BEFORE THE ARCHITECT – CUSTOM HOME DESIGNING BACKGROUND – HOUSE DESIGN ARTICLES

RADON MITIGATION PLAN, HOME DESIGN

By Before The Architect  Copyright 2008, 2009

YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION

INTRODUCTION 

      This e-article uniquely addresses practical aspects of radon mitigation design and construction in a custom home plan.*

       Please note well that this e-article is also published hereunder in among the home foundation articles.  In this home designer's opinion, if there were other places to cite this work within the website, he would.

SETTING THE STAGE

      Before The Architect (BTA) was chosen recently to develop a custom home plan, including a radon mitigation plan, for a to-be-built in Knoxville, TN. **
      
      The building authority having jurisdiction in Knox County, TN (and other such authorities across our fruited plain) requires that new home construction includes radon mitigation materials and methods.  Know County building authorities enforce the 2006 International Residential Code (IRC), which includes "Appendix F, Radon Control Methods," a thin and reedy presentation in this home designer’s opinion.
      
      Application of both thick layers of spirit and thin layers of letter of the IRC’s Appendix F must be tailored to a given custom home plan; however, several matters of radon mitigation can resonate with most any plans of custom home design and custom home building.

      Let's radon mitigate in design and construct from the ground up.  (This e-article does not recap code; the referenced code is barely over 2 pages of text and is presented well for as far as it develops the subject, which isn’t very far in this home designer’s opinion.)

DEALING WITH SUB-SLAB OBSTACLES

BACKGROUND

      This is where BTA's radon mitigation plan gets mostly done in materials and labor.

      BTA takes sub-slab-on-grade, substrate preparation, and slab-on-grade support seriously, in unique, home building detail.  Please bear witness in this section of the website to the 20+ entries in Articles>Home Foundations.

      This custom home design involves a lowest level L0 of 4406SF, of which –

      It's the habitable L0 to which a Radon Mitigation Plan directly attends; though, perimeter drains, including those bordering habitable, play a supporting role described subsequently.  (Notably, there is a vehicle garage at L1 elevation, too, which slab-on-grade is separately radon gas-mitigated.)

       Other custom home plan designs precede a Radon Mitigation Plan, most importantly including –

FOREGROUND

     In most radon mitigation plan design, sub-slab-on-ground application should be simplified by a single, uninterrupted layer of code-conforming gas-permeable material; however, this is not possible with almost any of BTA'S custom home plans. 

     BTA's custom home design foundation plans usually engage a honeycomb-like arrangement of grade beams and modified (lesser-sized) grade beams and, occasionally, reinforced concrete strip foundations within perimeter walls and strip footings, in order to bear interior loads and support expanses of reinforced concrete slab-on-ground, particularly at contraction joints, as in this bird's eye view of the major elements to the foundation plan in this article:

Elements of Both Foundation Plan and Radon Plan to Express Grid Patterns, Annotated, Plan View, Scaled

Crisscrossing foundation elements could, unamended by further home foundation design, create pockets of unrelieved, hydrostatic pressure to rise here and there through the slab-on-ground – areas boxed in by grade beams and interior stem wall.  

     So, BTA has altered its sub-slab-on-ground layering design methodology to pierce the perimeter-interior elements at the same level with pipes as sleeves, while holding those pipes' termini within the code-conforming gas-permeable gravel layer.

Comment:  This same-level design for permeability is intended to be effective for both radon gas up and out along with pipe condensate and sub-slab-on-ground moisture down and out.  A two-fer. 

ARRANGING SUBSTRATES 

      First, the substrates as section in elevation, scaled –  

Radon Mitigation System Substrates to Slab-On-Grade, Section in Elevation, Scaled 

       In the Radon Plan for this custom home plan set, each letter is keyed to specifics – some extensively described - of materials and methods involving – 

   A. Slab

   B. Fine aggregate

   C. Moisture and gas impermeable membrane

   D. Sand

   E. Radon code-conforming gravel sandwiched between a certain type of geotextile fabric; this is the gas-permeable (and moisture-permeable) layer

   F. Earth

   G. Contraction, or control, joint

   H. Expansion, or isolation, joint

   I. Stem wall or beam side of face 

RELIEVING SUB-SLAB-ON-GROUND PRESSURES

      Now the question: how to relieve both gas and moisture pressure throughout the foundation interior of habitable? 

      The answer: Smooth, Schedule 40 PVC sleeves through interior beams and stem walls on about 10 linear feet centers overall, whereby the sleeves are wrapped in a specific geotextile fabric at each end and are set at midline to the gas-permeable layer. 

