Attic Ventilation

venting attic

One of the most common problems I encounter in the majority of my home inspections is the lack of proper attic ventilation. Attic / roof ventilation is probably the least understood requirement necessary for achieving a healthy home in Massachusetts. Most homeowners do not understand the full meaning and benefits of proper attic ventilation. There's also a lack of understanding in how to properly size and position roof vents for an adequate air flow under the roof surface.

Proper ventilation is absolutely necessary and vital, not only to the health and well being of every home, but also to every home's occupant. Anyone who has been in an attic knows that attics get very hot! If the heat in the attic is allowed to sit there and not ventilate/circulate, it will conduct heat into the home, or, at the very least, prevent the built-up heat in the house and attic cavity from escaping. Without adequate ventilation, your home will encounter problems such as rapid shingle deterioration (from melting), mold build-up throughout the roof structure, wood rot and delaminating sheathing, mildew, peeling exterior paint, rusty nails, energy losses, and many other problems that are often the direct result of inadequate attic ventilation. Wood boring insects such as Termites and Carpenter Ants are attracted to moisture buildup that is often caused by any inadequate ventilation.

Ironically, improving ventilation conditions can often be accomplished with low to moderate cost expenditures. Once my home inspection clients understand the problems associated with poor ventilation, there is usually a willingness to make these improvements as soon as they move into their new home. When there is significant damage from the existing poor ventilation, such as curling of the roofing shingles and delaminated roof sheathing with substantial mold or mildew buildup, improving the ventilation becomes secondary to repairing the damaged areas first.

The most economical answer to this ongoing problem is to ventilate the attic and it must be cut-in properly. Moving air through your attic will absolutely reduce the temperature in this cavity. Most homes have passive attic ventilation in the form of a ridge vent at the peak of the roof, soffit vents in the lower outer eave areas and gable end vents at the top outside gables of the home, or some combination of these vents. Turbine and or roof vents (passive vents that penetrate the roof) are often used as a simple fix for older roofs with inadequate ventilation. The problem with passive vents is that they require some driving force - wind or temperature differential (hot air rising) - to move the hot air within the attic. Usually the hottest days of the year are the stillest, with little or no wind. Temperature differential doesn't have much energy, so it is slow. Just when you need venting the most, the vents work least effectively. There is also the installation problem. If your roof cavity was designed without sufficient attic ventilation, adding additional passive vents may be impractical.

 

There are two types of air vents that I will always highly recommend: 1.) inlet air vents, also known as Soffit vents and 2.) outlet air vents, also known as Ridge vents. Having only one or the other type of vent is the equivalent of having neither vent at all. Therefore, to obtain proper attic/roof ventilation, both types of vents must be present, and in equal amounts of net free air flow.

Another very important detail to these particular vents is to make sure there are fire-proof Styrofoam baffles properly installed between the insulation and the roof sheathing. These baffles will help maintain the air flow by preventing the insulation from blocking this vent area. See "STYROFOAM BAFFLE".

 

1.) SOFFIT VENT - (Allows outside air to enter the attic/roof cavity)

proper attic ventilation

 

 

2.) RIDGE VENT (allows air to properly exit attic/roof cavity)

ridge vent

 

If your house does not have the soffits or overhangs and your roof stops at the outside wall, you can vent the lower edge of your roof with a “starter” vent also known as a “drip-edge vent”. This will perform just as well as a soffit vent, but remember to install the baffles in order to prevent the insulation from blocking the incoming soffit ventilation.

DRIP-EDGE VENT

drip edge vent

 

PROPER INSTALLATION OF THESE VENTS AND BAFFLES WILL RESULT IN PERFECT AIR FLOW THROUGHOUT THE ATTIC/ROOF CAVITY.

properly venting an attic cavity

 

 

This is what happens to your roof shingles, if your attic ventilation is compromised.

The shingles are literally curling up due to the hot attic cavity (below) performing like an oven and baking these shingles until they crumble.

shingles atop an unventilated attic

 

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Last updated on  Jun 08, 2014