about your house

about your house
about your house
CE 37
The T e n a n t ’ s G u i de t o Mo ld
This About Your House is for people
living in rented houses. Cleaning up
mold can be either the tenant’s or
the landlord’s responsibility—or a
responsibility shared by the tenant
and landlord.
Mold can be harmful or helpful
—depending on where it grows.
Mold needs moisture to grow.
Mold does not grow on dry
Mold growing inside home can
affect occupants’ health.
Occupants can learn to recognize
You encounter mold every day. Foods
spoil because of mold. Leaves decay
and wood on the ground rots because
of mold activity. The fuzzy black
growth on wet windowsills is mold.
Paper or fabrics stored in a damp
place get a musty smell, which is
caused by molds.
Various kinds of molds grow on
different materials. Certain kinds
of molds like an extremely wet
environment. Other kinds of molds
may be growing even if no water
can be seen. Dampness inside a
material can be enough to allow
them to grow.
Molds, when carefully chosen and
grown under careful control, are
useful. We get penicillin from one
type of mold. Mold action helps
make some foods and beverages.
Why molds are a concern?
Molds are undesirable when they
grow where we don’t want them
—such as in the places we live in.
Researchers have identified more
than 270 species of mold as living
in Canadian homes.
What are molds?
What makes molds grow?
Molds are microscopic fungi. They
are part of the same family as yeasts,
toadstools and mushrooms. Fungi
grow and reproduce rapidly and
as they grow they produce spores
—specialized reproductive cells
—and mycelia—fine, white
filaments or threads.
Molds will grow when they have
moisture and nutrients. If we keep
things dry, molds do not grow.
High moisture levels can be the
result of water coming in from the
outside, through the floor, walls,
roof or plumbing leaks—when there
is a weakness or failure in the structure.
High moisture can also result when
there is not enough ventilation to
expel moisture produced by occupants’
daily activities like bathing, washing
clothes or cooking.
Damage to materials is one concern.
Mold can stain or discolour material
and, over time, ruin it. Moldy paper
and cardboard disintegrate over time.
Fabrics are damaged. Continued
mold growth can be a sign that
moisture conditions are favourable
for the growth of fungi that cause
wood rot and structural damage.
Molds inside a house can cause health
problems. They release spores as well as
chemicals, and both can affect people.
Health experts say the effects of mold
can range from being insignificant
to causing allergic reactions and
illness. Their effect depends on
the type of mold, the amount and
degree of exposure and the general
health of the occupants.
About Your House
The Tenant’s Guide to Mold
Pregnant women, infants, the elderly
and people with respiratory disease
or weakened immune systems are
more at risk when exposed to mold.
If you believe that you or someone
in your family is at risk, consult
your family physician.
How can you tell if it is mold?
One sign of mold is discoloration.
Not all discoloration is mold. Carpeting
near baseboards, for example, can be
stained by outdoor pollution entering
the dwelling. Smoke from burning
candles or cigarettes may also cause
stains or soot.
Mold may be any colour: black, white,
red, orange, yellow, blue or violet. Dab
a drop of household bleach onto a
suspected spot. If the stain loses its
colour or disappears, it may be mold.
If there is no change, it probably
isn’t mold.
Sometimes molds are hidden. A musty
or earthy smell is often a sign that
there is mold. But not all molds create
an odour. Even when you don’t notice
a smell, wet spots, dampness or signs of
a water leak indicate moisture problems
that can be followed by mold growth.
Is there a mold problem?
Molds are always found in outdoor
air and in all buildings. They come
into a house in many ways—through
open windows or doors, on clothing,
pets, food or furniture. The problem
starts when mold grows inside the unit.
Canada Mortgage and Housing Corporation
The presence of mold is a sign that
there is too much moisture—a
situation which must be corrected.
Some mold, for example on a
windowsill but not elsewhere, is not
a major cause for concern—it can
be removed as part of routine cleaning.
