Waterproofing or dampproofing: which R406 section applies
In areas where a high water table or other severe soil-water conditions are known to exist, exterior foundation walls that retain earth and enclose interior spaces and floors below grade shall be waterproofed from the finished grade to the higher of the top of the footing or 6 inches (152 mm) below the top of the basement floor.
Except where required by Section R406.2 to be waterproofed, foundation walls that retain earth and enclose interior spaces and floors below grade shall be dampproofed from the finished grade to the higher of the top of the footing or 6 inches (152 mm) below the top of the basement floor.
| Material line, verbatim | IRC 2021 (Hawaii, Connecticut, Colorado adoptions) | IRC 2018 (Wichita-Sedgwick adoption) |
|---|---|---|
| Two-ply hot-mopped felts. | Listed | Listed |
| Fifty-five-pound (25 kg) roll roofing. | Listed | Listed |
| Six-mil (0.15 mm) polyvinyl chloride. | Not in the list | Listed |
| Six-mil (0.15 mm) polyethylene. | Not in the list | Listed |
| Forty-mil (1 mm) polymer-modified asphalt. | Listed | Listed |
| Sixty-mil (1.5 mm) flexible polymer cement. | Listed | Listed |
| One-eighth-inch (3 mm) cement-based, fiber-reinforced, waterproof coating. | Listed | Listed |
| Sixty-mil (1.5 mm) solvent-free liquid-applied synthetic rubber. | Listed | Listed |
| Material line, verbatim |
|---|
| Bituminous coating. |
| Three pounds per square yard (1.63 kg/m2) of acrylic modified cement. |
| One-eighth-inch (3.2 mm) coat of surface-bonding cement complying with ASTM C887. |
| Any material permitted for waterproofing in Section R406.2. |
| Other approved methods or materials. |
Masonry walls shall have not less than 3/8-inch (9.5 mm) Portland cement parging applied to the exterior of the wall. Concrete walls shall be dampproofed by applying any one of the listed dampproofing materials or any one of the waterproofing materials listed in Section R406.2 to the exterior of the wall.
Start with the site condition, not the product. R406.2 waterproofing applies where a high water table or other severe soil-water conditions are known to exist. Everywhere else, R406.1 dampproofing applies. The calculator does not guess the condition: set the second field from a soil report or from what the local building department has told you about groundwater on your lot.
The edition changes the list. The first table sets the R406.2 material lines side by side: 6 lines in IRC 2021, as read in the Hawaii, Connecticut and Colorado adoptions, and 8 lines in IRC 2018, as read in the Wichita-Sedgwick adoption. The two extra lines in IRC 2018 are six-mil polyvinyl chloride and six-mil polyethylene. Under IRC 2021 the checker marks a 6-mil polyethylene sheet as not in the R406.2 list; switch the edition to IRC 2018 and the same sheet is listed and meets its minimum. Name the edition when you talk to a contractor, and confirm with your building department which edition your jurisdiction enforces.
Then read the membrane line of the quote. Four R406.2 materials carry a minimum the checker can test: 40 mil for polymer-modified asphalt, 60 mil for flexible polymer cement, 60 mil for solvent-free liquid-applied synthetic rubber, and 1/8 inch for the cement-based, fiber-reinforced coating. A line that reads “20-mil asphalt membrane” falls below the 40 mil listed for polymer-modified asphalt. A line that names polymer cement but states no thickness stays open: the checker asks for the figure instead of passing it. Hot-mopped felts and roll roofing are checked for their place on the list only.
A bituminous coating is a dampproofing line. It sits in R406.1, not in R406.2, so with a severe condition set the checker flags it as dampproofing only; with no severe condition known, the same coating is listed. R406.1 also accepts any R406.2 material, 3 pounds per square yard of acrylic modified cement, or a 1/8-inch coat of surface-bonding cement. On masonry walls, R406.1 adds not less than 3/8-inch Portland cement parging on the exterior. If your walls are block and the quote has no parging line, ask whether it is included.
The wall area a membrane quote should cover
exterior foundation walls that retain earth and enclose interior spaces and floors below grade shall be waterproofed from the higher of (a) the top of the footing or (b) 6 inches (152 mm) below the top of the basement floor, to the finished grade.
Depth treated below finished grade = the smaller of the depth to the top of the footing and the depth to the top of the basement floor plus 6 in.
R406.2 treats the wall from the finished grade down to the higher of two points: the top of the footing, or 6 inches below the top of the basement floor. Higher means closer to the grade, so read as a depth below grade it is the smaller of the two numbers.
