Guide to Attic Ventilation

Verify Before Ventilating
the Attic Space
Roof Equipped With
Other Attic Ventilation Products
Sloped Roofs with
Blocked Soffits
Sloped Roofs With
Limited Attic Height
Roof With
Dormers
Roof With
Asymmetric Slopes
Cathedral
Roofs
Mansard Roof
Lacking Adequate Aeration
Conventional Roof
with Turbine Vent Problems
Flat Roof
Ventilation
Verify Before Ventilating
the Attic Space
Roof Equipped With
Other Attic Ventilation Products
Sloped Roofs with
Blocked Soffits
Sloped Roofs With
Limited Attic Height
Roof With
Dormers
Roof With
Asymmetric Slopes
Cathedral
Roofs
Mansard Roof Lacking Adequate Aeration
Conventional Roof with
Turbine Vent Problems
Flat Roof
Ventilation

Verify Before Ventilating the Attic Space

Verify Before Ventilating the Attic Space

  • If the vapor barrier has been built into the home or building. Should there be any holes allowing moisture to escape, seal it shut.
  • If the attic insulation is sufficient and conforms to local standards.
  • If the soffit vents are vented, communicate with the attic space and are unobstructed.
  • If there are any HVAC ducts located in the attic space; if so, they should be insulated and none should be left bare.
  • If an attic access door or partial wall has been insulated according to local standards.

Steps for Installing a New Ventilator

  • Choose a ventilator that is adequate; avoid seemingly comparable substitutes that have not been tested nor approved by a reputable firm for their air drawing and exhausting capacity, durability and safety features. For help with this step, visit our online calculator.
  • Install the ventilator that is adequate for the specific location, the head being exposed to all directions of wind and the louvres rising above the peak of the building by 6 inches. The hole of the vent should be unobstructed and located between two rafters.
  • The base of the ventilator should be well weatherproofed using roofing cement sealant as per manufacturer installation requirements.
  • Make sure that the soffit vents are open and that insulation is not obstructing the openings.
  • Make sure that all other types of roof vents (such as ridge vents or turbine vents), other than the Maximum ventilators and the soffits, are condemned and well sealed. The goal is to create good air circulation from the intake source to the peak where the Maximum ventilator is located, ensuring efficient attic ventilation.
  • Avoid installing a vent near a parapet, wall, or a device that is higher than the ventilator.

Roof Equipped With Other Attic Ventilation Products

Roof Equipped With Openings Other Than Soffits or Roof Vents

It is very important to seal all openings that would allow air to enter elsewhere other than through the soffits. If this is neglected, the openings located at the rafter level will inhibit ideal air circulation, which starts at the bottom and rises. The air that comes in through these openings will be drawn up by the Maximum ventilator, limiting the circulation to the rafter and upper roof area only.

Roof Equipped with Shingle Roof Ventilators

Shingle roof vents do not produce a chimney effect. Their effectiveness is limited to evaporation. These types of exhaust vents also present a definite risk for snow or water seepage. Above all, as soon as snow accumulates and covers them, they become useless just when they are needed the most. The effectiveness of one Maximum vent is greatly superior to that of four shingle roof vents, with no risk of becoming ineffective because of snowfall accumulation or penetration.

Sloped Roofs with Blocked Soffits

Sloped Roof Soffits Blocked by Walls

Shingle roof vents do not produce a chimney effect. Their effectiveness is limited to evaporation. These types of exhaust vents also present a definite risk for snow or water seepage. Above all, as soon as snow accumulates and covers them, they become useless just when they are needed the most. The effectiveness of one Maximum vent is greatly superior to that of four shingle roof vents, with no risk of becoming ineffective because of snowfall accumulation or penetration.

Sloped Roof Soffits Blocked by Insulation

It is extremely important for the soffit vents to be totally unobstructed in order to allow the exterior air to pass freely. The combination of soffits and the appropriate Maximum ventilator, strategically placed, provides a chimney effect that uniformly sweeps the attic to eliminate all heat build-up or humidity.

Roof With Warm Air Vent in the Attic or Near a Soffit

With the presence of a hot air vent discharge in the attic or close to a soffit, moisture is drawn back into the attic forming condensation. This may causes serious damage to the attic and insulation as well as possibly creating ice dams on the roof. To correct this problem, Ventilation Maximum recommends the installation of a terminal exhaust unit located directly on the pitch of the roof or at a safe distance from the edge of the soffit vent. This prevents the possibility of exhaust heat, coming from the living spaces, to warm up the attic and either creating condensation on the roof deck or roofing nails or melting the snow accumulated on the roof, creating ice dams.

