Things You'll Need
General purpose saw blade to fit circular saw
Chalk line (optional)
Straightedge jig or 1-by-4-inch lumber
Weights or fasteners for straightedge jig
Cutting through your floor to access your crawl space is not a simple task. It should be undertaken only after you have exhausted all other possible options for accessing this space. When cutting through your floor for access, locate the opening in a closet where it can't be seen, or in a corner of a room where a rug will cover it.
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Locate the floor joists. Floor joists usually are constructed of 2-by-6-inch boards and spaced 16 or 24 inches apart, from center to center. Find the joists by determining which wall of the room faces the edge of the roof -- the lowest and longest outside line parallel to the ground. The joists are perpendicular to that wall. Your hardwood flooring is attached to the floor joists.
Measure 16 inches out from a wall that is parallel to the floor joists. Tap the floor lightly with a hammer. You will hear a hollow or low thud-like sound when tapping between joists. When you tap over a joist, the sound will rise in pitch. Locate a higher-pitched area and determine its center. Mark this spot with a piece of tape.
Measure 16 inches toward the center of the room from that location. Tap with the hammer to determine if the floor joist is located under that spot, or if the joists are 24 inches apart. Mark the location of the second joist with tape. Continue out from the wall across the room, marking each floor joist. It should now be easy to tell where the joists are, their spacing and if either wall begins directly over a joist and what the offset is, if there is one.
Choose the spot where you want the access hole cut. The access hole must span two joists. It also must be free of any plumbing or electrical wires, unless these are what you want to access.
Measure out the dimensions of your access hole. Mark the dimensions by running tape from the beginning to end of each proposed cut. Draw your cutting lines down the center of the joists.
Set your circular saw depth to 1/4 inch. Cut two floorboards along your cut line. Use a 1-by-4-inch board or straightedge jig to help you cut a straight line with your circular saw. Examine the cut to determine if you are cutting all the way through the flooring to the joist.
Adjust your saw depth to cut through the flooring, but not into the joist. Finish cutting both cut lines. Remove the flooring pieces, keeping them in the order they are removed.
Cut two 1-by-1-inch boards nearly as long as the cutting lines in the previous step. Create the cover for the access hole by fastening these two boards to the underside of the cut hardwood flooring pieces so they fit back into the access hole in their original positions. Fasten the flooring pieces to the boards with nails, screws, glue, or a combination of them. The 1-by-1-inch boards will keep the wood planks together so they move as one piece. Be sure that the 1-by-1-inch boards are not visible as this will spoil the effect of your hardwood floor.
Only do this project in your own single-family home. If you are renting or own a condo, cutting into the floor probably will violate a provision or the lease or association regulations.
A chalk line is a great help in marking straight lines.
The edges of the access hole cover that lie on top of the joists will have a 1/8-inch clearance due to the cutting width of the circular saw blade. You may need to trim one of the other sides so the access hole cover can be easily removed. Don’t trim too much off the end, as a snug fit is desired. Make the cover as seamless as possible so it doesn't detract from the appearance of your hardwood floor.
Cutting deeply into the joist will weaken it. Make sure you only cut through the flooring.
Take care not to cut through an electrical conduit, water pipes or anything besides the wood flooring.