In every region, warm air rises. Without suitable roof ventilation, the humid atmosphere that surrounds the top part of a commercial building has nowhere to go.  Several issues may arise when a commercial roof lacks adequate ventilation.

Why does a building require proper ventilation?

A building’s attic ventilation system works to allow any heat and accompanying moisture trapped in the upper part of the building to escape, especially in the summer months. At the same time, a proper ventilation unit prevents cold air from filtering to the inside. The balance of temperatures between the indoors and outdoors is achieved during winter by functional roof vents.

flat roof ventilation

A commercial roof ventilation system is crucial to keep the roof at a steady temperature. Without working roof ventilation, the following problems may occur:

Ice Dams

Ice dams are a consequence of inadequate roof ventilation during winter. The warm air that collects under the roof causes accumulated snow along the roof to melt. When snowmelt occurs in some areas of the roof but not in others, like the edge of the roof, then the melting snow can solidify into ice. Water accumulation and leaky patches are additional outcomes. The building’s roof is also at risk for collapse under the weight of the ice and water buildup that should have drained off under proper circumstances.

Melting ice dams pose as a property hazard. The water will leak into the attic, causing an influx of mould growth that will eventually compromise the rest of the property.

Water stains on the ceiling are a telltale sign that the roof has a moisture problem.  This is likely a consequence resulting from poor roof ventilation.

ice dam

Mould Growth

Along with heat comes moisture.  When heat is not directed away from the roof, moisture tends to build up.  Condensation pools in the attic, allowing mould spores to use the moisture as a feeding ground.  In a moisture-rich attic, mould will start to grow.  Mould spores can colonize along the roof within as little as 24 hours.

Mould growth in a commercial building is dangerous. Health hazards result from people breathing in scattered mould spores.  Also, the building’s structural integrity is compromised when mould eats away at the roofing materials.  This can lead to an outbreak of decay and rot.  Click here for more information on mould in attics.


Moisture causes metal components of the roof, like nails, to rust and potentially break — which can lead to shingle loss on commercial properties. The moisture caused by condensation on the inside of the attic can also rust things like plumbing, heating, and venting duct straps to rust and break.

rusted roof

Diminished Roof Life

Insufficient ventilation leads to a host of problems with the roof itself, often decreasing its lifespan. Roof deck warping, membrane degeneration and warping of the wood frame are all consequences of poor roof ventilation.  Building owners may also notice interior paint warping.  Insulation that has eroded is another outcome of inadequate roof ventilation. Overall premature aging of the roof accompanies poor roof ventilation in most cases.

Increased Energy Bills

The accumulation of heat in the attic space and along the roof will seep into the rest of the property. The building’s air conditioning unit will overwork, leading to soaring energy costs during the summer months. A strained AC system is also likely to fail in time.


Regularly inspecting and maintaining the commercial roof will avoid the host of problems associated with inadequate roof ventilation.  Roofing experts recommend a balance between air intake and air exhaust roofing vents to eliminate the emergence of potential problems.

Air flow throughout the roof

While the outflow of air is important, air intake ventilation is also necessary to provide optimum ventilation to the attic. On certain commercial properties, the air intake system is usually situated near the roof eaves and will provide continuous airflow. Several systems are available, including rooftop vents, under eave vents, vented drip edge, and mini louvers.

Air Exhaust

Continuous air flow out of the attic space is achieved with an air exhaust vent. Numerous vents are on the market, including ridge vents, power fans, turbines and roof louvers.  If you are unsure about which vents you require, consult a roofing professional.

What are some common commercial ventilation systems?

1. Mechanical Ventilation
Modern buildings will usually have mechanical ventilation systems installed to make up for the tightness of the building envelope.  These systems usually include single-point or multi-point fans to remove air from the building.  Single-point fans aren’t recommended for a larger building because they only ventilate a portion of the building.  Multi-point systems can get costly because of the duct work that has to be installed room to room.

Mechanical ventilation runs frequently and can make your energy costs increase, especially in the extreme warm or cold months. While multi-point systems can properly ventilate buildings, many people install other ventilation systems like ridge or eave vents to decrease the amount of time the mechanical ventilation runs.

mechanical ventilation

2. Ridge Vents
Ridge vents exhaust airflow at the ridge to help prevent heat buildup and moisture accumulation underneath the roof covering. They can be covered over to blend in with the roof and are usually paired with eave vents to provide maximum ventilation. If installed without an eave vent, the roof’s airflow could be unbalanced.  This can lead to a variety of other problems. Many contractors believe that the ridge vent is the best type of ventilation for a building.

ridge vent

3. Gable Vents
Gable vents work well if installed with other vents and the higher they are installed, the more effective they can be. However, gable vents can’t be installed alone.  They have to be paired with another type of vent in order to have a proper, balanced airflow. The airflow from gable vents can be limited because they are installed under the roof deck which results in hot spots.

gable vent

4. Static Vents
These types of vents are basically holes in the roof that are protected to prevent leakage. They are installed in an even line across the roof and come in a variety of different styles. Some professionals think these are the best vents to use, but others think they are prone to leaking and should be avoided.

static vent

5. Eave Vents
These are paired with the ridge vents that exhaust airflow at the peak of the roof. Eave vents allow the intake of fresh airflow at the eave to help prevent heat buildup and moisture accumulation under the roof covering.

eave vent

6. Down Blast Roof Exhaust Fans are curb mounted exhaust fans available in both variable speed direct driven models and single speed belt driven models. Down blast roof exhaust fans generally exhaust the air out of the building and then push the exhausted air back down towards the roof. Down blast roof exhaust fans are better suited for relatively clean air streams.

Down blast roof exhaust fans are suitable for commercial and institutional buildings like hospitals, retails stores or warehouses. Down blast roof exhaust fans are generally a low cost efficient means for exhausting bathrooms and other ducted applications while maximizing protection from harsh weather conditions. The fan wheels in down blast roof exhaust fans typically feature a curved blade design and lower sound levels.

downblast roof exhaust

One word of caution

Depending on the property type, many building owners make the mistake of using residential ventilation products in place of commercial ventilation. These products don’t provide enough airflow to effectively ventilate commercial buildings.  Roofing professionals have the ability to inspect a commercial roof to look for signs of poor roof ventilation.

How much does it cost?

Many factors are considered when costing out a commercial ventilation system.  Items such as the number and style of vents required, piping to the roof, vent line supplies, and specialty equipment are a few to consider.  Some commercial roofs require different ventilation systems than others. A knowledgeable commercial roofer will recognize the differences and help a building owner design the right ventilation system.