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:

"Life Cycle Analysis of Wood Products: Cradle to Gate LCI of residential wood building material", Wood and Fiber Science, 37 Corrim Special Issue, 2005, pp. 18 - 29.
www.canadianarchitect.com/asf/perspectives_sustainibility/measures_of_sustainablity

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.

We used data from a Dow Chemical study on its “Renuva” foam (http://www.dow.com/PublishedLiterature/dh_0155/0901b80380155d5c.pdf?filepath=renuva/pdfs/noreg/793-00021.pdf&fromPage=GetDoc). From this study, we found that it takes 95 MJ to produce 1 KG of conventional polyurethane foam and 62 MJ to produce 1 KG of soy based foam.

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.