What If? Lab

What if everything were made of wood?

Wood comes from trees. We make houses, tables and toys from it. What if everything were made of wood? Let's imagine it with Olly!

Wood is strong, it grows on trees, and builders already frame most American homes with it. Today engineers even build towers from thick layered timber. Imagine a world where everything is wood, and find out what would work well, what would need care, and why.

Wood is a natural composite of cellulose, hemicelluloses and lignin, built by trees from carbon, hydrogen and oxygen. This thought experiment follows three threads, fire, height and trees as producers, using the USDA's Wood Handbook and the Forest Service's report on a 25-story mass timber tower.

Explore

The big question

Look around you. Can you find something made of wood? A chair? A pencil? A door?

Now imagine everything is made of wood. Houses, bridges, even very tall buildings!

Wood is all around us: floors, tables, doors, pencils and the frames hidden inside walls. Builders use it for some of the biggest jobs too, from house frames to tall towers.

This lab is a thought experiment. What if everything were made of wood? We can't really swap every material, but we can follow the clues. What would wood do well, and where would it need help?

The Wood Handbook notes that engineered wood panels such as cross-laminated timber now offer an alternative for some building jobs that use concrete, masonry or steel. The USDA Forest Products Laboratory's Wood Handbook describes it as a renewable material and documents its strengths and weaknesses in detail.

This thought experiment imagines wood replacing other materials and follows the consequences through three threads: fire behavior, tall buildings, and trees as the producers of the material.

Explore the idea

Make a prediction

A very thick wooden post is in a fire. What happens to it?

A big, thick wooden beam is caught in a fire. Which is true?

Which best describes how a large timber member behaves in a fire?

It burns away in a few minutes
Its outside chars, and the char helps protect the inside
Wood can't burn at all

Established fact
Wood is strong, it comes from trees, and it can burn.

Wood is a strong building material that grows on trees; it burns, but thick pieces char slowly on the outside.

Wood is a renewable structural material; large sections resist fire through slow charring (USDA Wood Handbook).
An idea scientists discuss
A world made only of wood is pretend. We imagine it carefully.

Everything will not really turn into wood. What would change is an idea built from what we know about wood.

All consequences of an all-wood world here are reasoned from documented properties, not observed.
Established fact
Most homes in the United States have wooden frames.

About nine out of ten homes in the United States are framed with wood.

About 90% of U.S. residential housing is framed with wood (USDA Wood Handbook, 2021).
Established fact
Wood is made from just three kinds of atoms.

Wood's three main ingredients, cellulose, hemicelluloses and lignin, are all made only of carbon, hydrogen and oxygen.

Cellulose (40–50% of dry wood), hemicelluloses (20–30%) and lignin are polymers built only from C, H and O (Wood Handbook, chapter 3).
Established fact
When thick wood burns, a black crust called char forms on the outside.

A burning wooden beam forms a layer of char that insulates the wood beneath and slows the burning.

Char forms an insulating layer that retards further degradation; the average char rate over the first hour of a standard test is about 0.6 mm per minute (Wood Handbook, chapter 18).
Established fact
Big glued-wood posts passed a three-hour fire test.

In tests at the Forest Products Laboratory, big glued-wood columns stayed strong because their charred outside protected the layers inside. They earned a three-hour fire rating.

FPL burn tests showed oversized, unprotected glulam columns kept structural integrity because outer charring protected inner layers, qualifying for a three-hour fire-resistance rating (USDA Forest Service, 2022).
An idea scientists discuss
In a wooden world, people might make things extra thick.

In an all-wood world, builders might make beams and walls extra thick so they could char without losing their strength.

An all-wood built environment might lean on oversized members, as heavy timber design does; how far that could replace other fire protection is speculation.
Established fact
Some wood panels are made of layers glued crisscross.

Cross-laminated timber panels have three or more layers of boards, with the grain of each layer turned across the next.

CLT panels comprise three or more layers of lumber, often an odd number, with grain alternating by 90° between layers (Wood Handbook, chapter 12).
Established fact
A wooden tower in Milwaukee is 25 floors tall.

In 2022 the Forest Service reported that Ascent in Milwaukee, 25 stories and 284 feet tall, was officially the tallest mass timber building in the world.

Ascent MKE (25 stories, 284 ft, about 86.6 m) was reported in July 2022 as officially the tallest mass timber building in the world, ahead of Norway's 18-story Mjösa tower (USDA Forest Service).
An idea scientists discuss
Maybe one day towers could be made of wood all the way down.

Ascent, the record holder in 2022, still uses concrete at its base and core. A tower of wood all the way down might be possible, but no one knows how tall it could go.

