Roofing: It’s Elementary, My Dear Watson!

08/06/2009 | By Richard L. Fricklas

Buildings Greener Facilities, Helping Facilities Professionals Make Smarter Decisions

With all the science that has taken place in the roofing industry over the past half-century, one wonders why so many mysteries and crimes remain to be solved.

For the building owner or manager, most roofing decisions revolve around money. Oftentimes, lowest first cost prevails. A lightweight roof system usually means lower costs in terms of footings, framing, and other structural components. Since the 1950s, steel columns and decking have dominated for most of the country while wood joists and plywood/OSB continue to be a factor on the West Coast.

With the deck decision made, next comes thermal insulation. With a massive, monolithic concrete deck, we could skip the insulation altogether. For wood structures, flexible glass fiber batts could be placed between wood joists on the underside of the decking. This is still viable when condensation isn’t a factor. Structural wood fiber decking has insulating and acoustical value, so no additional insulation may be needed. Lightweight insulating concrete provides some R-value, but needs a sub-deck for support. The main advantage of insulating concrete is the ability to slope the fill to the drains. And, of course, steel decking requires a leveling board to bridge the ribs (flutes) of the deck. So, Watson, Question No. 1 is: What kind of deck do we have?

Vapor retarders have been and continue to be a design factor in colder climates, but more attention today is paid to air barriers. Question No. 2: What are our internal humidity conditions relative to our climate, and do we need a retarder?

And, of course, decisions have to be made on the roof membrane.

Membrane Choices of the Good Ol’ Days


  • Asphalt
  • Coal tar pitch


  • Organic felt
  • Asbestos felt
  • Glass fiber felt


  • Mineral surfaced cap sheets
  • Smooth surfaced
    • Glaze coat
    • Emulsion coat, fibrated or not
    • Cut-back, fibrated or not
  • Flood coat and aggregate

Thermal Insulation:

  • Asphalt treated wood fiber
  • Perlite
  • Paper-faced glass fiber board
  • Foamed glass

Some of the changes today would, of course, include the dominance of cellular foam thermal insulations, the use of cover boards, use of polymer-modified bitumens, single-ply roof membranes, reflective coatings, photovoltaics, and vegetated roofs.

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