The first step towards reuse of materials in buildings, is actually a step away from the current practice of designing for disposal.  This red list is a chance for me to explicitly call out those materials that are most detrimental to the future life of a material.  Sometimes people already know about the problem, other times it's never occurred to them that their current design solution could be voiding the future material use.  So this red list is a work in progress, give me a shout if you have a suggestion.

A deconstructor, a reuser and a C&D recycler get together at a materials summit - and they all agree on one thing. . . Spray Foam Insulation is total garbage.  Actually, it's a total garbage maker.  When new home builders and renovators spray that yellow or purple foam all over the rafters, joists and framing of your home - they are ensuring that everything it touches will go straight to the landfill.   

In short:

1. What is it? There are two types of spray on poyurethane insulation, open cell and closed cell.  They are both applied on site by combining two chemicals, which causes the applied fluid to expand and fill the wall cavity.  The two types of spray foam have different compositions, R-values, expanding agents, and benefits. Source
2. Why do people use it? A few different elements have pushed spray foam insulation towards widespread adoption.  Foremost is it's R-value; closed cell has an R-value of 6.5/in (fiberglass is 3.5/in).  A close second is the ability of closed cell spray foam to act as a vapor barrier - this means that a complete installation of closed cell spray foam installation is airtight.  The other really critical reason why people use spray foam insulation is because it is being really heavily marketed and sold to them.  Air sealant and energy efficiency workers and companies are trained to use this expanding foam, and present it to homeowners as the best all in one solution for simultaneous air sealing and insulating.
3. Why is it so terrible? Whether closed or open cell, all spray foam insulation is basically just a big foamy glue blob.  And it sticks, permanently, to everything that it touches.  This means that every joist, rafter, and stud that it touches is now a compound material of wood/foam.  You can't reverse the foam connection, you can't cut it off without leaving a layer of gluey crap.  So when that house is taken down either by demolition or deconstruction, that material cannot go anywhere but the landfill.  The wood would have great value for reuse if it wasn't covered in foam.  It could be recycled for landscape chips or even burned for waste to energy . . . if it wasn't covered in foam.   Spray on foam is a material death sentence and ensures that it will have no future opportunity for reuse or recycling.
4. What can I do instead? It's actually really simple to achieve the same results by using vapor barriers (plastic sheeting, external housewrap, interior paints), standard weatherstripping and caulking techniques plus reusable insulations like fiberglass or roxul batts/boards, EPS/XPS/Icynene boards or blown in cellulose installation.  

Thanks to Bill, Dave and Joe for the live action anecdote.

Image Credit: By Cdpweb161 (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons