During the winter, attic insulation prevents heat within the house from escaping through the ceiling and into the unheated attic space. During the summer, it reduces outside heat from radiating downward through the attic and into the house. All insulating materials work on the principle of trapping. They have millions of tiny air pockets to restrict heat that is trying to pass through.
The value of insulation is expressed in terms of R (RSI metric) values. In general, the thicker the insulation and the more tiny air pockets a material has the higher its R/RSI value and its ability to resist heat transfer.
Type of Attic and Roof Construction:
Gable and Hip Roofs - These are common and can be easily insulated by placing the insulation between the ceiling joists or bottom chords of trusses. A polyethylene vapor barrier must be placed under the insulation (warn side of insulation) to reduce any moisture entering the attic from the house.
Due to the inherent lack of access cathedral ceilings cannot be fully inspected for insulation or ventilation. It is very important that adequate ventilation be provided in these roof structures. The best ventilation system is one that uses continuous ridge and soffit vents to vent each rafter bay.
One-and-one-half Story Houses and Mansard Roofs
These types of attics have several small sections that must be properly insulated in the vertical knee walls, on the floor of the small attic, on the sloping ceilings and on the top floor portion of the 1 1/2 story area. The outer attic is treated as a non-heated area and it must be insulated and ventilated.
THIS IS AN EXCERPT FROM PILLAR TO POST® HOME INFORMATION SERIES
Contact Bjorn Rygg at 604-532-0530 or Bjorn.Rygg@pillartopost.com for a full version