Tag Archives: ventilation

Radon Gas Mitigation Solutions in Brief

While I do not personally perform radon mitigation, I wanted to share in brief what is generally entailed. The cost in the Dallas area for reducing radon below the EPA action limit of 4.0 pCi/l varies depending on the construction / size of the house and how high the levels are. In general, you can expect an estimate of anywhere from $2000 – $5000.

It is suggested that the solution follow the ASTM E-2121 standard for lowering radon and that information can be found in detail here:


While homes that contain excessive radon can be found in every state in the nation, many people (such as in Texas) are not aware that it is a problem, nor is testing / mitigation required by Texas law as of this writing. However it is not unusual for some relocation companies to require testing for radon gas first as a condition of a real estate purchase.

Bear in mind that radon levels do fluctuate with weather conditions and home ventilation, so before investing in a mitigation expense, it may be worth testing more than once.

The main idea behind mitigation is to ventilate the excess radon (which is heavier than air) to the outside so as to minimize impact to occupants. The method by which this is done depends on whether you have a basement (rare in the Dallas/Ft. Worth area) have a pier and beam or slab on grade foundation.

For slab foundations, sealing the interior spaces from the ground is generally not enough, and often a soil suction system is required to actively draw the radon out via a vent pipe and specialized fan. These systems are generally referred to as active soil depressurization, sub-slab depressurization or just simply soil suction.

In some cases, a heat exchanger or ERV (Energy Recovery Ventilator) can recover some of the energy lost in the process of exchanging the vented radon to the outside with fresh air.

For pier and beam foundations (houses with crawlspaces) you can cover over the base soil with a special heavy duty plastic sheet whose underside connects to a ventilation system similar to the one described above in a method known as sub-membrane suction.

Sub-membrane Suction Radon Mitigation

Sub-membrane Suction Radon Mitigation

Control of Formaldehyde (HCHO) and VOCs in Indoor Air Quality

One of the first issues to address for pre-existing construction is proper selection of materials that have low VOCs and formaldehyde content (UF or Urea-Formaldehyde) and/or that outgas (release the noxious vapors) relatively quickly. Low emission products include:

  • Low VOC paints
  • Low VOC carpeting (though carpets tend to have inherent issues with collecting/releasing dust)
  • Other mastic (waterproofing putty) products that have low levels of 4-phenylcyclohexane (4-PC) which produces a characteristic odor
  • Pressed wood products that have low formaldehyde (HCHO) levels
  • Formaldehyde-free varnishes and lacquers
  • Softwood plywood
  • Oriented-Strand board
  • Decorative gypsum board
  • Hardwood panels
  • Pressed woods with PF (Phenol-Formaldehyde) resin release less HCHO than UF resins

You might want to AVOID:

  • Medium-Density Fiberboard (MDF) sometimes used in cabinets, furniture and doors
  • Hardwood plywood paneling
  • Particleboard
  • Pressed wood products with UF
  • UF-based Acid Cured Finishes
  • Homes insulated with UFFI (Urea-Formaldehyde Foam Insulation) though this is unlikely to be an issue
  • High humidity (keep between 40 – 50 % RH)
  • Occupying the home or property until a proper out gassing period has passed – preferably during hotter weather
Formaldehyde Emissions from variou Construction Materials

Formaldehyde Emissions from various Construction Materials

Then having an outgas period before occupation is good when possible. Preferably during hot, humid weather which tends to accelerate the exit of gaseous residues from the building materials. If you have an existing wood material that is emitting formaldehyde, then the can be treated with scavenging coatings or encapsulated with vinyl materials.

ASHRAE Ventilation Guidelines 2013

ASHRAE Ventilation Guidelines for Acceptable Air Quality – 2013

Another critical factor is having adequate ventilation, particularly during the initial outgas period. Many homes and multifamily dwellings are often built rather “tight” as a response to the desire for energy conservation and reducing moisture intrusion. If it is not a security issue, keeping the windows open even a crack on opposite sides to create a flowing cross-draft can assist out-gassing as well as opening chimney dampeners.

Factors in formaldehyde levels:

  1. Composition of building materials (formaldehyde potency in manufacture)
  2. Loading factor (amount of material in exposed surface area and volume)
  3. Material age
  4. Adequate ventilation taking into account occupancy and room size
  5. Environmental conditions
Indoor Air Exchange Rate Per Hour Table

Indoor Air Exchange Rate Per Hour Table


Formaldehyde Levels Indoor Air Quality

How Formaldehyde Levels Decrease Over Time

The use of sorbents (gas absorbent materials) such as activated charcoal can be used to remove relatively high molecular weight VOCs such as toluene, benzene, xylene and methyl chloroform.

For lower molecular weight (MW) materials such as formaldehyde (HCHO), ethylene, and acetaldehyde then potassium permanganate, (KMnO4) activated alumina or specially impregnated charcoal are better choices than regular activated charcoal.

Other special air cleaners may also be used – consult ScanTech for further information.