Wood is a beautiful material to make things with. By choosing greener wood for your project, you can keep the Earth beautiful too. How do you choose sustainable wood?
Wood can be a fantastically "green" material, but it can be horribly bad, too. It's mostly a question of growing trees back as fast as they are harvested, because unlike food farms, tree farms and natural forests usually aren't dosed with much chemical fertilizers and pesticides. Of course, the way trees are harvested (clear-cuts vs. selective cutting) and the social impacts on the workers and local people are also important. Certified-sustainably-grown wood can do all these things.
For plywood, particleboard, and other composites, the toxicity of the glue is also important to your own health.
Of course, the wood has to physically stand up to your usage too, so you need to think about the strength, rot resistance, or other qualities you need for the stuff you make to last.
Here's a step-by-step guide to choosing "greener" wood!
(Above image: adapted/ cropped from "Slice from oak tree, about 400 years old, from Soling, Germany, sampled for tree ring chronology" Author: Hgrobe, Source link, Licensed under Creative Commons Attribution-ShareAlike 3.0 Unported: CC BY-SA 3.0)
Step 1: Raid the Scrap Bins!
The most sustainable wood is the wood that never felled a tree—there's a lot of it just sitting around. Many lumber stores have it for cheap, or even free! Local woodworking shops might have scraps of very fancy wood they're just throwing away. If you keep your own scraps when you're woodworking, you'll accumulate your own useful pile.
Sometimes you can even get great wabi-sabi aesthetics from using old weathered wood reclaimed from buildings, railroads, or other places. You can also sometimes find giant timbers that'd be super-expensive new. Though be careful for embedded nails or other safety hazards! This's a giant 12"x12" reclaimed timber:
Step 2: Find FSC-certified Wood If You Can.
The easiest way for you to measure sustainability is to let experts do it for you. There're lots of eco-labels for green forestry, but by far the most respected one is Forest Stewardship Council ® (FSC®) certification. Several other common certifications (like SFI) vary from weak to greenwashing.
It can be hard to find FSC®-certified wood at many hardware stores, but more and more stores carry it (for instance, Home Depot has some FSC® lumber). The more you ask store managers for it, the more stores will carry it. Don't be shy about explaining why SFI doesn't count and FSC® does.
Step 3: Choose Rapidly-renewable Wood.
If you can't find FSC®-certified wood, you can find wood that grows really fast, which makes it easier to be grown sustainably. Softwoods (evergreens) generally grow faster than hardwoods (deciduous), so they're preferable. But some wood grows much faster!
They say "the grass is greener…" In the case of bamboo lumber, they're right, because bamboo is a grass, so harvesting it is a little more like mowing a lawn than cutting down a tree—the plant is still alive and will regrow. Bamboo also grows really fast.
Cork is another rapidly-renewable wood. It's a proper tree, unlike bamboo, but harvesters don't cut down the tree, they just skin the bark and it regrows, allowing several harvests before a new tree has to be planted. It's not very structural, but it's more water-resistant and sound-absorbent than most wood.
Also lumped into this category is agricultural waste, because it's renewed every year from the leftover stalks of food plants like wheat or sorghum. Agricultural waste is also great because it's recycling.
Agricultural waste boards are always composites of lots of stalks glued or pressed together, like plywood or OSB (which we'll look at later). Ask your local stores if they carry wheat board, straw board, Kirei board, or other "agriboards".
Step 4: Choose Abundant Species.
If you can't find FSC®-certified wood or rapidly-renewables that fit your plan, you can guess what's more sustainably harvested by what woods are more common, less endangered species. This varies by country, but there're rules of thumb. Luckily, it's often easy to tell from prices: wood from common trees is usually (but not always) cheaper.
Abundant woods to use:
- Birch Cedar (red or white)
- Douglas Fir
- Oak (red or white)
Threatened / endangered tropical hardwoods to avoid:
If you want a particular wood because of its look, remember that a good stain can radically transform the look of a wood—not only color, but grain. It's easier to find a healthy stain than it is to find sustainably-harvested tropical hardwoods.
If you're curious about a particular tree species, you can look it up in the CITES list (Convention on International Trade of Endangered Species) or the IUCN red list (International Union for Conservation of Nature).
By the way, you may have noticed that I'm not mentioning local materials. Buying local is nice, but it doesn't matter anywhere near as much as sustainable harvesting, good choice of species, or non-toxic binders and finishes.
Here's a little chooser chart to help you choose more sustainable wood. You can also download a quality PDF of the chart below.
Step 5: Choosing Good Plywood / Composites
Plywood, particleboard, OSB, MDF, and other composites can be a greener choice than boards, and cheaper, if you're making things with big parts. (When was the last time you saw a 4' x 8' single board?) They make more efficient use of trees than solid boards do, and some can actually be stronger than solid boards. (Though things like MDF are much weaker.) However, the downside is that they're often held together with toxic glues.
