When you plan a custom home on an existing lot, drainage is one of the single biggest site issues that affects durability, livability and cost. Poor drainage can lead to basement or slab water intrusion, frost heave in foundations, accelerated erosion of graded slopes and chronic wet spots that complicate landscaping and outdoor living areas. Because RKM Homes designs and builds on our clients’ lots across the Denver metro area, we prioritize a thorough drainage evaluation up front so the building footprint, foundation type and site improvements are matched to actual site conditions rather than assumptions.
Our process begins with a detailed site walk and review of historical wet-weather behavior: where water ponds after thunderstorms or snowmelt, localized seepage, and how runoff from neighboring properties behaves. We combine that observational work with measured topo data, utility locations and a geotechnical report or soil borings to learn soil type, percolation, and seasonal high groundwater levels. We also check relevant municipal stormwater requirements and HOA covenants early, since grading permits, detention/retention standards and storm-sewer tie-in rules often dictate what mitigation is allowed or required.
Armed with that information we design practical, staged solutions that are integrated with the home rather than bolted on later: planned grades and swales, perimeter footing drains and membrane waterproofing, targeted retaining walls, properly sized gutters and downspout extensions, and, where needed, on‑lot detention or French drains. Landscape choices and driveway materials (permeable pavers versus impermeable concrete) are selected to reduce concentrated runoff, and we coordinate civil engineers and geotechnical consultants when complex drainage or hillside runoff is present. By assessing these elements during early design, RKM Homes minimizes surprises, keeps foundation and site-prep costs under control, and delivers a home that performs through Denver’s cycles of snowmelt and intense summer storms.
How do topography, slope and natural drainage patterns affect my lot’s drainage?
As a custom home builder I start every lot evaluation outside with my boots on — topography tells you where water wants to go before you disturb anything. Walk the site during or right after a rain and note the low points, ridgelines, swales and any obvious concentrated flow paths or gullying. Take photos from several angles, sketch arrows where water ran, and mark any spots where water ponds or flows onto neighboring properties — that on-the-ground reconnaissance is often more telling than a quick map review.
You can get practical numbers from simple measurements: use a string line and a line level or a smartphone app to measure rise over run, then calculate percent slope as (rise/run) × 100. For house siting, plan on at least a 5% grade away from the foundation for the first 10 feet (about a 6″ drop over 10′) to keep surface runoff from collecting at the foundation; gentler slopes (around 2%) work for patios and driveways but will not protect a foundation. Steep slopes increase runoff velocity and erosion risk, so note where you’ll need terraces, retaining walls or energy-dissipating features if the house or access road cuts across a slope.
Before finalizing plans, get a topographic survey so the proposed building pad and finished floor elevations can be drawn relative to existing contour lines — that allows your builder to show how much cut or fill will be required and whether the natural drainage can be preserved or needs modification. If the lot’s natural drainage routes would direct water toward the home, consider re-siting the slab to higher ground or redesigning the landscape grading so overland flow bypasses the structure; discuss these options with your builder early so grading can be coordinated with foundation elevations and roof runoff plans.
Soil type, permeability and percolation/test results — how will they affect my lot’s drainage?
As a custom home builder I treat the soil report and percolation/infiltration test as foundational design documents — they tell me how fast water will leave the footprint, how deep we can reasonably excavate, and what kind of foundation and drainage systems the lot will require. Practically, that means ordering a geotechnical report and infiltration/percolation tests in the proposed building envelope (and at low spots and septic/drainfield locations) before final plans. Ask the engineer for measured infiltration rates (k-values or minutes-per-inch), depth to any restrictive layers or bedrock, plasticity/expansive characteristics, and recommendations for footing depth and backfill; those specific numbers drive decisions on underdrains, gravel layers, and whether imported structural fill is needed.
What the results mean for construction is straightforward: coarse sandy or gravelly soils with high permeability let stormwater infiltrate quickly but can require stabilization and erosion control; silty or clayey soils with low permeability will hold water and typically require engineered subdrains, sump systems, or raising the building envelope. If tests show a high water-holding capacity or slow percolation you should budget for continuous perforated footing drains with crushed-stone envelopes, geotextile separation, positive exterior grading, and possibly a sump and pump for basements or crawlspaces. If a restrictive layer or seasonal high groundwater is present near the surface, plan for waterproofing and hydrostatic-relief details rather than relying on infiltration-based stormwater solutions.
For homeowners who want a practical checklist: insist the contract conditions include a geotech report and percolation tests done at representative locations and during a realistic moisture season, require the report’s drainage and foundation recommendations to be incorporated into the scope and allowances, and get written pricing for the common mitigations the report may recommend (underdrains, imported structural fill, gravel drainage layers, sump pump systems, and retaining-wall drainage). During grading and foundation construction, verify the contractor follows the geotechnical compaction and subgrade specs — deviating from those specs is the most common cause of post-build settlement and persistent wet spots.
How can I determine the seasonal high groundwater level and spot perched water or seeps on my lot before building?