Mold on grout in bathroom tiles
may or may not be a concern. Some
discoloration between tiles but not
elsewhere can simply be a sign that
these areas are moist most of the
time. The moldy spots can be cleaned
with a brush and unscented detergent.
In every case you must take further
steps to prevent the mold from coming
back. But if the grout is extensively
discoloured and there is staining or
damage to the ceiling or walls, there
may be a more serious mold problem.
Regularly look for signs of mold
—staining, discoloration or water
damage—in your house. If you find
signs of mold, you have to determine
the extent of the mold by estimating
the size of the affected area.
How much mold is there?
“Small” area
A small area is a patch no larger
than a square metre—about 10 sq.
ft. There should be no more than
three small patches in your house.
“Moderate” area
A moderate area is more than three
square metre patches, or one or more
isolated patches larger than a square
metre but smaller than 3 m2—about
the size of a 4 x 8 ft. sheet of plywood.
“Extensive” area
An extensive mold area is an area
larger than 3 m2—about the size of
a 4 x 8 ft. sheet of plywood. This
much mold is a health risk.
You’ ve found
mold—now what?
Tell your landlord that there is mold
in your house. Don’t try to clean
even small areas of mold without
your landlord’s permission. It is
more difficult to get something
done if the signs of mold are
removed. Furthermore, you are a
tenant and there is a limit to what
you can do. Cleaning moderate and
extensive areas of mold requires
safety precautions.
Once you have notified your landlord,
you can clean small areas as part of
your regular cleaning routine with
a solution of unscented detergent
and water. Wear household rubber
gloves and a dust mask for protection
and follow the steps in How to clean
up small mold problems on page 3.
Mold will return if you do not reduce
moisture levels. If mold comes back
after repeated cleaning, the conditions
that caused the mold to grow must
be changed. The changes may be
things you can do yourself or may
be work the landlord has to do.
About Your House
The Tenant’s Guide to Mold
Should you hire a
Should you hire your own
IAQ investigator?
Before you consider hiring someone
to inspect for mold, you should have
contacted your landlord and
explained the problem. Some
landlords are more aware than
others of the dangers of mold and
moisture and know that failing to
correct moisture problems can cause
structural damage. They are more
likely to act. Suggest that your
landlord get information, such as
the CMHC publications Fighting
Mold—The Homeowners’ Guide or
Clean-up Procedures for Mold in
Houses. (Both are available from the
CMHC website at: www.cmhc.ca,
or by calling CMHC’s toll-free
number: 1-800-668-2642.)
You would pay for the IAQ
(Indoor Air Quality) investigator
yourself. An IAQ investigator who
has completed the CMHC IAQ
Investigator Training Program and
who follows the CMHC Investigation
Procedure will give you a written
report telling you what is causing
the mold and recommending clean-up
Ideally, your landlord should hire an
indoor air quality (IAQ) investigator
to find what is causing the mold
and recommend solutions. If there
are problems with the building
envelope, the landlord may hire
a building envelope specialist.
Contact your public health unit
and ask for an inspection if your
landlord doesn’t act and if:
there is a lot of mold;
the house is very damp and moist;
mold comes back after repeated
you or a family member has
asthma or difficulty breathing—
or other health problems—that
seem to be worse inside the house.
As a tenant, you can take simple
measures, such as always using
the bathroom fan and cleaning the
bathroom tiles. But solutions relating
to the building—gutting a wall or
installing a bathroom fan, for instance,
are your landlord’s responsibility.
You could wind up paying for an
inspection that recommends measures
that you cannot do yourself.
What’s more, hiring an IAQ
investigator without your landlord’s
knowledge or permission can lead to
a situation where the landlord hires
another consultant whose report is
pitted against your consultant’s report.
Sometimes, when tenants feel their
landlord is ignoring their concerns,
they hire their own expert to test
the air for molds. They frequently
submit the test results to rental
tribunals to get them out of a lease
or to support mold-damage claims.
