# ASTM D7492D7492M-16a

Designation: D7492/D7492M − 16aStandard Guide forUse of Drainage System Media with Waterproofing Systems1This standard is issued under the fixed designation D7492/D7492M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide makes recommendations for the selectionand application of prefabricated drainage media used in con-junction with waterproofing systems on horizontal and verticalsurfaces. Drainage media considered include rigid and semi-rigid insulation boards and rigid materials including plastics.This guide considers drainage media as it relates to theperformance of the waterproofing system, so its primary focusis draining water away from the membrane. This guide doesnot cover in detail other aspects or functions of drainagesystem performance such as efficiency of soil dewatering. Thescope of this guide does not cover other drainage mediaincluding gravel and filter fabric systems that can be con-structed. The scope of this guide does not cover drainagematerials or drainage system designs used for vegetative roofsystems. Vegetative roof systems require specialized designs.1.2 The committee with jurisdiction over this standard is notaware of any other comparable standards published by otherorganizations.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4 This standard may involve hazardous materials, opera-tions and equipment. This standard does not purport to addressall of the safety concerns, if any, associated with its use. It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C165 Test Method for Measuring Compressive Properties ofThermal InsulationsC898/C898M Guide for Use of High Solids Content, ColdLiquid-Applied Elastomeric Waterproofing Membranewith Separate Wearing CourseC981 Guide for Design of Built-Up Bituminous MembraneWaterproofing Systems for Building DecksC1471/C1471M Guide for the Use of High Solids ContentCold Liquid-Applied Elastomeric Waterproofing Mem-brane on Vertical SurfacesD896 Practice for Resistance of Adhesive Bonds to Chemi-cal ReagentsD1079 Terminology Relating to Roofing and WaterproofingD2434 Test Method for Permeability of Granular Soils(Constant Head) (Withdrawn 2015)3D3273 Test Method for Resistance to Growth of Mold on theSurface of Interior Coatings in an Environmental Cham-berD3385 Test Method for Infiltration Rate of Soils in FieldUsing Double-Ring InfiltrometerD4511 Test Method for Hydraulic Conductivity of Essen-tially Saturated PeatD4630 Test Method for Determining Transmissivity andStorage Coefficient of Low-Permeability Rocks by In SituMeasurements Using the Constant Head Injection TestD4716/D4716M Test Method for Determining the (In-plane)Flow Rate per Unit Width and Hydraulic Transmissivityof a Geosynthetic Using a Constant HeadD5898/D5898M Guide for Details forAdhered Sheet Water-proofing1This guide is under the jurisdiction of ASTM Committee D08 on Roofing andWaterproofing and is the direct responsibility of Subcommittee D08.22 on Water-proofing and Dampproofing Systems.Current edition approved Dec. 1, 2016. Published December 2016. Originallyapproved in 2011. Last previous edition approved in 2016 as D7492/D7492M – 16.DOI: 10.1520/D7492_D7492M-16A.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D6622 Guide for Application of Fully Adhered Hot-AppliedReinforced Waterproofing SystemsE154/E154M Test Methods for Water Vapor Retarders Usedin Contact with Earth Under Concrete Slabs, on Walls, oras Ground Cover3. Terminology3.1 Refer to Terminology D1079 for definitions of termsused in this guide.4. Summary of Practice4.1 This guide describes a method to estimate the amount ofwater a drainage system may need to carry. The guide alsooffers descriptions of the various drainage systems in existencetoday along with suggestions on how different building situa-tions will require different performance characteristics from thedrainage medium chosen. Items to be aware of during theinstallation of drainage systems is also covered along withillustrations of typical drainage systems.5. Significance and Use5.1 This guide provides information and guidelines for theselection and installation of drainage systems media that are inconjunction with waterproofing systems. This guide is intendedto be used in conjunction with Guides C898/C898M, C981,C1471/C1471M, D5898/D5898M, and D6622 and to provideguidelines for the total waterproofing and drainage system.6. General6.1 In selecting a drainage medium for use withwaterproofing, consideration should be given to the design ofthe waterproofing system. In particular orientation of thesystem, attachment recommendations, connections to interiorand exterior drainage systems and external loads applied to thesystem. Additional considerations include the materials andconstruction over the drainage medium, installationrecommendations, durability, and penetrations and joints. (SeeFigs. 