Sorry for making my first post a long one but I wanted to get in as much detail as possible.
4 years ago I had a roof put over a mobile home and addition. The new roof is metal, 4:12 28'x52'. The old roof became what I suppose could now be called the attic floor. To keep the new roof as free as possible from vents the only vents extended through the new roof were the sewer vents.
The entire roof parimeter has soffit under the eaves (1'x50') and gables. There is also a 14'x30' unheated, uninsulated section with soffitting over a deck. Intake air wouldn't seem to be a problem. For exhaust a 1'x1.5' vent was placed in each gable end. Based on 1' for 300' (heated portions have a vapor barrier) this would seem to be ok.
In the last 3 winters I haven't seen any condensation problems so it must have been working. The problem I did notice this year was a heat build up during what was a rather hot summer compared to previous summers. Was this due to the gable vents being a foot lower than the peek?
I had planned to extend the vents upward but was convinced to add 2 12" turbine vents. From what I've been reading I should have researched before agreeing. The turbines were placed 18' from either end as close to the peek as possible. I guess the location was selected to let the gables handle the outside and the turbines the middle which is the main living space including kitchen and laundry area. Doing some digging around it looks like the turbines will use the gable vents as the inlet and not the soffit. I also think that there should have been 3 turbines instead of 2 and the gable vents should be blocked.
Both the trailer and addition are still vented so their intake air comes directly from outside. Given the amount of soffitting do you think the turbines attempt to pull air from the inside rather than from the intended intake?
I can either scrap the turbines and extend the gables or add another turbine and space them correctly.
I attached a sketch so it may be easier to see the lay out.
I personaly would get rid of all of them and add a ridge vent. This way the air is sucked in the soffits gets pulled though the rafter bays and out the ridge vent. It removes all the moisture and heat from the whole attic not just a circle.