The defaults show the arithmetic. Take 140 ft of earth-retaining wall, the top of the footing 8 ft below grade and the top of the floor 7 ft below grade. The floor limit sits at 7 ft plus 6 in, or 7.5 ft, which is above the footing at 8 ft. The floor governs, and the wall area is 140 × 7.5 = 1,050 sq ft. Move the floor top down to 92 in and its limit drops to 98 in, below the 96 in footing top. Now the footing governs, the depth is 8 ft, and the area becomes 1,120 sq ft. When both limits land at the same depth, the result names the footing.
Subtract what the membrane does not cover. Window wells or a door below grade go in the openings field: 30 sq ft of openings takes the default wall from 1,050 to 1,020 sq ft. If the openings exceed the wall, the area stops at zero.
Do not price a membrane on floor area. A basement 25 by 40 ft has 1,000 sq ft of floor but 130 ft of perimeter, and at the default depths that is 975 sq ft of wall. Only walls that retain earth belong in the perimeter, which is the scope the R406.2 text names.
Does your soil need a footing drain?
Drains shall be provided around concrete or masonry foundations that retain earth and enclose habitable or usable spaces located below grade.
Drainage tiles, gravel or crushed stone drains, perforated pipe or other approved systems or materials shall be installed at or below the top of the footing or below the bottom of the slab and shall discharge by gravity or mechanical means into an approved drainage system.
Gravel or crushed stone drains shall extend not less than 1 foot (305 mm) beyond the outside edge of the footing and 6 inches (152 mm) above the top of the footing and be covered with an approved filter membrane material.
Drainage tiles or perforated pipe shall be placed on not less than 2 inches (51 mm) of washed gravel or crushed rock not less than one sieve size larger than the tile joint opening or perforation and covered with not less than 6 inches (152 mm) of the same material.
Exception: A drainage system is not required where the foundation is installed on well-drained ground or sand-gravel mixture soils according to the Unified Soil Classification System, Group I soils, as detailed in Table R405.1.
| USCS symbol | Soil group | Description | Drainage |
|---|---|---|---|
| GW | Group I | Well-graded gravels, gravel sand mixtures, little or no fines | Good |
| GP | Group I | Poorly graded gravels or gravel sand mixtures, little or no fines | Good |
| SW | Group I | Well-graded sands, gravelly sands, little or no fines | Good |
| SP | Group I | Poorly graded sands or gravelly sands, little or no fines | Good |
| GM | Group I | Silty gravels, gravel-sand-silt mixtures | Good |
| SM | Group I | Silty sand, sand-silt mixtures | Good |
| GC | Group II | Clayey gravels, gravel-sand-clay mixtures | Medium |
| SC | Group II | Clayey sands, sand-clay mixture | Medium |
| ML | Group II | Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity | Medium |
| CL | Group II | Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays | Medium |
| CH | Group III | Inorganic clays of high plasticity, fat clays | Poor |
| MH | Group III | Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts | Poor |
| OL | Group IV | Organic silts and organic silty clays of low plasticity | Poor |
| OH | Group IV | Organic clays of medium to high plasticity, organic silts | Unsatisfactory |
| Pt | Group IV | Peat and other highly organic soils | Unsatisfactory |
Table note: The percolation rate for good drainage is over 4 inches per hour, medium drainage is 2 inches to 4 inches per hour, and poor is less than 2 inches per hour.
R405.1 asks for drains around concrete or masonry foundations that retain earth and enclose habitable or usable space below grade. Its exception waives the drain where the foundation sits on well-drained ground or sand-gravel mixture soils, the Group I soils of Table R405.1. Six symbols make up Group I in the table above: GW, GP, SW, SP, GM and SM. Every other symbol, from Group II through Group IV, keeps the drain in scope.
Take the symbol from a soil report or ask the local building department; do not guess it from the look of the dirt. The calculator starts on CL, a Group II soil, so the drain shows as required until you change it. Choose “Not known” and the drain question stays open: the result says the R405.1 exemption is undecided, and a blank drain rate is listed as missing. Choose a Group I symbol and the drain line leaves the missing list, though its length still shows.
The drain length is the foundation perimeter: 140 linear ft on the default wall. The placement figures come straight from the R405.1 text. Gravel or crushed stone drains extend not less than 1 foot beyond the outside edge of the footing and 6 inches above its top. A perforated pipe sits on not less than 2 inches of washed gravel or crushed rock, under not less than 6 inches of the same. These are positions to check on a quote drawing; this page computes no stone or digging quantity.
Read a waterproofing quote line by line
The calculator splits a quote into three lines. The membrane line is your rate per square foot of wall times the wall area. The drain line is your rate per linear foot times the perimeter. Everything else the contractor lists, digging and backfill included, goes into one lump sum. Leave a line blank and it counts as unknown and appears in the missing list; type 0 and it counts as included in another line. On a Group I soil, a blank drain rate is not missing, because R405.1 waives the drain.