Generally, CMHC does not
recommend testing the air for
molds. Laboratory tests are costly
and interpreting the results is not
simple and may not be conclusive.
For more information, see CMHC’s
About Your House: Should You Test
the Air in Your Home for Mold?
If you feel strongly that you need
to document mold contamination,
take detailed photographs of the
affected areas. You can also ask a
public health inspector or IAQ
investigator to take actual (bulk)
samples of the mold and send
the samples to a laboratory for
identification. Analysing bulk
samples is much easier that testing
the air.
Getting professional help
Your local CMHC office has a list
of people who have completed the
CMHC Residential Indoor Air
Quality Investigator program. A
trained IAQ investigator examines
your home’s indoor air quality,
identifies the problems, finds their
sources and suggests solutions in a
written report.
How to clean up
small mold problems
The minimum protective wear is:
safety glasses or goggles
a disposable dust mask
(3M 8210 or equivalent)
household rubber gloves
Infants and family members with
asthma, allergies or other health
problems should not be in or near
the work area when you clean.
Canada Mortgage and Housing Corporation
About Your House
The Tenant’s Guide to Mold
Table 1
Steps to clean-up a small mold problem
Washable surfaces
Moldy drywall
Step 1
Vacuum the surface with a HEPA vacuum cleaner, if possible.
Step 2
Scrub with an unscented detergent solution.
Step 3
Then sponge with a clean, wet rag and dry quickly.
Clean the surface with a damp rag using baking soda or a
bit of detergent. Do not allow the drywall to get wet.
Using an unscented detergent will make it easier for you
to detect residual moldy odours.
Staining that is not removed by this method should be
reported to your landlord.
Vacuum the cleaned area and surroundings with a HEPA vacuum cleaner.
Mold that comes back after cleaning
is usually a sign that a moisture
source has not been removed. Use
the lists in Mold-proofing on page 5
to identify possible causes.
Dealing with a
continuing mold
Your situation may require looking
at other options. Some of the other
situations are:
Mold comes back after
repeated cleaning
Check to see if the moisture is
coming from inside your house or
from something that you are doing.
Follow the lists in Mold-proofing on
page 5. Be prepared to give up
some things and make some
Water entering the building
is causing mold
The building owner is responsible
for repairing the building envelope
to stop moisture from entering the
Canada Mortgage and Housing Corporation
Basements have higher humidity
levels than upper floors. In the
summer, the wall surfaces are cooler
and moisture can condense. Most
basement floors have neither a
moisture barrier nor insulation and
dampness can migrate upwards
from the soil.
There are building techniques (such
as exterior insulated foundations,
good drainage) and measures (such
as continuous dehumidification,
supplemental heat outside the
heating season) to reduce mold.
Many basements do not have these
safeguards. When looking for a
home to rent, put a basement
dwelling at the bottom of your list.
Your best option may be to find
another place to live. The longer you
stay in a moldy house, it is more likely
that your personal belongings will
also get moldy. You don’t want to take
moldy belongings to your new place.
What to do until the problem
is fixed
It is not always possible to relocate
immediately. You may have no other
option but continue to stay in the
house. While you are waiting to move,
you can reduce your exposure to mold.
Wearing a dust mask and gloves,
discard moldy or damaged materials,
such as mattresses, carpets or sofas
that have been water damaged or
stored in damp conditions. Use
this opportunity to reduce furnishings
—it means fewer materials to
absorb moisture and grow mold.
Store cleaned clothes and other
fabric materials in sealed plastic
bags to prevent re-contamination.
Buy a HEPA vacuum cleaner and
vacuum frequently. Settled dust
contains mold spores. Walking,
activities inside the house and
even air movement can re-distribute
these mold spores into the air
you breathe. By thoroughly
Your house has an old, mustysmelling or water-damaged
carpet that your landlord
does not intend to remove
You are either experiencing
discomfort, worried about getting
sick or you believe you are already
suffering health problems from the
mold. Ask your physician to help
you document your health problem
and its possible relation to the mold.
