Roof Ventilation

I recently read this article by Paul Scelsi of Air Vent, Inc, one of the leading manufacturers of roof ventilation products, which we use on many of our roofing jobs. The article was written on behalf of the Roof Assembly Ventilation Coalition. It is spot on in describing the importance of roofing ventilation.


Top Five Attic Ventilation FAQs
By: Paul Scelsi, Air Vent, Inc., Roof Assembly Ventilation Coalition

On the surface attic ventilation may not appear to be a “top of mind” concern for contractors working on the roof and inside the attic. After all, there’s insulation, underlayment, shingles and flashing to tackle, too. However, based on the volume of questions the member companies of the Roof Assembly Ventilation Coalition (RAVC) receive about attic ventilation, it is clear contractors are thinking about it. Here are the five most commonly asked and answered questions the RAVC receives.

Q: Why is it important to ventilate the attic – what’s its purpose?

Attic ventilation provides year-round benefits to help fight heat buildup in the summer, moisture buildup in the winter, and ice dams in climates with snow and ice. This helps to prolong the life of the building materials – including the shingles, helps to improve the comfort level inside the home, and helps to lower the utility bills by reducing the load on the air conditioner and other appliances such as fans and refrigerators. RAVC member companies have case studies documenting these benefits.

The summertime benefits of attic ventilation are often more obvious to the contractor than the wintertime benefits. That’s understandable. It’s not too difficult to realize the attic can get very hot in the summer, and if that hot air is not properly removed through ventilation it can become problematic. However, the wintertime benefits are less obvious, but – quite possibly – more important. That’s because the average family of four generates an estimated 2 to 4 gallons of water vapor each day through activities such as cleaning, showering, breathing, etc. (see Moisture Control in Buildings, Heinz R. Trechsel). Some of this water vapor rises into the attic. In the summertime, the outdoor air temperature – as well as the air inside the attic — is warmer than it is in the winter, and warmer air can hold more moisture than cold air can. But in the winter, the amount of water vapor that the air can hold is substantially lower. As a result, it can condense as frost or water droplets, drip onto the insulation, and, in time, contribute to mold, mildew, wood rot and poor indoor air quality.

Q: How much ventilation does an attic need?

The starting point for any attic ventilation project is always, “What is the size of the attic space to be vented?” The International Residential Building Code (IRC) defines attic size in terms of its square footage – length x width, floor of the attic. Once a contractor knows the attic square footage, the amount of necessary attic ventilation can be calculated.

The code minimum for attic ventilation in the 2012 IRC, Section R806 – Roof Ventilation[1] is as follows: 1 sq. ft. of Net Free Area for every 150 sq. ft. of attic floor space. This means, for every 150 square feet of attic floor space there should be 1 square foot of Net Free Area. (NOTE: While the IRC does not address the need for more attic ventilation as the volume in the attic rises with roof pitch increase, member companies of the RAVC do in their various resources).

Q: What’s the ideal way to ventilate an attic?

It is the recommendation of the RAVC that the attic ventilation system always be balanced. This means an equal amount of intake net free area through vents positioned in the soffit/overhang or near the roof’s lowest edge and exhaust net free area through vents installed at or near the peak of the roof. This allows cool, dry air to enter the attic at the lowest point helping to remove any warm, moist air from inside the attic through the exhaust vents – along the entire underside of the roof deck. RAVC member companies have an extensive offering of intake and exhaust vents.

If the attic ventilation system cannot be balanced 50% intake/50% exhaust, it’s better to have more intake than exhaust because it’s been our experience most houses lack proper intake. Additionally, any excess intake will become exhaust on the leeward side of the house because the intake vents on the windward side of the house will have “pressurized” the attic. As a result, the intake vents on the leeward side of the house will work “with” the exhaust vents to release air.

However, if the attic has more exhaust than intake it is potentially problematic because the exhaust vents could become intake to compensate for the lack of balanced intake. For example, a ridge vent could pull air from its back side if it can’t obtain air from intake vents. Or, a wind turbine could pull air from a nearby wind turbine on the same roof because there is not enough intake low on the roof to pull from. In either scenario, the exhaust vent is potentially ingesting air and weather which it’s not designed to do.

