Basement Waterproofing Drainage Calculator

ANA›Life Services Authority›National Calculator Authority›Basement Waterproofing Drainage Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Basement Waterproofing Drainage Calculator

Estimate interior drainage pipe capacity, required sump pump flow rate, and perimeter drain sizing for basement waterproofing systems.

Basement Length (ft)

Basement Width (ft)

Soil Type

Sandy / Gravel (High Permeability) Loam / Mixed (Medium Permeability) Clay (Low Permeability)

Design Rainfall Intensity (in/hr)

Basement Depth Below Grade (ft)

Drain Pipe Slope (in/ft)

Drain Pipe Diameter (in)

3 inch 4 inch 6 inch

Calculate

function basCalc() { var length = parseFloat(document.getElementById('bas_length').value); var width = parseFloat(document.getElementById('bas_width').value); var soilK = parseFloat(document.getElementById('bas_soil_type').value); var rainfall = parseFloat(document.getElementById('bas_rainfall').value); var depth = parseFloat(document.getElementById('bas_depth').value); var slope = parseFloat(document.getElementById('bas_pipe_slope').value); var pipeDia = parseFloat(document.getElementById('bas_pipe_dia').value);

// --- Input Validation --- var errors = []; if (isNaN(length) || length 0) { document.getElementById('bas_result').innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; return; }

// --------------------------------------------------------------- // 1. DRAINAGE AREA & INFLOW // Roof/surface contributing area approximated as footprint area // Q_surface (ft³/min) = (Rainfall_in/hr / 12) * Area_ft² / 60 // Rational Method: Q (ft³/s) = C * i * A / 43200 // where C = runoff coefficient (soil-based), i = in/hr, A = ft² // --------------------------------------------------------------- var area = length * width; // ft² var C = 1.0 - soilK * 10; // runoff coeff (0.80–0.98 range) C = Math.min(Math.max(C, 0.70), 0.98);

// Rational method: Q (ft³/s) = C * i(ft/s) * A(ft²) // i in ft/s = rainfall_in_hr / (12 * 3600) var i_fts = rainfall / (12 * 3600); // ft/s var Q_surface_cfs = C * i_fts * area; // ft³/s

// --------------------------------------------------------------- // 2. GROUNDWATER SEEPAGE (Darcy's Law simplified) // Q_gw (ft³/s) = K * i_hydraulic * A_wall // Hydraulic gradient i_h = depth / (depth + 5) (conservative) // Wall area = perimeter * depth // K in ft/s: sandy=0.01, loam=0.001, clay=0.0001 // --------------------------------------------------------------- var K_map = {0.10: 0.01, 0.05: 0.001, 0.02: 0.0001}; var K_fts = K_map[soilK] || 0.001; var perimeter = 2 * (length + width); // ft var wallArea = perimeter * depth; // ft² var i_h = depth / (depth + 5); // hydraulic gradient var Q_gw_cfs = K_fts * i_h * wallArea; // ft³/s

// --------------------------------------------------------------- // 3. TOTAL DESIGN FLOW // --------------------------------------------------------------- var Q_total_cfs = Q_surface_cfs + Q_gw_cfs; // ft³/s var Q_total_gpm = Q_total_cfs * 448.831; // gal/min

// --------------------------------------------------------------- // 4. MANNING'S EQUATION — Pipe Capacity (full-flow) // Q = (1/n) * A * R^(2/3) * S^(1/2) // n = 0.013 (PVC/smooth pipe) // A = π * d² / 4 (ft²) // R = d / 4 (hydraulic radius for full circle, ft) // S = slope in ft/ft // --------------------------------------------------------------- var n = 0.013; var d_ft = pipeDia / 12; // diameter in ft var A_pipe = Math.PI * d_ft * d_ft / 4; // ft² var R_pipe = d_ft / 4; // hydraulic radius ft var S_pipe = slope / 12; // ft/ft (slope given as in/ft) var Q_pipe_cfs = (1 / n) * A_pipe * Math.pow(R_pipe, 2/3) * Math.pow(S_pipe, 0.5); var Q_pipe_gpm = Q_pipe_cfs * 448.831;

