Definition of Assembly

Per LEED Ref Guide, MRc4 under 6. Calculations, there's a section titled "Calculating Assembly Recycled Content":
"An assembly can be either a product formulated from multiple materials (e.g., a composite wood panel) or a product made up of subcomponents (e.g., a window system)."
It's pretty much anything that is made of multiple types/pieces of raw materials (ex. concrete, engineered wood floor, SIP, cabinet).

In the LEED Ref. Guide (same section as above), it says it has to be done by % weight. Of course right below that it talks abt. cementitious material in concrete being allowed to be broken out if you can provide the cost of the cementitious materials separate from the cost of the aggregate.

You could always try submitting the cost of the glass separately from the cost of the frame and have two line items in your materials matrix. However, in concrete, there's likely not very much cost associated with mixing the materials whereas with a façade glazing system there may be quite a bit more cost associated with assembling the glass and the frame, which would then be harder to take in to account and/or would reduce your material cost, thereby making the impact of the recycled content be less. But you could try it... Worst case, if the LEED Reviewer doesn't like it, they'll flag it and question it following your preliminary submission.

Martin—In the Reference Guide, the “Calculations” sections of MRc4, MRc5, and MRc6 each state, “Materials costs include all expenses to deliver the material to the project site. Materials costs should account for all taxes and transportation costs incurred by the contractor but exclude any cost for labor and equipment once the material has been delivered to the site.” Therefore, the starting point should be the assembly that arrives as a unit to the site and that you are able to itemize as a separate cost. For example:

Case 1: Your façade system might consist of glass panels delivered from one fabricator and aluminum framing pieces shipped from a different maker, along with gaskets, connectors, and other accessories from other manufacturers. If your contractor pays for each of these items separately, the most appropriate approach is to treat each component as a separate item or assembly.

Case 2: By comparison, I have worked with “unitized” curtain wall systems, wherein the glass and the framing components are preassembled and delivered to the site as pre-glazed panels to be lifted into place by cranes. The materials cost of such systems is usually considerably higher than the piece-by-piece system described in Case 1 because the cost includes the fabricator’s pre-assembly costs, which occurred off-site, prior to delivery. In this case, the most appropriate approach is to treat the entire façade as one assembly, and calculate the components by weight.

Case 3: Perhaps this is most common. Just as in Case 1, the components arrive to the site separately. However, the contractor pays one price to the glass fabricator for the glass, and one price to the framing supplier to cover, not just the framing, but also the gaskets and miscellaneous components. The framing supplier refuses to provide an itemize breakdown of all the parts and pieces. In this case, even though each framing component might be delivered separately, it would be appropriate to treat them as a single assembly. Since the glass is a separate line item, it would be a separate assembly.

In the end, much depends on how you pay for the product, how the product is delivered, and how much information you can put your hands on.