It's that time of year that requires home inspectors to enter the hottest part of the home...the Attic space.
And a good number of attics are not vented. Venting of attics is not only important to reduce energy consumption and the associated costs of heating and, mainly summer cooling, but having attic air flow also protects the attic and roof materials from deterioration and in some cases premature failure. Some of the sealed attics we've seen have roof sheathing (the wood supporting the shingles) that has been overheated for so long that the glue in the plywood or OSB (glued fiber board) has broken down so much that the wood begins to peel and flake off. In some cases, the wood is so weak that it is potentially dangerous to walk on the roof surface, as there is no longer structural support. And overheating solid wood rafters, beams, and other supporting members will cause them to discolor, and even loose their strength over time, and become more flammable if a fire were ever to occur.
In these homes, we note that deficiency in the inspection report with the statement that the next roof replacement will cost significantly more since the sub-surface wood sheathing will have to be replaced as well. And just hope a heavy tree limb does not fall on the roof before it is next replaced.
So a vented atic is a cool and happy attic.
Some design information can be found by clicking Here.