// --------------------------------------------------------------- // 5. SUMP PIT SIZING // Volume to handle 10-min peak: V = Q_total * 600 s // Pit diameter recommendation: V = π/4 * d² * h, h=24 in assumed // --------------------------------------------------------------- var V_pit_cf = Q_total_cfs * 600; // ft³ (10-min storage) var V_pit_gal = V_pit_cf * 7.48052; // gallons var pit_h_ft = 2.0; // standard 24-in depth var pit_dia_ft = Math.sqrt((4 * V_pit_cf) / (Math.PI * pit_h_ft)); var pit_dia_in = pit_dia_ft * 12;

// --------------------------------------------------------------- // 6. SUMP PUMP REQUIRED FLOW RATE // Pump must clear pit volume in ≤ 5 min with 25% safety factor // Q_pump = V_pit_gal / 5 * 1.25 // --------------------------------------------------------------- var Q_pump_gpm = (V_pit_gal / 5) * 1.25;

// ---------------------------------------------------------------
// 7. PIPE ADEQUACY CHECK
// ---------------------------------------------------------------
var pipeOK = Q_pipe_cfs >= Q_total_cfs;
var pipeStatus = pipeOK
? '✓ Adequate': '✗ Undersized — increase diameter or slope';

// --------------------------------------------------------------- // 8. NUMBER OF DRAIN PIPE RUNS (perimeter drain) // Each run max 50 ft recommended; round up // --------------------------------------------------------------- var numRuns = Math.ceil(perimeter / 50);

// Format helpers function fmt(v, d) { return v.toFixed(d !== undefined ? d : 2); }

var html = '### Results ' + 'Parameter' + 'Value';

var rows = [ ["Basement Footprint Area", fmt(area, 0) + " ft²"], ["Perimeter", fmt(perimeter, 1) + " ft"], ["Runoff Coefficient (C)", fmt(C, 2)], ["Surface Inflow (Rational Method)", fmt(Q_surface_cfs, 4) + " ft³/s (" + fmt(Q_surface_cfs * 448.831, 2) + " GPM)"], ["Groundwater Seepage (Darcy)", fmt(Q_gw_cfs, 4) + " ft³/s (" + fmt(Q_gw_cfs * 448.831, 2) + " GPM)"], ["Total Design Flow", "" + fmt(Q_total_cfs, 4) + " ft³/s (" + fmt(Q_total_gpm, 2) + " GPM)"], ["Pipe Capacity (Manning's, " + pipeDia + "" @ " + slope + " in/ft)", fmt(Q_pipe_cfs, 4) + " ft³/s (" + fmt(Q_pipe_gpm, 2) + " GPM)"], ["Pipe Adequacy", pipeStatus], ["Recommended Drain Pipe Runs", numRuns + " run(s) (≤50 ft each)"], ["Sump Pit Storage Required (10 min)",fmt(V_pit_gal, 1) + " gal (" + fmt(V_pit_cf, 2) + " ft³)"], ["Recommended Sump Pit Diameter", fmt(pit_dia_in, 1) + " in (at 24" depth)"], ["Required Sump Pump Flow Rate", "" + fmt(Q_pump_gpm, 1) + " GPM (5-min cycle + 25% safety)"], ];

rows.forEach(function(r, i) { var bg = i % 2 === 0 ? '#f9f9f9' : '#fff'; html += '' + '' + r[0] + '' + '' + r[1] + ''; }); html += '';

document.getElementById('bas_result').innerHTML = html; }

#### Formulas Used

1. Surface Inflow — Rational Method: Q = C · i · A where C = runoff coefficient (soil-dependent, 0.70–0.98), i = rainfall intensity (ft/s), A = basement footprint (ft²).

2. Groundwater Seepage — Darcy's Law: Qgw = K · ih · Awall where K = hydraulic conductivity (ft/s), ih = depth/(depth+5) (hydraulic gradient), Awall = perimeter × depth (ft²).

3. Pipe Capacity — Manning's Equation (full-flow circular pipe): Q = (1/n) · Apipe · R2/3 · S1/2 where n = 0.013 (PVC), Apipe = πd²/4, R = d/4 (hydraulic radius), S = slope (ft/ft).

4. Sump Pit Volume: Vpit = Qtotal × 600 s (10-minute peak storage)

5. Sump Pump Flow Rate: Qpump = (Vpit / 5 min) × 1.25 (25% safety factor)

#### Assumptions & References

Basement Waterproofing Drainage Calculator

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