Q: The more exhaust vents on the roof the better it is for the attic, right?

Well, it depends. If it’s more of the same type of exhaust vent, it is OK (as long as it does not exceed the amount of intake as explained earlier.). But if it’s a combination of types of exhaust vents, it’s potentially problematic.

In general there are five types or categories of exhaust vents: ridge vents, power fans (traditional electric and solar powered), wind turbines, gable louvers, and roof louvers. The RAVC recommends never mixing two types of exhaust vents on the same roof above a common attic because it could short-circuit the attic ventilation system. Here’s how it can happen. Air follows the path of least resistance. That path is supposed to be from low in the attic (intake vents) to the highest possible exit point in the attic (exhaust vents). If two different types of exhaust vents are combined (for example, a ridge vent and a gable louver) the primary path of air becomes the distance between the two types of exhaust vents. That short-circuits the proper flow of air and could cause one of the exhaust vents to ingest weather because it is suddenly functioning as an intake vent.

When it comes to intake vents, by the way, it’s OK to mix multiple types on the same roof (for example, rectangular undereaves and roof-top installed edge of roof vents) because they will be in the same wind pressure zone working together. That is not the case with multiple types of exhaust vents.

Q: How are multiple ridge heights handled?

The rule of thumb for ridge heights states that all ridges can be vented whether they run parallel or at angles to each other. If, however, the ridges are more than 3 feet apart in height, only ventilate the higher one or separate the attics. As wind passes over an externally baffled ridge vent, it creates low pressure zone, drawing air from the attic. The faster the wind moves over the baffle, the greater the pressure it creates. Typically, wind moves faster at higher elevations, therefore, the higher ridge will be exposed to high wind speeds. If the wind speed difference is adequate, the pressure at the higher ridge may be enough to pull air into the lower ridge vent. Thus, it’s best to separate the attics with plywood or poly sheeting to create two distinct attics. Once the attics are separated, ventilating all of the ridges is acceptable.

By Paul Scelsi, Air Vent, Inc. Scelsi is Chairman of the Roof Assembly Ventilation Coalition, whose mission is to be the leading authority and technical resource on ventilated roof assembly design and performance.

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Snowy roofs

Recently, the New England area has seen an above average amount of snow.  Boston has received nearly 90 inches of snow this winter!  Travel has been nearly impossible, schools have been closed…everything aspect of every day life has been affected for these people.

One thing that people do not always think of, however, is the effect of snow on a home’s roof.  A cubic foot of snow can weigh between six and eight pounds….that’s two and a half to three and a half times the roofs actual weight!

Obviously, some roofs aren’t built to take this additional weight, and roof collapses occur.

roof collapse  roof collapse 2roof collapse 3

Should Indiana see snow amounts like this, homeowners will definitely want to have roofs cleared, relieving roofs of the excess weight, and possibly avoiding structural damage.  Like any other project involving a roof, homeowners will want to hire a licensed and insured roofing professional who will want to keep the integrity of your shingles in mind.  A non professional, while clearing the roof of snow, may actually cause damage to the roofing material that could cause other damage down the road.  Above all, it is a very dangerous job that nobody should risk.

Even though we are in Indiana, Two Brothers Roofing actually has experience with roof snow removal.  Rick, our project foreman, worked in roofing over 20 years in Minneapolis prior to joining us.  So if you are ever in need of having your roof cleared, call Two Brothers Roofing!



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Modified Bitumen Roofing

Low sloped roofing projects call for different materials than a traditional steeper sloped roofing.  If we were to use traditional underlayment and shingles on a low sloped or flat roof, the nails use to attach our roofing materials would be a tremendous compromise to the integrity of the roof.  Hello leak city!

A material that we often use on residential lower sloped roof is called modified bitumen, and is build very similar to a traditional asphalt shingle.  The difference is that modified bitumen is applied from a roll, and is either torched on or applied with a self contained peel-and-stick adhesive.  When applied correctly, both base and cap layers provide an excellent roofing compound that protects for many years and is very leak-resistant.  It also comes in a greater variety of colors to better match your home’s exterior.

