How Much Ventilation Is Needed for a Flat Roof?

Balance

• You need to find the correct balance when ventilating a flat roof. If your roof doesn't have enough ventilation, moisture and condensation can build up in the roof and cause it to rot. However, if you have too much ventilation, you'll lose heat from the home and may have a difficult time staying warm without paying exorbitant prices for your heating system.

Moisture

• The main purpose of ventilation is to remove moisture from the air. Moisture damages the roof and, if left unchecked, will eventually destroy it. Thus, the amount of ventilation you need is the amount that will remove most moisture from the air. If the ventilation is not sufficient for this purpose, the moisture will have the same effect on the roof as if there were no ventilation at all.

Type of Ventilation

• To ventilate your flat roof, put openings on the inside of the roof as low as possible and connect them to vents on the top of the roof. The inside openings, called intake openings, allow air to travel through them and then out of the house. In addition, the ventilation system should be designed so air flows throughout the entire roof rather than only through some parts of the roof.

Insulation

• Most flat roofs are not insulated. However, if you're concerned about your house being cold during the winter, you can install insulation beneath the roof. Peat moss and sawdust are effective insulation materials. When insulating the roof, consider that insulation may absorb moisture and get wet, ultimately making the ventilation less effective.