Whether you are building new, remodeling, or putting on an addition, your building envelope is crucial to energy efficiency with a high ROI (return on investment). A contractor friend of mine once said it doesn’t matter what you do inside if your envelope is leaky.
In addition, there are a number of green construction materials to investigate according to your own area and climate that can help you gain maximum energy efficiency, and savings. This includes foundational materials, walls, insulation, and windows.
I’ll start from the bottom and work my way up.
Most foundations are poured concrete, which is durable and needs little maintenance. It’s a popular building material of natural materials, but it’s energy-intensive to make and transport. Read: not green.
There are several solutions to create a more eco-friendly, energy efficient foundation. Here are three.
- ICFs – Insulated Concrete Forms are panels of rigid foam insulation used as forms to pour concrete, instead of plywood, 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 walls above ground.
- Rastra – Recycled polystyrene beads are mixed with cement in block form in an 85/15 ratio. This is lightweight, easy to transport and move around on a building site, and has excellent insulating properties. It cuts your utility bills and has great acoustic quality.
- 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 be forewarned: Flyash is laced with toxic heavy metals, such as mercury, lead and arsenic. It is no cleaner that its parent, coal.
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.
Installing Radiant Heat
If you are installing radiant floor heat, the concrete slab must be completely insulated, otherwise the heat will go into the ground. Site work should be done, rigid foam insulation laid down, and a reflective barrier placed on top to reflect heat upward. Then, the tubing can be laid. Finally the concrete slab can be poured.
Code where I live 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 slab should have insulation beneath it.
The aim of the Passivhaus 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! [ED: your contractor should be familiar with local building codes in your area. If they're not, hire a new one.]
Energy Envelope-Friendly Walls
After your foundation is in place, the walls will be constructed. Increase the R-value and prevent air infiltration to reduce your energy use and avoid condensation. Use local and natural materials, and create as little waste as possible. Recycle whatever you can.
Here are some examples of sturdy, energy-efficient walls used through out the world and in my local area, according to climate and local materials on hand.
Optimum Value Engineering (OVE) reduces materials and labor costs, and cuts down on thermal bridging. Heat cannot transfer easily between outdoors and in.
Structural Insulated Panels are modular panels of two layers of sheathing with a foam core. SIPs construction is pre-fab, reducing labor costs and material waste. It has a higher that standard R value, and is straighter and stronger than conventionally framed walls. Being air-tight, it reduces fuel consumption and costs for heating and cooling.
This is the most common building material in Taos, New Mexico, where I live. It is local and natural, but it’s a funny material. Once you warm it up, it stays warm, since it’s excellent thermal mass. An adobe home is very cool in summer, like a consistent 65-70 degrees. But in spring and fall, that feels cool.
It’s more comfortable outdoors when the home is not being heated regularly. This extends the heating season, making it not so eco-friendly. The best use for adobe is thermal mass in passive solar applications. It absorbs the sun’s warmth and radiates it back out at night.
This is another popular building material in Taos. Strawbales are made from stalks left in the field after harvest, deeming it natural, recycled and renewable. The bales have high insulating properties, which reduces heating and cooling fuel needs and costs.
Like Rastra, strawbale has fabulous acoustics, creating a pleasant space inside. I have been in many strawbale homes, and they have a soft, warm, cozy feel to them.
Forms are put in place and mud poured into them and packed down for strength and durability. This is essentially the same as adobe, as far as properties, but adobe is made of bricks, making it more labor intensive than a pour.
Sometimes exterior walls are insulated as they are built, such as SIPs and ICFs, discussed above. 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.
When you are shopping for energy efficient windows, this information on the label will tell you about window performance:
- U-factor rating of the National Fenestration Rating Council (NFRC) – the lower the number, the more efficient the window, based on the glass, frame and spacer material.
- Solar Heat Gain Coefficient (SHGC) – This figure lets you know how much heat a window transmits. For passive solar gain, this number should be higher than .6. For windows on the north side that let sun in during the summer, this number should be lower to block the heat.
- Visible Transmittance (VT) – This number, between 0-1, states how much light comes through a window. For passive solar, this number should be high.
- Low-e – low-emissivity. A thin, invisible coating on the glass controls the amount of heat moving through it in both directions, in and out. This affects the U-factor and the SHGC. Low-e windows can save you 30-50% on your energy bills.
For northern orientation, you want:
• A low SHGC
• A low U-factor
• A low VT
• Low-e windows
Really, the only thing I can say about a ceiling is insulate, insulate, insulate. If you live in a cold climate, this will keep your precious winter heat in the house. If you live in a hot climate, this will keep the sun’s heat from penetrating into your living space. Look above at the Wall Insulation section for eco-friendly options. No matter where you live, ceiling insulation reduces the need for fuel and its subsequent costs to your wallet and our planet.
Work With A Reputatable Contractor
As always, when you are going to build, work with a reputable contractor, who is licensed, bonded and insured. Be sure s/he understands green building – the principles, the materials and the efficiency of the end product.