It is said that “he who is only armed with a hammer, treats everything as a nail.”
Ridgevents have become so popular that many roofing contractors are using them on every roof, regardless of whether they are appropriate for the roof style or current ventilation system. Unfortunately, because most contractors don’t understand proper ventilation they use ridgevents as the “panacea” to cure all ills and ward off all evil spirits, real or imagined.
A few rules of thumb apply when considering whether a ridgevent should be used:
1. NEVER mix a ridgevent with other type of exhaust vents on a roof: gable vents, static vents or power fans.
2. Always ensure that there is sufficient intake ventilation to balance the amount of net free venting area of the ridgevent.
We discussed the “why” behind these rules here: Technical Corner by Air Vent
If a ridgevent is going to be installed, Air Vent (the leading manufacturer of roofing ventilation) specifies that you must remove or block off the other open exhaust ventilators or the low to high draft will be short cut and diminish the ventilation effectiveness (to learn why, visit the Technical Corner by Air Vent .).
But before we make the determination that we need MORE ventilation… shouldn’t we ask these questions, first?
1. How much is enough ventilation? Who says so?
2. What is the case history of the patient? (And by “patient” I mean the existing attic and roof)
RE: HOW MUCH IS ENOUGH VENTILATION AND WHO SAYS SO? When determining how much ventilation is enough, there are recommended ratios specified by the industry that can easily be calculated. If you’re geeky like me, you’ll fall in love with this video and want to watch it over and over because of the sense of “completeness” you experience by calculating net free venting area:
1. What ventilation problems are we trying to solve? Do any presently exist? Have any existed in the past?
2. Has the roof shown any signs of shortened shingle life in the past, due to insufficient ventilation?
3. Have there been any moisture problems in the attic? Mold? What do the nails protruding through the roof deck look like? Are they rusty because of condensation in the attic?
4. Have there been any significant changes to the home? New windows or doors? New HVAC system or insulation? Any moisture in the crawlspace?
If the current ventilation system has worked well in the past, there have been no significant changes to the building envelope or if the alterations to the roof system would be prohibitively expensive in order for a ridgevent system to work properly, it is possible that changing a well functioning ventilation system to a ridgevent system might not be in your best interests.
There, I said it. That’s right. Read it again: you might not need a ridgevent!
But what if you DO need a ridgevent or decide that you want one? Which ridgevent should you get?
Short answer: only consider ridgevents with external baffles. Here’s why:
Your choices come down to two basic choices: a metal ridgevent or a “shingle-over” ridgevent. Air Vent has a model of each:
1. Multi-Pitch FilterVent is an aluminum ridgevent. It is quite inexpensive, easy to install and actually has a higher cubic foot per minute air flow rate than the shingle over style. Learn all about FilterVent by clicking on this link
2. Shinglevent 2 is a “shingle over ridgvent”. It is more expensive and a bit more involved to install than Filtervent but it looks sharp on a roof. Learn all about Shinglevent 2 by clicking on this link
A ridgevent is a great tool and is to be used properly as part of a properly designed system. As with any tool, it’s only as good as the application it was designed for. It’s no panacea or “magic bullet” and if not installed properly with a balanced ventilation system with proper intake and exhaust and no other open ventilators will not perform as it was intended. But what does?
Here are some more articles on roofing:
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