1-3.) In all designs, the potential slip planes should beconsidered.6.2 Compatibility—It is essential that all components andcontiguous elements of the waterproofing system are compat-ible and that the design of the system’s waterproofing anddrainage is coordinated to form an integrated waterproofingsystem.6.3 Basic Components—The various types of drainage me-dia available are outlined in Section 12 of this guide and allconsist of one or more of the following basic components. Thebasic components of typical drainage medium are a mountingsurface that is placed against the waterproofing membrane toprevent embedment of the media, a porous core that providesa drainage path, and a filter surface, often a fabric bonded overthe porous core to prevent clogging of the drainage paths.Fibrous and foam drainage media are homogeneous materialsthat are sufficiently dense that they can be placed directlyagainst the waterproofing membrane. However, fibrous andfoam media may not function properly in horizontal or nearlyhorizontal (6.61 L/s (Eq X1.3 and Eq X1.4 above), anotherdrain would be necessary to prevent water from filling up thedrainage media.X1.2.2 The assumption that flow is proportional to hydrau-lic gradient is conservative. Flow rate has been found to moreclosely correlate with (i)0.5or one can use the Manningequation (below) to determine flow in drainage composites inlow slope situations. Using the assumption that flow is propor-tional to (i)0.5, Eq X1.4 becomes:Q/length ~actual! 5 Q/L~@ i 5 1.0 3 @ i ~actual!#0.5!(X1.8)Q/length 5 3.31 L/s 2 m 3 ~0.0208!0.55 0.477 L/s 2 m @2.31 gpm/ft#X1.2.3 The Manning Equation provides another way toestimate flow for a low slope orientation of a drainagecomposite:Q 5 ~K/n! A ~Rh!2/3S0.5(X1.9)where:K = unit conversion constant, 1.49 IP/SI units; 1.0 SI/SIunits,n = Gauckler-Manning coefficient, material/surfacedependent,A = area for flow, perpendicular to flow, ft2,m2,Rk= hydraulic radius = area for flow/wetted perimeter, ft,m,S = slope of surface often equal to i, the hydraulicgradient, ft/ft; m/m, andQ = volume/time, ft3/s; m3/sec.X1.2.3.1 To use the Manning equation, certain features ofthe drainage media must be known. In the example aboveexample with an egg carton type drainage composite, theadditional data needed is as follows. Each cone of the drainagemedia will be assumed to be 12.7 mm high [1⁄2 in.], 9.5 mm [3⁄8in.] wide, and the gap between each cone: 9.5 mm [1⁄2 in.] wide.Thus in 0.3 m [1 ft] of drainage composite, there will be 0.3048m/(9.5 + 9.5) mm or 16 openings. As before, the slope (S) willbe 0.0208. The area for flow for a single opening will be:Cone height × cone spacing = 0.0127m×0.0095m=1.21×10-4m2[0.0013 ft2]Rh =Area for Flow/Perimeter of opening = 1.21 × 10-4/(12.7mm+9.5 mm + 12.7 mm + 9.5 mm) = 0.00272 m [0.00891 ft]X1.2.3.2 Gauckler-Manning coefficients can be found invarious Civil Engineering text books and, in this case, a goodestimate for a composite core made of polystyrene would be0.012. (This assumes a single opening of a drainage compositeis completely surrounded by the polystyrene core; however, ina typical drainage composite one of the wetted sides of anopening would be fabric, so a larger K may be appropriate. Butfor this example 0.012 will be used.)X1.2.3.3 Substituting the values into the Manning equation:Q 5 ~K/n! A ~Rh!2/3S0.55 ~1/0.012! 