Mould & Moisture In Your Home
by Robin & Audrey Barrett, Health Homes Consulting
UPdate Spring 1994

Wherever your have excess moisture or humidity you will have mould.  It can grow anywhere and on any surface.  Two sources of humidity are:

1.  Leaks in the house from various sources such as water pipes, roofs, walls, windows or basements.

2.  Common moisture sources such as cooking, showers or baths, breathing, earth floors in basements, water and/or moisture seeping in through brick, stone or concrete basement walls, and open floor drains in your basement slab.

How much moisture is too much?  People will likely always debate these levels, but the consensus is:  40 to 60% relative humidity (RH) is a good range for human health.  Unfortunately, to prevent problems in our homes it is recommended that we keep the RH down between 30 to 50% during the winter, with 40 to 60% being considered acceptable during the summer.  The reason for the 30 to50% winter guideline is that with current housing if you start getting the RH higher in the winter you will get more condensation, leading to mould on the windows and on cold spots on the walls.

It is worth noting here that dust mites love a humid environment (especially over 50% RH), so by keeping the RH below 50% in your home you will also be keeping down the dust mite population, which is nothing to sneeze at!  (Oops!  Sorry folks, that just slipped out!)

How do you know if your relative humidity is too high?  If you have any amount of condensation which lingers more than a short time (after a shower or doing the dishes, for example) or have any mould or mildew on windows, ceilings, walls or in the basement, you probably have too much humidity in your home.

You can use a humidity meter or “humidistat” to check the levels, but be warned that many of the meters on the market are not totally accurate.  Some tests done recently on the lower cost meters (less than $50.00) indicated that the Radio Shack model 63-844 was one of the most accurate, but when the relative humidity went below 30% it became more unreliable.  It was found that no matter how far below 30% the actual RH was, this model continued to read between 25 to 30%.

For more information on moisture and mould you can get a copy of the CMHC publication “Moisture and Air - Problems and Remedies” (Ref. # NHA5968) and the Natural Resources Canada pamphlet “Moisture Problems”, both of which are available free of charge from the respective organizations.  (Check the blue pages of your local phone directory for the number.)

Some Solutions

Prevention is the best way to combat moisture and mould problems.

Ø Fix any leaks as soon as you notice them.

Ø Seal any penetrations in your foundation (e.g. sump pump sites, water and sewer entrances, cracks, basement wells, and earthen doors).
* NOTE:  these penetrations can also be pathways for radon to enter the house

Ø Solve cold spot problems caused by poor insulation in areas such as around or on windows, in closets on the exterior walls, corners in the attic, and areas in the walls where there is no insulation at all.

Questions & Comments

One of the most common questions we hear is:  Should I buy an air exchanger?  The answer depends on many things, but here are some key points to consider.

1.  Is the air on the outside of your home better than the air on the inside?  You can filter out some of the outside contaminants, but the worse the outside air quality, the more costly and the less effective your filters will be.

2.  An air exchanger brings in fresh (outside) air and removes stale (inside) air.  When it does this, it removes (dilutes) the contaminants from pollution sources in the house (i.e. excess moisture, formaldehyde from building materials, carbon dioxide from our breathing, and many others).

3.  “Dilution is not the solution to pollution, but it does help.”  Ventilation is often the cheapest way to solve a problem if you cannot remove the source.  You may be able to install a good bathroom and/or kitchen fan to solve localized problems.

One word of caution - the fan needs to get air from somewhere and you can make things worse for a sensitive person if the fan pulls in air from the walls, taking with it fumes from insulation or possibly mould spores and/or dust of various types.

Robin is a believer in what is called a “balanced system”.  This means it brings in the same quantity of fresh air as the stale air it removes.  If your system exhausts more air than it brings in, you will not only get air coming in through the walls (bringing in contaminants as discussed above), but you also risk bringing in air from under the foundation (possibly bringing with it soil gases, radon, moisture, mould and other micro organisms).

If you have no easy areas for air to come in through the walls or foundation there is also the risk of “backdrafting” of combustion appliances - NOT a good idea!  If you bring in too much outside air, you risk driving moisture into the walls and causing decay.

When trying to decide what type of system to purchase, we usually recommend a system which is certified for the “R2000” program.  This helps to eliminate the less effective models and can save you time in evaluating the various types on the market.

We know people who have successfully used most of the major brands, but would suggest you take a look at several different machines before deciding which one you can tolerate best.  As with any product you contemplate using - TETS BEFORE YOU BUY!

We strongly recommend you hire a certified installer who has taken the HRAI (Heating, Refrigeration & Air Conditioning Institute of Canada) Course on Ventilation Design and Installation.  Any extra cost is more than justified when you consider the potential problems you can avoid by doing it right the first time instead of having to get someone in to redo the system later.

For more information on ventilation systems you can contact the Nova Scotia Department of Natural Resources through their toll-free ENERINFO line at 1-424-5727.  They can give you some information over the phone or you can request the ENERINFO ADVISOR SERIES fact sheets on Ventilation and Moisture Control.

Thank you for your response to last issue’s article - for the letters from Wendy and Kris, and all the requests for information from the patients and staff at the N.S. Environmental Medicine Clinic.

Due to the limited space in the UPdate we cannot answer all of your questions in one issue, but will keep them on file and get through them as fast as possible.  Again because of space, we will continue to give a sort of “Reader’s Digest Condensed Version” of information, but will include references to books or other publications which will go into more detail than is possible here.

Loose Ends

We are still waiting for information from the supplier on Lucite Paint, which was mentioned in the last issue.  All we can tell you for now is that those who have used the water-based type WITHOUT TEFLON recommend it highly.

That’s all for this issue.  Next time we hope to discuss air filters, ozone, finishing a basement floor, and why long-dead mould comes to life in the humid days of summer.

Healthy Housing Questions
Write to:
Healthy Housing Corner
C/O AEHA Nova Scotia
P.O. Box 31323
Halifax, NS
B3K 5Y5