Stormwater Basics for Sewickley Patios and Additions

Planning a new patio or a small addition in Sewickley? The fastest way to derail your timeline is an unexpected stormwater requirement. You want a smooth permit process, predictable costs, and a backyard upgrade that does not create drainage problems. In this guide, you will learn when stormwater rules apply, what reviewers expect, simple on-site solutions that work for Sewickley yards, and the steps to keep your project moving. Let’s dive in.

When stormwater rules apply

Stormwater rules follow a simple path: federal, state, county, then municipal. At the federal level, the Environmental Protection Agency (EPA) manages the NPDES program for construction stormwater. Pennsylvania’s Department of Environmental Protection (PA DEP) provides statewide guidance and supports enforcement. Allegheny County sets planning frameworks under Act 167, and Sewickley Borough enforces local ordinances and permits.

For most homeowners, federal permits are rarely triggered, but local stormwater rules still apply. Municipal ordinances, often tied to Act 167, control post‑construction stormwater for new impervious surfaces. Sewickley Borough’s building and zoning office can confirm the exact thresholds and submittal needs for your specific address.

Typical thresholds to know

• NPDES construction stormwater permits usually apply when you disturb 1 acre or more of soil, or if your project is part of a larger common plan that exceeds that limit.
• Post‑construction stormwater management often kicks in at smaller sizes. Across Pennsylvania, many municipalities use a few thousand square feet of new impervious surface as a trigger. A commonly cited benchmark is about 2,500 square feet, but you must confirm Sewickley’s exact number.
• Separate rules may apply in FEMA‑mapped floodplains, floodways, steep slopes, or riparian areas, regardless of project size.

What this means for patios and small additions

Most patios and bump‑outs will be below federal permit thresholds. Even so, your project may still need local documentation or stormwater controls if you add impervious area or change how runoff flows on your lot. Plan early to manage roof leaders and patio runoff so you do not create a nuisance on a neighbor’s property or in the street.

What reviewers expect in your submittal

You do not need to overcomplicate small projects. Reviewers simply want to see that your plan will not increase downstream flooding, erosion, or pollution. Here is what they commonly ask for:

Clear site plan

• Scaled plan with property lines, existing and proposed structures, and utilities.
• Existing and new impervious areas shown and labeled with square footage.
• Existing and proposed grading or spot elevations that show flow paths with drainage arrows.
• Distances to property lines and any wells or septic systems if present.

Short stormwater narrative

• Describe the work, the disturbance area, and the net change in impervious surface.
• State whether your project triggers NPDES or post‑construction requirements under local ordinance.
• Summarize how you will manage runoff on site.

Sizing and calculations

• For small projects, a simple before‑and‑after impervious comparison plus a statement that runoff will be managed on site can be enough.
• If you exceed a local threshold, you may need hydrologic calculations to show peak rate and volume control.
• Provide infiltration testing results if you plan to use infiltration measures like a drywell or rain garden.

Details for stormwater best management practices (BMPs)

• Plan view and sections with dimensions for the BMPs you choose, such as a rain garden, infiltration trench, drywell, or permeable pavers.
• Sizing that demonstrates required storage and safe overflow routing.
• Construction notes that call out clean stone, correct geotextiles where permitted, and no impermeable liners under infiltration areas.

Erosion and sediment control during construction

• Show the location of silt fence, stockpile controls, and a stabilized construction entrance.
• If you trigger NPDES, you will need a formal Erosion and Sediment Control plan and a Stormwater Pollution Prevention Plan.

Maintenance plan and sign‑off

• Provide simple inspection and maintenance tasks for your selected BMPs.
• Some municipalities require a recorded maintenance agreement before final approval.

Professional certifications

• Small, straightforward projects may not require an engineer’s seal. If your design or calculations are more complex, the reviewer may ask for a licensed professional to prepare or seal the plans.

On‑site solutions that work in Sewickley

The best choice depends on your soils, space, setbacks, and slopes. Infiltration is often preferred if your soil allows it. Here are proven options for patios and small additions.

Disconnect roof leaders

• Direct downspouts to a vegetated area, a level spreader, or a short stone trench that disperses flow.
• Keep flows away from your foundation and do not send water toward a neighbor or the street.
• This option is low cost and often accepted for small increases in runoff.

Rain barrels or small cisterns

• Capture roof runoff for reuse in the garden, which reduces peak flows during small storms.
• Plan a safe overflow route for bigger storms.
• Storage is limited, so you may still need other measures for larger control volumes.

Rain gardens and bioretention

• Attractive and effective for infiltrating and treating runoff while adding landscaping.
• Confirm infiltration capacity with testing and respect setbacks from basements and utilities.
• Include an overflow that directs excess water to a safe discharge point.

Infiltration trenches and drywells

• Store and infiltrate runoff from roofs or patios in a compact footprint.
• Size the storage to empty within the locally required time window, often within 48 to 72 hours.
• Use clean, open‑graded stone and geotextiles as specified. Keep a safe distance from foundations, wells, and septic systems.