About Your House
The Tenant’s Guide to Mold
vacuuming floors, walls, ceilings,
shelves and non-washable furnishings,
you can reduce your exposure.
Carpeted floors may require
multiple passes to remove particles
and dusts lodged in the fibres.
air and wind can push the
moisture to other parts of the unit.
Keep moisture generated within
the unit to a minimum by carefully
and regularly following the
prevention steps in Preventing
mold below.
Dry areas that get wet. Monitor
the relative humidity of the air.
Use a portable dehumidifier, if
necessary. Empty the condensate
drain pan of the dehumidifier
If the mold is limited to one
area, isolate the area if possible.
Cover affected surfaces with
plastic sheeting and duct-tape
the edges. Remember: this is a
temporary measure only.
Ask your landlord to find and fix
water leaks promptly.
Keep the house dry. Think of the
different ways activities such as
cooking or bathing produce
moisture inside the home. Exhaust
fans remove moisture as it is
produced. If there are no fans,
open windows for a short time,
but remember that moist outdoor
conditions will not dry the inside
Discard clutter and excess stored
materials. Molds grow on fabrics,
paper, wood and practically
anything that collects dust and
holds moisture.
Keep the house clean by
vacuuming regularly.
Adopt lifestyle practices that
reduce moisture.
Preventing mold
Mold needs moisture to grow.
Controlling moisture and keeping
the home dry prevents the growth
of mold.
Measure how much moisture is
in the air. To find out the relative
humidity, you’ll need a hygrometer.
You can buy one at a hardware
store or electronics store. A
hygrometer costs from $10
to $60. Your home’s relative
humidity should be under
45 per cent (or lower to avoid
condensation on windows) in
the winter. If necessary, use a
dehumidifier to lower the relative
Vacuum often. If you are buying
a vacuum cleaner, get one with a
HEPA filter. (See What are the
advantages of a HEPA vacuum?
on page 7.)
Clean hard floors with a
damp mop.
Do not bring anything into your
house that is moldy or that has
been stored in a moldy place.
Cut down the number of potted
plants in the house—soil is a
good place for mold. Frequent
watering of plants adds moisture
to the air. Aquariums are also
moisture sources.
Recognize conditions that lead
to excess moisture and mold
—overcrowding or too many
pets. Increase ventilation (open
windows and or use exhaust fans)
when there are more occupants
than the unit was designed for.
Don’t hang-dry laundry inside
the house or vent a dryer into
the unit.
Don’t use unvented space
heaters, such as kerosene or oil
heaters. They not only produce
moisture, but other contaminants.
All living areas
Separate footwear worn outside
from footwear worn inside.
Allow good air circulation by
reducing the amount of furnishings.
Heat areas of the house adequately.
Condensation occurs on cold
walls in unheated rooms or in
houses that are kept too cool.
If there is a fan over the stove,
ask your landlord if it exhausts
outside. Use it when you cook.
Recirculating fans do not remove
moisture produced from cooking.
Regularly wash the exhaust fan’s
grease filter.
Canada Mortgage and Housing Corporation
About Your House
The Tenant’s Guide to Mold
Minimize open and prolonged
Keep the exhaust grille free of
There’s a drip pan at the back of
the refrigerator. Pull the refrigerator
out to clean the drip pan. At the
same time, vacuum dust from the
coils at the back of the refrigerator.
Check under the kitchen sink to
make sure there are no leaks.
If there is no bathroom fan but
there is a window, open the window
after a shower when possible. Note
that moist outside conditions will
not dry the bathroom. Wind may
also push moisture to other parts
of the unit.
Take out the garbage daily to
prevent odours and spoiling.
Keep your drains in good shape.
To clean a drain
■ Pour a handful of baking soda
into the drain.
Add a cup of vinegar.
Put the plug in the drain.
Let the vinegar and baking soda
work for about 20 minutes.
Run fresh water into the drain.
If the drain is still clogged, ask
your landlord for help.
