46 | February 2020
Paint was also peeling off the siding close to grade,
where there was roof-water splash. Where the building
faced wind-driven rain, water got behind the siding at all the
butt joints.
How can such problems be avoided? Well, the obvious
answer is that cement-board siding cannot get wet – ridicu-
lous though that sounds.
Roof water should never flow down the siding, but this is
a particularly worrisome condition with this kind of cladding.
There must be kick-out flashings at roof edges that inter-
sect with vertical walls. It would also help if manufacturers
of this type of siding always back-primed the boards and
sealed the butt ends and end grains. Finally, I recommend
that factory-supplied sealants be applied to all cut ends,
which will reduce water absorption.
There is one more visual problem that can occur with
installation of this kind of siding. Wherever the planks have
been cut with a circular saw, the very fine dust that is pro-
duced adheres to the surface, giving the siding a flat, mot-
tled look. Unfortunately, the only thing that seems to remove
this dust is vinegar: a time-consuming chore! The cement
boards should really be cut with shears made for this pur-
pose, rather than sawed with a circular blade.
Founder and Principal Scientist of May Indoor Air Inves-
tigations LLC in Tyngsborough, MA (www.mayindoo-
rair.com), Jeffrey C. May combines his education as an
organic chemist and his over twenty-five years of experi-
ence investigating building problems to specialize in indoor
air quality (IAQ). He is a former Adjunct Faculty Member
in the Department of Work Environment at University of
Massachusetts Lowell, and is author or co-author of four
books on indoor air quality (published by The Johns Hop-
kins University Press), including My House is Killing Me:
The Home Guide for Families with Allergies and Asthma.
Jeff is a nationally recognized speaker at annual confer-
ences for the IAQ Association and the Maine IAQ Council,
among others. He is a Council-Certified Microbial Consul-
tant (ACAC) and a Certified IAQ Professional (AEE), and is
licensed in the NH and FL as a mold inspector/assessor. Jeff
holds a B.A. from Columbia College (chemistry) and an M.A.
from Harvard University (organic chemistry). See http://www.
mayindoorair.com for details about Jeff's company's
services, and www.myhouseiskillingme.com for more
information about Jeff's publications and work. You can con-
tact Jeff at jeff@mayindoorair.com or call 978-649-1055.
i
Much of my work is in residential
buildings, but I also do IAQ inspections
in offices, schools and hospitals.
If any of your clients are worried about
environmental issues in their places of
work, please refer them to my book
below, available on amazon.com.
