Building Trends, How to Avoid
Trouble, "The House as a System"
Part One of a Two Part Series
There are many new trends changing the way in which homes are
built and renovated. Each an improvement on its own, but when
combined, can lead to problems.
Over the years the way in which homes have been constructed have
changed as newer technology was developed. However, changes have
been due to mainly three driving forces: 1) increased energy costs
creating a higher demand for energy-efficiency, 2) the decline
in the availability of natural resources, resulting in higher
costs of building products and materials, 3) changes in homeowners
lifestyles and increased interest in a more comfortable and convenient
indoor environment. In order to avoid problems, the building industry
must continue to address the effects on the home, the comfort
heating and cooling system and the occupants.
The changing way in which we build homes, more than ever before
mandate that we view housing as a system. This approach, known
as, "The House as a System", recognizes that each part of a house
interacts and is inter-dependant on the each other. The issues
are complex. We want homes that provide us with healthy, safe,
durable, comfortable and affordable living. Manufacturers, architects,
designers, engineers, builders and all tradespersons must plan
and consider the interacting relationships that result from today's
well-built and renovated homes.
So, if we want our homes to be healthy, safe, durable, comfortable
and affordable, we must first understand how:
- Air flows in and out of a home by, both natural (infiltration or air leakage) and controlled (mechanical ventilation)
- Moisture moves throughout a home
- Heat loss and heat gain can be managed
- The environment indoors and outdoors is affected by new construction practices
Thinking of our home as "The House as a System" (whole home) allows us to visualize how each trend affects the others. So, if we change any one part, the whole is changed, either improving the system or making the system worse. Each change that occurs will affect three areas; health of the occupants and building structure, indoor comfort, and the efficient operation, and maintenance of the homes mechanical systems (heating, comfort cooling, ventilation, etc). All changes within the concept of "The House as a System" must be evaluated to determine the effects on moisture mitigation, heat flow, airflow, and the impact on the indoor and outdoor environment.
Changes have for the most part always been made with good intentions, to improve the home. All too often though, these changes have had unexpected results. Hopefully these 10 points will assist you in your new home project or home renovation by having you think of your home as a system.
- Tighter houses - We build tight homes in
Canada and some of the tightest ever built are located right
here in Manitoba. With the technology today we can tell you,
not just how tight your home is; but where those leaks are.
The EnerGuide for Houses program is a great evaluation tool
that can be used. Information gathered can assist in identifying
payback for an investment in energy conservation.
In a tight home there is less outside air leaking in and less conditioned air leaking out. Increased reliance on comfort cooling is more common. Odors are more noticeable, indoor pollutants pose more of a health threat if not dealt with and burning of candles are often used to mask odors, yet another problem arises, soot deposits on walls and furnishings.
In today's new and retrofit homes we must install and properly maintain mechanical ventilation systems in order to achieve a healthy home. However, there is one more very serious issue that arises in tight homes, negative pressure problems that were not seen in the past. This problem requires the knowledge and expertise of professionally trained technicians and is one more reason why it is so important to have your homes systems checked each year.
- More vent-free or vent-less fuel burning appliances
- There has been a huge upsurge of gas fireplaces into the marketplace
that do not require a vent or chimney. These appliances discharge
100% of the combustion gases into the home. While they are more
efficient and do burn much cleaner than regular fireplaces,
they still are and should be considered a source for increased
indoor pollutants and avoided. In the Province of Manitoba these
appliances are "NOT", allowed to be installed.
What about gas ranges? They too, are gaining in popularity. In addition, they release 100 % of the combustion gases into the home. The release of these combustion gases into the home carries with them, pollutants. When 100,000 BTU of natural gas is burned, 1-gallon of moisture is released into the air. While it is true that gas ranges and ovens have been tested and found high levels of carbon monoxide being produced, it is again important for us to remember that regular maintenance can help avoid problems. Further, by taking the proper steps using "The House as a System" concept can ensure safe and reliable operation.
- More exhaust fans and devices - There are
more exhaust fans and devices installed in homes today than
at any time in history. Think of how fans are in an average
1500 sq. ft. home? Clothes dryer, kitchen fan, main bathroom
fan, basement bathroom fan, master bathroom fan, work shop fan,
central vacuum exhaust, range downdraft fan, attic fan, radon
mitigation fan and I'm sure you may think of another one. These
fans and devices all compete for the same air within the home,
as do all vented appliances. Appliances such as furnaces, water
heaters, fireplaces and wood stoves all require sufficient air
to operate in a safe manner. When large volumes of air are exhausted
from the home, air is required. Make-up air is needed to ensure
that the vents or chimneys do not spill combustion gases back
into the home.
Many times homeowners are fooled by pilot lights that constantly go out. One customer I remember had over 18 service calls for pilot problems, the problem negative pressure caused by new exhaust fan that had been installed. What was happening was the air being exhausted by the new fan was causing the water heater to back draft the chimney and the main burner flame would roll out and extinguish the pilot. This was an extreme case and most often the back drafting goes undetected unless you have been trained to look for the signs and can conduct a proper test. Another good reason to work closely with a professionally trained technician.
- More higher efficiency appliances with lower vent
and chimney temperatures - The appliances today are
very efficient and have been designed to meet very stringent
Federal Government standards in energy-efficiency. This has
meant that special attention is needed in order to ensure the
safe, reliable operation of vented appliances. In fact, a complete
new set of venting sizing tables were designed to assist designers,
estimators and installers to ensure that the appliances were
properly vented. It is important that we understand that lower
temperatures mean higher efficiency, lower negative draft pressure,
and heavier gas vapor.
What does this mean? Well, it means that the smallest reduction of pressure within the home can have an even greater potential to create a problem. Back drafting of appliances is an area that unless taken into consideration and proper measures followed at the installation stage, can pose serious health problems. Even this, is no guarantee, the addition of an exhaust device in 6-months, one-year or two-years from now can be enough to tip the balance and create a problem. The best option is to install only sealed combustion appliances that bring combustion air directly into the appliance from outdoors and exhaust the products of combustion back to the outdoors. This entire process takes place in a sealed combustion zone that is isolated from the homes environment. While sealed combustion appliances may carry a higher initial installed cost, the overall benefits cannot be overlooked when all items affecting "The House as a System" have been taken into consideration.
- More Forced air systems - In well over 85%
of homes today the choice is to install forced air systems.
The air being distributed circulates between 800-2000 cubic
feet of air/per minute (CFM) and is the largest fan within the
home. The duct system that is connected throughout the home
serves as the distribution network for conditioned air to be
delivered to the various rooms throughout the home.
If there is air leakage in the ductwork (and a large percentage do), efficiency, comfort, health and safety as well as durability of the building structure are at risk. If there is air leakage in return air ducts in an enclosed furnace room as an example it is highly likely that a negative air pressure would be present and back drafting of the vents and chimney would spill combustion products into the home. It may even be possible to pull in unconditioned air from the attic through penetrations in the wall structure if not sealed properly. This is possible and has been found to be a major source of high- energy bills in some cases. This is possible because in Manitoba, we use wall cavities and joist spaces for return ducts.
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