Drilling Holes Through Floor Joists

Keep the hole at least 2 in.

Drilling holes through floor joists. That also means because of the one third rule that that the hole cannot be wider than 3 inches. The diameter of holes shall not be greater than 1 3 the depth of the floor joists. Or the amount specified by the manufacturer of web between the edge of the hole and the flange. Drill large holes toward the center of i beam joists not toward the ends.

Sometimes joists are notched at the end where they bear on a wall or sill. You can drill holes anywhere between the flanges of the i joist. Say you need to drill through a floor joist that is 9 inches tall. Select a hole saw that is the same size or smaller than one third the joist depth measurement.

Holes cannot be closer than 2 to the bottom or top of a joist or to another hole or notch in the joist drilling floor joists. For a 2 10 where actual depth is 9 25 inches the maximum allowable hole diameter would be just over three inches. If the cut outs are too large or in the wrong location the joist can be weakened and unable to support the load it was designed for. From the top and the bottom if it s a dimensional lumber joist.

Drill holes with a diameter of no more than one third the depth of the joist staying 2 in. Cutting notches and drilling holes in joists as part of any new installation work or a re wire a cable trunking or cable tray sometimes has to pass through an element of building construction such as a floor wall or beam necessitating the formation of a notch or opening in the element. The flanges are the thicker ends at the top and bottom of the joist. Where and how to drill joists for electrical cables or plumbing runs depends on what type of floor framing you have.

Leave at least 1 4 in. Away from the top and bottom. If you re drilling a hole in the center of the joist then you can drill up to a maximum of 4 inches in diameter 100mm. Area provided there are no other holes in the joist or notches along its top or bottom.

The hole would need to be within the middle 5 inches of the joist because of the 2 inch rule on the top and bottom. Although notches aren t allowed in the center third of a joist s length you can drill holes anywhere along the length of the floor joist in that 5 1 4 in.