system. Voids around tees should be grouted with material
recommended by the deck manufacturer.
b) Because of the vulnerability to moisture, insects,
and in some cases fire, these panels may be prohibited by some
Military Construction Offices. Request specific permission to
use before specifying.
c) Approved mechanical fasteners should be used for
anchorage of the roof membrane to the deck. The anchorage
recommendations of the manufacturer and insurance rating agencies
should be followed. Above-deck insulation board should be solid-
mopped to a mechanically anchored coated base sheet. Insulation
may also be mechanically anchored if provided in two layers
(e.g., bottom anchored, top set in hot bitumen).
Poured Gypsum Concrete Roof Decks
a) When insulation requirements and thicknesses
permit, insulation is generally incorporated in the formboards.
Because of the difficulties in applying a vapor retarder to this
material, poured gypsum should be avoided where upward vapor flow
is predominant. However, a vapor retarder should be considered
when specifications require the installation of additional
insulation on the top side of the deck.
b) The ceiling plenum should be adequately ventilated
to the exterior or supplied with dehumidified air to prevent
Lightweight Insulating Concrete Fills
a) To promote drying of the wet mix, lightweight
insulating concrete should be limited to decks with underside
venting: slotted, galvanized steel decks (minimum 1.5 percent
open area) or permeable formboards (e.g., fiberglass).
b) Where high thermal resistance is required,
additional, specially designed, closed cell insulation should be
incorporated into the concrete. The practice of installing
additional preformed insulation boards directly upon the deck is
not recommended because it inhibits the drying of the concrete
fill by solar radiation.