If the house has a leaking roof (most homes do), adding a vent without sealing all of the air leaks from the roof can make matters worse. The new crest-shaped ventilation grille contributes to the depressurization of the attic, and the result is that more air conditioning passes through roof leaks, increasing energy bills. In Lstiburek's article on roof ventilation, a key point is that there should never be more ventilation in the ridge than in the roof. I read that to the effect that if you don't have ventilation grilles in the ceiling, don't add ventilation grilles to the ridges.
The reason is that, due to convection and wind currents, the ventilation of the ridge will put the attic under negative pressure that sucks in air. If you have ventilation grilles in the ceiling, that's where the air will come out. If you don't have them, or if the ventilation grilles on the ceiling don't match those on the ridge, the air will come out of the house. It's air that you've already paid for to heat or cool it.
It's also likely to be loaded with moisture, which could cause condensation. I think you would be better off with equal gable vents than with an unbalanced ridge vent. If you place them in the lower part of the roof with a crest-shaped ventilation grille on top, air will flow through almost the entire roof covering, as will the ventilation grilles on the ceiling, and you will remove a lot of heat and humidity from the attic. The terrace ventilation grilles are a shallow wedge that goes under the tiles and covers a groove 1 (2 to 3 cm) wide to allow air to enter or exit.
If the source of the air entering the attic is roof leaks, then a larger ridge vent (or a new ridge vent where there was none before) worsens the situation. Depending on whether the ventilation grilles are placed in the ceiling, the path that offers the least resistance may be between the ventilation grilles located in the lower part of the ceiling and those in the upper part of the ceiling, or between the ventilation grilles in the ceiling and those in the lower part of the ceiling. Currently, the house has a 12 × 15 inch rectangular gable vent on each side of the house and a pair of small, mushroom-shaped roof vents. There are two gable vents, but one is covered by a flexible tube (the exhaust of the bathroom ceiling fan)).
The current roof has lasted 28 years with only two gable vents and about four metal vents along the 50-foot ridge. Adding ventilation to your porch roof would only be beneficial if you open the windows and exterior doors that lead to the porch. Eddie: The first thing is to open the ventilation covers on the outer eaves and check if the holes are cut and unobstructed. Even so, I recommend leaving a gap at the bottom of the installation and at the top of the roof, but even without ventilation, the surface temperature will drop considerably. Placing an exhaust vent in the lower part of the roof interrupts this airflow because the air will always follow the path of least resistance.
When inspected, there are 3 or 4 rectangular entrance panels that feed the vaulted ceiling from the outside, but the roof does not seem to have an escape (the two eyebrows of this roof feed from the attic that was sealed). I will be installing a metal roof in the coming months and, since I have the opportunity to do the ventilation properly, I would like you to tell me what it would be like. We have a garage from the 1940s (650 square feet) that was converted into an apartment with a cathedral-like roof and no ventilation grilles.
