Many buildings with a deck over living space have bad details and rot.
Insulated roof deck over conditioned space.
On top of this roofing you will be building a deck.
It is important that the roof cavity be totally air sealed from the conditioned space below to prevent moisture intrusion and roof degradation.
It happens especially when you do not have space on the top of the deck for the insulation layer.
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.
Venting the roof deck.
Let s look at figure 4.
Unfortunately this rarely leaves enough room for the batt insulation required to develop the appropriate r value.
Those darn architects again not giving the rest of us space to make things work for them.
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.
If you want to turn the attic into conditioned space or you ve got a room with a cathedral vaulted ceiling insulating and ventilating become more complex.
Epdm roofing our roofer jim mckenna prepared the roof surface by installing an underlayment over the t g deck ply.
The hot roof design allows more insulation to be installed in the roof cavity as the need for a vent space is eliminated.
The roof deck surface should sloped away from the house a minimum 1 8 inch per foot so the water will.
Unvented hot roof design cathedral ceilings are also an option.
The roof deck should be properly flashed with a highly durable material that is.
What if you can t insulate on the top of the deck and have to insulate underneath the deck.
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.
Ok now back to the condensation thing.
Roof decks over conditioned area.
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.
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.
Porch deck over conditioned space insulation question.
In a roof attic assembly the builder has two choices.
Usually you ll need sleepers and an air space between the roofing and the new deck to allow for drainage.
