geotexile fabric under drainage layer

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Author Message Margaret G. Chewning FCSI CCS Senior Member Username: presbspec Post Number: 373 Registered: 01-2003 Posted on Thursday, July 10, 2025 - 09:20 am:    I have a project where the contractor wants to place a geotextile fabric below the drainage layer of the the 4" slab on grade, 18" geofoam insulation and a 6' drainage layer. This is in an area where ground water is not a concern. The question from my architect is "is this common or necessary?" ken hercenberg Senior Member Username: khercenberg Post Number: 1662 Registered: 12-2006 Posted on Friday, July 11, 2025 - 11:27 am:    I know a lot of Contractors like having geotextiles down in areas prone to washouts since it keeps the soils in place while running equipment and even before concrete pours. Can't hurt having it there for soil stabilization. Since it becomes part of the permanent installation it's more than just means and methods. If the drainage layer is going over 18 inches of geofoam it does sound like overkill. I presume you're putting a vapor retarder over the drainage fill so the whole configuration should be pretty stable. Margaret G. Chewning FCSI CCS Senior Member Username: presbspec Post Number: 374 Registered: 01-2003 Posted on Friday, July 11, 2025 - 11:33 am:    Thanks Ken, Actually the geotexile will be under the drainage layer. The vapor barrier is placed above the geofoam insulation, just below the concrete slab.