Roof Replacement Confusion

I am in the process of getting estimates to have my roof replaced. I have contacted 6 contractors/roofers to provide estimates. Four have been out to look at my roof so far. Below are some comments provided that are causing me some confusion. Additional advice would be helpful.
1. I currently have an attic ventilation fan on a tstat and gable vents (no soffits and no ridge vent). I thought getting a ridge vent installed would be a good thing, but I'm getting conflicting advice. One contractor has said that a ridge vent works best with soffit vents (I have no soffits), and that a ridge vent in conjunction with an attic fan would cause a cooling effect primarily in a narrow zone between the ridge vent and the fan instead of the fan drawing from the gable vents. A couple other contractors, when I mention this, have basically said not so; that the more ventilation the better. Comments or advice?

2. The last contractor to visit me evidently walked my roof and found the sheathing to be very weak. He said the rotting most likely due to moisture/humidity in the attic during the winter months. He said if I were to go in the attic in the winter, I would possibly see small icicles hanging off the roofing nails. He suggested that they place a new layer of sheathing over the existing layer before reshingling. Said this would provide additional insulation, and be cheaper due to avoiding labor of removing old sheathing. I was concerned about the added weight which he said should not be a problem. None of the other 3 contractors so far have commented on this issue. Comments or advice?

Thanks!
Irwin

 

With regards to the ventilation.....Ridgevents are useless without soffits.

Technically, if you use a ridgevent/soffit system (considered the best by the shingle manufacturers) you will need to close up the gables.
Having gables affects the performance of the ridgevents by taking away the "negative pressure" where the ridgevent pulls air out of the attic.

It can be argued that "the more ventilation the better", but it is not technically correct. Some ventilation affects the performance of other ventilation.

The roofer is also correct about the fan. The fan would merely pull air IN through the ridgevent (ridgevent is used for OUTflow) and out the fan. That would not ventilate your attic properly.

Good luck

 

I'll second the comments by Delirious... There has to be the proper relationship between inflow and outflow for the ventilation to work properly. Your roofer knew what he was talking about, and the other guys need to brush up on their ventilation knowledge.

With respect to sheathing - it's easier (and therefore cheaper) to place the new plywood over the old, but I would recommend tearing off the old before replacing with new. As for the contractors that didn't check the status of the sheathing, get rid of them - they didn't do the basic homework that they should have done.

Hopefully, the guy that talked to you about the ventilation was also the one who checked the sheathing.