Is there such thing as over venting a roof?

Roofing/Construction Questions
#1

I originally had a cedar roof with 5 individual vents spread throughout the roofing.

I recently had the roof replaced with asphalt shingles so they removed the old roofing and the old vents and layed on plywood sheathing ontop of all the plank sheathing and installed ridge venting for ventilation

I was expecting them to keep the original vents along with the ridge vent but now with the all the additional plywood sheathing isn’t it going to make the attic more insulated and therefore needing more ventilation?

#2

The roofer tells me I can’t have both types of vent, is this true?

#3

One of the most Important Items on Venting is Balancing the Space .

Say half Your Roof Faces South - that side Gets Really Hot - so the Air comes in on the Cool Side -
runs straight Up to the Ridge as It gets Heated .

The South Side is Radiating Huge Heat Waves -
Hence the Cool Air never Enters the Bottom Soffits on that side very much .

You should have Larger and more Soffit Vents on the Hot Side - Sending the Cool Air Up the Underside of the Very Hot South Running Pitch !
After All It’s the Hot Side that will Fail !

#4

Your roofers saying your vents will short circuit. Your 5 roof vents would act as intake and the ridge exhaust. That would limit the air circulation in your attic to this area.

Now, not everyone believes this as you will soon find out. I will say major manufacturers of ventilation systems do not recommend mixing two different exhaust systems.

#5

I’ll also Add that My Attic Temp went from 165F
to 140F with Old Ridge Vent ( 18 yrs. ) vs. - New Ridge Vent and better Balancing - Now is 8-10 Degrees
above Ambient , Yeah !

Went from - 2 - A/C Units up stairs to - 1 Unit.

#6

As long as you got flow of air from soffits to ridgevent your happening… :mrgreen:

#7

We installed a roof with ridge vent and soffit vents years back. It was a ranch with 2 large gable vents on each end, the condensation was horrible!
We ended up taking out the ridge vent and cap over, it was fine ever since. Must of been fighting each other. Lesson learned

#8

Should have just blocked gable vents…

#9

I run across this from time to time and I try to expalin to the homeowner to use one or the other for the most effective ventilation. If they want to argue and tell me my business I just say ok how many vents do you want and where do you want them.

Your roofer is giving you the correct advice. Let the man do his job.

#10

I got warned about overventing – got a white IB roof on an old house, and they put in no vents at all (4:12 hip roof), and took out the one 10" vent that had been there.

A neighbor who used to work for NASA told me it was not as crazy as I thought, pointing out that the white “cool roof” product is a “high emissivity” material that actually works as a heat pump. It very effectively loses heat to a clear sky, day and night.

He was right. Turns out roofing is rocket science nowadays (he had dealt with this handling fuel tanks on satellites where heat loss causes a lot of condensation issues inside the tanks).

With the “cool white” high emissivity roof we get extra cooling under clear sky, especially on the north side, the one that gets least sunlight and is most exposed to the orth sky.

So the ex-NASA guy said, you definitely don’t want a lot of ventilation under a high emissivity cool roof, because the outside air circulating in under it will get cooled down and leave moisture behind, over and over.

He’s right – the roof deck will be 6-10 degrees colder than the outside air temperature during clear nights particularly on the north slope.

Of course this doesn’t happen on a cloudy night. Get a digital thermometer, one of those you aim at a distance, and compare the temperature reading you get from a clear north sky day and night, versus from a cloud deck – it’s amazing. No wonder these roofs get cold transferring heat out to the clear night sky.

Not real sure yet what we do want to do about ventilation. Ideally I’d find an active fan system with a control comparing the roof deck temp. and inside air humidity versus the outside air temp and humidity and some logic to do the dew point calculation – then only ventilate when the air coming in won’t condense water when it comes inside under the cool deck.

Might just do a dew sensor on the outside of the roof – if it’s cool enough to condense water on the outside, likely pulling outside air in under the roof would condense water there too.

Dunno yet. Rocket science. Hooboy.

Haven’t found anything that smart for sale yet, though it’s obvious and I’ve read about research buildings that do this.

#11

[quote=“skytech”]We installed a roof with ridge vent and soffit vents years back. It was a ranch with 2 large gable vents on each end, the condensation was horrible!
We ended up taking out the ridge vent and cap over, it was fine ever since. Must of been fighting each other. Lesson learned[/quote]

same here. i told the home owner we should not change the system he had in place (gable end vents) that worked well for the past 60 years and he had me add ridge vent with no soffit vent. (his brother told him he needed it) after it was installed there was a lot of condensation in the attic the next summer. se we ripped off the ridge vent and now its fine again.

#12

We just did a 200lf car wash, the old brushless ones, not the new laser kind. It had a ridge vent on it. We removed it, installed box vents and 4 power fans with humidistats because of how much moisture there is in there.