The building envelope consists of walls, roof, windows, doors, and ground level floor. These components are intended to keep out heat and cold, wind and water.
A well-insulated and tight building envelope is a must for any green home. Energy requirements for heating and cooling are directly related to the quality of the building envelope. The better the insulation and the tighter the construction, the lower the heating and cooling requirements.
The building envelope must also keep water and humidity out of your home:
Water entering walls, floor or roof can have disastrous consequences for the structure of your home as well as for the health of you and your family. Mold and mildew can make people very sick.
Drains need to be installed around the house, and possibly below the basement slab to help groundwater to naturally flow away from your basement. These drains are commonly called french drains. In addition, basement floors and foundation walls must be sealed.
One important component of the building envelope is the vapor barrier. The purpose of the vapor barrier is to keep humidity and moisture out of the building structure, as mentioned above. Humidity can get trapped in the walls, condense on the cold outer layer, and water will collect, and possible run down inside the wall, if the vapor barrier has any leaks. Small puddles of water can accumulate, unbeknownst to you, behind the drywall. Rotting wood, carpenter ants, mold and mildew are the result.
A “tight construction†means that all cracks at corners and around windows and doors are sealed and no drafts are felt in the house, even during severe winds. We all know how uncomfortable it feels in a drafty house and how our first reaction is to go turn up the heat. Green and sustainable homes feel wonderfully cozy, even with a blizzard raging outside.
Think about snuggling under a warm comforter. If there is just the smallest opening in your back, where cold can seep in, your whole body feels cold and the thickest down comforter won’t help. It is similar with a house. Any gaps in the insulation, any poorly sealed window or door, has a huge impact on the energy usage of your green home and on the level of your comfort. I cannot stress enough, how important a well built, high-insulation, tight building envelope is for your green home.
What about stuffiness in such a tight home? Green homeowners can either open windows periodically as required to air out the house, or equip their home with an energy recovery ventilation unit, which continuously circulates fresh air through the house.
Heat rises. That is why the roof on a green home must have a very high insulating value, generally R-30 or more. Did you know that a well-insulated roof will also help keep your home cooler in the summer?
Locations, types and sizes for windows must be optimized for passive solar energy heat gains. Correctly sized shading and overhangs for East, West and South-facing windows will keep the hot rays out of the home during the summer months, while allowing the winter sun to warm up the home. Windows are also important to allow the green homeowner a view of their garden or the mountains and have a connection with the surrounding landscape.
Replacement windows with a high insulation value can be the first step towards renovating your home into a green home. A windows manufacturer or a green builder will be able to help you determine which types of windows and what sizes are best suited for your green home. Placement, type and size of windows must all be considered to optimize the passive solar energy gain. No-to-minimal heat gain through the windows in the hot summer months, and maximum heat gain during the colder months is your goal.
Doors are an often neglected component. A poorly insulated, leaky door can add considerably to the heating requirements for your home. The location of your main entry door can also have a huge impact on the energy usage of your green home. Often, the main entry leads directly into the living room or a huge hallway. Every time this door is opened on a winter day, a blast of cold air enters the home. Green architects and builders understand this and design a low-energy home accordingly.
For example a vestibule with a set of doors, which forms a buffer zone between the heated or cooled home and the outdoors. These vestibules are very common in European homes an are sometimes called “wind catchers”.
Ground level floors are generally either slab-on-grade or wood frame floors over a crawl space. Many of us know the uncomfortable feeling of having cold feet in a basement room. Again, our reaction generally is to go turn up the heat.
Green homes are built with well-insulated floors, and often also have floor heat. When a floor heating system is installed, it is important to have a good insulation below the floor heating pipes, so you don’t end up heating the ground below or the garage.
I cannot stress enough how important a well-insulated, tight building envelope is for a home. The comfort level for you, the homeowner, will be high and your heating and cooling bills will be low.
A high-insulating, tight building envelope is also the first step to take full advantage of alternative energy sources.
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