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Treating SlabsBasementSlab-on-gradeDesigned to Make Sub-Grade Porous and aMeans to Collect Radon laden Soil GasCERTI If the slab is in direct contact with soil, the collection of radon laden soilgas is improved by making the sub-grade more porous such that thelateral movement of soil gases is improved.Appendix F:AF103.2 Subfloor preparation. A layer of gas-permeable material shall beplaced under all concrete slabs and other floor systems that directly contactthe ground and are within the walls of the living spaces of the building, tofacilitate future installation of a sub-slab depressurization system, if needed.The gas-permeable layer shall consist of one of the following:A uniform layer of clean aggregate, a minimum of 4 inches (102mm) thick. Theaggregate shall consist of material that will pass through a 2-inch (51 mm)sieve and be retained by a 1/4-inch (6.4 mm) sieve.A uniform layer of sand (native or fill), a minimum of 4 inches (102 mm) thick,overlain by a layer or strips of geotextile drainage matting designed to allowthe lateral flow of soil gases.Other materials, systems or floor designs with demonstrated capability to permitdepressurization across the entire sub-floor area.The alternate methods were expanded in Fort Collins adaptation Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201116

Improving Soil Gas CollectionDuring Construction Of Slabs1. Four inch layer of clean aggregate beneath slab. When gravel is incorporated for drainage or isinexpensive.2. Loop of perforated pipe beneath slab. When existing soils are permeable.3. Interconnected strips of drainage mat beneathand around interior perimeter of slab. When soil is well compacted.CERTI The concept for dealing with slabs is to provide a means for gases in the soil,such as radon, to move freely through the soil to a collection point. It has beenshown that this can occur by at least three proven methods. The choice of whichmethod is to be used is purely a matter of economics. It would appear, at thepresent time that all three are equivalent.If gravel is inexpensive, or placing gravel beneath a slab is a normal feature ofconstruction, then gravel option would be the most cost effective.If native soils are permeable enough to allow for water drainage then the poorerporosity of uncleaned fills can be overcome by installing a loop of perforated pipein the subgrade to facilitate collection.The perforated pipe may be replaced by lengths of 1 inch tall matting laid betweenthe subgrade and the bottom of the slab and connected to form a rectilinear looparound the interior of the foundation perimeter. The choice of the mat over theperforated pipe is made upon the degree of difficulty and cost in trenching in aperforated pipe, compared to laying a strip of material on top of the prepared subgrade immediately prior to pouring the slab. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201117

Option 1: Aggregate Option 4 inches of clean aggregate Between 1/4 inch and 22-inch in size CaulkSoil gas retarder Minimum 6 mil polySlabFootingAggregateFill or native soils6-mil sheeting4-inches Overlapped and extended to edges Punctures and tears to be sealed Slab joints to be caulked andsealed.Note: Fort Collins opted to: Eliminate sealing of plastic with well sealed slab Allow pea gravelCERTI AF103.2 Option 1:A uniform layer of clean aggregate, a minimum of 4 inches (102 mm) thick. Theaggregate shall consist of material that will pass through a 2-inch (51 mm) sieveand be retained by a 1/4 -inch (6.4 mm) sieve. A uniform layer of washed gravelwill provide a path for radon to flow through provided it is not obstructed byintermediate footings or concrete that sinks into the voids within the gravel layer.Note: if smaller aggregate is used than specified above, its ability to collect soilgas is to be enhanced with one of the other options (perforated pipe loop ordrainage mat.Gravel is often a normal design feature of a building for the collection of water. Ifthis is the case, then little additional cost is involved by selecting this method.Fort Collins Adaptation:The Fort Collins Code does not require a sealed polyethylene sheeting beneaththe concrete. Rather the gas resistant seal is accomplished by caulking andsealing floor-to-wall joints, control joints and plumbing penetrations. This doesnot prevent the use of moisture barriers under slabs, but rather that specialprecautions for sealing plastic for radon control methods is not required. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201118

