How to insulate a finished attic Add exterior insulation when replacing the roof, drill holes between beams and studs for complete insulation, remove panels or drywall from walls and ceiling, apply insulation between uprights and wall beams, and cover new panels or drywall. The main difficulty of this technique is to seal the barrier to the top plate of the wall, especially on the eaves, where there is little room for maneuver. This area must be well sealed. Aerosol foam or rigid plate insulation can help close the gap in this area. Cut a rigid board so that it fits between the ceiling beams and extends from the top plate of the outer wall to the attic.
A second piece of rigid insulation, installed vertically, attaches the polyethylene to the horizontal rigid plate. Carefully caulk joints or seams between materials. Expandable two-part spray foam kits (or the service of an aerosol foam company) are also ideal for sealing areas around beams and tables. The foam blocks airflow, doesn't need a vapor barrier, and has a higher R value per inch than loose padding or blocks, so you'll get more protection with less depth.
With aerosol foam, unlike loose fillers or loose sheets, you must cover the ceiling vents (they are not necessary to keep the roof cool). Then cover the foam with drywall as needed to prevent fires. In addition, a warm cover is more likely to create ice accumulations on the roof or allow condensation and mold to form. When re-roofing, remove the roof finish and coating, seal with air and fill cavities with insulation, and then install new roof materials, including an ice-protection membrane.
Thermal insulation is installed at the bottom of the roof cover, at the top of the attic, just below the roof cover. Nearly every building code and every asphalt roof manufacturer requires adequate ventilation of a roofing system, regardless of the type of insulation used. When the roof extends beyond the outer walls, it is possible to use ventilation grilles on the ceiling in combination with ventilation grilles on the roof or ventilation grilles constructed in the form of ridges. Attics or roofs without work space will be discussed later in this chapter, in part 5.4, Narrow Attics, Cathedral Ceilings and Flat Roofs. Another method is to build the existing roof or frame a new roof and fill it with insulators in the form of blocks or loose filling, which are introduced by blowing.
If the temperature of the attic exceeds freezing, the roof covering heats up, which melts the snow cover that is in direct contact with the roof. The insulation is especially likely to be damaged by water if the wood in the roof covering has rotted, as this means that moisture has been present on the roof for some time and it is likely that there will be penetrated into the insulation.
