Let me elaborate on the critical reasons why you might want to vent, and the anti-venting school of thought rebutting those reasons. Shingle life One of the most common reasons given for venting is that it is supposed to prolong the life of asphalt shingles by reducing heat build-up under the roof deck. Many shingle warranties are specifically voided if the roof is not adequately vented. The anti-venting faction says that venting does very little to reduce heat buildup beneath the roof deck, let alone the actual temperature extremes the shingles are exposed to. The single greatest factor affecting how hot the surface of a roof gets is the color of the shingles.
Dark shingles absorb much more radiant heat from the sun than light ones do.
Check manufacturers' warranty specifics carefully when purchasing shingles. Installation instructions are very specific and it is very easy to render the warranty void. And many shingle warranties don't cover labor, the most expensive part of the repair job, should the shingles fail. Heat buildup in the attic Related to the claim of reducing heat damage to shingles is the claim that venting will lower the temperature of the attic and reduce the heat transfer to the living quarters, making for a more comfortable house and reducing your cooling bills. Not so fast, say the anti-venters.