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How Much Ventilation Does a Warm Flat Roof Need in NY?
June 10, 2020

Anyone that has ever stepped foot inside an attic whether for any period of time knows how much heat build-up there is.  One of the most important cost savings aspects of a roof is that it can decrease your utility bills by providing more efficient insulation to the whole house. This is only possible because of roof ventilation and the best roofing companies always incorporate proper ventilation.

All-day in the summer the sun beats down on your flat roof, absorbing the heat and passing it through to the deck and insulation, Inevitably some of this heat gets through and is trapped in the air separating the home from the roof. The opposite is true for the winter, and without ventilation, the lifespan of your roof will decrease and repair costs will certainly increase.

Why do flat roofs need ventilation?

Your flat roof needs the ventilation to keep, more or less, the inside of the roof the same temperature as the outside. This is the easiest way to prevent condensation, and there we are all aware of how much damage moisture can be to a roof.  Imagine taking a warm bowl of soup, covering it with plastic wrap and putting it in the fridge, very quickly there will be condensation that accumulated on the bottom of the plastic. A similar situation can happen with roofs and this is more true in the winter when we are not thinking about the outside heat.

This is even more true for something called cold flat roofs, which is when the roof insulation is below the deck and the outer material. Cold flat roofs are more common as on ad-on, and new constructions typically have the superior warm flat roof, where the ventilation is above the deck but below the outer materials.

How much ventilation?

How much ventilation is needed is not a set answer. This depends based on climate, building type, size, residential, or commercial. In some places, building codes require a 50mm gap between the insulation and the deck of the flat roof. The best is to discuss these options with your local flat roofing experts who know the local regulations and what works best for your specific climate and building styles.

What is always used for flat roofs are a thermal control lawyer and a vapor control layer:

  • The thermal control layer goes on the top of the bottom layer of the roof.
  • The vapor control lawyer goes on the bottom of the top lawyer of the roof.

Together these two promote airflow, prevent moisture from condensing on the roofing materials, and help direct their air to the roof vents. This allows a more balanced temperature between the outside and inside air.

The roof vents are essential to maintaining the equilibrium. They are typically installed along the underside along the edge, or can extend vertically from the roof, and must be properly sealed to prevent moisture from entering where the vents meet the roof.


If you live in the Bronx then one of Royal Renovator’s locations is just around the corner. Call for an inspection to see if your roof’s ventilation is prepared for the summer heat. Royal Renovators Inc. 1231 Lafayette Ave, Bronx, NY 10474 (718) 395-5061 https://www.nycrenovators.com/

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