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Carbon Footprint Addendum

This is an explanation of how we determined our claim that:   If you choose synthetic fabric for your sofa, then the carbon footprint of the fabric exceeds the carbon footprint of both the foam and the frame combined – even if you use soy based foam.

Wood:

An 84” foot sofa uses about 32 board feet of lumber.  For kiln-dried maple, the embodied energy for 32 board feet is 167 MJ.

In order to arrive at these figures, we had to find an LCA of wood products, and used two:

These LCA’s published energy values based on weight of wood, or 2.5 MJ per KG of kiln dried hardwood, so we had to translate board feet into KG. We used http://www.csgnetwork.com/lumberweight.html to determine board foot weight, and found that   32 board feet of lumber has different weights for the type of wood; for hard maple, 32 board feet weighs 147 lbs.

The production of 32 board feet of kiln-dried hard maple with a weight of 147 lbs (or 66.8 KG) totals 167 MJ, based on the data above.

Foam:

 We made the assumption that the cushioning material is foam, by far the most popular cushioning material. (Other cushioning products include natural latex, wool batting, horsehair, down and feathers; but they are rarely used). Our typical 84” sofa requires 12 cubic feet of foam, with a density of 4 lbs. per cubic foot, and a weight of 4 lbs per cubic foot.   Total weight of the foam in our sofa is therefore 48 lbs. or 21.8 kg which has a total embodied energy of 2071 MJ if conventional polyurethane is used and 1352 MJ if soy based foam is used. 

 

FABRIC:  The fabric needed for our typical 84” sofa:

    • 25 yards of decorative fabric
    • 20 yards of lining fabric
    • 15 yards of burlap
    • 10 yards of muslin

We used data from three different analyses of fabric to develop the embodied energy chart below:

  • "Ecological Footprint and Water Analysis of Cotton, Hemp and Polyester", Stockholm Environment Institute, 2005;
  • "LCA: New Zealand Merino Wool Total Energy Use", Barber and Pellow;
  • Composites Design and Manufacture, School of Engineering, University of Plymouth UK, 2008, tech.plym.ac.uk/sme/mats324A9520NFETE.

Embodied Energy in production of various fibers:

 

energy use in MJ per KG of fiber:

flax

9.6

cotton, organic

13

cotton, conventional

55

wool

63

recycled polyester

88

Viscose (regenerated cellulosic)

100

polyester

125

acrylic

175

nylon

250 

Based on the embodied energy for the production of various fiber types (above), and assuming the weights of the various fabrics as below, the total embodied energy for each of these fabrics (by fiber type) is: 

 

 

 

 

Total embodied energy in MJ per KG

 

oz/lin yd

total wt in lbs

wt in KG

polyester

nylon

cotton, conventional

cotton, organic

25 yds decorative fabric

22

34

15.45

1931

3862

849

201

20 yds lining fabric

15

19

8.64

1080

2160

475

112

15 yds burlap

10

9.4

4.27

534

1068

235

56

10 yds muslin

7

4.4

2.00

250

500

110

26

Based on the above data, we can assume:

Wood: total embodied energy for 32 board feet of kiln dried hardwood (hard maple) is 167 MJ

Foam: total embodied energy for 12 cubic feet of foam at 4lb density, using 20% soy, is 1352 MJ; and for conventional polyurethane foam is 2071 MJ. 

TOTAL for kiln dried maple hardwood + soy based foam: 1519 MJ – this can remain constant and we made that assumption for ease of comparison; alternatively we can look at kiln dried maple hardwood + conventional polyurethane foam totals, which is: 2238.