Insulating The Roof Deck

Whether or not there is an inner roof lining and the total thickness of the roof structure.

Insulating the roof deck.

There are different roof decks that require different insulation techniques. Cold roofs have insulation between the rafters allowing for ventilation space below your roof deck. Air sealing hot roofs is critical. 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.

Insulating the roof is a priority if the ceilings of your home happen to be part of the roof deck as is the case with cathedral ceilings. Rigid foam insulation boards. Box out light fixtures. Hot roofs are insulated above the rafters.

Typically this would be achieved by adding polyiso insulation above the plywood deck. Add insulation above the roof deck this approach fits current building science thinking in terms of putting the thermal control layer on the outside of the building structure. 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 lights from the floor below it s a fire hazard. Materials commonly used for the insulation of the roof deck include.

The right thickness would need to be calculated to move the dew point above the plywood deck where air infiltration is minimized. The moisture is held in place by the insulation which allows for damage to the framing and other building components. The technically correct approach depends on a number of factors. The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system.

But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. T he problem with the insulation against the sheathing expands. If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. The problem arises with moisture.

Generally more insulation is needed for condensation control in colder climates. You may also insulate your roof to help regulate the temperature in an attic that is a part of your living space. The ratio of insulation above the roof deck or air permeable insulation below the roof deck is a matter of climate and interior conditions. Install baffles or make sure there s 1 minimum of airspace between the roof deck and insulation.