NC Lyme Disease Foundation, Inc.

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Follow-up Questions and Answers from Hillel Abrams after his talk on “How to Make

your House Inhospitable to Mold” on February 11, 2018 to the NC Lyme Disease

Foundation Support Group meeting in Raleigh, NC.

Question 1. Is it true that one should have NO grid openings to a crawl space?

Answer - The Crawl should always be sealed because throughout most of the year an unsealed /

vented crawl will have higher relative humidity entering it than you want.  This problem leads to

two additional problems I spoke of:  mold propagation (for existing mold) and dew point (which

feeds mold creation).  Remember 50% and above is considered the general cut off.  Above 50%

relative humidity molds (it varies by genus and species) begin to propagate; below it, mold will

go dormant.  The building biology approach is to remove the mold without toxic / questionably

safe fungicides and to address the humidity conditions that allow it to flourish.  Our crawl space

has a dedicated dehumidifier that is ducted to all four corners with both supplies and returns to

insure maximum distribution, thus avoiding the inherent problem with most dehumidifiers - they

only dehumidify the immediate area then cycle off.

Question 2. Should one have a fan to blow warm air out of a bathroom?

Answer - The goal throughout the entire house should be relative humidity below 50% (45% is

even better) to avoid both mold propagation and dew point.  In the bathroom (which will have

higher relative humidity at times because of usage) the goal is to move the dry air coming from

out of your registers throughout that space while avoiding dew point (do not have a ceiling vent

directed into the shower area blowing cool air hitting warm moist air from a shower).  You can

do this with a portable fan or a customized built-in shower dry system (what was installed for us

by Mead).  Many exhaust fans are not powerful enough or keep clean enough to do the job by


Question 3. You recommended an HVA (??) system. Please clarify.

Answer - The HVAC system we had installed has all the ductwork and air handler seams sealed

with non-toxic duct sealant/mastic (Dynaflex)) and non-toxic tape (Shurtape - AF973).  The

dehumidifier is ducted into the air handler so that dry air is distributed through the ductwork into

each room through the registers.  Ideally each bedroom should have both supplies (bringing air

in) and a return (taking air out) to keep the air moving - standard in new homes.  The

dehumidifier is also dried out by ductwork from the HVAC.  Much of this type of customization

is proprietary to Mead Indoor.  The acronym HVAC actually means 'Heating Ventilation And


Question 4. If you have a slab, you must add extra moisture barriers under your carpet or flooring. What is recommended? I am about to rip out the carpet in my den because it “smells” after mildew.

Answer - The Moisture barrier (capillary break in building biology terms) should actually be

between the soil and the slab (installed before the slab is poured).  This capillary break prevents

the moisture from rising from the ground into the slab and then whatever is above it.  The

problem with putting a moisture barrier over the slab is that you are now trapping the rising

damp into the slab which can lead to its compromise.  My recommendation is that you replace

the carpet with an inert product like ceramic tile (stay away from imported tiles - many have

glazes with lead and can be radioactive).  I recommend reading the section on Tile in

"Prescriptions for a Healthy House" to learn about different sets, underlayment, sealants, and grouts. There are many non-toxic choices to choose from.

Question 5. Do you have any articles dealing with the increase in mold production caused by increased EMF production?

Answer - Mold and EMF (electrical magnetic fields) are problematic by themselves; together they

appear to go from bad to worse.  The research that I have read appears to indicate that mold

regards EMF as a threatening fungicide so it produces additional MVOC (microbial volatile

organic compounds) and/or mycotoxins (dependent on the mold species) to combat the threat.  I

have included a couple of different links about that:

Hope this helps.

Hillel Abrams