The building envelope – The most important factor in energy savings

You hear it talked about – the “envelope” of your home. But what is it?

The envelope is comprised of the foundation walls, basement floor slab (or ground-level floor slab if no basement), exterior walls, windows and doors, and the top floor ceiling. These are the areas of living space that are exposed to outside air or the ground, and are the surfaces that leak heat, air and moisture either in, or out, of your home. Regardless of how “efficient” your heating system may be, if the envelope does not seal off air flow and insulate properly, you’re wasting huge amounts of energy, and money. On top of that, the comfort level of your home will be very difficult to control.

Newer homes are built with better air-sealing characteristics in order to meet building code standards, and are (usually) built with higher levels of insulation. Often, the airflow is not blocked from entering the wall cavities, but does get stopped at the back of the drywall against the plastic vapour barrier – this still causes much heat loss, even though air leakage into the interior of the house is kept to a minimum. Older homes tend to have poor insulation levels and even poorer air-sealing, giving them an even larger potential for energy savings.

Let’s start with what can be done with new construction. Opinions differ on what the “best” construction methods are, and there are several options for very efficient buildings, with varying price tags attached to them depending on just how far you want to take things. Whether you build to Passive House standards,  use ICFs, or my InnovaWall system, keeping outside air out of the envelope and having a high level of properly installed (and I can’t stress that part enough) insulation are critical to ensuring your house uses little energy to heat it. Passive solar features should always be incorporated as much as possible to utilize the free energy from the sun, basements should be insulated on the outside to allow the concrete to act as a heat sink, and the combination of all these features means your heating/cooling system needs to do very little to keep you warm or cool. Of course in all cases, a properly designed and balanced (again, cannot stress this enough) HVAC system with a high-efficiency heat-recovery ventilator is required to ensure fresh air circulation and comfort.

When it comes to existing homes, especially older ones, creating major energy, and comfort, savings requires some renovation work. We often see people replacing their windows, doors and siding all at once on an older home and this is a prime opportunity to upgrade the insulation and air-sealing of a large portion of the home`s envelope. By furring out the new siding a couple of inches, this creates a void that can be filled with closed-cell sprayfoam insulation which is extremely good at sealing air leaks and providing a significant insulating value, even in just a 2″ layer. I have seen many homes with rigid styrofoam insulation boards added at some point, yet the house is still cold. Why? – because they did not seal off airflow from getting under, around or behind it. Once you allow airflow by, you just wasted your money on that insulation.

Because it is such a great insulator, vapour barrier and air-seal, closed-cell sprayfoam is also ideal for those basements and ceilings you’re looking to upgrade the insulation on…just be sure you have taken care of any water leakage first.

These are the basics, and there are many details involved in complete installations, so please send along your questions or comments on this topic.

Andrew W. Alcorn, CET
Innova Builders

Andrew is a member of the Halifax Chamber of Commerce Energy Advisory Group
and the Canada Green Building Council (Atlantic Chapter) Residential Committee

2 responses to this post.

  1. […] This post was mentioned on Twitter by Anthony Martin and Andrew W Alcorn, Andrew W Alcorn. Andrew W Alcorn said: Catch my blog about the building "envelope". […]


  2. […] make it effective. In fact, an alarmingly high percentage of building envelopes (see my previous post on this) are not properly installed, making the insulation much less effective than the R-value of […]


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