Building Envelope

The best way to reduce the amount of energy you need to heat/cool your house is to lessen the need for it in the first place; the cheapest heating system is the one that you don’t need. This is accomplished by good design and lots of insulation. A well designed and constructed building envelope will keep you warm and comfortable in the winter, and will ensure that your house is easy to maintain, and has a long healthy life.

Design Elements

If you are building a new home there are several design elements that you should consider to decrease the energy required to keep your house warm in the winter and cool in the summer.

Site Selection

Energy savings will result from orienting your home on your building lot to maximize solar gain during the day, and to lessen convective heat loss from wind exposure. It is best to have a south sloping site, with a windbreak of evergreen trees on the north. Having a shade tree (deciduous) on the south will help with shading during the summer, and will not impede solar gain during the winter. In a city lot, or in a sub division, it is more difficult to get an ideal spot. When you are looking for a lot with these limitations, analyze each potential lot for sun exposure/shading, and windbreak potential.

House size/shape

House geometry has long been overlooked as an important parameter of energy efficiency. House geometry has two components: size and complexity. Canadian homes have been built with more and more insulation over the past 50 years, however their size and complexity have increased, which have negated those gains. On average Canadian homes use the same, if not more energy than they did before. One of the encouraging trends in new home construction is the choice to build a more practically sized home. The more complex the shape of a home (ie more corners) the more surface area is available for heat loss to occur. A rectangular shape with a length to width ratio of approximately 1.15:1 is the most energy efficient.

The floor layout of your new house should be designed to allow maximum usage of the sun’s heat. The rooms you use first in the day (kitchen/bath) should be on the southeast corner of the house. The rooms you spend the most time in during the day (living room/office/den) should be on the south side or southwest corner. Bedrooms and utility rooms should be on the north side of the house.

Window placement/overhangs

Having the longer side of the house south (having the ridgeline of the roof run east-west) will allow your house to be in a position to maximize its solar gain potential. There should be more windows on the south side of the house, and fewer on the north. Too many windows facing west could contribute to overheating in the late afternoon hours. If you have a scenic view to the north or to the west, choose an appropriate window construction (number of panes and lowE coating type) to minimize heat loss(north) or overheating(west).

Appropriately sized overhangs will allow the winter sun to penetrate your windows, while shading them in the summer.


Insulation helps keep your heat where it belongs, in your house. Heat has only one goal in life, to move somewhere colder; the only thing that can stand in its way is insulation. Insulation should not be viewed as an option, but rather necessary to achieve increased comfort levels and lower energy costs.


Although it is a misnomer that heat rises (it will go in any direction, as long as it is colder there), hot air does rise. Since there is always air movement within your house, chances are the temperature of the air next to your ceiling will be warmer than anywhere else in your house. In the summer time, the attic space above your ceiling can get very hot. For these reasons, and because it is a very easy space to insulate, you should aim high with the amount of insulation you choose to put in your ceilings.

Current building practices result in a value of R40, and the proposed National Building Code will soon recommend R50; why not go with R60? The most common type of attic insulation is blown cellulose, made from recycled newspapers. It is blown into the attic space allowing it to be placed around all of the truss members, nooks and crannies. The incremental cost of having a final R value of 60 is very small relative to R40 or R50. Other insulation options are blown fiberglas or spray foam. Fiberglas batts are discouraged because it is more difficult to fit it around all the physical components of your attic.


We strongly recommend you insulate your wall assembly in such a manner that you reduce thermal bridging. Thermal bridging by framing members (studs, top & bottom plates, window framing, etc.) “short circuits” your insulation; and leads to undesirable heat loss. Ways to reduce thermal bridging include using external rigid insulation outside of the framing cavity, or use Insulated Concrete Form (ICF) construction. Our minimum recommendation for walls is R20 within the wall cavity plus R5 rigid on the outside. Our Effective Insulation Calculator will show the true insulating value of various wall assemblies. If you have extra money in your insulation budget, it is far better to spend it on the exterior layer than to put additional insulation in the framing cavity.

Rim Joist Header

If your house will have a basement and/or a second story the area around the outside perimeter of your floor joists must be insulated in such a manner that there is thermal continuity between the insulation in the walls above and the walls below. If you have a standard cast-in-place concrete foundation, and a 6” framed basement wall, you will need to bring your floor joist header insulation in at least 12” from the rim joist. insulation; and leads to undesirable heat loss. Ways to reduce thermal bridging include using external rigid insulation outside of the framing cavity, or use Insulated Concrete Form (ICF) construction. Our minimum recommendation for walls is R20 within the wall cavity plus R5 rigid on the outside. Our Effective Insulation Calculator will show the true insulating value of various wall assemblies. If you have extra money in your insulation budget, it is far better to spend it on the exterior layer than to put additional insulation in the framing cavity.


