Timber

Question 1

What are the two main types of trees?

Answer 1

1) Deciduous- Broadleaf/fruit or nut-bearing- Hardwood

2) Coniferous- Needle and cone-bearing- Softwood

Question 2

What primary softwoods are used in construction?

Answer 2

Spruce (whitewood) and pine (redwood).

Question 3

What percentage of cellulose is in wood?

Answer 3

40-45%

Question 4

What percentage of hemicellulose is in wood?

Answer 4

20-35%

Question 5

What percentage of lignin is in wood?

Answer 5

20-30%

Question 6

What are deciduous and coniferous tree separated into?

Answer 6

1) Sapwood

2) Heartwood

Question 7

What does the sapwood do?

Answer 7

Encases the trunk directly under the bark and transports the sap up the trunk.

Question 8

What does the heartwood do?

Answer 8

Provides strength and wood from this stem region is normally more resistant to decay or insect attack.

Question 9

What are the colour difference between heartwood and sapwood?

Answer 9

Heartwood is darker in colour providing aesthetic value.

Question 10

What is timbers specific strength compared to other materials?

Answer 10

Timber has a higher specific strength than concrete which is comparable to that of steel and aluminium alloys.

Question 11

Is timber environmentally friendly per unit strength?

Answer 11

Yes, but concrete is better.

Question 12

Name 6 advantages of timber.

Answer 12

1) High aesthetic value
2) Reasonable stiffness and strength
3) Resistant to fire
4) Resistant to corrosion and chemicals
5) Thermally stable
6) Locally available

Question 13

Name 6 disadvantages of timber.

Answer 13

1) Creep
2) Flammable
3) Suseptical to insect attack
4) Deforestation
5) Poor biodiversity
6) Trees grow slowly hard to keep up with demand

Question 14

What is does it mean when the wood is thermally stable?

Answer 14

Not change in dimension or lose strength or performance in extreme conditions hot or cold.

Question 15

Why is wood used in marine environments?

Answer 15

It is resistant to most chemical attacks such as chlorine corrosion attacks.

Question 16

Why is timber fire resistant?

Answer 16

Wood forms a charred layer which protects the remaining timber and slows the rate of combustion.

Question 17

What effects the durability of timber?

Answer 17

1) Timber is properly sawn avoiding cracks
2) Timber is properly pre-dried, to avoid large drying shrinkage
3) Timber is properly assembled to allow for dimensional changes upon humidity changes.

Question 18

How does timber prevent major shrinkage?

Answer 18

Wood is usually dried down before converted into building material, either by long exposure to drying air which unlikely to reduce moisture content below 18% and might take several years or done quickly in drying kilns which lower moisture content to 6% or less.

Question 19

What are the two stages in the drying process?

Answer 19

1) The rapid loss of liquid water from the cell lumens which are hollow voids at the centre of wood cells.
2) The slower drying out of the surrounding cell walls.

Question 20

What is anisotropic?

Answer 20

Movement due to changes in moisture content.

Question 21

Give an example of engineered timber?

Answer 21

Glulam- alternate orientation of fibres therefore isotropic.

Question 22

The advantage of engineered timber?

Answer 22

More flexibility and freedom.

Question 23

The disadvantage of engineered timber?

Answer 23

Higher CO2 emissions than solid timber.

Question 24

What type of timber has the lowest CO2 emission?

Answer 24

1) Sawn Softwood

2) Sawn Hardwood

Question 25

How can you be sure the wood is sustainably sourced?

Answer 25

Certification from FSC, PEFC or “Forest Forever Campaign”.