Attic Short Circuits

It’s always fun to peek my head into another attic, where many mysteries can be solved: what type of wood is the home constructed of, is there evidence of structural damage, moisture, and pests, or even previous fires, and what is the type of insulation and ventilation. Homes require ventilation and the attic is no exception. There are three basic types of ventilation seen in the attic: soffit, ridge, and gable.
Proper ventilation is important for many reasons:

• Preventing moisture (and mold!) buildup, which can lead to structure damage.
• Lowering energy bills.
• Preventing ice dams (icicles are a huge red flag for potential damming!)
• Preventing premature wear on shingles.
• Required by building codes across North America.

You might think the biggest problem I run into is a lack of ventilation. It’s actually the opposite, with too much ventilation! Yes, there is such a thing as too much.

Less is (Sometimes) More!
The biggest issue I see is a home that has all three types of vents. This is usually because when roofers do a roof job, they frequently add a ridge vent. Great idea, but it ignores one of the main principles of building science: balance!

The issue is known as an attic short circuit. Like an electrical circuit, air flow will follow the path of least resistance. Home builders understand this and know how to balance ventilation (usually 1:300 of the total roof area) between intake (usually soffit vents) and exhaust ventilation (usually ridge vents). While disagreements can result about closing off gable vents when installing ridge vents, the fact remains that a home is a delicately balanced system, and the attic space is no exception. 

This is an example of how a ridge vent works.

What To Do About It? 
The answer is that is a favourite one among lawyers: it depends. If there is no sign of moisture, mould, or condensation it is probably best to leave it alone. If, however, there is clear and obvious organic growth, it is time to take action. Attic spaces should not have visible mould or moisture and a roofing or insulation contractor can provide guidance on the best way to correct this. Remember, simply removing mould isn't good enough: it WILL return unless the root cause is identified and corrected. Luckily, this is an area where I rarely see problems as usually only skilled professionals work in attic spaces.