Site Grading and Foundation Drainage

This content is produced by Pass The CSLB, an independent audio-first study companion for busy California B General candidates. I build these lessons from official CSLB study-guide topics and reputable source-backed California materials so you can study on the go. This is exam-prep reinforcement, not legal, professional, engineering, or job-specific advice. Exam content is set by PSI and the CSLB and may change, so always verify current requirements against official CSLB materials. No exam outcome is guaranteed. Now let's get into it.

A patio can slope away from a house and still leave water trapped beside its foundation. I want you to follow that water past the edge of the concrete. If it reaches a low strip of soil with nowhere to go, the drainage problem is still there.

That is the central field decision in this lesson. I check a continuous drainage route, starting near the foundation and continuing to the approved collection or discharge point. A good slope at one location does not establish that the whole route works.

Water held against a foundation can increase moisture exposure and contribute to water intrusion. Depending on the soil and foundation conditions, changes in soil moisture can also contribute to uneven movement. I do not need to predict structural damage to recognize that directing runoff toward the building is a defect worth correcting.

Finish grade means the final ground elevation and shape after the site work is completed. When I check drainage, I care about that finished condition, including the paving and landscaping that will actually be there.

For the standard exposed-earth condition, the CRC requires a minimum fall of 6 in. within the first 10 ft. away from the foundation. The CBC expresses its baseline as a 5% slope for at least 10 ft., measured perpendicular to the wall.

Those are equivalent slopes. 10 ft. is 120 in. 6 in. divided by 120 in. is 0.05, or 5%. I put both measurements in the same unit before dividing.

The direction matters just as much as the amount. The ground next to the building is the higher end, and the grade falls as it extends away. 6 in. of fall toward the house is the wrong result, even though the difference in elevation is 6 in.

I put the main slope comparisons in a table. The baseline for exposed earth is 5%, expressed as 6 in. in 10 ft. Impervious surfaces within 10 ft. of the foundation generally need at least 2% away from the building. Impervious means a surface such as concrete or asphalt that does not readily let water pass through it.

For drainage swales used within that foundation zone, the CBC specifies at least 2% along the swale. A swale is a shallow surface channel formed to collect and carry runoff.

I want you to attach each number to its condition. Earth next to the foundation uses the standard 5% baseline. Paving uses the general 2% baseline. The swale measurement describes fall along its drainage route.

These are baseline provisions. The applicable code, its exceptions, and the approved project requirements still control. I would not apply a general slope number to every special condition without checking those requirements.

For a quick paving calculation, suppose the approved drainage layout calls for a 2% slope over 10 ft. 2% of 120 in. is 2.4 in. of fall. A 2-inch fall over that distance is less than 2%.

You may hear someone call 2% a 1/4 in. per ft. That is a useful approximation, but it is not an exact equality. A 1/4 in. per ft. gives 2.5 in. over 10 ft., slightly more than 2%.

A tight lot changes how water is carried away. It does not eliminate the need to carry it away.

Imagine a new house with only 5 ft. between its foundation and a boundary wall. There is no room for the normal 10-foot run. The residential drainage provision allows drains or swales where physical barriers prevent the standard fall and distance.

Under the CBC provision, the earth slopes toward an approved alternative drainage method when the full distance is unavailable. That provision retains the 5% approach slope, subject to its applicable exceptions. A swale used for that purpose within 10 ft. of the foundation needs at least 2% along its length.

There are two different directions in that description. Water first travels away from the foundation into the swale. Then it travels along the swale toward its destination. I do not substitute the swale's lengthwise slope for every adjoining ground slope.

If the approved layout uses a drain inlet instead, I check how surface water reaches that inlet and where the connected drainage goes. A grate in the yard is only a collection point. Its presence alone does not establish a working drainage route.

For that hypothetical narrow side yard, I would coordinate the approved drainage arrangement before final grading. If the proposed elevations cannot fit between the house and the boundary wall, I raise the conflict for resolution. I do not leave a low pocket against the building and call the lot too small to drain.

The next coordination point is where the finished ground meets a stucco wall. Raising the ground can improve one slope while covering a part of the wall that needs to remain exposed.

The weep screed is the drainage edge at the bottom of the exterior stucco assembly. It allows trapped water to drain to the outside. That makes its clearance part of the drainage check, even though the stucco and grading may be done by different crews.

I put the two clearance requirements side by side. Keep the weep screed at least 4 in. above earth and at least 2 in. above paved areas. These are vertical clearances. They are separate from the slope requirements.

4 in. above earth does not mean 4 in. of fall across the yard. 2 in. above paving does not mean a 2% slope. The words after the number tell you which measurement you are checking.

If earth or concrete covers the drainage edge, water cannot leave through that edge as intended. Stucco can also draw moisture through contact with wet material. I therefore check both the visible gap and whether the drainage outlet remains unobstructed.