Here are a few “before” and “after” pictures of a recent project which required the removal of a previous (and leaking) rubber roof and skylights.  We installed new decking, base and cap layers of GAF Liberty modified bitumen, three new VELUX skylights, and custom made flashing.

Old Rubber Roof Rubber Roof Skylight FlashingGAF Liberty with VELUX Skylights GAF Liberty with VELUX skylights 2 GAF Liberty with VELUX Skylight

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Gutter Gaurds / Gutter Screens

Clogged Gutter
Gutter guards and screens were created to ease the maintenance required to keep gutters clear of debris, enabling rainwater from your roof to flow freely away from your home.  Some gutter guard companies offer very expensive systems that promise to be maintenance-free with long warranties.  Cheaper systems are offered at big-box home improvement stores.  So what is the best option?

Here is my opinion on the different products available:

I absolutely do not like the expensive systems that advertise on television.  They are often sold via a home demonstration and pressure sale, and cost in the thousands.  It is a specialty product that is only offered by the company selling it.  The problem is, if you ever have a problem, the only place you can get replacement parts is from the company you purchased it from, and at an exorbitant price.  It is my opinion that they are absolutely not worth the cost.

Gutter Guard

On the other end, I have not seen any cheap system that stands up to time.  Lightweight plastic and screen will simply not withstand the environment that your roof sees throughout the year.

Quality, metal gutter screens are the only option that I have seen that are, in my opinion, worth the money.  Water falls through the screen, (most) material does not, and falls over.  Easy to understand.  Additionally, as long as they are installed correctly (screwed to the front of the gutter), they seem to last quite a while.  Select a screen hole size that best deflects the type of material found in your yard, and you should be happy with the results.

EZ-Lock Gutter ScreenDrop-In Gutter Screen

This said, nothing is maintenance free.  No matter what is promised, nothing is maintenance free.  Luckily, there is a cheap tool that allows homeowners to safely hose out their gutters: telescoping wands that attach to a garden hose.  They are available at your local home improvement store, and obviously super-easy to operate.

Gutter Wand Two Brothers Roofing With a combination of a properly installed gutter screen, and the cleaning of your gutters a couple of times every year, anyone should be able to keep gutters clear and flowing.


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What goes up must come down.

Even bullets.

There are a few out there who think its a fine idea to shoot guns into the air for new years and other celebrations, without thinking about where the bullet might land.  Of course, its a practice that can kill people.  We have also seen roofs damaged by the falling bullets, piercing the shingles, sometimes going through the decking as well.

Here are a couple of pictures of the last roof we saw that held a fired bullet:



Obviously, that spot is going to leak.

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Ice Dams

icedams As the temperature dips below freezing, we are given a yearly reminder of the damage caused by ice dams.  Left unchecked, ice cams can damage shingles and gutters, and lead to leaks causing damage to interior walls and ceilings, mold, and other serious problems.

Ice dams are caused by heat loss through your ceiling into your attic.  When an attic air is warmer than the freezing outside air, heat is transferred through your roof deck and shingles, melting the snow on the roof.  As the water from the melted snow flows down the slope of the roof, it eventually reaches the colder eaves (as they are not receiving the heat from the warmer attic air), and the water re-freezes.  The ice continues to build up, damming the water on the roof, causing leaks.

Fortunately, ice dams are relatively easy to prevent by improving on one, or all, of three areas.

Ventilation: proper ventilation will help exhaust any warm air trapped in your attic, pulling cool air from soffit vents.  Proper ventilation also vents unwanted moisture year-round, preventing any mold build-up.

Attic air leaks: gaps between the interior and the attic space near fixtures, chimneys, fans, attic hatches, wiring holes, etc.  All of these should be sealed, keeping warm air in the interior.

