Installing a basement floor can be extremely easy especially if you are planing to install carpet as subfloors are not required for carpet unless the basement suffers from excessive moisture. For all the other floor covering types it is strongly recommended to install a basement subfloor.

Main Steps to Building a Basement Floor

  • prepare the concrete surface
  • install a moisture barrier
  • build the subfloor support
  • install the subfloor top
  • install the desired floor covering

Planning Tips:

  • if you are planing to install carpet there is no need for a subfloor unless the basement has moisture issues
  • if excessive moisture is present in the basement, the issue must be solved before installing any floor covering type
  • assess the need for moisture mitigation with the clear plastic sheet method
  • for additional moisture and radon protection it is a good ideea to paint the basement cement floor
  • if radon has been detected in your home, take all the radon mitigation actions before building the basement subfloor

Required Tools and Materials

Detailed Steps to Building a Basement Subfloor

  • remove loose cement using a chisel and a putty knife
  • roll out 6 mm polyethylene strips – overlap them 6″ and expend them 30″ on the walls
  • lay 2×4″ sleepers along the walls at 1/2″ from walls
  • cut and lay 2×4″ sleepers at 16″ spacing from each other – leave 1/4″ gap at each end
  • fasten the sleepers using masonery screws at 16″ intervals
  • use a piece of chalk to mark a line for the first row of plywood
  • run a 1/4″ bead of adhesive along the required sleepers for the first plywood board
  • lay the first plywood sheet at 1/4″ form the walland the tongue edge flush with the marked line
  • fasten the sheet with 1 1/2″ wallboard screws or shank nails every 6″ along the edge and every 8″ in between the screw rows
  • install the reminder of the plywood sheets
  • install the desired floor covering by following here the specific steps for carpet, laminate, ceramic floor

Subfloor Installation Tips:

  • make sure your nails or screws used for the sleepers are rated for concrete use
  • if concrete floor is uneven, use tapered cedar shims to compensate
  • make sure the shims get fastened to the concrete
  • to increase strength and prevent sqeaks, stagger the plywood sheets of each row in respect to the previous row
  • do not fasten the plywood sheets along the tongue until the next row of plywood is placed
  • if there is no tongue and groove at the ends of the plywood sheets, make sure you leave 1/8″ expansion gap
  • leave a 1/8″ expansion gap around all edges of the subfloor

Building Interior Basement Walls

  • set the interior stud wall on top of your new subfloor – build and your 2X4 frame on top of the subfloor
  • screw the plates of the frame into the cement through the underlayment – use one self-tapping concrete screw every 6 feet
  • if the frame is built out of metal studs, secure it every 2 feet
  • screw the plates of the frame into the ceiling joists – use one wood screw every 4 joists

Alternate Basement Subfloors

  • a basement subfloor is that it can raise the floor by at least 2”
  • pre-manufactured alternate subfloors raise the floor height by 1” only
  • come as 24” x 24” interlocking tiles typically made from plywood attached to a dimpled rubber or plastic layer
  • blocks moisture while allows air to pass underneath
  • the interlocking tiles allow for an easy installation

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