Why Insulation Should Not Contact Roof Deck

During cooler night times and in winter periods the deck temperature can then be below the dew point of the interior air.

Why insulation should not contact roof deck.

The moisture is held in place by the insulation which allows for damage to the framing and other building components. Box out light fixtures. Edges of steel decks typically are overlapped to provide structural continuity but this generally adds incremental amounts to the flutes overall spacing. The roof deck is cold wood decks without insulation above them will readily equilibrate to the exterior temperature.

This is because the top floor ceiling is no longer the air barrier for the house the spray foam at the roof deck underside in the attic is the air barrier. Can you place fiberglass insulation against metal roofing. Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be. Here is a fact.

The ratio of insulation above the roof deck or air permeable insulation below the roof deck is a matter of climate and interior conditions. Moisture goes right through fiberglass and will condense on the cold underside of your roof. So in choosing insulation for a cathedral ceiling you really want a material that stops air and moisture from reaching that sensitive roof deck. Even if you use vent chutes to provide an air space above the insulation you can still have problems.

Either insulate the air handler and ducts or insulate the roof underside and remove the floor insulation. Unless you re using mineral wool insulation or your fixtures are rated safe for contact with any type of insulation don t allow the material to touch or cover recessed cans or. Furthermore not sealing ceiling penetrations helps the attic become indirectly conditioned. Also the higher the indoor humidity the more insulation is needed to avoid condensation.

With no ventilation your warm air convecting up into the attic will condense most likely in the attic floor. Hence the term cold decks construction materials wood based products absorb moisture. Generally more insulation is needed for condensation control in colder climates. Steel deck panels can be slightly out of alignment or out of square when installed.

If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. The problem with the insulation against the sheathing expands. Insulation boards directly attached to a steel roof deck should not cantilever over the open flutes. If you use air permeable insulation and it is not in direct contact with the air barrier in this case the plywood roof deck you will experience convective loops within your assembly as well as unwanted radiant heat transfer.