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. 

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.  

Five Golden Rings of Electrical Safety
Electrical is probably the most important part of an inspection: while there is no doubt there is an issue when there is a waterfall in the kitchen or a large horizontal crack in the foundation, electrical issues can be difficult to detect by the untrained eye. Here are five that I always look for:
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Single strand aluminum branch circuits: Not all aluminum wiring is problematic; it's commonly used for electrical conduction due to its cost-effectiveness and lightweight nature. I also look for Knob & Tube (K&T) although it has largely been removed and replaced over the years. 
Inspection of Electrical Receptacles: Checking a representative sample for missing grounds, reverse polarity, and signs of arcing, such as burn marks. 

Reporting on the status of Ground Fault (GFCI) and Arc Fault (AFCI) Circuit interrupters: Building and Electrical Codes evolve; retroactive changes are rare. In spite of this, I always suggest updating electrical systems to the latest standards. 
Assessing DIY Modifications: Any signs of makeshift "improvements," like the use of extension cords for permanent power supply, are noted.
System Overview: Assessing the entire system for adequate amperage, checking for undersized wires (oversizing is acceptable but wasteful), and ensuring no reasons exist for the power utility and insurance company to refuse service to the home.

Six Geese-a-Laying Insulation Tips
In older homes, insulation sometimes becomes an issue due to DIY attempts. While modern homes adhere to updated building codes, some retrofits fall short. For instance, in one inspection of an older brick house, the added insulation was carelessly installed, defeating its purpose. Remember, proper insulation traps air in pockets; compressing it renders it ineffective. Wet fiberglass insulation? Only fit for the trash. More insulation is beneficial, but not when compressed to squeeze more in.