Soil Gas RetarderCan beexpensive Labor intensiveto seal May requirespecial additivesfor concrete CERTI In some publications, it is suggested the membrane under the slab be sealed at allpenetrations, seams and around sumps (See ASTM 1465).This can be very labor intensive and can also cause cracking issues with theconcrete if it cannot properly de-water.In considering this in Fort Collins, it was decided that a vapor barrier could go downas is normally done, but the top of the slab be well caulked. Note it is easier for aninspector to see caulk in a basement before it is finished than to inspect the plasticmembrane before the concrete arrives. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201119

Aggregate Option:Allowing for Lateral Air FlowPost and BeamFoundation with Grade BeamRiserRiserSleeves Minimum of two grade beampenetrations. Minimum of 12 sq. inches ofopening per 10 ft. of grade beam.CERTI Often a grade beam or intermediate footing is installed beneath a slab to provide support of a loadbearing wall. These grade beams can present a barrier to the lateral flow of air beneath the slab tothe system collection point. This can be avoided by using post and beam construction where teleposts that support overhead beams are set on pads rather than continuous footings.If a continuous grade beam is used then a means to allow the air to flow through the grade beam mustbe provided. This is typically accomplished by inserting at least two 4 inch pipe sleeves between theform boards or trench and pouring the grade beam over them. The spacing of these pipes should beat opposite ends of the grade beam with a spacing of one every 10 feet, with a minimum of twoinstalled. The pipe can be 4 inch schedule 40 PVC or 4 inch corrugated ADS pipe. Be sure to tapethe ends so concrete does not enter the ends of the pipe while pouring the footing. Remove tape afterforms are removed.Appendix F does not specifically address this approach, but rather specifies a separate vent pipe foreach area as follows:AF103.6.2 Multiple vent pipes. In buildings where interior footings or other barriers separate thesub-slab aggregate or other gas-permeable material, each area shall be fitted with an individual ventpipe. Vent pipes shall connect to a single vent that terminates above the roof or each individual ventpipe shall terminate separately above the roof.Other code jurisdictions have used the following language to allow for more cost-effective sub-slabcross-overs:In buildings where interior footings or other barriers separate sub-grade areas, penetrations throughthe interior footing or barrier equal to a minimum of 12 square inches (0.094 m2) per 10 feet (3.048 m)of barrier length shall be provided. A minimum of two penetrations shall be provided per separationand be evenly spaced along the separation. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201120

Aggregate Option:Connecting Gravel to Vent PipeSch. 40 PVC PipePVC Pipe CouplingSlabSlab“Tee” MinimumRequirementSch. 40 PVC PipePortion of vent pipe to beconnected to sub-gradebefore concrete pour. Minimum 3-inch “Tee” orPVC Pipe Couplingequivalent Means to keep fitting fromfilling with gravel ispreferred.SlabReducesAir BlockageSch. 40 PVC Pipe PVC Pipe CouplingSlabComplies with codeand reducespotential blockageShort length or perforatedpipe beneath slab. “Tee” should be same sizeas riserCERTI AF103.5.1 Vent pipe riser. A minimum 3-inch-diameter (76 mm) ABS, PVC orequivalent gas-tight pipe shall be embedded vertically into the sub-slab aggregateor other permeable material before the slab is cast. A “T” fitting or equivalentmethod shall be used to ensure that the pipe opening remains within the sub-slabpermeable material.It does no good to go to the trouble of placing gravel beneath the slab and insuringgood air flow, if the pipe is stuck directly into the gravel. You need to allow for easyentry of the air into the pipe. In the case of the gravel alternative this is mostcommonly accomplished by using 4 inch corrugated and perforated pipe (drain fieldpipe) at least 10 feet in length. This can be accomplished with a PVC Tee (asshown) or a PVC 90 degree elbow with a single length of perforated pipe securedinto the throat of the 90.In the case of large buildings such as schools or apartment buildings, largerectangular metal pits have been constructed and located in the gravel beneath theslab. It is constructed from angle iron which supports a solid metal decking uponwhich the slab rests. Around the perimeter of the box is expanded metal that facesthe sub-slab aggregate and allows the radon to enter the interior of the box. Thevent pipe is connected directly to the box. (See Radon prevention in the Design andConstruction of Schools and Other Large Buildings, Third Printing with Addendum,June 1994, EPA/625/R-92/016) Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201121

