please explain this about Maximum vents : Any openings other than Maximum Ventilators or the soffits must be completely sealed.

This was taken from the website. what i dont get is the way i see it the more ‘‘holes’’ you have on you roof, the better is the ventilation, no?

maxi vent.jpg

The ratio of the upper to soffit vent net opening needs to be around 1:1.
The soffit openings can be more than the upper vents but not the other way around.

No. Absolutely untrue.

I agree.

The idea is to let hot air and moisture out of the attic. Placement and types are very important to achieve a balanced effect.


If the upper vents openings are larger than the soffit openings, the upper vents will draw from themselves, and not through the soffits.

I’ve been told many times that the general guidline is 1 roof vent per 300Sq Ft of attic “floorspace”. Does anyone know if there is a similar guideline for soffit venting?

Soffits are to allow the escaping air to be replaced. The airflow capactiy must be balanced between intake and exhaust vents. In general the NFA (net free area) of intake (soffit) venting should be equal to or greater than the net free area of exahust venting.

My understanding is that any other roof openings other than the Maximum (s) ventilator must be sealed but not soffits.

Below is what I report when a Maximum vent is present along with other roof vents:

· **Improve: **When a Maximum type roof ventilator is installed, other roof vents be sealed. More info at:


This ia a good graphic and it just about sums it up!

Patrick, as you know, warm air flows up as heat rises, in through weap holes joining air from soffits which grabs all humidity it can carry as it races to the exterior through the maximum which by itself creates a chimney effect.
All this is gravitational and non mechanical.

If lateral vents are not blocked, then the air goes through laterals and out through the maximum leaving walls and soffits non ventilated, therefore the conditions may deterriorate, the roof surface will not last as long and so on!

Salut, :slight_smile:

Makes sense, thanks

More thoughts … Roy

More Info… Roy