The importance of ventilation?


#1

after the winter we have had in the northeast, we came across many situations with laeks that were the result of “ice dams”. after having experienced and ultimately going through the process of investigating the cause for these particular types of compromise in the roof integrity :smiley: i now believe that ventilation is not only vital, but there is almost a bit of a science behind it?


#2

You said the V word…

/e hides


#3

proper ventilation and ice & watter shield = no more problems


#4

There is quite a bit of established science and research behind ventilation theories.

Many people don’t understand the scientific principles involved though.
Or they may leave key things out to promote there beliefs.

In a cold climate ventilation is needed to help prevent ice damming, insulation plays a large part also.
Ventilation also lets humidity from the home escape so that condensation doesn’t occur.

The broad theory of roof ventilation applies in different ways for different structures.
A ventilation system that is ideal for one structure may not work in another.
In some cases ventilation is not needed at all.

An example: My home has very good ventilation, ridge vents and soffit vents.
There is also gable vents, they are not plugged up.
My roof is a straight gable, no valleys, no walls.
No ice damming at all, ever.

Standard ventilation theory says that my gable vents should be blocked off for this system to work correctly.
This obviously is not the case because it works very well as is.
If I were to plug up my soffits, I believe that it would be a different story.
I think that I would get ice damming if I were to plug up my ridge vents also, this is an educated guess.

The most destructive results of poor/non existent ventilation are ice dams and condensation.
This is why ventilation is important in cold climates.
I personally am not a big believer that it affects the shingles that much if at all.


#5

Tar doesn’t know what he is talking about.

Me, I just advocate putting a nice, big, blue tarp up on your roof over the winter.

Then again, I’m in Texas & we don’t worry much ‘bout freezing down in my neck o’ the woods.


#6

try here…buildingscience.com/buildingphysics


#7

I didn’t check out that particular link, but am familiar with the site.

I know that Joe Lstiburek has many things to say about not needing ventilation and that closed cell foaminsulation and a non-ventilated system are better performers, but read all of the lines to look for exclusions to his theories and disclaimers.

Proper Balanced Ventialtion works in my area where I install roofs. Period!

I have personally seen way too many roof decks and shingles completely prematurely burned out or degraded over tha past 2 1/2 decades to completely agree with a tight building envelope theory.

Firstly, with todays construction specifications and quality, or lack thereof, of installations and building, i believe it is unrealistic to consider that this structure would be achieved on a regular basis, during real world construction site environments, without paying substantially for the additional efforts.

This is a better link, by the way.
www.buildingscience.com/systemsapproach … ain_topic/

Ed


#8

I agree with that Ed…
I listed the link only to give a source for technical data relating to soffit/ ridge ratios etc, that are listed in other location on that site, as well as
other building envelope issues, and the options for solutions to those problems.

David


#9

Axiom, same here, I have 54 ft. of ridgevent, 54ft.X 2 of continuous soffit vent and a 6 sq ft gable vent on each side of the house. You will never find aan icicle or ice dam on my roof.

actually, venting a roof is about #4 on the list of reasons you have ice dams or icicles.

  1. geographic location
  2. direction roof faces
  3. shingle color
  4. ventilation
  5. slope of roof

#10

1. geographic location
2. direction roof faces
3. shingle color
4. ventilation
5. slope of roof

Not for nothing but what does “shingle color” have to do with ice damming?!
:shock:


#11

He has taken that right out of one of Rose and Tenewolds documents, relating to “Roof Surface Temperatures” comparisons in several different geograpic climates, in relation to which offers more bang for the buck versus ventilation affecting the “Roof Surface” temperatures.

Their point they were trying to establish in those documents, was that shingle temperatures are affected more by shingle color and orientation to the sun and the other items he listed, which they presumed to debunk the theory that ventilation is relative to warranty length and longetivity.

The papers are discussing “Roof Surface Temperatures”, not internal temperature climatic conditions in the attic and the living quarters.

The color is irrelevant in regards to ice-damming, especially if the home is under 6" to 12" of snow.

Ed


#12

I beg to differ, shingle color has quite a bit to do with ice damming. Any roofer who lives in Michigan and is roofing a house in the winter, to get warm will lay on the dark colored shingles because the sun will warm up the dark shingles. The sun will not warm up the light colored shingles.

Dark shingles, when the sun hits them, will melt the snow on the roof ALOT faster…even when the temp outside is below freezing. Unlike a light colored shingle will not melt the snow on the roof. The melted snow on the dark colored shingles will run down the roof and either freeze back up when the water hits a shaded area OR when it hits the edge of the roof at the soffit, where the air has cooled the roof. hence, causing an ice dam.


#13

I will agree that black or any dark shingle which is relatively exposed to the sun and only has remnants of snow on them, being mostly exposed to the sun, will cause more roof surface heat, which in turn will more readily melt and steam off of the roof surface.

But, to put shngle color as more imperative than ventilation is inaccurate, in your list.

Ed


#14

ed, I don’t really think so, lets more forward to the middle of the summer. if you have 2 of the same houses, same venting, and on one you have a black shingle and the other is a white shingle, the black shingled house’s attic will definetly be hotter than the white shingled roof’s attic.


#15

I can’t pull the source, but it may have been Air Vent, but the temerature spread between a true white roof versus a true dark black roof, not considering ventilation, is around 40* inside the attic.

Now put proper balanced ventilation on the black roof and the temerature spread is only about 10*.

Like I say, I don’t have the publication that proves this readily handy, but I don’t recall it being from a company marketing promotional material.

Ed


#16

Ed, thank you VERY much for that ‘improved’ link. I’ll have some reading to do for quite awhile to come.


#17

Ranch,

Make sure you click on all of the different tabs, or if you can get to the site map instead.

That place is loaded with info, but not organized in a way that you would know it on the home page glance.

Check out Joe’s 10 Things for a little Southern and Northern humor.

The other guys link was not active and still would have brought you to the right place, but not the page that zeroed in on the related documents.

Here is Bay’s original link:
buildingscience.com/buildingphysics

Ed


#18

Most roofs are white in the winter.


#19

[quote=“ed the roofer”]He has taken that right out of one of Rose and Tenewolds documents, relating to “Roof Surface Temperatures” comparisons in several different geograpic climates, in relation to which offers more bang for the buck versus ventilation affecting the “Roof Surface” temperatures.

Their point they were trying to establish in those documents, was that shingle temperatures are affected more by shingle color and orientation to the sun and the other items he listed, which they presumed to debunk the theory that ventilation is relative to warranty length and longetivity.

The papers are discussing “Roof Surface Temperatures”, not internal temperature climatic conditions in the attic and the living quarters.

The color is irrelevant in regards to ice-damming, especially if the home is under 6" to 12" of snow.

Ed[/quote]

That was precisely the point I was trying to make earlier. Now, due to an excessively “Hot” attic, which is not properly ventilated, the upper regions DO melt off quicker, but due to the internal heat emmanating through the roof and not due to the hidden under snow, roof shingle color.

Now that the upper 95% of the roof has finally melted off mostly, then the darker color of the shingle could become a factor.

Sean, you said it yourself, that if a worker in the middle of winter were to lay down on the black shingles, they would feel the warmth. Well, for them to be able to do that, the snow is already melted off of the roof.

Ed


#20

Yes, I said that, but 9 times out of 10 times, my scenereo is correct, because,

  1. the wind will keep the snow off the top of the roof so some shingles are always exposed and

  2. if the snow covers the whole roof, then the snow is usually covering the roof vents, making them obsolete anyways.