As a custom home builder I treat seasonal high groundwater (SHGW) as one of the first “hidden” site conditions to verify because it drives foundation type, waterproofing and drainage details. Walk the site in spring thaw and within a few days after heavy rains to look for persistent wet areas, standing water, saturated ground that doesn’t drain within 24–48 hours, moss or water-loving vegetation, and damp staining on slopes or cut banks. Talk to neighbors about wet basements or soggy yards — local patterns are often the fastest clue that groundwater rises close to the surface at certain times of year. If you see water pooling near the proposed footprint or within a few feet of finished grade, treat that as a red flag until proven otherwise.
To confirm what you observe, ask for subsurface testing targeted to groundwater: hand-auger holes for shallow checks, at least one test pit in the lowest part of the lot and one near each corner of the proposed house, and temporary monitoring wells (standpipes) to record water levels over several weeks in wet season. I recommend testing during spring melt or after an extended wet period rather than a dry spell — seasonal highs are commonly missed by summer-only checks. When you hire a geotechnical engineer, request a written SHGW elevation with the date(s) observed, the depths and locations of test pits/monitor wells, and a clear statement of how close that elevation is to your proposed basement or slab elevation.
Perched water and seeps behave differently from a regional high groundwater table and require different fixes. Perched pockets form above an impermeable layer and show up as sudden wet zones on slopes, spring lines, or at the bottom of fill pockets; they often drain slowly after storms and can show up inside excavations as a muddy lens. Practical mitigation options I specify are targeted: intercept the seep with a shallow subdrain tied to daylight or a storm system, replace the saturated lens with free‑draining backfill, raise the finished floor or use a crawlspace instead of a basement, and detail perimeter drains plus a sump if the SHGW is within a few feet of the foundation. Before you finalize plans, ask your builder or geotech three concrete things: where exactly the measured SHGW was found, how many test locations were used and where, and what foundation/drainage methods they recommend if the groundwater is too high for a standard basement.
How do FEMA flood zones and local floodplain regulations affect my lot’s drainage and what do I need to check before building?
As a custom home builder, the first thing we do when evaluating a lot is confirm its floodplain status with both FEMA maps and the local jurisdiction. Ask the seller, your surveyor or the county for the Flood Insurance Rate Map (FIRM) panel and the property’s Base Flood Elevation (BFE). If the lot is in a Special Flood Hazard Area (SFHA) the lender will typically require flood insurance, and the building department will have minimum elevation and permitting requirements that directly change how we design drainage and the foundation. If the map shows uncertainty or the house footprint is close to the mapped boundary, get a licensed surveyor to prepare a flood elevation survey—sometimes a LOMA or LOMR can remove the requirement, but that takes time and money.
Local floodplain ordinances usually dictate specific mitigation measures that affect on‑site drainage: required freeboard above the BFE, allowable foundation types, flood venting, and strict prohibitions on placing fill that alters floodplain storage or obstructs flow paths. Many municipalities require a floodplain development permit, an elevation certificate for final occupancy, and engineered stormwater plans if your grading changes runoff patterns; they may also require compensatory storage if you add fill. From a practical standpoint, expect costs for engineered grading, permitting, potentially elevating utilities, and installation of detention/retention systems—get those estimates before you commit to a lot so you can compare true build costs.
To keep a project on schedule we recommend these concrete steps: ask the jurisdiction’s floodplain administrator for any recent studies or local amendments to FEMA rules; include a licensed civil engineer and surveyor on the pre‑purchase team; request any existing elevation certificates or historical flood claims on the property; and budget a contingency for mitigation measures and flood insurance. On projects in or near regulated flood zones, we write permit compliance and long‑term maintenance of drainage structures into contracts so the grading and stormwater solutions remain effective after handoff.
What existing drainage infrastructure, easements, and required stormwater management or grading plans affect my lot and buildability?
Walk the lot after a heavy rain, then get the paper trail: review the recorded plat and title report for drainage or utility easements, request public works or engineering maps from the city or county showing storm mains, curb inlets, culverts and regional detention/retention basins, and call 811 for underground utility locates. From a practical standpoint you want to know exactly where public or private storm lines run, whether there are inlets or outlets on or adjacent to the property, and the condition and slope of those conveyance points — these determine where you can place permanent structures and how roof and site drainage must be routed. Photographs, a simple site sketch showing inlet/outlet locations and a short rain-event video are inexpensive ways to document existing flow paths before you alter the site.
Easements are legal constraints that are often non-negotiable: most drainage easements prohibit buildings, require access for maintenance, and forbid altering the grade without formal approval. Ask your title company or surveyor to flag all easements and confirm who is responsible for ongoing maintenance (neighbor, HOA, municipality). If the planned build needs storm infrastructure relocation or easement vacation expect engineering drawings, agency approvals, and permits — these can add time and significant cost, so have a civil engineer or experienced builder review feasibility before finalizing house siting.
From the builder’s side we make required stormwater management and grading plans a gating item before foundation work. We hire or coordinate with a civil engineer to produce runoff calculations, a grading plan showing finish contours, inlet/pipe sizes and approved outlets, and erosion control details for construction; that plan becomes part of permitting and inspection checklists. Include a contingency for stormwater work in your contract, require as-built certification at project completion, and insist that roof leaders and site grading tie into approved drainage paths — failure to do so can trigger rework, fines, or requirements to remove structures placed inside protected easements.