Suppose a concrete patio is formed with the correct 2% fall away from a stucco wall, but its finished surface will sit only 1 in. below the weep screed. The slope can be correct while the clearance is deficient. I want that elevation conflict resolved before the pour.

The screed itself also has installation requirements. The residential provision identifies corrosion-resistant metal at least 0.019 in. thick, or an approved plastic weep screed. Its vertical attachment flange must be at least 3.5 in., and its placement is at or below the foundation plate line.

That attachment flange is the part secured to the wall. Its height is a product and installation dimension. It is not the required gap above earth or paving.

For grading supervision, I keep the clearance check simple: 4 in. above earth, 2 in. above paving, with the drainage edge left open. Then I confirm that the finish grade still carries water away.

The CBC requires the procedure for establishing final ground level beside a foundation to account for additional settlement of the backfill.

Backfill is soil placed back into an excavation. Disturbed soil can consolidate after placement. If it settles near the wall more than it settles farther out, the fall away from the building becomes smaller.

That is why a good measurement on the day of grading does not settle the whole question. I coordinate the specified backfill preparation, compaction, and final elevations instead of treating freshly placed loose soil as a permanent surface.

Here is a useful distinction. Settlement can reduce a slope without reversing it. If a location begins 6 in. higher than an outer point, and only that higher location drops 4 in., it remains 2 in. higher. The original fall has been reduced, but the overall direction has not reversed.

Further or uneven settlement could create a low pocket or a slope back toward the wall. The result depends on where the soil moves and by how much. I do not assume every settlement event produces the same outcome.

The practical lesson is to allow for settlement through the approved work procedure. Simply piling extra dirt against the stucco can create a clearance problem while trying to solve a grading problem.

Surface drainage and subsoil drainage handle water in different places. Surface drainage carries runoff over the finished site. Subsoil drains collect water below ground.

Where subsoil drainage cannot reach its discharge point by gravity, the CPC calls for an accessible sump with an approved automatic electric pump. The sump is the collection basin from which the water is pumped.

For this subsoil drainage arrangement, the minimum pump capacity is 15 gallons per minute. That is a minimum, not proof that the same pump suits every project. The pump must also handle the water entering the sump and deliver it to the required discharge point.

I keep the scope of that number attached to it: 15 gallons per minute for the subsoil drainage sump provision. It is not a universal selection rule for every pump used on a construction site.

The discharge destination is part of the approved drainage arrangement. I do not assume the nearest sanitary sewer connection is an acceptable outlet for storm or subsoil water.

A pump also does not excuse a surface grade that sends runoff back toward the building. I check the surface drainage and the below-ground drainage as connected responsibilities with different functions.

Water during excavation brings a separate decision: whether employees can safely work in that excavation.

California occupational safety rules prohibit work in excavations containing accumulated or accumulating water unless adequate precautions protect employees from the associated hazards. Depending on the conditions, precautions can include special support or shield systems and water removal.

Suppose water starts collecting in a footing excavation and the existing precautions do not address it. I stop the exposed work until adequate protection is established. Finishing quickly is not a substitute for that protection.

I also do not treat the presence of a running pump as automatic proof that the excavation is safe. The precautions have to address the actual conditions. Pumping and protection against a cave-in are not interchangeable decisions.

Keep this distinction clear: the permanent drainage system protects the completed project, while excavation precautions protect employees during the work.

For a new residential project subject to the grading and paving requirement in the CALGreen, the construction plans must show how grading or drainage will manage surface water and keep it from entering buildings.

That places the drainage arrangement in the plans before it becomes a finished-yard problem. I coordinate the grading, concrete, stucco, landscaping, and drainage work against that arrangement.

I put a short field-review table on screen. I start with the approved route for the water. I check the finished slopes and the places where surfaces meet. I check the weep screed clearance. I confirm that the backfill procedure accounts for settlement. Where the design uses a sump, I check the specified pump and discharge arrangement.

Those checks connect the trades. A concrete crew can establish the right slope and still pour too high against the wall. A landscape crew can place soil that changes an inlet's collection area. I want those interfaces considered while elevations can still be coordinated.

My role as the General B contractor is to coordinate the work, recognize visible conflicts, and arrange their resolution. Civil drainage design and surveying belong with appropriately qualified professionals. If the design does not fit the actual site, I seek the necessary clarification before changing it.

The published General Building study outline includes landscaping. These drainage decisions connect that topic to field coordination, defect recognition, and safety. That supports studying the concepts; it does not predict a particular examination question.

I have an audio practice quiz specifically for this episode on site grading and foundation drainage. The questions are read aloud, and you answer by tapping. I designed it for studying on the go, so you can fit practice around a busy workday. If you are driving, wait until you are safely parked before tapping answers.

Go to the description below this video. You will see a link that says PassTheCSLB. Tap it. It will take you straight there.

If you have a question about anything I covered, comment below. I want to help you work through the distinction that is giving you trouble. Subscribe so you can stay on track with me through every episode until you get your license.