Page 244 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED Materials and Resour ces 217

Given these, in LEED 2009, one point is earned for MRc4 if the following is true:

100[MATL$ + (0.5 × MATL$ )]/MATL$ ≥ 10 (5.4.1)
RECPOC RECPRC T
An additional point is earned for MRc4 if the following is true:

100[MATL$ + (0.5 × MATL$ )]/MATL$ ≥ 20 (5.4.2)
RECPOC RECPRC T
Most construction items are not 100 percent made from recycled materials. Therefore,
the recycled value is only a portion of the value of the item, whether these items are one
piece (such as a steel beam) or an assembly (such as a prebuilt window unit). The value
determination is usually made on a mass percent basis. So for any item the following can
be defined:
MASS Mass (weight) of the postconsumer recycled portion of unit i
RECPOCi
MASS Mass (weight) of the preconsumer recycled portion of unit i
RECPRCi
MASS Total mass (weight) of unit i
UNITi
MATL$ Total cost of unit i
UNITi
MATL$ Value of postconsumer recycled portions of unit i
RECPOCi
MATL$ Value of preconsumer recycled portions of unit i
RECPRCi
The value of the preconsumer and postconsumer recycled portions for each individual
unit i can be determined from the following equations:

MATL$ = MATL$ (MASS )/MASS (5.4.3)
RECPOCi UNITi RECPOCi UNITi
MATL$ = MATL$ (MASS )/MASS (5.4.4)
RECPRCi UNITi RECPRCi UNITi
And, in similar manner, the total values of the recycled portions needed in Eqs. (5.4.1)
and (5.4.2) can be determined from the summation of the individual unit contributions
as follows:

MATL$ =∑ MATL$ over all units i (5.4.5)
RECPOC RECPOCi
MATL$ =∑ MATL$ over all units i (5.4.6)
RECPRC RECPRCi

Special Circumstances and Exemplary Performance (LEED 2009 MRc4)
There are some cases in which the value of the recycled content in some materials is
disproportionately high compared to the costs of the other material contents. In these
cases, it may be appropriate to use an alternative to the listed weight-based
calculation, but these should be justified. An already accepted alternative is in the
case of Portland cement–based concrete. Many concretes are made with a combination
of Portland cement and fly ash or other supplementary cementitious materials
(SCMs), usually up to 25 percent. Costs for cement and other cementitious materials
are generally a large percent of the cost of concrete, and therefore it is appropriate to