High-performing building considerations

Control water, air, vapour, and temperature in your home.

In order for a building to perform well and last for decades to come, it must defend against all of the conditions of the outside environment that it is located in. This includes the following conditions in order of importance:

 Water Management:

If building materials get wet and can’t dry out, it leads to many issues including mold, mildew, rot, and decay. Therefore, the first goal of a roof or wall system is to keep water out. While this may sound simple, there are often dozens of penetrations through a wall or roof system and each one is in danger of allowing water in.

The most obvious solution would be to create a completely waterproof exterior to the building, but this is much easier said than done. The most common exterior finishes used in Ontario are siding (often vinyl) and masonry veneer. Neither of these is waterproof, but both can function quite well when part of a properly detailed wall system. For an exterior to function well, we must construct it so that it will deflect water away, and allow water that does get in behind to flow down and out.  Masonry veneer and siding can both do this job exceptionally well when installed with an air space behind them. This air space allows any residual water to easily flow behind along the WRB (water-resistive barrier) installed behind the exterior finish. The most important, and often overlooked, keys to water management are properly detailed and well installed flashings at windows, doors, and mechanical or electrical penetrations, as well as every change of plane (wall to roof) on the exterior.

Air Tightness

Saying a house needs to be air-tight can sometimes be controversial. Older homes used to have no air barrier and allowed huge amounts of air to pass through the wall system and into the home. Over time, heating costs rose, and comfort became more and more of a priority which led to insulation being installed into walls. With more insulation, people wanted to keep their warm air inside the house and began increasing the air tightness in their house. This led to old buildings, with poor water management allowing large amounts of water into the wall system, without the air flowing through the wall drying it out. This created a haven for rot and mold and led many to the conclusion that ‘a house needs to breath’.

While a house that allows air through the wall is much easier to build and will be able to dry out any water that gets in, it has an exponentially negative effect on the comfort and efficiency of your home. A good wall system will have plenty of air flow on the exterior of the WRB to keep the exterior dry, and an extremely air-tight WRB to keep the conditioned air inside the home, and the exterior unconditioned air out.

Vapour Control

Vapour control is also an extremely important key to a good wall or roof system, but it can be difficult to detail and changes with the climate. To understand vapour intrusion, consider a wall in the middle of winter. Warm, somewhat humid air inside the home wants to mix with cold, dry air outside. The humidity (or vapour) inside will want to migrate towards the exterior and at some point will reach a point in the wall that is cold enough that the invisible vapour will turn to liquid water in the form of condensation. This condensation will grow and grow through the winter season creating massive water problems inside the wall cavity. In typical modern construction in Ontario, this is dealt with by installing a plastic sheet (known as poly) over the entire interior of the walls and ceilings in a home. This poly is continuous over and behind walls and functions very well in the winter season and also typically serves as the air barrier for the house as well. The installation of poly in Ontario is detailed quite well in the Ontario Building Code and has been given considerable attention to create consistently good results for air and vapour control. The only downside with this method is that with the increased use of air conditioning, the vapour conditions flip in the summertime with hot humid air outside and colder, less humid air inside. If the conditions are right, vapour might condense on the exterior side of the plastic and create the same problem as before. Combine this with increased exterior insulation typically in the form of extruded plastic board insulation, the moisture created in the wall cannot dry towards the interior or the exterior. It is important to consider each individual wall system in its environment to build a system that will keep water and air out, and allow moisture to dry.

Thermal Insulation

Thermal insulation is usually the most considered layer of environment management and is very important in keeping your home comfortable, but it falls towards the end of the list in importance. This might seem backwards, but without keeping water out it won’t last, and if it doesn’t last it doesn’t matter. Also if you don’t keep air out, it doesn’t matter how much insulation you use if the conditioned are can freely escape. Building code in Ontario has mandated a considerable amount of insulation for new homes and additions in modern construction and, possibly most impactfully, has mandated continuous insulation on all walls, basement and above grade. This is very important when you consider how adding more and more insulation will exponentially decrease in efficiency; meaning that adding some insulation will have a large positive impact but doubling that insulation value will only increase the energy efficiency of the wall system a little. Pretty quickly it is more efficient to add a continuous layer of insulation around the entire perimeter of the home, than to pack more insulation into the stud cavities. The studs in a wall take up about 15% of the wall area and every space where the insulation meets the studs, or the studs meet the wall plates, has a high chance of having a small gap with no insulation value at all. This makes a small amount of exterior, continuous insulation, greatly increase a wall system’s efficiency.

There are many types of wall systems used in buildings, and each one has different ways of tackling these issues, but every type must deal with them well to create a long-lasting comfortable home. Reach out to us with any questions on what will be best for you and your home!