Placement of roof vents


#1

My attic currently gets pretty warm. I have run the numbers and will be adding more eave intake area to balance the system. My current roof has what I would call “box” style vents. On my house (and most others) I see these located on side of the ridge that is least visible. My main ridge runs north and south 10/12 pitch. The original builder choose to put the majority of them on the west side of the ridge as its less visible to most people. I’m getting a new roof put on and going slightly darker. I’m considering adding a couple on the east side of the ridge because.

To get airfow or venting your need a temperature difference. The roof deck facing west will be the warmest. I think this slows down/reduces air movement.
If there were vents on the east side of the roof they will be in the shade sooner and the hot attic air would be more likely to escape since the roof deck will be cooler on that side.

Current roof is only 11 y/o - just trying to fix it right the first time… this board has opened my eyes quite a bit.


#2

Many people favor a ridgevent. One of the reasons being that air passing across the ridge will help pull air out of the attic. If you don’t want to remove your current vents then I’d say you have the right idea. Add a couple on the other side of the roof and balance with some soffit or eave style vent.


#3

Hi,

Why are you replacing an 11 year old roof?

Hot air rises. Putting a vent in the shade will not pull the air. Leave them where they are. Maybe you need to add a couple.

If you think you need one on the front of your house. Add a power vent on the back instead.

Your attic will always be hot when it is hot out. It will always be cold when it is cold out.


#4

When we do a roof that has pot vents in it we remove the vents and sheet over the holes.
Then we cut a ridge slot and install ridgevent on all the ridges.
It takes a lot of pot vents to equal the venting capability of a continuous ridgevent.
Pot vents look tacky…
To get the house to breath correctly we often need to add soffit vents and rafter vents, it depends on the house and how it was built and insulated.


#5

Lefty,

The rate of air movement is related to the difference in air temperature between the attic and outside environment.

Ventilation Basicslink


#6

remember to balance that extra air flow with added insulation. adding cool air lowers cooling bills but raises heating bills.


#7

Hi Dennis,

So you are saying that a 750 vent will let out more hot air on the shady side of the roof?


#8

If the attic is properly insulated this is a non-issue.
All the parts of the system need to work properly.
Roof, siding, and insulation are all parts of weatherproofing your home and they need to all be done properly or you will have issues.
Insulators are notorious for plugging up vents…
In my area the current trend is to fix old houses ventilation problems by filling the attic with Icynene.
This is a rather new approach to my knowledge, and I don’t think it is going to work…
It is the insulators that are pushing this fix not roofers.
I think it is going to cause moisture problems.
I hope it works, but it doesn’t address the issue of humidity in the house.
Any thoughts on this?


#9

this its true. if eveything is done properly it is a non-issue, however it rarely is thats why this forum is here.
if you work with a good insulator who knows his trade and understand why the vents are there than that is a non-issue…
as far as Icynene thats not made for ventilation problems its for insulation. it also controls mold and mildew which is becoming a new fast growing issue.

they are probably freezing now that the roof has a bunch of holes in it. lol air flow the the only solution. we can argue the best way to get it all day long. airflow also equals energy lost thats tis function.

i am just saying as did you axiom, everything needs to work together. if you add air flow add proper insulation to balance the big picture.
how much energy a house looses is important to the customer also.


#10

I agree with you Hoss. :smiley:

I just quoted that because I thought the non-roofers reading this forum need to understand that there is frequently more work that needs to be done than just the roof.
Especially on the old houses.
A lot of people get what they think is a good deal on an old house only to find out later that it needs exterior work well into 5 figures…
They expected the expense of the interior work (because they can easily see it) and usually plan for it so the exterior expense is a shock to them.
There are a lot of houses in my area that have 3 layers of asphalt over cedar.
we call them “pigs”.
These are very nice homes, solidly built.
They need to be stripped (don’t you just love the sharp little rusted out nails left after removing the cedar :cry: ), they need rafter vents at least, a cold roof if they go for it.
They need to be redecked, they usually need extensive soffit and facia work.
They need new flashing which can be quite the pain in the butt to get under old clapboard siding…
And the chimneys need to be repointed or totally replaced…
The houses are all very close together and frequently cannot be roof loaded because of trees and power lines…
Throw in a nice turret or rounded roof and it gets expensive very quickly…

The people just called about a new roof…

All of the above issues need to be addressed for the roof to perform correctly.
All of these things need to be done at the time of re-roofing, not after…
It is a hard sell.
Then after all that they need to insulate it too.
You can see their eyes start to glaze over when you start explaining all of this to them.
Then comes my favorite phrase “can’t you just…”

I love my job, I tell myself that every morning.


#11

Thanks all.

I believe attic is hot because exhaust area is 1.7 times bigger than intake.- So I’m adding intake area.

Thought about ridge vent but my roof is hipped and has a lot of detail-all hand cut no trusses. The main ridgeline is fairly short. So probably not enough exhaust area with ridgevent.

Why am I replacing- poor materials, poor installation,- I lose a dozen pieces of hip and ridge EVERY winter. And when I replaced the LP siding a few years ago the siding co. nailed toe boards thru the roof in many places. They didn’t leak the first winter. Had the moss taken off and boy did I find leaks this past winter!

Oregon only 35 inches of rain/yr. Just continuous from Oct to April.