Attic Ventilation

Attic Ventilation -Ice dam protection, minimize home repairs & black mold formation.

Attic Ventilation

Improper attic ventilation can lead to poor ice dam protection, formation of black mold, and excessive home repair bills. Build Green and prevent this from happening to you.

Green Living Made Easy on Facebook
Bookmark and Share Subscribe Attic Ventilation

Attic Ventilation plays an extremely important role in the life and durability of a home. As many people make their homes tighter and more compact in an effort to become more eco friendly.

Save Ten With Angie's List!

Many homeowners are also adding additional insulation in an effort to save energy as well. We love smaller, more compact home structures and we think insulation is great - however, they can cause a problem with ventilation as a result and becomes one of the primary home repair costs we come across..

Organic Garden

Proper Attic Ventilation for Ice Dam Protection

Some Of Those Problems Include: Dry Rot,
Black Mold Buildup and Other Health Related Issues
Termites and Carpenter Ant Colonies
Ice Issues, Including Ice Dams and Icicles
An Increase In Energy Costs Due To Poor Ventilation.
How Much Attic Ventilation Should You Have?

The Association of Heating, Refrigeration, & Air Conditioning Engineers (ASHRAE), The Federal Housing Authority (FHA), and the Department of Energy (DOE) have developed standards relating to the amount of attic ventilation that each home should have. In short, the standard is,"Provide one square foot of free ventilation for each 300 square feet of attic area." Since you need ventilation both high and low, figure 150 square feet for soffit ventilation and 150 square feet for ridge ventilation.

Calculate Your Occupied Floor Area

Attic Ventilation - Calculate Your Occupied Floor Area

But, how can you figure out what this number is for you? It's easy! Start by calculating the square footage of your attic area. For most homes this should be close to the building's footprint. The easiest way to calculate the attic area is to measure all outside walls of your home.  Then multiply  to find the area.

Once you know that, you can calculate the amount of attic ventilation space you need. Here's an example for a typical 2,800 square foot home.

Example Attic Calculation Method:

In example 2,800 sq. ft. Typical Living Area
Divide this result by 150
2,800 / 150 = 18.67 sq. ft. Free Area
Multiply this by 144 (To Get Square Inches Req'd)
18.67 x 144 = 2,688 sq. inches
Divide this number by 2
2,688/2 = 1,344 sq. inches free area.
Required Soffit Ventilation = 1,344 sq. in.
Required Ridge Ventilation = 1,344 sq. in.

So, What Exactly is Free Area?

Free area is the space of actual ventilation that a vent will produce. The amount of free area you'll get with a vent depends on the type of vent that you use - we'll explain the types of vents available in a minute. Right now it's important to note that each type of vent will specify the amount of free area that it has. Often, it's expressed in the amount of free area per lineal foot of vent that you use. 

As an example, if you need 1,344 square inches of free space for attic ventilation, and you choose vents that offer 11 square inches of free space per foot of vent - you'd need to install a minimum of 122 feet of venting to meet the suggested free area requirements.

It is also our recommendation that the ventilation be weighted a bit heavier toward the soffit ventilation. A good rule-of-thumb would be 60% soffit/40% ridge, which helps the complications of ridge venting.

Types of Ventilation Materials Available

Once you've figured out how much free area you need, you'll have to decide on a type of ventilation material to use. There are many choices, we explain many of them below:Ridge Vents Ridge Vents: These vents run the entire line of the roof peak and blend into the roofline of the home. They are low profile and are hardly noticeable. If you choose ridge vents, you'll want to make sure that you chose ridge vents with baffling included, as the baffling will allow air to flow from one side of the vent to the other. Soffit Vents

Soffit Vents: Just like their name implies, this venting material is installed in the soffit of a home. They can be continuous vents, or frill type vents that are installed apart from one another. Soffit vents typically have 9 square inches of free area per foot of vent material. Gable Vents

