Solar chimney? What is it? and some really important steps to insulating a foundation

We are using a passive solar cooling technique in this home that is referred to as a solar chimney. A solar chimney is a little hard to explain but I will do my best. To fully understand how a solar chimney works you need to know a little bit about building science and the term commonly referred to as the " stack effect". The stack effect is what happens within a home when warm air is allowed to escape from your roof or through your attic. Something we try hard to stop in most homes by air sealing the attic space. The pressure created from the stack effect causes air to be drawn in from other places in your home, commonly your basement or a leaky envelope and windows within the home. Not something you want to do on a normal basis. The higher the point in which the air escapes the higher the pressure gets.

   This home uses the stack effect to our advantage. We are building a box located on the roof of the home. This box will not only contain the wood stove pipe but a whole house fan system as well. This box ( chimney) will be uninsulated and covered with a dark siding material. The heat created within the chimney will want to rise and escape from the vent pipes located on top. When the insulated (R-38) doors to the whole house fan system are opened, this will create negative pressure within house. In this home we are able to control where the air entering the home is able to come from. We have placed windows low to the ground on the north side of the house that need to be opened to allow the chimney to work. This will draw cooler air in from the north, fully shaded side of the house. If the system does not provide enough natural ventilation the whole house fan can be turned on to really move the air through the house. While not enough research has been done on solar chimneys to fully calculate how much cooling effect this will have on the house. It will be interesting to see how well it works next summer. What I did feel was the effect it will have on the building when constructing it. The last piece of the chimney was the top and when I was placing it I had to hold it down and could feel the air trying to escape, it wasn't even a warm day.

Foundation insulation, important steps!



  Foundations in most homes have little or no insulation at all and it has a negative effect on the whole house. Most basements here in the northeast contain the mechanical systems of our homes.( heating, domestic hot water and cooling) When these spaces are not conditioned we loose a percentage of our energy to this location. Conditioning this space for most homes means running a de-humidifier to control the moisture and consuming a large amount of electricity in the process. In this home we are using a better approach that includes insulating the foundation on the exterior from the footing all the way up to the sill of the home. We are using a product called Geofoam that is made of high density EPS, 2" thick with an R-11 insulation value. While building codes here in MA require you to insulate your foundation most builders stop this insulation at ground level, leaving a large hole in the homes thermal envelope. It does create additional work ( insulation, stucco and flashing) to do this but the result is a much better home in the end.

The other area of the foundation that needs attention in the basement floor or slab.

In this home we also insulated under the entire floor of the slab and up the side of it as well. This is commonly referred to as a thermal break, we have stopped or slowed the movement of thermal energy from moving through the basement floor. Along with this we place a 6-Mil vapor barrier under the concrete to stop the movement of water through the slab also. This eliminates the need for an energy hogging de-humdifier.

      When attempting to reach the standards for passive solar homes, all energy uses need to be considered. From the top to the bottom, no details is to small to overlook and in the case of the foundation,

it is no small detail.

 To finish off the foundation insulation, we simple cover it with a stucco and flash to top of it. Once again a little more work but in my opinion well worth the efforts.

Stay tuned

Tom Pittsley

tom.pittsley@nextsteplivinginc.com