During our discussion of roofs and roofing materials, we briefly discussed how many of the most common roof problems relate to the composition of roofing materials themselves - predominately asphaltic materials. Over a period of years, the actions of nature - especially the sun - tend to drive off the volatile components of these asphaltic materials, leaving them dull, hard and brittle.

We also discussed that while sunlight itself causes some of these problems, heat is particularly damaging. Excessive heat usually caused by improper or inadequate vented space beneath the roof causes very high roof temperatures, accelerating loss of volatiles. As this process continues shingles tend to curl and crack, aggregate is lost from the shingle surface due to the combination of erosion and lack of retention and the throats (or flutes) that channel water down the shingles begin to wear out.

While we can't practically do too much to prevent the sun from shining on a roof, conversely, the excessive heat and related deterioration due to an unvented attic space is avoidable by installing proper ventilation.

Probably one of the best ways to accomplish this is with a passive system. Modern approaches to this type of venting include a combination of soffit vents and roof ridge vents. With this arrangement, the natural convection of heated air causes it to travel up the underside of the roof inside the attic, pulling cooler air from the outside in through the soffit vents as the hot air escapes through the ridge vents in the peak of the roof. This movement or circulation of air beneath the roof helps keep it cool and prevents premature roof covering deterioration.

Vents in gable ends of a house or in the roof itself can be helpful but are not always completely effective - especially if they are not installed near the peak. That's because there's no good way to maintain movement or circulation of this air by natural means if there isn't a good breeze blowing in just the right direction.

In these cases a fan can provide the mechanical means of moving the hot air out and the cool air in. These fans can be controlled manually by switches located in the living space or automatically by a thermostat located within the attic itself. Of course, installing a fan requires a source of electrical power. Therefore you may also have to have power installed to the proposed fan location if it is not already available.

Regardless of the means used to provide roof ventilation, care must be taken to ensure the installation is weatherproof - particularly if it involves penetrating the roof.

Finally, any opening to the outside of your house must be properly screened and secured to prevent entry by animals, insects, etcetera.

While providing venting to an existing house can sometimes be a challenging project, the resulting increase in the life of your roof covering can make the effort worthwhile.