If there is a bathroom fan, check
that it is able to exhaust air. The
fan should be able to pull a piece
of tissue paper held over the grille
towards itself. Another fan exhaust
test is determining how quickly
it clears a mirror that usually fogs
after a hot shower. Turn the fan
on when you shower or bathe
and keep it running for a few
minutes or longer after you finish.
Canada Mortgage and Housing Corporation
If there is no fan or window,
consider a small, portable
Keep surfaces that get wet, such
as the walls around the bathtub
and shower, clean and dry.
Hang wet laundry to dry in
the bathroom as infrequently
as possible.
Condensation or dampness in
the bathroom may be due to
temperature being kept too low.
Make sure there is heat.
If the bathroom has a carpet, ask
the landlord to remove it.
Check for water leaks.
Basement or crawl space
Note: For this section, the “Furnace
room,” “Laundry areas” and “Exterior”
sections, talk with your landlord to
establish who is responsible for the
tasks—the tenants or the landlord.
Reduce the number of clothes,
paper and furnishings stored in
the basement. Throw out badly
damaged materials. Eliminate clutter
to improve air circulation. Only
washable items should be stored.
Dehumidify the basement as soon
as the heating system is turned
off until it is turned on again in
the fall.
Avoid carpets on slab-on-grade
or below-grade floors.
Regularly clean the drain in your
basement floor. You can clean the
drain with baking soda and vinegar
as in Kitchen, using a freezer gel
pack or plastic to temporary seal
the drain. Keep the drain trap
filled with water.
Avoid standing water. Keep sump
pits covered (you can use plywood
wrapped with plastic).
Keep drains in good shape by
removing debris from them.
Follow the steps in Kitchen.
Closets and bedrooms
Get rid of unused clothes and
other stored items. Keeping your
closets and bedrooms tidy makes
it easier for air to circulate—and
harder for mold to grow.
Do not humidify unless necessary.
If your physician advises you to
humidify, measure the relative
humidity first. Cycle the humidifier
on and off to maintain the desired
relative humidity. Allow the room
to dry the following morning.
About Your House
The Tenant’s Guide to Mold
Furnace room
Furnace filters must be replaced
regularly. Use pleated, one-inch
filters, not coarse filters.
If there is a heat recovery
ventilator (HRV), clean the filter
inside the HRV often.
If you notice molds or signs of
dampness, such as water on your
windows or wet spots elsewhere,
do not humidify. Disconnect
furnace humidifiers that are no
longer used.
Tips for selecting a
house that is not
When you look for a house, there’s
a lot to consider. Location combined
with availability may be a determining
factor. The “Relocating” section of
The Clean Air Guide is a good starting
point for selecting houses with good
indoor air quality. If mold is a major
concern for you, avoid houses with
one or more of these features:
A wet, moldy basement
No bathroom fan, or a fan that
doesn't work
Check that the clothes dryer
exhausts to the outside.
No kitchen exhaust fan or fan is
a recirculating fan
Remove lint every time you use
the dryer.
An old carpet
Known history of roof or
plumbing leaks
Difficult to heat because it is
leaky or inadequately insulated
Laundry areas
Don’t hang-dry laundry indoors.
Dry your laundry tub and washing
machine after you use them.
Regularly check the condition of
the roof and exterior finish for any
places where water might enter.
Make sure that eavestroughs and
downspouts are connected, work
properly and are free of debris.
Install downspout extensions to
lead water away from the building.
Deal promptly with any
problems that you find.
Frequently asked
questions about
The air feels dry—can I
Before you add moisture to the air,
measure the relative humidity. Air
that feels dry may not really be dry.
It may be moldy. High relative
humidity (over 45 per cent) promotes
the growth of molds and dust mites.
The moisture in the air may condense
on colder exterior walls where molds
start to grow.
What are the advantages
of a HEPA vacuum?
