Insulated Roof Deck Over Conditioned Space

Unvented hot roof design cathedral ceilings are also an option.

Insulated roof deck over conditioned space. What if you can t insulate on the top of the deck and have to insulate underneath the deck. The subject might seem overly particular but properly designing a deck over living space demonstrates architectural sophistication and consideration to the design process. Those darn architects again not giving the rest of us space to make things work for them. Drain and not pond the finished walking surface of the roof deck surface should be below the level of the interior floor by at least 1 1 2 inches.

Ok now back to the condensation thing. Many buildings with a deck over living space have bad details and rot. Venting the roof deck. The thermal boundary can be at the ceiling plane leaving the attic space above uninsulated and vented or the thermal boundary can be located at the roof line creating a sealed insulated conditioned or semi conditioned attic space.

Unfortunately this rarely leaves enough room for the batt insulation required to develop the appropriate r value. The roof deck should be properly flashed with a highly durable material that is. The roof deck surface should sloped away from the house a minimum 1 8 inch per foot so the water will. Usually you ll need sleepers and an air space between the roofing and the new deck to allow for drainage.

The hot roof design allows more insulation to be installed in the roof cavity as the need for a vent space is eliminated. Epdm is typically installed over rigid insulation board or a proprietary soft fiberboard. However concerned that the weight of the deck on top of the membrane would compress a soft underlayment and cause damage or. It is important that the roof cavity be totally air sealed from the conditioned space below to prevent moisture intrusion and roof degradation.

Let s look at figure 4. Porch deck over conditioned space insulation question. In a roof attic assembly the builder has two choices. The venting path is essentially the same air flows up from the eaves and out at the ridge but creating a vent channel under the roof deck can be challenging.

It happens especially when you do not have space on the top of the deck for the insulation layer. Roof decks over conditioned area. According to section r806 4 of the 2006 irc unvented assemblies are allowed if no interior vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly and if air impermeable insulation is applied in direct contact with the underside interior of the structural roof deck space below the foam. Open or closed cell spray foam is applied to the underside of the roof sheathing and additional fiberglass or cellulose insulation is blown in as a cost saving method for meeting high insulation requirements and filling in the cavity space between the rafters to the ceiling deck.