Adequate Ventilation and what that means for your roof system

Ventilation codes in roofing can often be overlooked, misinterpreted or even unenforced. The combination of these issues can lead to shortened roof life, health complications from mold or viral particle concentration, and voided warranties. All these things, at the end of the day, fall onto our customers, the homeowners. As licensed roofing professionals, we all strive to deliver the best product for the best price, to solve problems and fulfill the needs of our customers. My intention with this article is to arm roofing professionals with information they need to be confident in their journey in this industry – leading to better, stronger, and longer-lasting roofing systems. I will discuss the protections that ventilation provides, the code and how to interpret it, and the sciences behind why we ventilate.

               Roofing ventilation is linked directly to the protection of three main categories: protecting our homeowners, protecting our investments, and protecting our warranties and insurances. The common misconception about ventilation is that its only function is to cool our homes and to lower our energy bills. While this is true, it is actually just a happy biproduct of why we vent attics in the first place.

               Research studies have concluded that the average person produces about ¾ of a gallon of water vapor each day, in the form of cooking, cleaning, perspiring, etc. This water vapor, without the proper ventilation, collects in attic spaces. And that collection of water can lead to mold and mildew growth, which in turn can cause health problems for our homeowners. The worst part about mold and mildew growth is its rapid invasion. Left unchecked, they flourish in these warm, dark environments. Proper ventilation allows air flow and provides the necessary air changes to get this heavy wet air out of attic spaces.

               More than the obvious cost of the roof itself, ventilation is linked to a handful of other investments our customers are making. Not surprisingly, energy efficiency is a hot topic for them, and they are making significant investments to strengthen and fortify their homes with, among other things, new doors and windows, added insulation, and solar panel systems. With new doors and windows, homeowners are unknowingly tightening the building envelope. The water vapor we produce from our daily lives that would normally escape through leaky doors and windows is now accumulating even more inside our homes and attics. This moist air, with nowhere to go in an improperly ventilated roof, condenses and falls onto current, or even updated, ceiling insulation, causing it to lose its R- value. And even after this insulation dries out, the lower R-value remains, never returning to its original numbers. Solar panels produce energy, but also cause extra heat on the roof, and can even block heat from dissipating off the roof. Adequate ventilation alleviates all the pain that these issues cause.

               Finally – and importantly – ventilation is linked to our manufacturer warranties. While many contractors are out there offering warranties and making promises, some of them might be empty promises. Many of our major manufacturer partners call for adequate ventilation to validate their warranties – and rightfully so!  Our manufacturers of shingle and underlayment want their products to work to the best of their ability. A lack of adequate ventilation causes increased temperatures build up. This increased temperature can decrease the life of our underlayment and shingles by causing blistering, curling shingles and expedited granule loss. This decreased life expectancy of roofing systems impacts our homeowners directly and indirectly. On top of that, insurance companies have been adding even more stress to our homeowners as they send out nonrenewal letters. These letters have been an attempt to get older roofs replaced. A better-quality roof system, built to code, would last longer and give insurers more confidence.

What is the code and what does it mean?

Before we talk about the code, we can get a better understanding of why it exists by understanding the sciences behind it. The key players in the sciences of the code include convection and the Coriolis Effect. Convection is the transfer of heat off a surface area through air or water, in this case air. All this heat that is produced from an attic floor needs a place to go. This is why we use the total attic floor, non-livable space, required ventilation. Convection, the rising of heat through liquid or gases, will be amplified and aided by a properly balanced intake and exhaust system. The Coriolis Effect is the movement of air caused by the rotation of the earth. If the earth is spinning heat will rise.

The Florida Building Code states that 1 square inch of Net Free Ventilation Area (NFVA) is required for every 150 square inches of attic floor space. This space includes all enclosed attic areas, including garages, overhangs, and non-livable areas as well. There are two exceptions to this code that allow us to vent at 1 square inch of NFVA for every 300 square inches of attic floor space. The first part of the exception is climate zone related, which fortunately does not apply to any parts of Florida. The second part of the exception is that 40-50% of the ventilation needs to be at the upper portion of the roof, 3 feet from the ridge, creating a balanced system. This means that the intake and the exhaust need to match. An easy way to visualize this is thinking about how air moves when you have the front and back doors of your home open -- a cross breeze generates and air moves through. If the doors are not open by approximately the same amount, then the cross breeze will not occur.  A continuous perforated soffit intake, therefore, needs to be balanced at the ridge with an exhaust venting of equivalent NFVA. When the intake NFVA is amplified, more vents become necessary to balance the system than what would be needed if the intake NFVA was closer to the calculated number for the size of the home.

In conclusion, in Florida, 1/300 with a balanced system is the most cost efficient and productive means of meeting the code, validating our warranties, lengthening the life of our roofs, and supporting insurance industry concerns. The one thing we can all agree on – builders, contractors, manufacturers and city officials – is that we need to put an end to unlicensed and improper work. Understanding and applying this code will hopefully be the step forward that we need in this industry.