Ordinary vacuums capture large particles
only, which allows small mold spores
to pass through the vacuum exhaust
back into the air. HEPA vacuums have,
in addition to a regular filter, special
filters to capture small particles. A
central vacuum cleaner that exhausts to
the outside also prevents re-distribution
of fine particles into the air. A regular
portable vacuum is useful only if its
exhaust goes outside the home.
Vacuuming removes settled dust that
contains an accumulation of mold
spores over time. Reducing the settled
dust reduces molds. Vacuuming
with any vacuum cleaner (ordinary,
central or HEPA) stirs dust and mold
during the process. Wear a dust mask so
you will not be breathing more mold.
Is vacuuming with a HEPA or
externally exhausted vacuum
cleaner recommended for
serious mold problems only?
Vacuuming regularly with a HEPA
or externally exhausted vacuum cleaner
to prevent the ongoing accumulation
of dust and molds is beneficial for
any dwelling, with or without mold.
The need for HEPA or external
exhaust vacuuming increases with
the severity of the mold problem.
If a furnishing has been wet at
some time in the past or exposed to
dampness over a prolonged period,
vacuuming with a HEPA or externally
exhausted vacuum is unlikely to
remove the mold growing beneath
the surface. It is better to discard
the item.
Canada Mortgage and Housing Corporation
About Your House
The Tenant’s Guide to Mold
Where do you find a HEPA
vacuum cleaner?
Does cleaning stop mold
How can moldy clothes
be cleaned?
Vacuum cleaner dealers carry HEPA
vacuums. Consider purchasing one
as an upgrade. A HEPA vacuum is
a good investment in the long term
whether you have mold or not.
Better-built HEPA vacuum cleaners
have airtight housing that prevents
fine dust from leaking out.
Mold will reappear until you
remove its source of moisture. High
moisture levels that are not corrected
can allow the molds to grow back
quickly. Cleaning is a temporary,
but essential, measure.
Dry clean non-washable clothing.
Does painting over a moldy
surface take care of the mold?
Painting over mold only masks the
problem. Paint neither kills the
mold nor stops it from growing.
Clean washable surfaces with a
detergent solution, following the
procedure suggested in How to clean
up small mold problems on page 3
and Dealing with a continuing mold
problem on page 4 and allow the
wall to dry. If you are going to
paint, remove mold first.
You can help by making a conscious
effort to keep your home dry.
Obviously, water must be prevented
from entering the home. But you
can help by controlling moisture
that you produce.
Wash clothes with a detergent
solution to which a cup of bleach is
added. Make sure the detergent you
use does not contain ammonia. Repeat
as necessary until the moldy odour
is gone.
Store cleaned clothes and other
items in sealed plastic bags to
prevent re-contamination.
To find more About Your House fact sheets plus a wide variety of
information products, visit our website at www.cmhc.ca.You can also
reach us by telephone at 1-800-668-2642 or by fax at 1-800-245-9274.
Priced Publications
Cleaning Up Your House After a Flood
A Guide to Fixing Your Damp Basement
Clean-up Procedures for Mold in Houses
The Clean Air Guide : How to Identify
and Correct Indoor Air Problems in Your Home
Order No. 61094
Order No. 65886
Order No. 61091
Order No. 61082
Free Publications
Moisture and Air: Householder’s Guide
—Problems and Remedies
About Your House fact sheets
Measuring Humidity in Your Home
The Condominium Owners' Guide to Mold
Should You Test the Air in Your Home for Mold?
Choosing a Dehumidifier
Fighting Mold—The Homeowners’ Guide
The Importance of Bathroom and Kitchen Fans
Order No. 61033
©2005, Canada Mortgage and Housing Corporation
Printed in Canada
Produced by CMHC
Revised 2005, 2008
Although this information product reflects housing experts’ current knowledge, it is provided for general information purposes only.
Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. Readers
are advised to consult appropriate professional resources to determine what is safe and suitable in their particular case. Canada Mortgage and
Housing Corporation assumes no responsibility for any consequence arising from use of the information, materials and techniques described.
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