Gable Vents: These vents are typically installed in the vertical surface of the gable end of a roof. They can boost the ventable area very quickly. If you have gable ends on your home, these may be your best option. Another key benefit to gable vents is that they don't compromise the roof's waterproofing. Roof Ventilation

Pod Vents: Pod vents are installed high on the roof to promote ridge line ventilation. A considerable amount this venting material is needed to meet the free area requirements for attic ventilation. They are also not the most attractive choice on the market, and extremely careful installation is required if they are installed on an existing home. Power Roof Ventilators

Power Ventilators: A power ventilator is an electrically charged fan that can be used to ventilate attic space. It's important to note that power ventilators use energy and should be chosen as a last resort.

What's the Problem?

While installing ventilation shouldn't be difficult, there are some common installation problems that are worth noting.

Attic Ventilation Blocks Soffit Vents:

By far the most common problem, attic ventilation is often in the way of space for a soffit to be placed. Because insulation installation is often awarded as part of a bid process, careful installation procedures are not always followed. If you're overseeing your own insulation installation, make sure that ventilation baffles are installed at each rafter or truss space to ensure proper ventilation.

Install Insulation Barriers For Free Ventilation

Install Insulation Baffles For Free Ventilation

Air Flow from Soffit Vents Blocked by Framing:

We've actually seen soffit vents that have been installed properly but don't work because there is no air path into the attic. This typically happens because the air pathway was completely blocked by wood framing during the rough-in phase. Inspect your roof space and soffit areas to make sure that the ventilation space is not blocked.

Cathedral Ceiling Block Air Flow:

This is a difficult problem. Many homes today feature cathedral ceilings because they are attractive. However, when cathedral ceilings are constructed, the ceiling is typically constructed by applying a layer or drywall directly tot he bottom of roof joists and the remaining air space is packed full of insulation. The result? No air flow, which can result in huge problems with ice dams. Unfortunately, if your home is constructed like this and you have issues with ice dams/icicles, you'll need a major renovation to fix it. The best thing you can do is to consult with an architect.

If you are building a new home with cathedral ceilings, make sure that there is adequate space above the insulation. Again, an architect who specializes in residential design can assist you with making sure that your ceilings are properly designed.

Ridge Venting

Attic Ventilation - Ridge Venting

Ridge Vents May Provide Inadequate Airflow:

Since most ridge vents have such a low free area per foot of length, there often isn't enough ridge length available for to meet the minimum suggested free area for attic ventilation. If your home has a lot of hip roofs, this is especially true and ridge vents may not be the best option for you.

If you're set on ridge vents, or already have them, one option is to install pod vents or a power ventilator in combination with your ridge vents.

Debris Blocking the Ridge Vents:

Make sure that no leaves or other debris is blocking your ridge vents. It's also important to be sure that there is adequate open area in the plywood that approaches the ridge where the vents sit.

Complex Roof Shapes Present Venting Challanges

Complex Roof Shapes Present Venting Challenges

Complicated Rood Shapes Block Air Flow:

Roofs on new homes are constantly becoming more complicated. This makes that art of creating air flow exponentially more difficult. Add a few cathedral ceilings and you've got a ventilation nightmare on your hands. The end result is ice dams and icicles all over the place. These issues should be well thought out and planned for BEFORE a home is built.

If you are planning to build or buy a home with complicated roof lines, cathedral ceilings, or numerous skylights, it's important that you consult with a good architect and an experienced builder who is accustomed to building homes with complex designs. These issues can be handled easily during the design phase, but once construction has begun, changes become extremely costly.

Do you have a problems with ice dams or icicles? If so, chances are it's a result of inadequate attic ventilation. Check out our article on ice dam protection for tips on preventing ice dams and curing existing issues.

Here are some additional articles you may be interest in on insulation for new and existing homes, eco-friendly choices and more:

Attic Insulation
Blown Attic Insulation
Blown Cellulose Insulation
Green Insulation
Insulation Types
Rockwool Insulation
Soy Insulation
Spray Foam Insulation