If you decide to put a basement under your home, then it should be insulated to provide comfortable living space. If you are not going to use your basement for living space, you should consider building on a slab. The two most common construction techniques used for basements are cast-in-place concrete and ICF. ICF basements are more expensive, but will generally save in energy consumption compared to a framed and insulated cast-in-place basement. Insulating a cast in place foundation from the outside is more desirable than insulating it from the inside; however, insulating from the inside is the most common and practical approach.

An alternative approach to enhance the R-value of your cast-in-place basement, and to help with moisture issues as your green concrete dries, is to put a water resistant rigid insulation against the concrete, behind the insulated framing layer. This also lessens thermal bridging, which is always a good thing. ICF construction does not have much thermal bridging because of its design.

Whether or not you have a heated basement floor, insulating under the basement floor is important, both from an energy efficiency perspective and to prevent condensation during periods of high humidity. This condensation is responsible for those musty smells and leads to the growth of undesirable organisms. It is also important to provide a thermal break around the edge of the slab to prevent it from making direct contact with the concrete walls. This will prevent heat from the slab being transferred from the inside of your house to the outside.

Slab on Grade

There are very good reasons to build a new house on a slab (or crawl space), rather than on a basement. If you decide to choose this option, it is important to ensure measures are taken to reduce heat loss caused by concrete-to-concrete contact. Your slab must have an insulated frost wall. ICF is a good choice for this. A cast-in-place frost wall must be insulated as well, and it would be good to aim for beyond the common practice of R10. Since the floor of your house is above the frost line, it is vital that it be insulated. Again common practice is R10 for an unheated slab, again more is better. If your slab is heated then R15 should be considered minimal, and R20 is preferred. One other area of your slab that should be insulated is around the edge where it makes contact with the frost wall. If your frost wall is ICF, this has already been done; if you are using cast in place concrete, insulation must be used. It would be good to have 2 inches here, keeping in mind that you will have to detail your wall assembly to cover it.


Windows are the weak link in the building envelope of your new home. Whereas an energy efficient wall has an effective R-value of 22, or higher, a window can have an R-value of only 10% of that. Over the years, much progress has been made to increase the R-value of windows and to increase the ability of windows facing the sun to allow solar gain during the day, while preventing loss of this gain during the night.

Double or Triple Glazing

Two panes are better than one, and three panes are better than two. Multiple panes create a stagnant “layer” of gas between them, thus increasing the R-value by reducing the rate of heat loss.

Low E (emissivity) glass

Certain surfaces of window glass can be coated with a metallic or ceramic vapour that lowers its emissivity. Glass with low emissivity can prevent heat from being radiated through it at night, increasing its R-value. There are a wide range of low E coatings to serve a number of purposes. The type of low E coating influences the Solar Heat Gain Coefficient (SHGC) of a window. On the south side of your house you should have a high SHGC, but on the other sides SHGC can be sacrificed for a higher R-value.

Argon fill

Argon is an inert gas that is heavier, and more “sluggish” than air. When it is put in between the two (or three) panes of window glass, there is a reduction in the the amount of convective heat loss within the space between the panes.

Insulating Spacer

The material that is used around the edge of a window’s two (or three) panes should be made from an insulating material. This will reduce the conductive heat loss in this area of the window.

Air Tightness

The air tightness of your building envelope is an important factor in the energy efficiency of your house. Air sealing techniques must be employed to ensure that your house does not leak heat through unintentional holes in your building envelope. The heat loss becomes more pronounced on windy days. More information on the correct application of an air barrier, is available in Intro to Building Science. On a cold windy night, a tight house will not feel drafty, and your heating system will be able to keep up to the demands placed on it.

Heat Recovery Ventilation

Since one of the important features of an energy efficient house is its air tightness, you will have to install a ventilation system. This ventilation will allow fresh air to enter your home and stale air/moisture to leave in a controlled manner. As important as this exchange of fresh and stale air/moisture is to your health and comfort, there is an important energy efficiency consideration. As your ventilation system is exhausting stale air, something else is going outdoors along with it- heat, which you have spent your hard earned dollars generating in the first place. It is important that your ventilation system have heat recovery capabilities.

A Heat Recovery Ventilator (HRV) will recover a certain amount of the heat contained in the stale air stream and transfer it to the cooler fresh air. Subsequently the stream of incoming air in the winter time gets preconditioned and is not cold as it enters your home. The thermal efficiency of your HRV, and the amount of energy it consumes as it operates, are important to the energy efficiency of your home. Most run-of-the-mill HRV’s used today are only about 60% efficient, meaning 40% of the heat in the outgoing stream is lost to the outdoors. It is ideal to install an HRV that has a Sensible Recovery Efficiency of at least 80%. These units are not common, but would contribute to your home’s energy efficiency.