Foundation Drainage Board (Dimple Mat) Takeoff
Dimpled drainage board to cover a below-grade foundation wall, ordered by the roll.
Example
You enter
- Foundation perimeter (ft) 150
- Average below-grade height (ft) 8
- Roll width (ft) 4
- Roll length (ft) 50
- Waste (percent) 10
You get
- Below-grade wall area 1,200 sf
- Rolls 7
- Termination (LF) 150
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeThe dimpled drainage board (dimple mat / composite drainage sheet) to cover a below-grade foundation wall over the waterproofing, ordered by the roll -- it relieves hydrostatic pressure to the footing drain and protects the membrane during backfill. Area = perimeter x average below-grade height; rolls = ceil(area x (1 + waste) / roll coverage); plus a top-edge termination bar per perimeter. A 150 ft perimeter, 8 ft below grade is 1,200 sf, so at a 4 x 50 ft (200 sf) roll with 10% waste it takes 7 rolls plus ~150 lf of termination molding. Orientation follows the product: a plain dimpled membrane goes dimples to the wall; a fabric-faced composite goes flat side to the wall, fabric to the soil. Order the termination bar, corners, and butyl tape separately and lap per the maker's detail. A material-ordering estimate; the roll size and lap, the assembly detail (membrane below, footing drain per IRC R405), and the AHJ govern.
Formula or tablewall_area_sf = perimeter_ft x below_grade_height_ft; roll_coverage_sf = roll_width_ft x roll_length_ft; rolls = ceil(wall_area_sf x (1 + waste_pct/100) / roll_coverage_sf); termination_lf = perimeter_ft.
Source and editionFoundation drainage board (dimple mat) material takeoff (area over roll coverage), by name; the product roll size and lap, the assembly detail, and IRC R405 (foundation drainage) and the AHJ govern.
Free accessThe takeoff is public first-principles (wall area over the roll coverage); the roll size comes from the product data sheet and the dimensions from the foundation.
What governsEstimate. AHJ and licensed professional govern.
API field namesperimeter_ft, below_grade_height_ft, roll_width_ft, roll_length_ft, waste_pct, wall_area_sf, rolls, termination_lf
- Area over roll coverage area = perimeter x below-grade height; rolls = ceil(area x (1 + waste) / roll coverage); termination bar per perimetermaterial-takeoff practice
- Orientation and detail plain dimple mat dimples to the wall; fabric-faced composite flat side to the wall, fabric to the soil; relieves hydrostatic pressure to the footing drain (IRC R405); lap and accessories per the makerIRC R405 / product data sheet