I have a colonial house in the Boston area. After some measurements, my
attic temperature can be 40F higher than the outside temperature on a
warm day. This is in spite of ridge and soffit vents. There is 10-12"
of attic floor insulation and an air handler for the A/C in the attic.

I have questioned if I have enough venting area. My attic is about 1500
sq. feet, I believe I should have a total of 1500 sq inches of venting
(750sq in. for soffits and 750sq in. for ridge). According to my
calculations, I have about 900 sq inches of ridge vent and 1200+ sq
inches of holes for the soffit vents (many 7/64" holes in the vinyl
soffit). BTW, the attic volume is about 5300 cu. ft. in a ~ 5 pitch
roof.

The soffits appear to be clear (I can see daylight in the attic near
the soffits), but it still gets very hot. Also, in the winter the
hunidity is very high in the attic.

So, I am told it is a bad thing to install a gable vent when you have a
ridge vent.

Some suggestions I have had:
1) One contractor suggested stapling heavy aluminum foil across the
rafters to within 18" of the soffits and ridge to create a channel for
the rising air.
2) Install a solar powered roof fan near the center of the ridge (down
12-18")

Is there any way to measure the draft (maybe smoke, etc)? Has anyone
had this problems?
Any comments?
thanks, Jack