Underside Of Garage Roof Decking

Warm wet air rises and meets the cold roof and cools.

Underside of garage roof decking.

Picture a cloud of moisture floating overhead between the rafters. My question is about the unfinished interior of the garage. This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. Lower than the purlin along the house 12 x 1 4 3.

As it cools it can t hold as much moisture. To stabilize the rafters support the roofing material and hold the entire roof together roof sheathing is installed. The portion of interior ceiling i am concerned with faces west so i thin it would make a difference to the garage temps if i. The unfinished garage ceiling has 2x4 joists on 24 centers.

That excess moisture ends up as drops of condensation on the roof. If the span under your deck is 12 ft for example the purlin at the outer end of the deck should be 3 in. I am wondering if it is okay to hang insulation up against the inside of the roof in the garage. The skeleton of a roof is formed with rafters or trusses generally spaced 16 inches or 24 inches apart from the center of one rafter to the center of the next.

To provide drainage the panels should slope toward the outside edge of the deck about 1 4 in. The snugness of the foam itself should be sufficient to hold the strips. Under deck ceiling systems provide an all in one drainage and ceiling finish that is particularly suitable for areas beneath a deck that are high enough off the ground to provide a sheltered outdoor living space below. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

Plan to space the 2x4 purlins parallel to the house and 3 ft. Essentially condensation occurs at night when the temperature inside a building is warmer than outside.