Timber Properties and Ecological Footprint
How a timber behaves, and what it costs the planet to get it. Two questions that usually pull in opposite directions, which is exactly why the marks are in the trade-off.
Learn it by doing, the way you will be assessed
Free and interactive, so you can rehearse the thinking away from the workshop or studio.
Start revising freeWhat you'll cover
Two questions about every board
You already know how to tell a hardwood from a softwood and where each one grows. A designer then asks two more questions, and this module is about both. How does this timber behave? Will it dent, split, rot, bend or hold a screw? And what did it cost to get here? Not in pounds, but in forest, fuel and waste. The awkward part, and the reason the marks are here, is that the best answer to the first question is often the worst answer to the second.
What you can see and feel
Physical characteristics are the ones visible in the board in front of you:
The trouble with knots
A student is choosing a length of pine for a shelf that will carry heavy books. Why would they avoid a board with a large knot in the middle?
- The knot interrupts the grain, creating a weak point where the shelf could fail under load
- Knots always look bad and would spoil the appearance
- Knots make the timber rot faster indoors
- Knots make the board significantly heavier to lift
How it behaves under force
Working properties describe what happens when you push, pull, hit or leave a timber alone for ten years. Grouping them this way makes them easier to recall under pressure.
Match each property to what it actually means
- Hardness
- Toughness
- Durability
- Elasticity
- It resists scratches, dents and everyday wear
- It takes a sudden blow without cracking
- It survives damp, decay and insect attack over years
- It springs back to shape after being bent
A bench left outside all year
Select the TWO properties that matter most when choosing timber for a public park bench.
- Durability
- Compressive strength
- Elasticity
- Low density
What it cost to get here
A timber product's ecological footprint is the whole story, not just the felling. Every stage adds to it: • Deforestation and habitat loss where the tree grew • Processing: sawing and kiln drying both use large amounts of energy • Transportation: fuel burned moving a heavy material, sometimes across the world • Wastage: offcuts, sawdust and rejected boards • Pollution from treatments, finishes and adhesives There is a social footprint too: logging changes the livelihoods of the communities around the forest, and some products are far easier to recycle or dispose of than others.
Which cuts the footprint most?
A workshop in Britain needs timber for indoor shelving. Which choice does most to reduce the ecological footprint?
- European-grown pine from a certified sustainable forest
- Amazonian mahogany, because it lasts longer so needs replacing less often
- Whichever timber is cheapest, since price reflects environmental cost
- Using thicker boards of any species, so the shelves last longer
Specify the material
You are designing outdoor picnic benches for a school. Work through the specification decisions.
- The benches live outside all year. Which property leads the decision?
- A tropical hardwood would be ideal for durability, but the school has an environmental policy. What is the reasonable compromise?
- Cutting the components leaves a pile of offcuts. What does the lowest-footprint answer do with them?
The whole life story
Put the stages of a timber product's ecological footprint into order, from forest to end of life.
- Felling: trees are cut, and habitat is disturbed or lost
- Processing: sawing and kiln drying, both energy hungry
- Transportation: fuel burned moving a heavy material to the workshop
- Manufacture: cutting and finishing, creating wastage and pollution
- Use: the years of service, which is what the whole footprint buys
- Disposal: recycled, reused, burned for energy or sent to landfill
Along the grain, not across
Timber is much stronger along the _____ than across it, and a _____ is a weak point where a branch once grew. The property that decides whether an outdoor product survives is _____. A footprint covers felling, processing, _____, wastage and disposal, not just the felling. The property that describes springing back into shape is _____.
Justify the choice
A furniture company wants to make a range of children's toy boxes that will be used indoors and handled roughly. Recommend a timber or manufactured board, and justify it on both properties and footprint.
- Name the material you recommend
- Give two working properties that suit it to this product, and say what each means for the user
- Explain one way your choice keeps the ecological footprint down
- State honestly what your choice gives up compared with an alternative
- Finish with a recommendation that holds despite that drawback