Click here to read the introduction to the Sourcing local wood building materials article

By Chris Briley

I’ve heard it many times. “I like wood and I want to be as sustainable as I can, but I’m tired of painting. I also want my siding to be affordable, attractive and require little maintenance. What are my options?” The good news is that there are many options, and this article will review some of the more readily available.

NORTHERN WHITE CEDAR

One of the most sustainable choices for siding in our region is northern white cedar, also called eastern white cedar. Cedar is naturally rot-resistant thanks to the oils and acids (polyoxyphenols) contained in its heartwood. This is also what gives it its pleasant and strong aroma. In fact, it starts to become evident that the more pungent and “piney” the coniferous wood smells, the more of these natural phenols it has, and the more rot-resistant it becomes.

Eastern white cedar is a smaller tree and so is often used for smaller pieces, i.e. shingles. If the shingles are thick enough and made from the heartwood of the cedar tree, they can be installed over a rain-screen matrix, be left completely untreated and perform beautifully for decades. If the cedar is also sustainably harvested (meaning it is from a managed forest that is growing as fast or faster than it is being harvested), then this is an extremely environmentally responsible material.

Though harder to come by, white cedar can also come in shiplap, board and batten and any variety of clapboard profiles. Its life can be lengthened by the application of sealants, stains and a vast array of other coatings, though many products come pre-finished.

PINE (SPRUCE, PINE, FIR, HEMLOCK, LARCH)

There are numerous other species of affordable woods available in siding profiles (clapboards, shiplap, etc). These are typically meant to be sealed or painted — and should be — to greatly extend their life span. When installed properly, with ALL sides coated, and over a rain-screen layer, these wood sidings can be very durable, especially if the coatings (finish paint, sealer and/or primer) are factory-applied. Indigenous to the northeastern US, pine is widely available in building supply outlets.

WESTERN RED CEDAR

Like its eastern cousin, red cedar is naturally rot-resistant. It is a much bigger tree and yields more useable clapboards and shakes. As its name implies, the wood has a reddish, warm hue. Because of this and the higher level of tannins in it, it tends to age to darker tones than eastern white. One drawback for us here in the East is that this species must be transported across the country, adding to its carbon footprint and cost.

EXOTIC WOODS

If one’s value set is focused more on durability and appearance than on cost or sustainability, then exotic woods may enter the picture. There are numerous species available for decking and siding, primarily mahogany, teak and ipe.

Most of these come from South America and most do not come from sustainably harvested forests. In fact, most contribute to the deforestation of tropical rainforests, where up to 50 acres of forest are clear cut for every one good “marketable” tree. This statistic is arguable but, regardless, harvested exotic woods from South America simply do not play a role in the sustainable low-carbon future.

FIBER CEMENT SIDING

This type of siding has grown tremendously in popularity in the last decade or so, and it’s easy to see why. It is affordable and often the same price as (or even cheaper than) painted pine clapboards. It comes in a wide range of styles, finishes, textures, sizes and configurations and is readily available. It is made from cement, wood pulp and silica (or fly-ash for some products). It is highly durable, rot-resistant and, when installed correctly, moisture-resistant and able to hold its finish for a long time.

When cutting fiber cement with a saw, it erupts into a cloud of very fine silica dust that is hazardous to inhale (though not directly toxic). Most manufacturers recommend cutting shears for this reason. Some builders, for ease of construction, choose saws and (hopefully) masks anyway.

In almost all cases, fiber cement is a painted product, and while it absorbs far less moisture than wood, it is still absorbent. Care must be taken in detailing to ensure its predicted lifespan. Fiber cement siding is very high in embodied energy and embodied carbon.

ENGINEERED WOOD

There are newer players to the stage with different composites to offer. LP makes a composite lap siding made from wood strands, wax and a binding resin, coated with a zinc-borate primer. This combination avoids the embodied energy issues and silica dust clouds of fiber cement and also offers better toolability. Our office has some reservations about its proprietary “resin” as the manufacturer will not disclose what it is, though it is not PVC. It has been around a while and is proving to be durable, but it is still too new to know its exact durability.

FLY-ASH POLYMER

Another new composite product is a “polyash” composed primarily of fly-ash, a byproduct of the coal industry, mixed with a proprietary polymer as a binder. TruExterior® made its entrance to the market as a trim material, where it has been very successful. Being a polymer-based composite, it absorbs even less moisture than the others mentioned in the composite category. Its siding products are very new to the market, and so its true durability remains to be seen. The polymer’s full chemistry is not publicly known. It is more difficult to tool than SmartSide, being very hard and “chippy” but easier than fiber cement.

VINYL SIDING

Vinyl siding gets a bad rap, and it deserves it. Mostly. Many have argued that this is an affordable material that lasts forever, and for those on a tight budget, it is the only option. It is true that it is fairly durable and certainly cheap. Typical vinyl siding, however, does not have the durability that its proponents might claim. It gets brittle, it breaks, it fades or chalks, it slumps. The substrate of a vinyl siding project needs to be weather-resistant and detailed well.

From a sustainability standpoint, vinyl gets a failing grade. Its pros are that it does not require paints and coatings and that it has low embodied energy. But vinyl, or PVC, is toxic to make and difficult to recycle. Here in Maine, where we have some excellent recycling systems in place, when vinyl siding is removed it invariably ends up in the mainstream trash. If not disposed of carefully, it can end up being incinerated (50% of Maine’s garbage is incinerated), in which case the dioxins of burning PVC will be released into the atmosphere.

METAL SIDING

Once relegated to commercial projects, metal siding is beginning to find a market share in the residential sector, usually on modern homes. Most metal sidings are thin steel sheets (20-24 gauge) that metal sidings are thin steel sheets (20-24 gauge) that have been coated in a highly durable paint such as Kynar® or an alloy coating such as zinc (galvanized) or galvalume (an alloy of zinc and aluminum). This siding either comes in panels or it is formed in place, much like a standing seam metal roof. There are truly countless options in color, pattern, gloss, orientation, size and fastening technique. From a sustainability standpoint, metal siding is not a bad option. Steel is relatively high in embodied energy. However, its durability, recycled content and recyclability are also high.

Chris Briley is a partner and principal architect at BRIBURN, specializing in energy-efficient, environmentally friendly design. He is a founding board member of PassivhausMAINE, a blogger at greenbuildingadvison.com and co-host of the Green Architects’ Lounge podcast.