Exterior Treatments: Siding & Roofing

Show off your green building on the outside — by using green materials!

Because a building's exterior must endure rain, big swings in heating and cooling, and ultraviolet rays, durability is a central concern for exterior materials. So are moderating heat gain and stormwater runoff, and repelling microbial attack.

1 Use durable roofing materials
2 Use a cool roof
3 Use a green or living roof
3 Use sustainable siding materials
3 Use sustainable decking materials

Unfortunately, many durable, natural woods are endangered, and some durable synthetic materials are the products of toxic manufacturing processes. Green alternatives range from high–tech new "cool roofs" to time–tested standards such as stucco or stone.

Goal: Make a sustainable roof

Typical roofing is a major non–recyclable component of our solid waste stream. More sustainable alternatives provide many benefits such as longer service life, lower maintenance costs, energy savings, and superior stormwater management, and can even be an environmental signature piece for a green project.

area one

Use durable roofing materials

What is this?

Roofing can be considered durable if it has a life span of 40 years or more.

Why do it?

Re–roofing represents one of building owners' largest maintenance costs — buying two roofs in twenty years costs a lot more than buying one good roof that lasts for forty.

How to do this?

Durable roofs include high–end single–ply membranes and composite shingles, stone or clay tile, and sheet metal. Roofs that wear out rapidly are often made of cheap asphalt shingles or built–up tar and gravel rolled layers. Get the longest possible warrantee from your roofing subcontractor, and write durability into your contract and specifications.

Who does this?

Architects, specification writers, contractors, roofing subcontractors.


area one

Use a cool roof

What is this?

Cool roofs are designed to reflect the heat that comes with sunshine. They can be bright white membrane roofs, paint-on coatings (for retrofit applications), or light-colored or specially designed tiles and shingles. While metal roofs are reflective, they will only release heat gain if specifically coated to do so.

Why do it?

A cool roof alone can decrease the air conditioning costs of the space below by 20% or more and increase comfort dramatically. Cool roofs are also more durable than hotter roofs because there is less degradation from heating/cooling and UV exposure. Lastly, they reduce the heat island effect for the surrounding region (see Chapter 2).

How to do this?

Ask your architect or roofer for cool roof options. The ratings for the roof product should be 75% or greater reflectivity and 85% or greater emissivity. Cool roofs are especially appropriate for large flat roofs such as on industrial buildings, warehouses, and shopping malls but as new options become available, they will become more applicable for houses and small commercial buildings as well.

Who does this?

Owners, architects, specification writers, knowledgeable roofing contractors.


area one

Use a green or living roof

What is this?

Green roofs have a layer of soil and living plants on top of root barriers, waterproofing layers, and a structural roof deck (usually made of concrete). They range from a thin soil layer that supports groundcover plants to gardens that include shrubs and even small trees.

Why do it?

Green roofs reduce heat gains inside (as with cool roofs), and protect your roof's waterproofing layers, adding great durability. They prevent stormwater runoff (see Chapter 2). They can even replace habitat for species that is lost under the footprint of new construction. Many can be used as beautiful outdoor garden spaces for building occupants.

How to do this?

Plan early for a green roof, because it has a significant impact on your building. It can change building height, and often requires a somewhat stronger structure to carry the soil weight (heavy trees can be located directly over columns). A number of manufacturers offer complete green roof systems including waterproofing, drainage layers, soil–holding layers, and even plantings.

Who does this?

Architects, structural engineers, green roof manufacturers and installers.



Goal: Support healthy environments and sustainable forests

The health and environmental impacts of the production and extraction of building materials are substantial. Siding and exterior decking are two areas where these concerns are especially important because of the visibility of siding and the shortage of choices for exterior decks.

area one

Use sustainable siding materials

What is this?

Wood siding, like structural framing, uses large boards that come from mature trees (see Chapter 5). Sustainable alternatives include fiber, cement and stucco.

Why do it?

FSC certified wood reduces loss of old-growth trees and keeps forest ecosystems healthy. Fiber–cement or stucco are lower–maintenance than wood siding, which requires frequent painting. However, vinyl siding, made from polyvinylchloride (PVC), and the dioxins that come from manufacturing it are among the worst and most common environmental toxins in the United States. Dioxins don't break down in the environment, and cause numerous health hazards. PVC also creates toxic fumes in building fires and becomes non–recyclable solid waste once its service life ends.

How to do this?

Green choices for siding include salvaged or FSC certified wood, brick and stone, stucco, fiber cement panels and boards, and non–PVC plastics such as polypropylene boards.

Who does this?

Owners, architects, specification writers, contractors.


area one

Use sustainable decking materials

What is this?

Typical decking is made of durable woods that are endangered — particularly redwood — and that are generally not sustainably harvested. Plastic lumber (which contains recycled high density polyethylene, not PVC) and plastic–wood hybrid lumber are more sustainable substitutes for decking.

Why do it?

Outside of a few very small logging operations that are moving to sustainable harvesting, using redwood for decking contributes directly to the loss of California's last stands of coastal oldgrowth forest. Plastic lumber contains recycled materials, has lower maintenance than wood, and does not give splinters.

How to do this?

Check with local lumber yards for FSC certified redwood decking and plastic lumber or plastic–wood hybrid lumber. Also, consider using a brick or stone patio instead of a wood deck to create usable outdoor space.

Who does this?

Owners, architects, remodelers.


More Information

The Cool Roof Rating Council
Plastic Lumber Trade Association
Healthy Building Network
Green Roof Industry Resource Portal