Sloped Roofs With Limited Attic Height

Sloped Roofs With Limited Attic Height

Ambient temperature and humidity rise rapidly in any attic with a limited attic space. The solution is to increase ventilation, making sure that there are no openings other than the soffits and the Maximum ventilators, positioned at the most upper location on the roof at the gable.

Roof With Dormers

Roof With Dormers

Dormer windows, being located at the soffit level, reduce the air intake because of the loss of soffit space. In this case, Ventilation Maximum recommends the installation of a special product: our 50% Soffit enabling adequate ventilation to this problem area. It is also preferable to position the vents on the side of the roof opposite the dormers. This type of building requires installing a Maximum Ventilator for every 600 square feet of insulated ceiling.

Roof With Asymmetric Slopes

Roof With Asymmetric Slopes

The soffit on the side of the shortest slope be 50% blocked, leaving the soffit of the opposite slope completely open. This balances the chimney effect and makes ventilation more efficient due to the joint action of the soffits and the Maximum ventilator. Drawn air enters and circulates evenly; the ventilator then uniformly exhausts excess humidity and heat from both sides of the roof.

Cathedral Roofs

Gable Roof Having One Cathedral Ceiling

Since the side with the cathedral ceiling is more difficult to ventilate, leave the soffit 100% open on this side and install Maximum ventilators on the non-cathedral side in order to pull the flow of air to its direction. Partially obstructing the soffit on the non-cathedral side produces a balanced attic ventilation. This type of building requires installing a Maximum ventilator for every 600 square feet of insulated ceiling.

This type of building requires installing a Maximum ventilator for every 600 square feet of insulated ceiling.

Cathedral Roof With Trusses

A cathedral roof with trusses results in a limited attic height of 12 to 16 inches. The Maximum ventilator must be installed at the gable of the roof with a two-sided ridge flashing. It is necessary to keep soffits unobstructed and to ventilate from the roof’s peak to maintain even air circulation. Install a Maximum ventilator model # 301 for every 600 square feet of insulated ceiling.

The Solution to Cathedral Roof Problems

For cathedral roofs the Maximum cathedral system is absolutely essential. Given its superior drawing capacity it evacuates a large amount of hot, humid air. In addition, because of its height, you can always be assured of its efficient performance as it will never become covered by snowfall. An insulated duct, designed to the exact pitch of the roof, is installed along the entire length of the roof’s ridge. This will ensure sufficient ventilation is pulled between each roof joist. Air is drawn in through the holes of the soffit vent and up between each joist before being evacuated by the Maximum ventilators.

Mansard Roof Lacking Adequate Aeration

Mansard Roof Lacking Adequate Aeration

Inadequate aeration through the soffit may be caused by a piece of wood or brick at the junction of the mansard and the roof which is blocking air passage. Ventilation Maximum recommends using its special products installed near the edge of the roof; the mansard fresh air intakes or a roof intake vent model VMAX AT-1 OR VMAX AT-2. The mansard intake vent, being positioned directly at the edge of the mansard and the roof, allows for ventilation in both the mansard roof and the attic space.

Conventional Roof with Turbine Vent Problems

Conventional Roof with Turbine Vent Problems

Is your turbine vent causing problems? It’s noisy, stop operating in freezing rain, and lets in water and snow! Here’s the solution: Ventilation Maximum manufactures replacement heads to exchange those noisy and defective turbine vents.

A very simple installation is required:

  1. Remove the screws from the existing turbine
  2. Remove the old turbine vent and
  3. Install the VMAX-401 by securing it over the existing hole. Our adapters make it easy to install.

Most old turbines can be replaced whether it is 10, 12 or 14 inches in diameter, leaving in its place a ventilator that is quiet, efficient, reliable and safe.

Flat Roof Ventilation

Multi-Level Flat Roofs

The ventilator heads must always rest higher than the surrouding parapets in order to be exposed to wind from all directions. The ventilator heads must be uniformly leveled: they must be installed at an identical height. Never install two different models on the same roof. Never position a Maximum ventilator close to a parapet, a wall or an adjacent device that is higher than the ventilator.

Positioning of Ventilators on Flat Roofs with or without Soffit Air Intake

The location of the ventilators on a flat roof is of the outmost importance. Positioning of ventilators on flat roofs with or without soffit air intake: Divide the roof area by the number of ventilators required according to manufacturer’s standards and install Maximum ventilators at the center of each of these divisions.
A ventilator should never be installed any closer than 6 feet from a wall or unit which is as high as the ventilator itself.
The opening within the wooden curb will determine the Net Free Area (NFA) for model VMAX-101, 201 and 102.
It is important to measure the free air space between the underside of the roof deck and the insulation to determine the right model of ventilator. It is also important when ordering these ventilators that the size of the wooden curb (exterior), as well as the thickness of the roof membrane being applied on the wooden curb be considered to ensure the right dimension of the ventilator.