Ascent rests on concrete; a fully timber tower of that height is untested here, so its limits are open questions, not facts.
Established fact
Growing trees take in carbon. Wood keeps it.

Growing forests capture carbon, and wooden products store that carbon while they are being used.

Forests capture carbon and harvested wood products store it in use and at end of life in landfills (Wood Handbook, chapter 1).
Established fact
Dry wood does not rot.

Wood that is kept air dry will not decay, but wood that stays wet can be attacked by fungi.

Air-dried wood, usually no more than 20% moisture, gives a reasonable margin of safety against fungal decay; existing decay will not progress while it stays dry (Wood Handbook, chapter 14).
An idea scientists discuss
A wooden world would need many, many trees.

If everything were wood, people might need far more forests, and might have to keep a great many things dry.

Supplying every structure and object with wood would require forest growth on a scale no source here estimates; treat it as an open question.

In our world

Many homes have wooden frames inside their walls. You can't see them, but they hold the house up.

One house can have lots and lots of wood inside it!

Wood already does a big job. In the United States, about nine out of ten homes are framed with wood, according to the USDA's Wood Handbook. An average single-family house in 2012 held roughly 22,000 kilograms of structural wood: about 22 tonnes.

Wood is made mostly of three natural substances: cellulose, hemicelluloses and lignin. All three are built only from carbon, hydrogen and oxygen atoms.

The Wood Handbook reports that about 90% of U.S. residential housing is framed with wood, and that an average 233 m² single-family house in 2012 contained roughly 22,000 oven-dry kilograms of structural wood.

Chemically, cellulose makes up 40% to 50% of wood's dry substance, hemicelluloses 20% to 30%, and lignin 26% to 32% in softwoods (20% to 28% in hardwoods). Long cellulose chains bind into microfibrils that give the wood cell high tensile strength along its main axis, while lignin encrusts and binds the cell wall.

Imagine a wooden world

In our pretend world, Olly builds everything from wood. Wooden houses. Wooden bridges. Wooden towers!

Some things would work well. Some things would need extra care.

In our pretend world, every building, bridge and object is wood. Some things might work well, since wood already holds up most homes in the United States. Others might need special care. Wood can burn, and it rots if it stays wet.

These are ideas, not predictions. Choose a path in the lab to explore three questions: what happens in a fire, how tall wood can build, and where all that wood would come from.

Removing every other material is not realistic, so the useful question is which jobs wood could take over and what each would require. Three constraints stand out: fire resistance, structural height, and supply.

Everything in this lab marked as an idea is reasoned speculation from documented properties, not a forecast. Even the record-setting wooden tower described below rests on a concrete base and core, a reminder that real buildings mix materials.

Why wood behaves this way

Wood can burn. But a very thick wooden beam burns slowly. Its outside turns into a black crust called char.

The char is like a coat. It helps keep the inside strong.

Wood is made of tiny cells whose walls are built from strong cellulose fibers, held together by lignin. That makes it strong along the grain. But wood also burns. When a thick beam is in a fire, its outer layer turns into char, a black crust. The char slows the heat, so the beam burns inward only slowly.

Water is wood's other challenge. The Wood Handbook explains that wood kept air dry will not decay. Wood that stays damp can be attacked by fungi.

In standard fire tests, the Wood Handbook reports, wood ignites after about 2 minutes, then chars inward at roughly 0.8 mm per minute for 8 minutes; after that the insulating char slows it to about 0.6 mm per minute. Designers commonly assume about 38 mm of char in the first hour, and large members keep much of their load-carrying capacity for a long time.

Moisture governs decay: fully air-dried wood usually holds no more than 20% moisture, which gives a reasonable margin of safety against fungi, and decay already present will not progress while wood stays air dry.

Wooden towers for real

Engineers now build tall towers from thick layers of wood glued together.

One wooden tower in the city of Milwaukee is 25 floors tall!

Engineers now build with mass timber: big panels and beams made from layers of wood. Cross-laminated timber, or CLT, stacks three or more layers of boards with the grain of each layer turned across the one below.

In 2022 the USDA Forest Service reported that Ascent, in Milwaukee, Wisconsin, was officially the tallest mass timber building in the world: 25 stories and 284 feet (about 86.6 meters). Its glued-wood columns passed a three-hour fire test.

CLT panels have three or more layers of lumber, often an odd number, with the grain alternating by 90° between layers (Wood Handbook). The 2021 International Building Code added three construction types that allow mass timber buildings to rise higher than earlier heavy timber rules permitted.

