A lot of Poway owners with land skip the roof. The roof faces the wrong way. Or it’s tile. Or it’s shaded by oaks. So the panels go in the yard on a rack.
That rack is a structure. It sits on footings. It has to hold the panels up in wind and stay put when the ground gets wet. On Poway acreage, the ground under those footings can be anything from hard granite to clay fill.
This post isn’t about the electrical side. Your solar installer handles that. It’s about the footings, and the plain questions worth asking before anyone digs.
What the City asks for on a ground mount
Poway’s Building Division lists ground-mount requirements in its solar submittal guide. Here’s the short version:
- Planning approval is required. Engineering approval may be required, too.
- Septic matters. If the property is on a septic system, County Health approval is required. The City suggests checking with the Health Department before submitting plans, since permits can’t be issued without that approval.
- Plans include the foundation. On top of the usual solar plans, a ground mount needs construction plans for the racks, including the foundation system.
- Inspections include the foundation. The guide lists underground electric, foundation, rack framing, any service upgrade, rough electric, and final.
So the footing isn’t a detail the City ignores. It’s drawn, reviewed and inspected.
Why the footing is the hard part
A roof mount uses the house as its foundation. A ground mount has to make its own.
Panels act like a sail. Wind pushes on them and tries to lift them. The footings resist that by weight, by depth, or both. The City’s solar compliance list asks about racking listings and how the rack is attached. The rack maker’s tables assume certain footing sizes and soil. Your ground has to match those assumptions, or the design has to change.
Then there’s movement. If one footing settles or heaves and the next one doesn’t, the rack twists. Panels can bind. Clamps loosen. A rack that’s out of line is also harder to keep wired and bonded right.
Know what’s under the array
Poway’s Safety Element describes two very different kinds of ground. Granitic rock, like the Woodson Mountain Granodiorite, forms the high ground and big boulders. Sedimentary layers like the Friars Formation hold expansive clays. The Element ties most fill settlement and expansive soil problems to fill made from the Friars and Mission Valley formations.
What that means for a solar field:
- Hard rock. Augers and driven posts can stop short. Boulders may need to come out, or the layout has to shift. Some sites call for drilling into rock.
- Decomposed granite. Often easier to dig and drains well. It can be loose near the surface and firmer below. Erosion on slopes is the bigger risk.
- Clay or clay fill. Swells when wet, shrinks when dry. Shallow footings can move up and down with the seasons. Deeper footings get below most of that.
- Old fill on a graded pad. Uncompacted fill can settle. Ask if there’s a grading report.
If you don’t know what’s under the spot you picked, find out. A test hole or a soils report beats guessing.
Slope, drainage and where the array goes
Big lots tempt people to use the slope that faces south. That can work. It also adds questions.
- Is the slope stable? The Safety Element calls out landslides and notes that saturated slopes lose strength.
- Where does water go after a storm? Panels shed rain in sheets along their low edge. That water lands in the same line every time. On bare ground, it can cut a trench.
- Will grading for the array change drainage for the house, the barn or the septic field?
- Do you need a grading permit? The City has its own rules for that.
Keep the array out of drainage paths. Keep runoff from panels away from footings and from the top of slopes.
Septic fields and buried lines
On a septic lot, the leach field is often the flattest, sunniest open spot. It’s also the worst place for footings. Driving posts or drilling piers through a leach line damages it. Heavy equipment compacts the soil it needs.
Find out where the tank and leach lines are before laying out the array. The County’s review is there for this reason. While you’re at it, mark buried water lines, irrigation, propane lines and power. A ground mount also brings its own trench for the new electric run.
Do and don’t
Do:
- Locate the septic tank, leach field and buried utilities first.
- Ask what footing type the design uses and what soil it assumes.
- Get a soils look if the ground is clay, fill or on a slope.
- Plan where panel runoff will go.
- Keep the foundation inspection on the schedule. Footings get looked at before they’re covered.
Don’t:
- Set the rack on the leach field.
- Assume rock is “solid” everywhere. Boulders aren’t bedrock.
- Shorten footings because the auger hit something hard. Ask why it stopped.
- Grade a slope flat without thinking about drainage and permits.
- Let the array crowd the house, barn or retaining walls.
Questions for your solar installer
Bring these to the bid meeting:
- What footing type are you using, and how deep?
- What soil conditions does that design assume?
- Who designed the foundation, and is it on the plans for the City?
- What happens if you hit rock or soft fill during installation?
- How will you handle runoff from the panels?
- Where are the septic and buried lines in relation to the array?
- Who fixes it if a footing moves later?
Good installers like these questions. Vague answers are a sign to keep shopping.
Where a structural check fits
Most ground mounts never need us. Where we help is the overlap: an array near a retaining wall, on a slope above the house, on old fill, or close to a barn or guest house footing. We look at how the new footings and the existing structures share the ground, and coordinate with licensed engineers as needed when a slope or soil question calls for design.
Our large-lot estate foundations page covers how we look at acreage as a whole. Our hillside foundation repair page covers slopes.
Straight to the site
We work all of Poway, from Green Valley and Old Coach to the older tracts in town. If you’re planning a ground mount near a slope, wall or outbuilding and want a second look at the ground, request a Free Quote.