31.21x1024m23 ~0.00272 m!2/33 ~0.0208!0.55 2.83 31025m3/s ~0.449 gpm! (X1.10)X1.2.3.4 This is the flow through one space between twocones and since the circumference around the drain is 0.3048 m[1 ft, see above] there will be 16 of these openings thus theflow into the drain predicted by the Manning equations is:16 3 Q 5 16 32.83 31025m3/s 5 4.53 31024m3/s @7.18 gpm#(X1.11)X1.2.3.5 As can be seen, the linear analysis gives the mostconservative value while the Manning equation gives thehighest value of flow at the drain/drainage composite interface.All three of these analysis methods are used in water flowanalysis in construction design. Also as mentioned above thelimiting factor in plaza deck drainage in many cases will be thenumber and size of the drains. Thus since many areas havedrain requirements for flat roofs, this drain requirement couldthen be used for a starting point to determine the number ofdrains for a plaza deck with the above analysis used todetermine if for a particular plaza deck system that the numberof drains could be reduced.X1.2.3.6 The above analysis strongly indicates that thedrainage composite/drain interface will be the key designfeature in many plaza deck drainage systems and shows thewater flow through this interface is affected by the diameterand number of drains, slope of the plaza deck, and character-istics of the drainage composite (cone height and spacing).Thus the designer can manipulate these variables to achieve thebest design.D7492/D7492M − 16a9X2. USEFUL EQUATIONS FOR ESTIMATING DRAINAGE REQUIREMENTS FOR VERTICAL WALLSX2.1 To determine the drainage capacity needed for avertical orientation, decide either to size the media to handlepossible water flow before the backfill has consolidated or tobase the water flow rate on the permeability ratings of thesurrounding soil. If the drainage rate needed is to be based onunconsolidated soil, the conservative approach would be simi-lar to the approach used above on plaza decks. The drainagecapacity would be the agreed upon rainfall rate multiplied bythe area that has the potential to catch this rain and direct ittoward the vertical wall. This would be very conservative asobviously some of this rain would either bypass the drainagemedia and go directly into the foundation footing drainagesystem or be retained by the soil.X2.1.1 The approach used on consolidated soil would useDarcy’s equation (Eq X1.3) where Qdis the flow rate in L/s, kis the soil’s permeability coefficient in mm/s, (i) is thehydraulic gradient in metre head loss/metre of liquid travel andA is the area in m2perpendicular to the flow Q. In virtually allcases, this is the surface area of drainage media on the verticalwall. A number of ASTM tests are available to determine soilor rock permeability coefficients, such as see Test MethodsD2434, D4511, D4630, and D3385. Once the appropriate testhas determined the permeability coefficient of the soil, then agood assumption for the hydraulic gradient is 1.0 and thesenumbers along with the surface area of drainage media can besubstituted into Darcy’s equation above to determine thedrainage capacity (Q) needed. Except for soils consisting ofgravel or coarse sand where drainage media would likely besuperfluous, the calculated Q will generally be quite small.Sample calculation:Qd5 kIAv(X2.1)where:Qd= see Eq X1.1 (L/s),k = soil permeability constant (mm/s), see Test MethodsD2434, D4511, and D4630,I = amount of head lost/length of fluid travel (in verticalflow this equals 1.0),Av=m2of below grade wall per m of wall length, andA = area of soil/drainage media interface per metre ofvertical wall length, m2/m;I=1;kdetermined bytesting, approximately 0.00167 mm/s for clay soils,approximately 1.67 mm/s for sand.X2.1.2 Assuming a 2.44 m [8 ft] high piece drainage systemin a clay soil: Drainage Capacity Required = kIA = 0.00167mm/s×1×2.44 m2/m length × 1.0 L/m2-mm = 0.00407 L/sper metre wall length; [14.9 in3/min per foot wall length]X2.1.3 This approach will also work in areas where poten-tial water tables may exist. In these cases, the permeability ofthe soil layer or layers which are below the water table orwhich may transport water during wet weather periods shouldbe determined and used in Darcy’s equation to size thedrainage media. Of course if there are soil layers that have ahigher permeability than the layers that are in the water table,then using the higher permeability coefficient would be appro-priate and conservative.X2.1.4 There are other sources that can be used to determinewater flows and amounts in various areas. The (NRCS)National Resources Conservation Service (formerly the USDASoil Conservation Service) provides models such as the TR-55which models small watersheds. There are also softwareproviders which have programs to model watersheds such asHydrocad (trademarked) at Hydrocad.net. Information can alsobe found in Section 4 of the National Engineers Handbookavailable from the NRCS.These resources can be used to refinethe above analysis on vertical wall drainage systemsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headqu