A full basement is the biggest hole most homes ever need. We dig basements across the Treasure Valley, plan around groundwater and rock before the first scoop, and come back to backfill once the walls are ready.
Basement Excavation in Boise and the Treasure Valley
Drive through a new subdivision in Meridian or Kuna and you won't see many basements going in. Drive up into the Boise foothills, or through older parts of Boise, and you'll see plenty. Where a basement makes sense here has a lot to do with what's under the ground.
We dig basements in Boise, Eagle, Kuna, Meridian, Star and Middleton. If you're still deciding between a basement, a crawlspace or a slab, we're glad to talk it through. Our foundations page compares the three.
Why Many Newer Valley Homes Skip the Basement
A lot of newer homes in the valley are built on crawlspaces instead of basements. That's mostly a ground and budget decision, not a style one. A few reasons come up again and again when owners and builders weigh it.
- Groundwater. Near the river and in areas with heavy irrigation, water can sit only a few feet down in summer.
- Caliche and rock. A cemented hardpan layer or basalt a few feet down makes a deep dig slow and expensive.
- Cost. A basement means more digging, taller walls, waterproofing, drainage and more backfill.
None of that rules a basement out. It just means it pays to check the ground first. A test hole on the lot, or a soils report if you have one, tells you more than any guess from the street. We can dig a test hole to basement depth so you can see the soil layers, and whether water seeps in, before you commit to a plan.
Groundwater Near the River and in Irrigation Season
This is the big one. In Eagle, Garden City and other areas near the Boise River, the water table can be shallow, and it often rises once irrigation season starts in April. A hole that's dry in March can have standing water by June. Canals, laterals and flood-irrigated fields nearby add to it.
Before committing to a basement in those areas, it's worth digging a test hole or getting a soils report that shows the seasonal high water level. If the dig does hit water, the hole may need to be pumped while footings go in, and the engineer may call for a more serious drain system. Timing the dig for early spring or late fall can help too.
Caliche, Basalt and Cobble at Basement Depth
A crawlspace dig might stay above the hard layers. A basement goes through them, so whatever sits several feet down matters a lot more. These are the layers we run into most around the valley, and each one changes the dig in its own way.
- Caliche under much of Meridian, Nampa and Kuna is cemented hard enough that cutting through it at basement depth takes real time, and that shows up in the price.
- Basalt close to the surface in parts of Southeast Boise and Kuna can stop a basement plan or turn it into a partial basement.
- River cobble near the river digs easily but the walls ravel, so they need to be laid back.
- Decomposed granite in the foothills digs well and drains well, which is one reason walkout basements are common up there.
Decisions to Make Before We Dig
A few choices on a basement change the size and shape of the hole. Changing them after the dig starts usually means more digging or more fill, so it helps to have them settled with your builder or designer first.
- Wall height. Taller walls mean a deeper hole, more sloping at the sides and more backfill later.
- Egress and window well locations. Each one needs extra room dug in the right spot.
- Where the footing drain goes. Out to daylight on a sloped lot, or to a sump pit, which changes what we dig and where.
- Walkout or full basement. A walkout cuts into the slope and changes how much dirt leaves the lot.
- Keep or haul the spoil. Some can go back as backfill and yard grading. The rest may need trucking.
Egress Windows and Window Wells
Any basement bedroom needs an egress window big enough to climb out of, and that window needs a window well outside it. We dig the over-dig wide enough at each well, set the bottom so the well can drain, and keep those spots in mind when we backfill. On a sloped lot, a walkout or daylight basement can replace some of the wells with full-height windows and doors on the low side.
Digging a Basement Safely
Basement walls are usually 8 feet or taller, so the excavation is well past the 5 feet where OSHA requires sloping, benching or shoring for anyone working at the bottom. Most of the time we slope the sides back. That makes the hole wider at the top and adds to the spoil, so we plan where the piles go, what gets hauled off and how trucks get in before we start.
Footing Drains and Backfill
Most basements get a perimeter drain at the footing, wrapped in gravel and run to daylight or a sump. The walls get damp-proofing or waterproofing from the foundation crew before any dirt goes back. That's why the over-dig has to stay open and dry until they're done. The drain needs a steady fall from one end to the other, so we shape the bottom of the trench along the footing before the gravel goes in.
Then comes backfilling, and timing matters. Basement walls are usually backfilled after the floor framing or bracing is in, so the soil pressure doesn't push them in. We place the dirt in layers, keep big rocks off the wall and the drain, and finish with the ground sloping at least 6 inches in the first 10 feet away from the house. For problem sites, our drainage excavation page has more.
Why Hire Ultimate Excavation LLC
We're an Idaho registered contractor (RCE-65836) based in Caldwell, with a 5.0 rating on Google. One customer who had us put in drainage around their home said we "paid attention to all the small details." On a basement, the drain and the backfill are where those details live. Call (208) 697-2429 or request a free estimate.
