These days, as our society begins to look for ways to reduce carbon emissions, there is a whole new set of reasons to renovate a home. Cutting back on the amount of energy we need to operate our homes is an obvious way to save energy that has become a billion dollar industry in Canada. I am all for people who want to save energy and improve their homes, provided they go about things in the right manner the job is done properly (I will save the "Home Inspection Nightmares I Have Seen" article for another day).
But have you ever thought about the ways that improving energy efficiency can have unintended negative impacts which may make the home unsafe - this is something I see all too often during my home inspections. Take, for example the case of poor air quality that is a common condition in many older homes where renovations have not included a furnace upgrade.
For reasons of cost and reliability, natural gas heat systems have been the most popular way of heating homes in BC since the 1960’s. The gas belching forced air furnaces that were installed in most homes prior to the 1990’s required huge amounts of air to operate and almost never have a source of fresh air supplied to them. Throw in the gas burning hot water heater that is installed in most of these homes, which almost never shuts off, along with a fireplace or two, and you have the conditions where literally 1000’s of cubic feet of air are being used up inside a home.
This is all well and good, as long as we are talking about your run-of-the-mill home, built during the 1980’s and before, where the air needed to operate the heating systems can be easily replaced through breaks in the building envelop. Heating homes was less of a science during this era and most houses didn’t have much in the way of fresh air ventilation systems. It didn’t make much sense to worry about installing expensive air control systems at a time when building standards dictated that all the air that could ever be needed could be supplied through gaps in walls, windows, and doors - all at zero expense.
While it may be the most efficient method of heating a home, it has to be said that the older style heating systems installed in so many older homes worked very well, and often would keep chugging along, almost forever, as long as they were left alone. Problems can arise, however, in when homeowners, who will have nothing but the best intensions, decide it’s time to renovate. They the will spend large amounts of money and effort to tighten up the exterior of the home and improve its energy efficiency (things like new windows, cladding, and attic insulation will make a huge difference to the ease at which outside air enters the building). Which sounds like a great plan until we think about the gas burning monster that is still hiding in the basement (“Oh, we decided not to replace the furnace, since it is still working. And besides, they’re sooo expensive…”) and remember the steady supply of air it needs that is no longer available.
Negative air pressures that can cause back-drafting can build inside the building, as the air available air is used up faster than it is replaced. Back-drafting is a situation where chimneys flow backwards and C02, along with all kinds of other nasty stuff that you wouldn’t want to breathe, is drawn into the living space. Negative pressure will also contribute to the densities of “off- gasses” that will be present (gasses originating from chemicals used in building products), this can be especially true in homes where the floors and kitchens have been replaced (think glues and solvents). Buildings work best and people will feel most comfortable in environments with the slightly positive air pressure that modern houses are designed to provide. Some of the worst air conditions you are likely to come across, that can be unhealthy or even downright dangerous, can be found in the type of home described here.
It is certainly something that every prospective buyer or person living in the home should know about. The good news is that providing adequate air to combustion appliances is normally a pretty straight forward repair. These days, lots of homeowners are choosing to replace those old clunker furnaces anyway, especially since the energy retrofit program has been re-instated.
