Page 230 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers
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204    Cha pte r  F i v e


                Requirements
                Maintain at least 75% (for LEED 2009 this is either 55%, 75% or 95% for one, two or three points
                respectively) (based on surface area) of existing building structure (including structural floor
                and roof decking) and envelope (exterior skin and framing, excluding window assemblies and
                non-structural roofing material). Hazardous materials that are remediated as a part of the
                project scope shall be excluded from the calculation of the percentage maintained. If the project
                includes an addition to an existing building, this credit is not applicable if the square footage
                of the addition is more than 2 times the square footage of the existing building.
                Potential Technologies and Strategies
                Consider reuse of existing, previously occupied buildings, including structure, envelope
                and elements. Remove elements that pose contamination risk to building occupants and
                upgrade components that would improve energy and water efficiency such as windows,
                mechanical systems and plumbing fixtures.
                  (As noted in Table 5.0.0, LEED 2.2 has a now modified MRc1.2 credit for maintaining 95
                percent of the existing building structure and envelope.)

             Calculations and Considerations (LEED 2009 MRc1.1)
             MRc1.1 is not listed with the EB icon, presumably because it is not really applicable for
             existing building reviews. This credit is not applicable if there are substantial additions to
             the building, totaling more than double the existing gross floor area of the project. If GFA
                                                                                    PEX
             is defined as being the gross floor area of the existing building portion of the project which
             is to remain and be added on to, and GFA  is the proposed total gross floor area of the
                                                 P
             project, both existing and new, then MRc1.1 cannot be obtained if

                                          GFA > 3 × GFA                          (5.1.1)
                                              P        PEX
             It is important to note that the calculations are based on the area of the structural walls
             or deckings (floor or roof) and the cladding less the window and door areas. This is
             simplified from the LEED-NC 2.1 calculations which had some volume and some area
             calculations based on the volume of many structural units and the area of the cladding
             items. A simplified summary of how to itemize each of the components is as follows:
                  •  Deckings: Itemize separately the square footage of structural roof decking,
                    interior floor decking, and the foundation with decking or slab on grade.
                    Exclude any areas that are considered to be structurally unsound or hazardous
                    materials. Exclude nonstructural roof surfaces such as asphalt shingle. The total
                    summation of these can be referred to as STRDECK . The summation of the
                                                                 T
                    decking areas that are to be retained can be referred to as STRDECK .
                                                                             RE
                  •  Exterior walls: Itemize separately each exterior wall area excluding windows
                    and doors. Exclude any areas that are considered to be structurally unsound or
                    hazardous materials. The total summation of these can be referred to as
                    STREXWALL . The summation of the exterior wall areas that are to be retained
                               T
                    can be referred to as STREXWALL .
                                                 RE
                  •  Interior structural walls: Itemize separately each interior  structural wall area
                    excluding openings, and count only one side of the wall elements for LEED 2009
                    (both sides were previously counted in LEED 2.2). (It is assumed that the interior
                    sides of exterior walls are already included in the exterior wall variables.)
                    Exclude any areas that are considered to be structurally unsound or hazardous
                    materials. Also, do not include any nonstructural interior wall sections. The total
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