In July 2022 the USDA Forest Service reported Ascent MKE (25 stories, 284 ft) as officially the tallest mass timber building in the world. Forest Products Laboratory burn tests showed its oversized, unprotected glulam columns kept their structural integrity because outer charring protected the inner layers, earning a three-hour fire-resistance rating. Ascent is a hybrid: its timber rises around a concrete elevator and stair core above a concrete parking structure.

Amazing facts

One house can hold tons of wood.

An average American single-family house in 2012 held about 22,000 kilograms of structural wood.

An average 233 m² U.S. single-family house in 2012 contained roughly 22,000 oven-dry kg of structural wood, storing about 11,000 kg of carbon at 50% carbon content (Wood Handbook).
Thick wood burns slowly from the outside in.

Designers usually assume thick wood chars only about 38 millimeters deep in the first hour of a standard fire test.

A char depth of 38 mm (1.5 in) at 1 hour is generally used for solid-sawn and glued-laminated softwood members (Wood Handbook).
Some wood panels are glued crisscross.

Cross-laminated timber panels have their layers crossing at right angles, like a woven mat.

CLT layers alternate grain by 90°, and the outer layers run in the direction of gravity loads or major spans (Wood Handbook).
Wood is mostly made of cellulose.

Cellulose, the main ingredient of wood, makes up 40 to 50 percent of dry wood.

Cellulose, 40–50% of dry wood, is often described as the most abundant organic substance in nature (Wood Handbook).

Words to know

timber: wood prepared for building
mass timber: large, strong building parts made from layers or pieces of wood joined together
cross-laminated timber: a big wooden panel made of layers of boards glued with their grain crossing
char: the black, burned crust that forms on the outside of wood in a fire
cellulose: the main natural substance in wood, made of long chains of sugar molecules
decay: slow rotting caused by fungi, which happens when wood stays wet

Discovery challenge

What forms on the outside of thick wood in a fire?

What forms on the outside of a thick wooden beam in a fire and helps protect it?

What layer slows a large timber member's burning in a fire?
- Ice
- Char
- Paint
Show the answer

Char

A black crust called char. It is like a coat.

Char: it insulates the wood beneath and slows the burning.

Char, which insulates; the rate falls from about 0.8 to about 0.6 mm per minute.
About how many homes in the United States have wooden frames?

About how many homes in the United States are framed with wood?

What share of U.S. residential housing does the Wood Handbook say is wood-framed?
- About 1 in 10
- About half
- About 9 in 10
Show the answer

About 9 in 10

About 9 out of 10! Most homes.

About nine out of ten, roughly 90 percent.

About 90%.
How many floors tall is the wooden tower in Milwaukee?

How many stories tall is Ascent, the mass timber tower in Milwaukee?

How many stories did the Forest Service report for Ascent MKE in 2022?
- 5
- 25
- 100
Show the answer

25

25 floors!

25 stories, 284 feet tall.

25 stories and 284 ft; it is a timber–concrete hybrid.
What keeps wood from rotting?

What helps stop wood from decaying?

According to the Wood Handbook, which condition prevents fungal decay?
- Keeping it dry
- Keeping it wet
- Painting it red
Show the answer

Keeping it dry

Keeping it dry. Wet wood can rot.

Wood kept air dry will not decay.

Air-dry wood, usually at or below 20% moisture, gives a margin of safety against fungi.

Experiments to try

Explore next

For parents & teachers

What children will learn

Wood is a natural material made by trees, mostly from cellulose, hemicelluloses and lignin.
Wood burns, but thick timber chars on the outside, which slows the fire's progress inward.
Engineered wood such as cross-laminated timber is used to build tall buildings, often together with concrete.
Wood lasts when it is kept dry; damp wood can be decayed by fungi.

Recommended ages: 7 to 17 · About 15 minutes

Talk about it

Which things around you could easily be made of wood, and which would be hard? Why?
Why do you think Ascent, a record-setting wooden tower, still uses concrete at its base?
What would a town need to do to have enough wood for everything?

Try at home or in class

Go on a wood hunt at home: list ten wooden things and sort them into solid wood, plywood or other layered wood, and painted or hidden wood.
Look closely at the end of a pencil or a piece of scrap wood with a magnifying glass and draw the grain and growth rings you can see.

Key vocabulary: timber, mass timber, cross-laminated timber, char, cellulose, decay

Where these facts come from

Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021), chapters 1, 3, 12, 14 and 18 , USDA Forest Service, Forest Products Laboratory
World's tallest timber building opens , USDA Forest Service

Checked, not yet human-reviewed. Last updated October 26, 2026. Spotted a mistake? Tell us.