Every now and then, clients ask us if it’s okay to build a deck over a septic tank. The short answer is a “yes.” But we don’t recommend it. If you do decide to add a deck over the leach field, then follow our advice as outlined below.
Depending on where you live, zoning ordinances may require at least a 5-foot setback from an underground septic system. You must also be sure not to apply deck loads and not install frost footings directly over the septic tank. This could damage or interfere with the waste lines. Every now and then, our septic inspections reveal damage due to homeowners’ attempts to construct a deck or large gazebo.
Another problem is that septic systems and decks often require different soil conditions. Decks require more compact soils to prevent the frost footing from sinking. Compacted soil conditions, however, are less permeable, thus interfering with a leach field’s ability to remove effluent.
We will not be able to install, inspect, repair, or pump a septic tank if a solid deck is directly above the drain field. This is why decks need an access hatch directly over the septic opening. Be sure this is something the contractor can add. Without it, a septic inspector would have to remove some of the deck floorboards to reach the septic opening.
Building a deck over a drain field isn’t absolutely out of the question. However, we don’t think it’s the best idea. If you still decide to proceed, give Woodinville Septic Service a call. We’re not deck builders, but we can determine whether it’s okay to build a deck over a septic system depending on the location and condition of the septic and soil.
Edited by Justin Vorhees
Serving Woodinville, Redmond, Kirkland, Bothell, Mountlake Terrace, Bellevue, Sammamish, Duvall, Issaquah, Snoqualmie and more