Attic Ventilation & Insulation – Keys To A Healthy Roof


First-time homeowners rarely give much attention to the roof of their new home much less attic ventilation systems and attic insulation. They look at the shingles on the outside and decide if they like the color. Maybe they worry about storm damage. Few Madison WI homeowners spend time thinking about what’s beneath the roof.

Underestimating the importance of what’s sheltered directly below the roof can be a costly oversight.

Threat to your roof and home from poor insulation and ventilation in the attic never take a day off.

The first signs of potential problems show up on your heating and cooling bills. Have your energy bills this summer been higher than expected? Poor attic ventilation is a likely contributor. Add an insulation problem and you’ve got a recipe for high energy bills and, eventually, costly roof repairs. Problems building beneath the roof literally wear it out from the inside.

Dangers Of Poor Attic Ventilation

You can make a quick assessment of your home’s situation with a visual inspection. All you need is a ladder and a flashlight. Every home has at least one access point leading to the attic. Open it and inspect your attic insulation and the inside of the roof. You’re not a trained roofing professional so you’re not sure what to look for, right? Here’s a guide:

  1. Extreme heat – if your roof isn’t properly vented the attic becomes an oven in the summer. Heat comes up from inside the house and combined with heating from the sun outside is trapped beneath the roof. With no way to escape the heat leaks back into the house putting a strain on your AC unit.
  2. Mold and mildew – heat causes condensation of moisture when there isn’t enough ventilation. High summertime humidity makes the situation worse. Hot, moist air is the ideal breeding spot for mold and mildew. You’ll be able to see the black and blackish-green smudges. You might even be able to smell it. Once mold gets started it contributes to serious health issues.
  3. Roof damage – condensation is the enemy of any roof. It causes roof decking and supports to break down – the wood rots. Unchecked it works through the base layer and breaks down shingles from the bottom up, too.

There’s another sure sign you may have noticed last winter: ice dams. An ice dam is not only a sign of deeper problems, it’s a threat to your roof on its own. Heat escaping from the attic melts snow on the roof which refreezes on the edge. Ice builds up and backs water under shingles and decking. An ice dam left untreated damages shingles, underlayment, nearby insulation and possible drywall and paint in some room of your house.

Attic Insulation + Ventilation = Efficiency

Statistics show that as much as 85% of a home’s heat loss goes straight through the attic. Older homes are likely to have inefficient insulation – uneven layers with gaps or empty spaces. Poorly insulated attics waste energy – and that wastes money! A home with excellent ventilation and poor insulation is no more efficient than one with plenty of insulation and poor ventilation. You cannot have peak efficiency without both components in place.

The amount of insulation any material provides is measured by its R-value. The higher the R-value number the better the material insulates. Houses built in the 1970s or earlier probably had original insulation with an R-value of around 11. Considered poor by today’s standards. Modern construction includes insulation with R-values of at least 38 and as high as 60 in cold climates. For hints on how to evaluate your home’s insulation check the Environmental Protection Agency’s guide to attic insulation.

There’s no “one size fits all” when it comes to the right vents for modern roofs.

Insulation materials vary from standard fiberglass to blown-in fibers, foam and recycled denim. No matter which material you choose, improving insulation lowers heating/cooling costs.

The R-values for most of the commonly used insulation materials include:

  • Blown-in Fiberglass – R-value of 2.2 – 2.9 per inch of material
  • Fiberglass batts – R-value of 2.9 – 3.8 per inch of material
  • Blown-in Cellulose – R-value of 3.1 – 3.8 per inch of material
  • Loose Rock Wool – R-value of 2.2 – 3.3 per inch of material
  • Sprayed Foam – R-value of 3.6 – 8.2 per inch of material

You can figure the R-value of your current insulation by measuring the thickness of the material in the attic and applying these numbers. For example, a 6-inch layer of common fiberglass batts will likely have a maximum R-value of around 23. That’s not enough for a Wisconsin season.

Attic Insulation Suggestions

Depending on where you live recommendations for appropriate insulation change. A home in Madison might get by with less than a summer home or year-around cottage “up North.” Recommendations for the Madison area fall into the realm of a “moderate climate” where and R-value of from 38 to 60 is expected. For that, consider:

  • Blown-in Fiberglass – 17 to 22  inches of material
  • Fiberglass batts – 13 to 17 inches of material
  • Blown-in Cellulose – 13 to 16 inches of material
  • Loose Rock Wool – 15 to 22 inches of material
  • Sprayed Foam – 6 to 14 inches of material

To be sure your Madison area home is protected, or for a home farther north, consider cold climate recommendations for an R-value of 49 to 60:

  • Blown-in Fiberglass – 19 to 25  inches of material
  • Fiberglass batts – 14 to 19 inches of material
  • Blown-in Cellulose – 14 to 18 inches of material
  • Loose Rock Wool – 17 to 25 inches of material
  • Sprayed Foam – 7 to 15 inches of material

If there’s one recommendation to base your plans on it’s: “You cannot have too much insulation.”

Don’t Underestimate Importance Of Attic Ventilation

Unlike insulation, you can have “too many” roof vents. Too much ventilation is as bad as too little. Anywhere a roof is opened the possibility of leaks increases. You want your choice of roof vents to be “just right.”

How do you know what your home needs? Work with the professionals at Sims Exteriors & Remodeling. Dedicated long-time roofing professionals know how to evaluate your home’s needs for maximum efficiency.

Even within the ranks of roofing professionals few agree on which ventilation system is the best. That’s because roof shapes, styles and materials vary so much. Ridge vents are considered the most cost-efficient and are effective. Some roof designs include gable vents and soffit vents. A common and effective system combines soffit and ridgeline installation. But even these require variation from roof design to roof design.

No matter which kind of ventilation system you home has, making sure it works as designed is the key. If the system is working properly and you have the right amount of insulation, air from inside the home should not reach the attic. At the same time, outside air should not reach the inside of your home through the attic. Adequate ventilation prevents moisture that leads to condensation.

Attic ventilation plus attic insulation protects your family, possessions and structure. The attic is far more than an empty space.

Seek Attic Ventilation Advice From The Pros

Sims Exteriors & Remodeling has been installing and repairing residential roofs in the Madison area for decades. Our crew members are well-trained and experienced. No company in the area matches our experience. When you need a new roof or just want to be sure the one you have is working at peak efficiency, give us a call at 608-825-4500.  Or email us and we’ll arrange an interview to review your needs. We’re your best local resource for efficient roofing products including attic ventilation for your Madison WI area home.

Attic Ventilation Basics

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