Air Quality Starts at the Foundation

To improve your home’s air quality, start at the foundation.

I received a call from a woman who had placed an offer on an expensive home in Vancouver. She wanted a renovation to this home, since she could not be in this home without quickly feeling sick. The home smelled musty, and she couldn’t bear the thought of living there. I concluded that a band-aid fix would not be satisfactory, considering her health issues.

I phoned my friend and ventilation expert, David Hill. David lives locally, yet his expertise takes him all over Canada and the U.S. for speaking engagements. He confirmed my suspicion that the smell and mould/mildew originated from the basement.

Nearly all new homes are built to the lowest common denominator – the BC Building Code. With respect to the foundation, let me show you what you get when you only build to code. We have two problems.

Firstly, traditional construction places the footing on dirt or clay. Footings, much like snow shoes, increase the surface area and spread out the load. The foundation wall sits on top of the footing. This footing, when sitting in water, can wick up 3 pounds of water per day per square foot. This moisture finds its way to the basement wall assembly.

Secondly, traditional basement wall assemblies are a victim of building science principles.

Allow me to illustrate my point.

Take one cold coke out of your fridge and put it on your counter. Take another one out of the pantry and put it beside the first coke can. Wait 5 minutes. What do you notice? The can out of the fridge has accumulated condensation on the outside of the can, while the other is dry. Moisture in the air condenses on cold surfaces.

Concrete is cold. Once moisture in the air gets past the vapour barrier, it condenses on this cold concrete wall. Furthermore, the poly sheeting prevents adequate breathing of the wall assembly.

What can be done?

Firstly, place your footings on a thick bed of ¾ inch free draining clear crushed rock. Water may wick up through sand and dirt through capillary action, but water will not wick up through ¾ inch clear crushed rock. Placing poly at the base of the footings will also prevent footings from making contact with water.

Free draining clear crushed rock and poly under the footings will prevent your foundation from making contact with water.

Secondly, choose a basement wall assembly that prevents air vapour from making contact with the cold concrete wall. Insulated Concrete Forms is one solution. Another would be to place rigid insulation on the interior/exterior of the foundation wall. Eliminate the poly vapour barrier and replace with a vapour barrier paint. This increases the breathability of the wall assembly.


Insulated concrete forms prevent air vapour from making contact with the cold wall.

When building a custom home, you have one chance to get it right. Strategically, build above code. Spend a little extra money and build a home that is healthy, comfortable, durable and energy efficient.

Wall Assemblies: Have your Cake and Eat it Too!

When it comes to wall assemblies, you can have your cake and eat it too!

I grew up in a home built in 1911. Houses were different back then. This home had sawdust for insulation and single pane windows. As it got colder, we put more wood in the fireplace. There were days in the winter when the house was so hot that we kept the front door open to cool off the home. Neighbours would drive by and think, “There are those Crazy Clays, it is -20° and they have their doors wide open!” That was the past.

Conserving energy was not a concern, since we just put another log on the fire. Firewood was free. Insulating the wall and achieving air tightness was just not a priority.

Homes eventually made a move to oil/gas fired furnaces. This new fuel cost more than the wood, which was free, so energy efficiency became more important. Thus, people began to place a greater emphasis on putting insulation between the studs.

In the 1970’s, the energy crisis hit us hard. We increased the insulation levels even further, and improved air tightness. The vapour barrier poly sheathing became standard construction. While increasing insulation values and airtightness can be a good thing, it can also have some negative consequences. Remember the condo crisis with wall assemblies rotting from the inside out?

Allow me to share a building science principle.

Take one cold coke out of your fridge and put it on your coffee table. Take another one out of the pantry and put it beside the first coke can. Wait 5 minutes. What do you notice? Yes, the can out of the fridge has accumulated condensation on the outside of the can, while the other is dry. Moisture in the air condenses on cold surfaces.

One important objective of a well-built wall assembly is to warm up surfaces where condensation may occur.

There are three problems with traditional batt insulation:


  1. We can stuff only so much insulation between the studs.  There is a limit.
  2. Eliminate thermal bridging. While insulation has an R-value of 22, the wood studs have an R-value of around 6. The framing is about 23% of the wall. So 23% of the wall is only R-6. The wood promotes thermal bridging.
  3. Poly sheeting does not allow the wall assembly to breathe.
Is there a better way?

Dr. Joe Lstiburek is a world-renowned building science expert. He has been a proponent of the perfect wall assembly. This wall assembly reduces thermal transfer and keeps the exterior sheathing warmer, thus reducing the propensity for moisture buildup.

For greater detail on this wall assembly, see my article, The Perfect Wall.

By choosing the correct wall assembly, you will achieve the following benefits:


  1. Thermal transfer is eliminated.
  2. Inside of the exterior sheathing is now warmer reducing the propensity for condensation.
  3. Effective R-value can easily double.
  4. No poly sheeting allows the wall assembly to breathe.


A well-built wall assembly is breathable and free of moisture.

I speak to builders who remember the condo crisis. They make comments like, “I just slash the poly, so that the wall can breathe.” This is prehistoric thinking; there is a better way. Why sacrifice air tightness to improve the breathability when building science proves you can have both?

Homes of the future will be more energy efficient and air tight. This wall assembly will breathe and be free of moisture and mildew, making homes healthier. Yes, you can have your cake and eat it too!