Q. We need a new roof on our house and have sought numerous estimates from various companies for the work. Most of them mention the option of a ridge vent installed at the top of the roof, some mention it in passing and don't really push it too hard one way or the other, and others, while not exactly insisting it be installed, say that without the installation of a ridge vent, the attic would receive inadequate ventilation, which, in the event of shingle failure, would invalidate the warranty on the sh ingles. Some companies also offer to install another vent about a foot from the edge of the roof for those houses which don't have vents or proper ventilation under the eaves.

My concern is that our house was build in 1947. From what home inspectors told us when we bought it, and tried to sell it, and what the roofing companies have told us when they've done their estimates (some inspected the attic area as part of their esti mate), they say it is a solid, well built house and there appears to be no indications of leaking, water damage, etc.

My question is do we need and or how necessary is it to have these vents installed? I know almost all the new houses have at least the ridge vent but my thought is, if it ain't broke, don't fix it! Something goes against my thinking to intentionally cut holes in my roof when there doesn't appear to have been any problems regarding leakage in the past- why risk the trouble, right? On the other hand, I want this next roof to last as long as possible and if these various vents are better for the roof and the shingles then I would definitely want them installed.

A. I’ll bet you think you asked a simple question but you didn’t. Let’s start at the top. Ridge venting is a continuous vent strip that is installed at the very peak of the roof. It requires an opening to be cut between two to three inches across the very peak of the roof to expose the attic below over which the ridge vent will straddle. The ridge vent is only half of the venting system if that’s the venting system you’re going to use. A ridge vent needs a continuous air supply from the bottom of the roof edge on both sides of the roof to work-- often called soffit vents. The way this very simple, yet state of the art system works is air enters the attic at the lower soffit vent and using the heat of the sun as an accelerator, convects air up u nder the roof deck, washing the underside of the roof with fresh air, somewhat continuously. It’s called a cold roof because the intent is for the temperature of the roof to be close or equal to the temperature of the outside air. It works. I first saw them as a manufactured item routinely installed on roofs starting in the mid-1970s.

Roofers like them because they don’t have to take the time to individually cut cap shingles as they would if the roof was installed traditionally without ridge vent. So the roofers who casually mentioned them were planning to install them. The roofers who told you not having them was going to void the shingle warranty really wanted to use them and employed some sales hyperbole to boost the argument. Almost any ventilation would suffice for the shingle warranty and shingle warranty is a whole other su bject.

Certain ridge vent configurations can leak under extreme conditions. I have seen little snow drifts up in attics under ridge vents after a period of high winds coupled with fine, blowing snow but that was rare.

You need to be sure you have adequate soffit venting to supply the air for ridge vents before you rely on them. That’s what the roofers who offered the lower roof vents were trying to do by suggesting them. There is a continuous roof edge venting now ma rketed to use in conjunction with ridge vents on roofs with insufficient eaves or overhangs but I worry about leakage during ice damming so I reserve judgment on them just yet.

Your house was built with gable vents-- those square or triangular openings at each end of the attic. They work fine by themselves but what we have learned in past couple of years through research is that if you have proper ridge venting system then you should block off the old gable vents. It turns out they work against one another and pockets of dead air begin to form in areas in the attic and that’s not what you want. But keep in mind the function of ventilation over the course of the entire year is more to exhaust moisture that migrates up from the house than to dissipate summer heat. However make sure your attic insulation is up to snuff. It should be about eight inches of fiberglass or its equivalent.

Ensuring a long shingle life has more to do with selecting the best shingle for the job and having it applied by a crew who is careful and does it to manufacturer’s specifications. Talk to the roofers about drip edge, ice-damming protection and the type of felt underlayment paper they’ll use. If they want to install ridge vent be sure you like the way it looks and preview a sample before it goes up.