The tightness and efficiency of your building envelope is crucial to energy savings. A friend of mine once said it doesn’t matter what you do inside if the outside is not tight. I’ll start from the bottom and work my way up to show you the options.
Foundation
Most foundations are poured of concrete, which is durable and needs little maintenance, making it a popular building material. Concrete is made of cement, sand, water and stone. The last three are natural and generally local, which are green attributes, but cement is energy intensive to make and transport. Read: not green. There are several solutions to create a more eco-friendly foundation.
ICFs – Insulated Concrete Forms are panels of rigid foam insulation used as forms to pour concrete. This eliminates the need for plywood forms, which get used a few times and taken to the landfill. ICFs also insulate the wall in one move saving time and costs. These can also be used for your walls.
Rastra – Recycled polystyrene beads are mixed with cement in block form in an 85/15 ratio. This is lightweight and easy to transport and move around on the site, has excellent insulating properties cutting utility bills, and is durable in extreme weather conditions.
Flyash – Flyash, or coal ash, is a waste product from coal burning power plants. It is recommended to replace cement in a concrete mixture with at least 15% flyash. Recycling waste products is very eco-friendly. BUT! BUT! BUT! Flyash is toxic, laced with heavy metals, including mercury, lead and arsenic. It is no cleaner that its parent, coal. Consider yourself warned about the use of this product!
Outside foundation walls of crawls spaces and basements need to be waterproofed and insulated. A perforated pipe for drainage should be laid at the base of the wall by the footings in a gravel bed.
Newer homes here in Taos, New Mexico have concrete slab floors, with radiant floor heat tubing installed. The floors must be completely insulated, otherwise the heat will go into the ground. The site work should be done, rigid foam insulation laid down, a reflective barrier placed on top to reflect heat up, then the tubing laid, and finally the concrete slab poured. Code says only two feet in from the exterior wall needs to be insulated, but common sense tells me (and several contractors I know) the entire floor should be done.
A client of mine, a green architect, Joaquin Karcher, designs and builds Passive Haus’s. The aim is to combine an air-tight envelope with a high efficiency ventilation system so that no heating system is needed. The standard for this is 9” of insulation under the floor!
Walls
After your foundation is in place, the walls go up. Energy efficiency is achieved by increasing the R value and preventing air infiltration to reduce your energy use and avoid condensation. You also want to use local and natural materials, and create as little waste as possible.
Advanced framing – OVE, Optimum Value Engineering reduces materials and labor costs, and cuts down on thermal bridging, reducing heating and cooling costs.
SIPs – Structural Insulated Panels are modular panels of two layers of sheathing with a foam core. SIPs construction reduces labor costs and material waste, has higher R values, and is straighter and stronger than conventionally framed walls. It is also air-tight, lowering heating and cooling costs.
ICFs – See above
Adobe – This is the most common building material in Taos. It is local and natural, but it works its best magic as thermal mass in passive solar homes. It absorbs the sun’s warmth and radiates it back out at night.
Strawbale – This is another popular building material in Taos. Strawbales are made from what’s left in the field after harvest, so they are recycled and renewable. They have high insulating and acoustic properties, which reduces heating and cooling costs and creating a pleasant space. I have been in many strawbale homes, and they have a soft, warm, cozy feel to them.
Rastra – See above
Rammed earth – Forms are put in place and mud poured into them and packed down for strength and durability.
Windows
This previous post, Buying Energy Efficient Windows, says it all.
Wall Insulation
As you can see, sometimes exterior walls are insulated as they are built. If you need to insulate after the fact, there are a few green options. These hold true for interior walls, too. I recommend insulating interior walls for noise reduction, good acoustics, privacy and comfort.
Recycled cotton batts – These are usually made of denim and are installed just like standard fiberglass batts.
Cellulose – This is shredded newspaper that you can buy or shred yourself, and it gets blown into wall cavities.
Recycled fiberglass – These look and perform just like regular fiberglass batts, but are formaldehyde-free.
Once your walls are up and insulated, caulk and/or foam all connections, corners, openings for an air-tight structure.
When your home is air-tight, you will need some ventilation, either through operable windows or a whole-house ventilation system.
Now that the outside of your house is energy efficient, Iearn about the interior.
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{ 2 comments… read them below or add one }
I would think that Rastra would be used more than it is. I did not know that Flyash was as toxic as it is. I hear about Flyash used often, but never Rastra.
I agree on the Rastra front. It has excellent insulating and acoustic qualities.
Here is a link to the 60 Minutes show on flyash that aired last fall. http://www.cbsnews.com/stories/2009/10/01/60minutes/main5356202.shtml