In this exterior roofing comparison report we’re going to take a look at the main differences between a ridge vent and a box vent, as well as explaining exactly what they both are. If you’re a homeowner having a new roof installed or replaced and you’re not sure if you should be installing ridge vents or box vents (or both) as part of your roof insulation then read on.
Roofing professionals know that an efficient attic space ventilation system is crucial to the longevity of roofing material of any kind. Why? Because it conquers the two main enemies of a healthy roof – heat and moisture. Ridge and Box vents are used to ventilate (or exhaust) old hot air from inside your roof to outside.
Ridge and box vents are both a type of exhaust vent. Pro roofers consider roof ridge vents as essential. Indispensable. Box vents are not.
But if the roof is exceptionally large, with long distances from the peak of a roof to the eaves, then box vents are useful in assisting in venting heat and moisture.
Very few roofs are constructed with box vents and no ridge vents.
You will also need other types of vents to ventilate (or intake) cool air from outside to inside your roof. These include soffit vents, gable vents and fascia vents.
Best practices – and most roofing material warranties – require 1 square foot of ventilation for every 150 square feet of roofing surface. So, for example, if you have a 2,000 square foot home with 2,400 square feet of roof surface, you’ll want 16 square feet of ventilation.
50/50: Half the ventilation should be intake soffit vents beneath the roof eaves (preferred) or gable vents in the gables, if the roof doesn’t have soffits.
The other half should be exhaust ridge vent or ridge vent plus box vents at or near the roof peak. As hot, moist air naturally rises and exhausts out ridge and box vents, cooler, drier air is pulled in through soffit vents. And the attic remains healthy.
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WHAT ARE RIDGE VENTS?
Ridge vents are hard plastic vents about 12 inches wide and around 1 inch high. Most are 48 inches long. They are constructed of hard plastic formed with openings to allow air the vent laterally out the sides.
Ridge vents cover a narrow gap of about 4 inches that is left in the roof deck at the peak of the roof to allow heat and moisture to escape.
WHAT ARE BOX VENTS?
Box vents are rectangular, often square, metal vents that are installed over a hole cut through the roof deck into the attic.
Most box vents, and those we’re discussing here, are “static,” which means they don’t have moving parts such as a turbine or electric fan. They allow warm air to rise and escape the attic. The vent has a solid top with venting on three sides – not the peak side.
A standard box vent has 50 square inches of ventilation, the number used when determining the number of vents used to meet the 1 square foot of ventilation for every 150 square feet of roof.
You will see box vents referred to as low-profile, flat, and turtle roof vents.
OTHER DIFFERENT TYPES OF ROOF VENTS
Box and ridge vents are common options for air extraction but they are not the only type of vent. Other roof vents include off ridge vents, powered vents, solar powered vents, roof turbines (Whirlybirds) and cupola vents.
ROOF VENT INSTALLATION
Ridge vents are nailed to the roof deck at all roof peaks and are typically covered with shingles to blend with the roof, but roof installers must take care not to cover the ridge ventilation.
Most asphalt shingle brands make specially designed ridge and hip shingles, but standard shingles can be modified for use in covering ridge vent.
As noted, the roof deck stops just short of the peak, leaving an opening of about 4 inches for hot, humid air to escape through natural convection. The best method is for the gap to run the full length of the peak, covered by vent, but some builders stop it 6-10 feet short of the end of the peak. There’s no good reason for this other than a little corner-cutting for cost-saving purposes.
Box vents are placed in the roofing field usually within a few feet of the peak. Spacing varies from about 8 feet to more than 20 feet based on the total size of the attic being vented.
The vents might be flashed, and roofing glue or caulk is used to help prevent leaks around the vent base. A good roofer will cover the top and side edges of the vent base with roofing material for additional protection against leaking.
BOX VS RIDGE VENT COST
There are several roof vent manufacturers across the US and your local roofing constructor can include them in their quote or you can buy them from big box stores like Home Depot or Lowes.
Ridge vent costs $2.50 to $4.00 per linear foot for the vents and nails. With pro installation at $40 to $80 per hour, the total cost typically comes to $7.75 to $14.00 per linear foot, or $385 to $700 on most homes.
Box vents cost $17 to $35 for the vent. Installation is more labor-intensive, so the total cost per vent at the same labor rate as ridge vent is $60 to $150 per vent. A typical 2,000 square foot single-story home utilizes around 10 vents for optimal ventilation, or a total project cost of $600 to $1,500.
LIFESPAN/DURABILITY
Ridge vents should last as long as your shingles. And they should be replaced every time the shingles are – so, 20 to 30 years on most homes. In that time, the plastic ridge vent can become brittle and prone to cracking, so replacement is recommended.
Box vents are constructed of metal, usually aluminum which is less prone to corrosion, or coated steel. Durability is better, so a ridge vent can be reused if in good condition and without rust. If the plan is to reuse them, roofers should be careful not to damage them when removing old roofing.
ROOF VENT MAINTENANCE
Both box and ridge vents are low-maintenance building materials. However, roofs should be inspected annually and after major storms, especially as they age, to ensure all materials including ridge and box vents are in good working condition.
Box vents must be checked to ensure that the caulk around them is in good shape and keeping water out.
If you have access to your attic, check for signs of water intrusion – staining, dampness or obvious water dripping – around both ridge and box vents. Make your inspection during or immediately after a heavy rain when leaks are more easily identified.
CONCLUSION
It’s worth repeating: Ridge vents are essential. Box vents are not.
But properly placed and installed box vents will improve the ventilation in any attic, the space below the roof. They are particularly beneficial – even recommended – on large roofs with more than 30 feet or so from peak to eaves.
Jamie Sandford is the Chief Editor at RenoCompare (