Don't freak out too much—most people don't get sick from it right away—but breathing in urea formaldehyde (a standard composite glue) increases your risk of cancer and other problems. It's a "VOC" (volatile organic compound). If you're making a whole room out of composite wood, a small percentage of people might get sick building syndrome from spending time in that room. It's rare, but how lucky do you feel? Of course, cutting and sanding these materials will expose you to a lot more of it than someone sitting around your finished project.
So to avoid toxic glues, choose composites with "no added urea-formaldehyde". Many kinds of wood naturally contains small amounts of urea formaldehyde, you just don't want the glue to add a lot more. And some other compounds, like melamine formaldehyde, are ok because they don't offgas the formaldehyde into the air like urea formaldehyde does.
If you're super-green cutting-edge, you can buy plywood with a non-toxic biomimetic binder. Columbia Forest Products's "Purebond" plywoods use a soy protein chemistry based on the way mussels stick to rocks and boats! (And yes, you can get it at many stores, even big chain stores.)
If you want to geek out on the engineering specs and variety of composites, check out the Wood-Based Composite Materials chapter of the USDA Forest Products Laboratory's Wood Handbook. And for more on clean-air composites, the California Air Resources Board has a nice little FAQ on composite wood binders.
Step 6: Physical Strength, Hardness, Density
If your project breaks, that's not very green, no matter how eco-friendly the materials are. So make sure you choose a wood (or composite) with the right physical properties for your thing!
Are you making something structural, like a bed or table? Then you care about strength (not breaking under force). Are you making a nice surface finish, like a floor or counter? Then you care about hardness (resistance to dings and scratches). Are you making a vehicle? Then you probably care about density (to reduce weight). There might be other physical qualities important for your particular project.
For most projects, pine is fine. Especially when you're starting out, prototype everything in a cheap, abundant, easy-to-work-with wood like pine before you start handling expensive and higher-eco-impact woods.
If you're advanced, though, and engineering properties are important to you, here are three graphs ranking common woods by hardness, density, and rupture strength. People make a big deal of the difference between hardwoods and softwoods, but these categories don't always determine which species score better, and bamboo technically isn't in either category.
Note that freshly cut ("green") wood is weaker than properly-dried wood, sometimes by quite a bit. It's also heavier, because water is denser than cellulose. However, "green" wood is more flexible, and thus tougher (more crack-resistant) than dry wood. That could be useful for you, particularly if you're bending it.
Step 7: Physical Endurance Vs. Rot, Mold, and Bugs
If your project will live outside, or exposed to moisture or termite invasion, you'll be tempted to use "pressure treated" (actually chemically treated) wood. Be careful with this. A lot of these treatments are toxic. The default treatment used to be arsenic! You don't want that in your garden or your kid's playhouse.
These days many treatments are safer, and some are totally benign, but a lot are still toxic. Before buying treated lumber, find out what the chemicals are, and see if they're safe.
Or you can just buy wood that's naturally resistant to rot, mold, and bugs. For instance, western red cedar and redwood. Much easier for us non-chemists! Some rare tropical hardwoods also have great weather resistance (like teak and ipé), but it's still best to avoid those unless you're sure your project will be used for a long time (decades!) to make it worth it.
Step 8: Working With Wood
What you do with wood can be even more important as the material itself. If you leave perfectly good wood out in the rain or sun, it can warp and get ruined before you even make anything. You can have a super-sustainable wood but put a super-toxic finish on it. And you can have a strong wood that you split by nailing or joining it badly.
To avoid warping, store your wood somewhere that has fairly stable temperature and humidity if you're not going to use it anytime soon.
To avoid toxic stains, paints, and sealants, be sure to buy low-VOC or no-VOC coatings. If you're looking for particular products and how they perform, the EPA did a bunch of case studies with different companies.
Even when you're working with low-VOC finishes, you should still wear a respirator. Same thing when sanding. Here're some good tips for general wood dust safety from The Wood Database. Particulates in general are bad for you to breathe, and some woods are actually toxic, or can cause allergies. Check this great list also from The Wood Database (red text shows the few inherently toxic woods).
I'm smiling in this picture, really!
To join parts well, think about where the stresses will be and how the joint handles them. Tongue-and-groove or other fastener-free joints can be stronger than nails, or weaker, depending on the cuts you make and the stresses on the joints. Glues can reinforce both nailed and fastener-free joints, and common wood glues are usually non-toxic.
Screws are better than nails if you think there's any chance at all of you ever maybe taking your project apart, to reuse the wood, or maybe just to transport it. However, because they're thicker than nails, they can be a little more prone to splitting wood when close to edges or going end-on into thin boards. To avoid this, you can clamp the workpiece, pre-drill a hole smaller than the threaded diameter, drive the screw in, and then release the clamp afterwards.