Option 2: Perforated PipePassive Vent Riser Continuous loop ofperforated pipe. Roughly 12 inches fromwalls. Suggest 2 foot clearancefrom sub-grade drainagelines if present Flexible or rigid pipe Wrapped with filter cloth.Perforated PipeFlexible andperforated pipecan be purchasedwith “sock”sock” on.CERTI In some regions of the country native soils are permeable enough not to require theimportation of gravel for water drainage. In other areas, the importation of gravel is veryexpensive. In the case where gravel is not already being used, or is expensive, it may bemore cost-effective to use the native fills beneath the slab and improve soil gas movementby laying in a loop of perforated pipe. This works well because the soil gases need onlymove to the loop rather than all the way across the slab (as would be the case if a singlecollection point was used.)The following addendum was added to the Fort Collins Code to allow for the use ofthis approach:A foundation drain pipe system installed under concrete floor slab areas less than 2,000square feet (186 m2), consisting of a continuous loop of minimum 3-inch (76 mm.) diameterperforated pipe shall be laid in the sub-grade with the top of pipe located 1 inch (25.4 mm)below the concrete slab. The pipe may be rigid or flexible but shall have perforations fullyaround the circumference with a free air space equal to 1.83 square inches per square foot(127 cm2/ m2) of exterior pipe surface area. Such pipe shall be wrapped with approvedfilter material to prevent blocking of pipe perforations. The pipe loop shall be located insideof the exterior perimeter foundation walls not more than 12 inches (305 mm) from theperimeter foundation walls. In buildings where interior footings or other barriers separatethe sub-grade area, the loop of pipe shall penetrate, or pass beneath such interior footingsor barriers.Note: The perforated pipe should be a “nominal” 12-inches off the walls. It can veer awayfrom wall to distances greater than 12–inches to avoid plumbing penetrations, etc., butshould return to the “nominal” 12-inches after avoiding interference. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201122

Trench Option CVCInstead of gravel throughout Gravel and perforated pipe in trench Loop design CERTI Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201123

Sub-Grade Pipe Size and Loops4”3”20003”3”60004000Footprint (S.F.)4”4”LoopsDiam.Up to 2,00013"2,000 to 4,00014"4,000 to 6,00023"8,00024"orLoopsDiam23"Loops should be interinter-connected8000CERTI The reason for laying it out in a loop is to allow for the soil gas to enter the verticalvent pipe from two sides. Another reason for the loop is that if it is crushed at onepoint during construction the soil gas will still be drawn to the vent pipe.Fort Collins Verbiage:AF103.2 Option 2:A foundation drain pipe system installed under concrete floor slab areas less than2,000 square feet (186 m2), consisting of a continuous loop of minimum 3-inch (76mm.) diameter perforated pipe shall be laid in the sub-grade with the top of pipelocated1inch(25.4mm)belowtheconcreteslab For slab areas greater than2,000 square feet (186 m2) but less than 4,000 square feet (372 m2), the precedingconfiguration may be used provided a minimum of 4-inch diameter (102 mm) pipe isinstalled. Slabs in excess of 4,000 square feet (372 m2) shall have under themseparate loops for every additional 2,000 square feet (186 m2) of slab area when 3inch (76 mm) diameter pipe is used; or, slabs may have separate loops provided foreach additional increment in area between 2,000 square feet (186 m2) and 4,000square feet (372 m2) when 4-inch (102 mm) diameter pipe is used. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201124

