Is wood a sustainable building material???

A critical view on the use of wood in the structure of buildings.
Prof. Ir. Rob Nijsse

Why do I call the use of wood in big structures : A big mistake.

  • Trees  grow in the forest during a lot of years, taking their nutrients or ‘building materials” from the earth and atmosphere.
  • If we remove a tree trunk from the forest, to make shelfs and beams from it, we take a way a lot of these “building materials”. The forest becomes poorer and the new (hopefully re-planted) trees will be weaker and less healthy. 
  • It is stealing from the forest without “paying” for what you take.

How many can we safely ( = without cracks) make wooden structural elements like floors and walls from a big tree trunk?

By cutting the tree trunk in little shelfs and glue them together in two perpendicular directions. This is called Cross Layered Timber. ( CLT ).
Attention! This requires a lot of sawing and glue!

A close-up of a slice of a tree with visible growth rings and a central crack. The stump is surrounded by green plants and potted flowers on a concrete surface.
A schematic drawing of cross layered timber

Everybody says that building high rise buildings with wood as structural material is

 “the Golden Road to a sustainable future”. 

  • Let’s look a a high rise appartement building of 50 meters height built with wooden walls and floors.
  • We calculate how much trees are required for this building.
Schematic drawing of the floor in a 50 meter high building.

High Rise Building 50 m tall.
Four appartements of about  6 by 8 m on each floor. Total 16 floors.

CLT walls, thickness = 0.4 m.
CLT floors, thickness = 0.3 m.

Length walls = 4 X 12 + 3 X 18  = 102 m.

Volume walls = 102 X 50 X 0.4 = 2040 m3.

Volume floors = 12 X 18 X 0.3 X 16 = 1040 m3.

Total Volume Wood = 3080 m3.

(and we still need a lot of steel for connections!)

Okay, so we need 3080 m3 for our wooden high rise building. If we take 100 year old, 20 meter tall trees; how many trees do we need ?

A hand-drawn diagram of a tree with measurements, showing the tree's height (20m), the trunk's height (10m), the diameter of two logs (1.5m and 1.25m), and a cross-section of a log, with a calculation indicating the wood volume as 6.4 cubic meters.
  • We need 3080 m3 of wood for our high rise building.
  • Each 100 year old tree delivers usable 6.4 m3 wood.
  • So we “use” for our building 3080 / 6.4 is
    481 trees !!!

This is a forest on its own.
And the expected lifetime of this building?
50 years, if not rotted away before this time!

  • Hence: be more reluctant to make big structures out of wood.
  • Of course wood is a beautiful material to look at. So use it only on the outside of building elements! As a removable item.
  • And use complete tree trunk as columns / beams for structure. Their fibres are not cut up and damaged. So they a large bearing capacity!
Photo of the Dutch Pavilion during the EXPO 2000 in Hamburg, Germany

Dutch pavilion

EXPO 2000 Hannover

Architect MVRDV
stacked landscape.

  • cellar for services
  • concrete dunes
  • flower layer
  • flowerpot-layer
  • a forest
  • cinema, water curtain
  • pond with island
  • windmillls

Tree trunks return after 1000 years in our buildings, this time with a German certificate, issued by the German Prufingnieur.

A big crowd waits patiently till they are allowed in the pavilion.

A big crowd waits patiently till they are allowed in the pavilion.

Posbank restaurant (NL)

Architect : SeARCH

Truss with met
Tree trunks as
Compression diagonals

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