[Greenbuilding] Mold questions

[Bruce Donelson]

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org]On Behalf Of Jefro
Sent: Monday, August 28, 2006 1:29 AM
To: Greenbuilder list
Subject: [Greenbuilding] Mold questions


We live in northern coastal California where mold is a special problem.
Relative humidity averages something like 80% here.  Mold is a big
concern for us, as my wife has asthma and we both have allergies.  We
are currently living in a 70s home that has some moisture infiltration
issues, and just today we discovered that our expensive organic cotton
mattress is moldy.  (Anyone know how to get mold out of a mattress?)

However, I am most concerned about the house we are building this fall.
Positives:  it will be in a warm meadow a few miles inland with lots of
sunshine, out of the fog.  It will be very well-insulated and will have
hardwood floors and a house vac, and the cats will live outside
(mostly).  None of these things are true right now; we live under the
redwoods in the fog zone with wall-to-wall carpeting and unruly indoor cats.

Some potential negatives we have identified:

- The aforementioned humidity, though we can deal with that with a
dehumidifier if necessary.

- We are planning to use cellulose insulation.  Mold loves cellulose.
Do the borate additives help prevent mold growth?  Since this is a
health issue for us, should we be looking more seriously at icynene foam?

Borates will do the job.

- I am concerned about getting vapor barriers right.  We are building a
double 2x4 wall on 2x10 plates, with plywood sheathing and stucco
outside, plaster inside.  I have been expecting to use a vapor barrier
outside the plywood.  Should I plan for a barrier under the interior
plaster as well?  How about in the floor?

The stucco side of the wall will have the vapor barrier. You want the wall
to be able to dry out if it ever gets wet, so you should not use a vapor
barrier inside. The floor sheathing should be an adequate vapor barrier. To
make sure that it is also a good air barrier, glue the edges of the sheets
together as they are laid down. Also be careful to seal all of the
penetrations for pipes etc. State of the art is a conditioned crawlspace (or
short basement.) You can find details about most of these things in a
reference guide from the Energy & Environmental Building Association (EEBA)
called the Builder's Guide. You would want the version for mixed-humid
climates.

- Our building cycle is very close to the winter rains, as our escrow on
the property in question has dragged out unceasingly.  We are worried
about embedding moisture in the house as we build it, particularly as we
are building with green lumber that we will be milling on-site.  Right
now the plan is to get the framing, sheathing, and roof done before the
winter rain starts and work on the interior carpentry all winter, and
probably won't put in the insulation until next spring in order to get
the framing good and dry.  How do we make sure everything dries out
completely before we seal things up?

You will need to insulate before the interior finish carpentry is done.
Interior framing shouldn't take very long at all, unless it is abnormally
complicated. The framing materials should be checked with a moisture meter.
If necessary, the vents can be sealed, and the building can be heated with
DRY air to help the framing lumber dry out.

I understand that these are questions for the contractors who are
advising us and actually doing the bulk of the work, and I am asking
them as well.  However, my experience talking with many contractors,
engineers, architects, tradespeople, etc. in this process is that people
often base firm opinions more on their limited experience than on
widespread research.  Also, many people don't necessarily see mold as a
serious problem.

Mold is vastly overrated as a health problem. It is true that some people
have reactions to it, but most typically constructed houses these days will
have a lower concentration of mold spores inside them than outside them,
except if there is snow on the ground outside. In the redwoods, there is
lots of outdoor mold as fungus is continually digesting all the cellulose in
the mulch layer. Climate may be a bigger factor than housing in some cases.
Find a contractor who is familiar with these issues, there are probably lots
around there. A well-detailed set of plans can help also. You might look for
contractors who build Energy Star houses, they will tend to be better
educated on some of these details.

A house is a complex array of interacting systems. Some older house types
were more forgiving of water intrusion in windows, because their walls dried
out very quickly. Today's houses are not so drafty, and are made of
materials that like to be kept drier. So there have been quite a few
examples of houses that have rotted badly when large amounts of water have
been trapped inside the walls.

Good luck with you new house.

Bruce Donelson
A Better Builder