Perforated Pipe Option: Cross-OversRiserGarage Grade BeamMake provisions for pipe topenetrate obstructions. Short lengths laid in trenchesPipe Loop Tape ends to keep clear ofdebris. Attach to main loopafter grade beam finished Pipe sleeves in intermediateImportant:When passing under grade beamsmake sure that perforations of pipeallow drainagefootings. Pass perforated pipe through.CERTI The riser can be anywhere on loop(s) of perforated pipe that is convenientfor routing vent pipe up through structure.Perforated and corrugated ADS pipe is flexible which makes it is easy to laydown in a trench. The perforations also allow for good soil gas collection.Be sure the pipe is covered by at least 1 inch of fill to keep concrete fromfilling perforations.Where perforated pipe is to pass through or under grade beams/intermediatefootings:If pipe is beneath grade beam, water must be able to drain from inside ofpipe.Put short-lengths through trench before pouring and later connect stubs tomain system (be sure debris cannot enter pipe, while unattached.Or install pipe sleeves through which pipe can be passed through afterintermediate foundation is set. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201125

Perforated Pipe Option: RiserSch. 40 PVC PipePVC Pipe CouplingSlabCorrugated, PerforatedPolyethylene pipe8” stub of 4” PVC PipeTee and perforated pipe same diameter as vent pipe.CERTI Locating where you want the riser to come up through the slab is a functionof where you want to route the piping up through the house. Typicallyhaving it come up in the furnace (utility) room is preferred because it is anout-of-the way place and you can run the vent piping up through the fluechase. Furthermore having the pipe enter warmer areas, such as the furnaceroom will enhance the stack-effect and reduce the need for an active system.Where the riser connects to the sub-slab loop doesn’t make any differenceprovided that you have made a complete loop with the perforated pipe.The corrugated and perforated pipe should be connected to short pipe stubsand connected to opposite legs of a 4 inch PVC Tee. When three inchcorrugated pipe is used, the corrugated pipe can be inserted into the pipestubs and secured with sheet metal screws. When 4 inch corrugated pipe isused, 4 inch by 4 inch rubber couplings can be used to connect theperforated pipe to the solid PVC pipe stubs. Copyrighted by the Center for Environmental Research and Technology Inc - Revised March 201126

Option 3: Mat OptionExploded Viewof MatCaulkMatFilter FabricMinimum 1 inch high & 12 inches wide. Lay mat directly on subgrade Pour concrete over mat CERTI In some regions of the country native soils are permeable enough not to require the importation ofgravel for water drainage. In other areas, the importation of gravel is very expensive. In the casewhere gravel is not already being used or is expensive it may be more cost-effective to use thenative fills beneath the slab but to improve air movement by laying in a rectilinear loop of soil gascollection mats. When it is easy to dig a trench and lay in corrugated pipe that option is typicallyused. Where sub-grade soils are compacted, the ground is frozen, or labor is expensive drainmats are often used.Drain mats consist of a plastic material that resembles an egg-crate. Wrapped around the “eggcrate” is a geotechnical filter fabric that allows for the passage of air but prevents the infiltration ofwet concrete. Because of this, the mat can be laid directly on top of the prepped sub-grade andthe concrete poured directly over it. It is a little more expensive than perforated pipe, but theinstallation is very fast.Note: a minimum of 3.5 inches of concrete must be maintainedAF103.2 Paragragh 2: A uniform layer of sand (native or fill), a minimum of 4 inches (102 mm) thick,overlain by a layer or strips of geotextile drainage matting designed to allow the lateral flow of soilgases.Fort Collins Addition:A foundation drain soil gas collection mat system installed under concrete floor slab areas of 2,000square feet (186 m2) or less, consis

Radon Control Techniques in New Colorado Homes Sponsored by: The Colorado Department of Public Health and Environment Presented by: Doug Kladder Center for Environmental Research and Technology, Inc. March 2011 . Colorado Springs, CO 80903 phone: 719-477-1714 email: DKladder@Certi.us