Permeable paving

• Permeable pavers or porous concrete can reduce runoff across a larger surface.
• Proper base design is critical. Use open‑graded aggregate and ensure pretreatment to limit clogging.
• Plan for maintenance such as vacuuming and sweeping. In poor soils, an underdrain and stone reservoir may be required.

Vegetated swales and level spreaders

• Slow and spread runoff so it can soak into the ground.
• Work best on gentle slopes with adequate length.
• Avoid short, steep, or concentrated flows that can cause erosion.

Winter performance tips

Allegheny County winters bring freeze‑thaw cycles and deicing salts that can reduce performance. Choose salt‑tolerant plants for bioretention, keep inlets clear of ice and debris, and maintain permeable pavements so the base drains freely.

Avoid common missteps and delays

Save time and money by steering clear of these pitfalls:

• Underestimating impervious area. Count all new hardscape, not just the patio or roof. Include walkways and driveway changes.
• Calling a surface “permeable” without the correct base. Reviewers look for the right open‑graded stone, pretreatment, and maintenance plan.
• Skipping infiltration testing. Without test results, infiltration designs may be rejected or require redesign.
• Routing runoff to a neighbor or the street. Concentrated flow off‑site is a common reason for denial. Provide positive overland routes to a safe discharge point.
• Forgetting erosion controls during construction. Even small projects may need silt fence and a stabilized entrance to prevent tracking and sediment issues.
• Missing a required maintenance agreement. Some BMPs need a recorded covenant before final approval.

Typical timeline and fees

• Pre‑application check with Sewickley Borough: same day to 1 or 2 weeks to schedule. A quick conversation early can prevent redesigns.
• Plan preparation: a few days to several weeks depending on whether you need testing or professional design support.
• Municipal or conservation district review: often 2 to 6 weeks for simple projects. More complex designs may take longer.
• Inspections: plan for an inspection during or after construction. Schedule in advance.
• Fees: vary by municipality and whether county review is involved. Ask Sewickley Borough for the current schedule.

Step‑by‑step: your Sewickley checklist

Use this quick list to get organized before you apply:

• Confirm your property boundaries with a deed or survey.
• Measure all proposed impervious areas and calculate the net change.
• Check FEMA flood maps to see if your lot is in a mapped floodplain or floodway.
• Sketch a scaled site plan with existing and proposed features, grading, and drainage arrows.
• Write a short stormwater narrative that states the scope, disturbance area, and how you will manage runoff.
• Conduct infiltration testing if you plan to use a rain garden, drywell, or infiltration trench.
• Gather product cut sheets for permeable pavers or rain barrels.
• Add simple erosion and sediment control notes for construction.
• Draft a maintenance plan that lists tasks and who is responsible.
• Collect contact information for your contractor and any designer or engineer.

Who to contact for your address

• Sewickley Borough Building and Zoning Office: confirm local thresholds, impervious coverage limits, setbacks, and floodplain requirements.
• Allegheny County Conservation District: ask about erosion and sediment control, NPDES applicability, and whether county review applies.
• PA DEP Stormwater Program: consult statewide BMP guidance and best practices.
• FEMA Flood Map Service Center: verify floodplain and floodway mapping for your parcel.

Bringing it all together

The smoothest projects start with accurate measurements, early calls to the Borough and County, and simple on‑site solutions that fit your yard. If you are planning a patio or addition in Sewickley and want to avoid surprises before you list, buy, or break ground, reach out for local guidance tailored to your property. For help coordinating the right steps around your home goals, contact Shelley Wood to request your complimentary market consultation.

FAQs

Do small Sewickley patios need stormwater approval?

• Many small patios fall below federal permit thresholds, but local rules can still apply if you add impervious area or change drainage. Confirm with Sewickley Borough for your address.

What counts as impervious surface for a permit?

• Roofs, patios, driveways, and walkways typically count as impervious. Calculate the total net change, not just the main patio or addition footprint.

How big before an NPDES permit is required?

• NPDES construction stormwater permits generally apply at 1 acre of disturbance or more, or if you are part of a larger common plan that exceeds that size.

Do I need infiltration testing for a drywell or rain garden?

• If you plan to infiltrate water into the ground, testing is commonly required to show that soils can accept and drain the stored volume within the allowed time.

Can I send downspout water to the street or a neighbor’s yard?

• No. Routing concentrated flow off‑site is a common reason for denial or complaints. Use on‑site BMPs and safe overland flow routes.

How long does a basic stormwater review take in Sewickley?

• Simple reviews often take 2 to 6 weeks after you submit a complete package. Plan preparation and scheduling inspections add time.

What is the easiest stormwater solution for a small addition?

• Disconnected roof leaders to a vegetated area, a small rain garden, or a properly sized drywell are common solutions. The best choice depends on your soils, space, and setbacks.