The Effects of Roof and Wall Insulation on the Energy Costs of Residential Buildings

Energy efficient buildings are in high demand, both for commercial and residential customers. There are a number of advantages to building or retrofitting your home so that it is energy efficient. Energy efficient homes are:

  • More cost effective
  • More environmentally friendly
  • Sold at a premium to buyers concerned with environmentally conscious living

Energy efficiency and insulation go hand in hand. We’ll go into details explaining why throughout this article, but there’s one important concept we need to address before going further: the building envelope.

Building envelopes are what separates your home’s interior environment from the exterior environment. Heat naturally flows to cold places, so in the summertime heat will try to enter your home, while in the winter heat will try to exit your home. Insulation serves many roles, and impeding heat transfer in order to maintain a comfortable interior environment is one of the most important ones.

The Basics

The more insulated your home is, the less you’ll have to spend on energy costs. That’s the easy part. The more difficult part is figuring out how much roof and wall insulation affects your energy costs, and from there, determining how worthwhile insulation is.

Fortunately, we have some help. Natural Resources Canada revealed that an astounding 61% of energy usage in the average Canadian household goes toward space heating. That means if you can cut your heating costs, you’re substantially decreasing your overall energy use.

How effective, then, is wall and roof insulation at stopping the cold? As it turns out, very effective. Data from the US Energy Department reveals that 50% of a residential building’s heating costs come from heat seeping out from the roof, walls, and foundation. 

In a hypothetical universe where we could stop all heat transfer from the roof, walls, and foundation, we would cut our heating costs in half. Obviously this is (almost) impossible, but it gives us a good idea of how much we can decrease heating costs. 

Let’s say you have an annual energy bill of 1000$. Approximately 610$ of that bill would go to space heating, and 50% of that space heating would be due to thermal transfer through the roof, walls and foundation - about 305$. Were you to reduce that thermal transfer by half through insulation, you’d save about 152$ a year - that adds up pretty quickly. 1000$ was chosen because it makes the math easy to demonstrate, but check your annual natural gas bill and you’ll be able to do the math yourself.

Accounting for Climate

You may have noticed that Canada is...well, a pretty big place. When you look at the stats provided by Natural Resources, it’s important to consider that some of us live in Winnipeg, while some of us live in Victoria. The folks living in Winnipeg are going to be using a lot of energy to heat their homes, while those living in Victoria might do fine with good insulation and a heat pump.

This is to say that you may find it more useful to add up all of your energy consumption, then determine what portion of it is dedicated to heating. This will allow you to get a more accurate impression of how insulation can reduce your energy bills.

All About That Insulation

Another huge factor in the effect of roof and wall insulation is the type of insulation you install, as well as how much you install.

As we discussed, insulation requirements will vary pretty significantly depending on where you live in Canada. That said, you don’t have to follow the R-value recommendations made by the government and building associations - you can always use more insulation.

There are, in fact, housing standards that use this exact premise - Passive House being one of the most prominent - to drastically reduce the amount of energy a home uses. Keep in mind that if you’re using particularly dense insulation, it will impede airflow, which may mean you need a ventilation system to keep air in your home from getting stale.

Now the kind of insulation you’ll use can have a big impact, too. What’s more, the construction of your home, the weather conditions near where you live (moisture, etc.), and other factors will influence how well insulation performs. Ted Cullen, president of Quik-Therm Insulation, brings up an excellent point in his blog on how R-values are tested in laboratories, and that “Zero wind, zero moisture, zero solar radiation and meticulously installed insulation is not the real world”.

Another important factor to consider is that, while we’re focused on the roof, walls, and foundation, a tightly sealed building envelope is your best defense against heat transfer. When your windows aren’t insulating, your door isn’t weatherstripped, or you have other weak points in your envelope, those points are where heat transfer will occur. Having a fully insulated envelope means much more energy efficiency.

Now the more insulation you have, the more insulated your home will be, but quality can often replace quality. You’re not going to insulate with hay, even though you could. You might opt to insulate with closed-cell foam covered in reflective materials, but that might be more expensive than necessary. The answer to these questions depends in part on how much you want to reduce heat loss, what your budget is, and how well insulated your home is already.

A Quick Conclusion

Here’s the takeaway: there’s no doubt that roof and wall insulation can seriously improve your home’s energy efficiency. An energy audit can help you figure out exactly where you need insulation, and what type of insulation you need. The warmer the climate you live in, the less insulation you’ll need to reduce your heating costs to almost zero. You’ll need to crunch a lot of costs to understand exactly how valuable insulation is, and these costs include:

  • Your overall energy consumption
  • How much of your energy consumption is due to heating
  • How much insulation could reduce heat loss
  • How much your insulation/installation would cost

And now you know! 


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