid
interior air, tape a 2-ft. square sheet of plastic to the masonry. If moisture
collects on the front of the plastic, you have condensation. The method we
show for finishing will take care of that problem. If moisture collects on the
backside after a few days, then water is wicking through the foundation wall
from outside. The basement should be treated the same as if it were leaky.
If you have regular seepage or water puddling after storms (even once
every few years), you have to fix it permanently before finishing. Remedies
for damp or wet basements can be as simple as rerouting downspouts,
regrading slopes away from foundation walls, or applying water-resistant
paints to interior surfaces. As a last resort, hire a pro to install perimeter
drains and a sump pump. The bottom line is that it's senseless to spend
time and money finishing a basement if leaks or moisture will ruin your work
or cause mold to grow.
Insulating Basement Walls
Start by gluing 3/4-inch extruded polystyrene foam insulation to fit
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against the rim joists and foundation walls.
Note: Extruded polystyrene foam can be yellow, pink or blue
depending on the manufacturer for insulating basement walls.
Avoid “expanded” foam insulation (the type that has little white
beads pressed together) when insulating basement walls because
it isn’t as durable and has a lower R-value.
Make cuts by snapping chalk lines to mark and then score it with a
utility knife as deep as the blade will penetrate. Then snap the sheet
just like you cut drywall.
Carefully cut around obstructions and fill spaces with small chunks of
foam wherever it’s needed, working for tight fits.
Spread a 1/4-inch bead of adhesive on masonry walls and press the
sheets into place.
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Step 3
Caulk Gaps
Caulk seams and gaps between the framing
Foam along the rim joists with more foam to seal against air infiltration
and leaks.
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Note: You’ll add fiberglass later for a higher R-value. The foam
greatly reduces heat transfer through the masonry and framing,
and it eliminates the need for a plastic moisture barrier later.
Pro tip: Be sure to use adhesive formulated for use with foam
(about $3 per tube) when insulating basement walls. Conventional
construction adhesive won’t work for insulating basement walls.
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Step 4
Cut Top and Bottom Plates
Snap chalk lines 4 inches away from the insulation on the exterior walls.
Cut 2x4 bottom and top plates and lay out stud locations every 16
inches on each plate as you're insulating basement walls.
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Step 5
Anchor the Bottom Plate
Squeeze a 1/4-inch bead of construction adhesive to bottom plates
and position them.
Pre-drill with a hammer drill and anchor them with concrete screws.
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Step 6
Install Blocking
Nail 2x4 blocking about every 3 feet into the first floor joist to support
the top plate.
Toe-screw them to the rim joist through the foam to continue insulating
basement walls.
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Step 7
Install the Top Plate
Plumb from the edge of the bottom plate to the blocking with a straight
2x4 and level.
Snap a chalk line and screw the top plate to the blocking with 3-inch
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screws.
Step 8
Install the Studs
Measure between the plates at each layout mark and cut each stud to
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length.
Toenail the studs into place at the top and bottom with two 8d (2-3/8
inch) nails in one side and a third centered on the other side.
Step 9
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Half-Wall Studs
For framing half walls, make all of the studs the same length and cut
them so the wall is slightly taller than the masonry.
Pro tip: The wall may be uneven because of floor inconsistencies,
but you can always sight along the top plate and then shim it until
it’s flat before installing the finished top cap.
Lay out the stud locations on the plate and nail the studs in place with
16d nails.
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Step 10
Install the Knee Wall
Tip the knee walls up and fasten them to the floor.
Fasten blocks through the foam into the masonry at every third stud
with 3-inch concrete screws.
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Plumb and screw the studs to the blocking for a solid wall.
Pro tip: Be sure to sight along its entire length to make sure it’s
straight.
Step 11
Building soffits
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Most basements have ductwork and plumbing mounted at the ceiling along
an existing wall. Boxing in those pipes and ducts and then drywalling the
assembly is the best way to conceal them. The whole structure is called a
soffit.
Step 12
Install 2x4s
Measure to the floor to find the lowest pipe or duct in the room; that’ll
define how low the soffit must be.
Mark a point 2 inches lower on the wall to allow space for the framing
and drywall.
Nail on a 2×4 nailing strip using the chalk line to position the bottom of
the strip.