      In an abundance of caution, BTA and clients both preferred –  

      In plan view, this is how BTA expressed sleeve passages (left to right, through grade beam, stem wall, modified grade beam) – 

Pressure Relief Sleeves in Radon Mitigation Plan, Plan View, Scaled  

Comment: Concern over weakening structure with pressure relief sleeve passages would be, in BTA's opinion, overdone:  the lightest reinforcement of this foundation element's passage will be through the modified grade beams at 12 linear inches square, 3500 psi concrete extensively prescribed and proscribed, with 3-Grade 50 #5 deformed rebars continuous top and bottom under not more 3 linear inches cover and not less than maximum aggregate diameter plus ¾ linear inch and crossing bars top and bottom on 16 linear inch centers similarly covered. 

WORKING ACROSS CHANGING ELEVATIONS

      Two occasions arise in this custom home plan whereat pressure relief levels change elevation at L0 –

      In both occasions of such change in elevation, contractors are guided to apply smooth Schedule 40 PVC fittings through foundation elements –

A WHOLE LOT OF SEALING GOING ON  

SITING RADON PIPE RISERS

        Three considerations –

        How many radon pipes shall rise to atmosphere?

        "Typically, one collection point is needed for every 65 m²." Source: footnoted article by C. P. Connell.   

        Quote the client who wrote it better than could the author:  "So that means a collection point for every 700SF of slab-on-ground.  The basement is about 3000SF, implying . . . 5 collection points.  I don't suppose each collection point has to have its own stack [2006 IRC, "Appendix F" is herewith inexplicably moot]. . . Now, to put it in context, he is talking about remediation.  The 700SF is related to how well the sub-slab-on-ground ‘communicates'.  Our gravel base should give good sub-slab-on-ground communication and thus extend the ‘pressure field' beyond 700sqft.  However, I don't know what kind of sub-slab-on-ground environment the author is typically working with when he says that a collection point is typically need for every 700SF.  Additionally, the current design incorporates a continuous sub-slab-on-ground barrier.  Do most of the author's remediation projects have such a barrier? [Doubtful.] Nevertheless, this is the only article I've seen that actually gives any collection point/SF and we would be foolish to ignore this data point." 

        This designer agreed for L0 (noting that the garage in this custom home plan passages to L1, whereat, another radon mitigation system is designed for construction, thereby, there'll be more).

        Where to set the radon mitigation pipe risers through the slab-on-ground? 

        Reckon that the radon pipes should be more or less evenly distributed across the vented slab-on-grade, and may, to code (and, in this custom home designer's opinion and in the client's, should always) be required to extend past the roof deck –

1. There are several code-compliance matters in regard to the radon pipes, including but not limited to IRC, AF103.6.1, §2, "The pipe shall be extended up through the building floors, terminate at least 12 inches above the surface of the roof in a location at least 10 feet away from any window or other opening into the conditioned spaces of the building that is less than 2 feet below the exhaust point, and 10 feet from any window . . ."
2. Be guided by this custom home designer that such pipe shall not be visible to the casual passer-by – usually meaning below a roof ridge and in roof deck planes facing Back Of House  
3. Know that vent pipes commonly are required to be no more than 1/3 of their length on the horizontal (pitched for radon pipe condensate at 1/8 linear inch:1 linear foot), and can be a lesser fraction (this custom home designer is informed as to have been as low at a maximum 1/5 total length on the horizontal), and,  again, radon mitigation code is silent  

       How to tell the contractors where the pipes pierce the slab-on-ground? 

      Same way this custom house designer tells ‘em where to site the sanitary DWV stubs – dimension statements, right on the drawn sheet – referencing strip foot corners (dark hatches designate pilasters atop strip footings, little squares are anchor bolts, intersecting member is a grade beam).

Radon Pipe Siting through Slab-On-Grade, Plan View, Scaled (the DWV "WET A" site is dimensioned on the Foundation Plan, of which this excerpt from the Radon Plan is a stripped-down version)

Comment:  Temporarily seal radon pipe stubs from leftovers to a messy placement, just as with DWV stubs. 

UP, UP, AND AWAY – IDENTIFYING RADON PIPES

      As radon mitigation pipes rise through the home, and aside from limitation on length of horizontal runs (see above) –

WIRING RADON MITIGATION SYSTEMS FOR IN-LINE FANS

The code's reference to power source herewith is amplified as follows –

* For further perspective, please consider searching ‘truth about radon' and the likes generally and, among others, specifically, http://www.forensic-applications.com/radon/radon.html for "Radon – A Brief Discussion" by Caoimhín P. Connell, Forensic Industrial Hygienist

**  Note please that the author knows of no other home radon mitigation plan as broadly and deeply prosecuted and presented as the one done by BTA for the Knoxville custom house plan.                 

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