Here is the arithmetic with illustrative rates, not prices from any survey or contractor. At $4 per sq ft of wall on 1,050 sq ft, the membrane line is $4,200. At $60 per linear ft on 140 ft, the drain line is $8,400. Another $500 covers the other lines. The total is $13,100. Divided by the wall, that is $12.48 per sq ft; divided by a 1,000 sq ft floor, it is $13.10 per sq ft. Both ratios describe the same job.
That is why two quotes can look far apart when they are not. If one states a wall rate for the membrane alone and another a floor rate with the drain and digging folded in, put both into the same three lines and compare totals.
Basement waterproofing cost questions
How much to waterproof a 1000 sq ft basement?
Floor area alone does not answer it, because the membrane is priced on the wall. A 1,000 sq ft basement laid out 25 by 40 ft has 130 ft of perimeter. With the footing top 8 ft and the floor top 7 ft below grade, the treated wall is 975 sq ft. At illustrative rates of $4 per sq ft of wall and $60 per linear ft of drain, with no other lines, the total is $11,700. Your own quoted rates decide the real figure.
How much to waterproof basement on a 2000 sq ft house?
The floor area of the house does not tell you the basement wall area. The same 2,000 sq ft house can stand on a full basement, a partial one or a crawlspace, each with a different length of wall that retains earth. Measure that perimeter, the depth to the top of the footing and the depth to the top of the basement floor, then add the rates from your quote. This page gives no national price for a house of that size.
What does basement waterproofing cost per square foot?
Two different square feet are in play. The membrane line is priced per square foot of wall; whole quotes are often compared per square foot of floor. With illustrative entries on the default foundation, a $4 per sq ft membrane rate becomes $12.48 per sq ft of wall once the drain and other lines are added, or $13.10 per sq ft of a 1,000 sq ft floor. Enter your own rates and the tool shows both.
What is the average cost to seal a basement?
We have no primary national figure to give. The American Housing Survey, which we use on other project cost pages, has no basement waterproofing job type; its nearest lines are a catch-all category and a small sample, so we do not quote them. The calculator works from the rates in your own quote instead, line by line.
Is waterproofing expensive?
This tool cannot tell you whether a price is high. It shows what drives the total: wall area times the membrane rate, drain length times the drain rate, and the lump sum of other lines. It also shows whether each part is in scope: R406.2 waterproofing where severe soil-water conditions are known, and the R405.1 drain on any soil outside Group I. If a line falls outside both, ask the contractor what it covers.
Is waterproofing a basement worth it?
That decision is yours; this page makes no value claim. What the code text gives is the scope. R406.2 waterproofing applies where a high water table or other severe soil-water conditions are known to exist. Where they are not known, R406.1 dampproofing is the section that applies. Set the condition field to what you know about your site, then compare each quote with the section it selects.
What does it cost to waterproof a basement from outside?
Exterior work is what R406.2 describes: a treatment on the outside of the wall from finished grade down to the higher of the footing top or 6 inches below the floor top. The calculator prices exactly that area with your membrane rate, plus the R405.1 footing drain with your drain rate. Digging and backfill are real quote lines, but this page does not compute them: enter their amount under other lines.
What does it cost to waterproof a basement from inside?
This tool does not check interior systems. R406.1 and R406.2, as read here, describe treatment of the exterior of the wall. If your quote is for an inside drain, a sump or a coating on the inner face, enter its amount as one figure under other lines. The membrane check and the treated wall area on this page describe exterior work only, so read them as a comparison, not as a check of that quote.
What is the cheapest way to waterproof a basement?
This page does not rank methods by price. It answers the scope question first. If no high water table or other severe soil-water condition is known, R406.1 dampproofing is the section that applies, not R406.2 waterproofing. If your soil carries a Group I symbol in Table R405.1, the R405.1 exception waives the footing drain. Both answers change which lines a quote needs before any rate is compared.
How does this basement waterproofing cost calculator work?
Work from top to bottom. Pick the IRC edition your jurisdiction enforces and say whether severe soil-water conditions are known. Enter the perimeter of the walls that retain earth, the depth to the top of the footing and the depth to the top of the floor, then any openings and, for a per-floor figure, the floor area. Choose the soil symbol, the membrane line named in the quote and its thickness, then your three rates. The result gives the section, the treated wall area, the drain decision and length, the membrane check, the total and both per-square-foot figures.
Read the result with its boundaries
- Code text as read on UpCodes in four local adoptions of IRC 2021 and IRC 2018. Your jurisdiction may enforce another edition or local amendments: confirm with its building department.
- Exterior wall treatment and footing drain only. Interior drainage, sump equipment and crack repair are not checked here; enter their quoted amounts as other lines.
- No stone, excavation or backfill quantity is computed on this page.
- Every price is a rate you enter. No national price and no price band is shown.
- No engineering, legal or insurance advice.