Snap another line on the bottom of the joists with a 2-1/2 inch
clearance.
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Step 13
Build the Soffit Front
Rip 1/2-inch plywood strips to the depth of the soffit and screw 2x2s
even with both edges with 1-5/8 inch screws.
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Pro tip: It’s easiest to preassemble the 8-foot-long soffit side
sections and screw them to the bottom of the floor joists. If soffits
end at walls, build the walls first.
Step 14
Fasten Soffit Assembly
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Snap a chalk line on the floor joists 2-1/2 inches away from the nearest
obstruction and parallel to the wall.
Position the assembly along the chalk line and fasten it to the bottom
of the floor joists with 3-inch screws.
Step 15
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Install Lookouts
String a line even with the inside edge of the plywood and use it to
determine exact lookout lengths.
Nail them in place every 16 inches.
Step 16
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Framing partition walls
Partition walls are any walls that aren’t against exterior foundation walls or
walls that support floors above. Lay out partition walls by snapping chalk
lines to mark both sides of the bottom plates.
Also, in a basement, the top and bottom plates are often different lengths.
That's because top plates may project past foundation walls and be longer
or run into soffits and be shorter. When you line up the plates to mark stud
locations, be sure to account for differences.
Step 17
Install Backer Boards
Mark both sides of partition walls with chalk lines, then center and nail
2×6 backer boards in walls that they join.
Note: The chalk lines keep you from building walls on the wrong
side of single lines!
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Step 18
Cut the Plates
Mark door openings on the floor to avoid putting glue under doors.
Frame partition walls as you did the outside walls, installing blocking
between joists wherever it’s needed.
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Add 2×6 backers on walls that meet partitions.
Pro tip: Before you tie the partition walls to exterior stud walls
(non-masonry, without foam), staple 2-foot wide strips of
polyethylene over the 2×6 backers. That way you’ll be able to seal
this type of outside wall with a continuous moisture barrier in
cooler climate zones.
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Step 19
Assemble the Wall
Frame the door openings 2-1/2 inches higher and 2-1/2 inches wider
than the door you're installing.
Note: This “rough opening” allows adequate space for the door
plus its frame.
Use a regular stud plus a “trimmer” on each side of the door.
Pro tip: If you have low headroom, you may need to cut your
doors down or special-order shorter ones. Remember to allow
overhead space for the door trim. Trim that's either missing or
ripped too narrow over doors with inadequate clearance will really
detract from the appearance of the room.
Partially cut through the underside of the bottom plate at the edges of
the door rough opening to make removal easier later on.
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Step 20
Frame Around Obstructions
Nearly every basement has something that will project past finished
surfaces. That can include beams, posts, drain lines, water piping or
surface mounted wires. It’s a simple matter to frame or fur out around
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projections and then drywall and finish them to blend in with surrounding
surfaces. You’ll have to maintain access to other things like electrical
junction boxes and plumbing shutoffs and clean-outs. If you need future
access to anything, just frame around it and cut out the opening when you
drywall.
Frame Around Valves
Frame around ceiling valves with 2x2s.
Pro tip: If you need future access to anything, just frame around it
and cut out the opening when you drywall. Then, after taping and
painting, screw a “return air” grate over the opening to conceal it
but still have access. Return air grates are available in various
sizes for about $5 at home centers. Check the sizes of available
grates and frame the accesses slightly smaller.
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Step 21
Frame Around Plumbing Pipes
Frame around protruding plumbing with 2x6s nailed to adjoining studs.
Frame clean-outs for an access panel.
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Install Furring Boards
Use either 2x4s or 2x2s running perpendicular to the joists to add 1-1/2
inches of dead space so you can drywall over the top of everything.
Be sure to run all the wiring and other things you might want before
hanging the drywall.
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Note: Sometimes furring down part of or the entire ceiling is the
best way to bury surface-mounted pipes or wires.
Pro tip: If you have a lot of deep projections from the ceiling or
you need a lot of access, consider installing a suspended ceiling
rather than drywalling. The downside is that you’ll lose at least a
few additional inches of ceiling height.
Finish round steel columns by framing around them with 2x4s. You can
then face the framing with drywall or decorative wood as shown in the
opening photo.
Check out these wall framing tips for new construction.
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