Insulation: the ceiling is the most important area to insulate, as 45% of heat loss on an un-insulated house is through the ceiling.  A level of at least R-38 is recommended, and easy to achieve over a lower level of existing batt or blown-in insulation.  Additionally, the energy savings will be immediately felt, both in comfort and savings on energy bills.insulation1

Obviously, the best solution is to properly ventilate, seal, and insulate an attic so that the air in the attic matches the temperature of the air outside.  If you find yourself in a bind, salt applied directly to the ice dam will cause it to melt, allowing the water to flow to the gutters.  Read the following link to a blogger in Minnesota battling ice dams on his home:




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Spraying Rubber Doesn’t Fix a Problem

I recently helped a homeowner fix a leak at her newly purchased home. Days after moving in she discovered a leak in a rear bathroom, and immediately called someone to help her.

Unfortunately, the handyman she hired to fix the leak didn’t do what he needed to. The leak was fairly easy to diagnose: the homes previous owner had told her of a box vent that had been recently stepped on (with no explanation on why people were on the roof), and water was now getting past the box vent.

The handyman didn’t fix the problem, though.

We have all seen the commercial with the pitchman showing his great spray rubber that can be used to fix roof leaks, gutter leaks…he even sprays it on a screen door mounted to the bottom of a row boat to show how it seals.


While that sort of product may work well with some roofing materials such as metal or plastic, I would never recommend using it to fix a leak. In fact, the whole premise isn’t about fixing the leak…it’s about hiding the leak.

Often the best way to fix a leak is to replace the leaking part of the roof. It is easier and cheaper to replace a pipe boot or box vent once than to have someone come out every year to again remedy a leak. Do it right the first time, and you will be better in the long run.

In our homeowner’s case, all it took was a few shingles, a new box vent, and an hour to properly fix the leak. Easy and done.

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A Clean Gutter Is A Happy Gutter

As we get into the full swing of autumn, the leaves will continue to fall giving us one of the more important maintenance tasks that you should be doing for your home: cleaning your gutters.

A clogged gutter can damage your home in several ways. A clean gutters channel rainwater to your downspouts, and away from your home. If you gutters are clogged, the rainwater will back-up and overflow the sides, damaging and rotting your gutter boards, soffit, siding, and even your foundation. In the winter, those clogged gutters can cause ice dams, possibly forcing the ice under your roof causing leaks in your home. The weight of clogged gutters can cause them to pull away gutter boards, possibly detaching themselves from your home.  Gutter debris can rot, creating odors and attract insects.  Enough debris in your gutter can even create an environment for new plants and trees.


Cleaning your gutters can be done on a ladder or from the ground. Using a ladder while clearing and inspecting the gutters from up-close is the best way.  However, there are risks involved with hanging on a ladder one or two stories above the ground, and there is a bit of work to continually move the ladder and get is safely anchored.  Contractors spend their lives on ladders, and if you are at all apprehensive, hire someone to do this for you.

If you don’t want to risk the ladder or to pay a contractor for the job, there are telescoping gutter cleaners that hook to your garden hope and use the water pressure to clean the gutters, all while you stand on the ground. Your nearest hardware, Lowe’s, or Menard’s should have these in stock for a reasonable price.  The disadvantage is that you are not able to get the full, up-close visual inspection, and may have trouble with some blockages.  Keep an eye on your downspouts, and make sure that you have a constant stream coming out.

Whatever means you do chose to clean your gutters, please remember to use common sense and so it safely.  Or, if you would to prefer to have a contractor clean your gutters, feel free to give us a call and we can have one of our guys take care of it for you.

Remember: a clean gutter is a happy gutter!

clean gutter

Speaking of gutter screens and helmets, if you would like to look into one of these products, have someone come out to take a look at your situation before you decide to go with any one product.  Your environment should dictate the product…you don’t need protection from pine needles if you are miles from a pine tree!

Thanks for reading,

Dana, Juan, Rick, and Alex
Two Brothers Roofing

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Ummm…anyone want to take care of that gaping hole?

We recently re-roofed a home in Meridian-Kessler.  It is a great old house that had been neglected until the new owners did a wonderful job re-habbing it.  The roof had a hole in the decking that had been ignored by the previous three roofers.  They simply papered and shingled over the hole, as did the next two roofers (the roof had three layers).


We re-decked that section of the roof, as well as some other problem sections, and the new owners have a roof that will last for many years!


Dana, Juan, Rick, and Alex

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Two Brothers Roofing

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