Snow Photos On Roofs With And Without Proper Ventilation

Ed the Roofer

Can you guess from the photos which ones have adequate ventilation and a cold roof or which ones allow the heat to remain in the attic, causing ice dam problem potential?

FRONTAL VIEW OF HOUSE WITH HIP AND RIDGE VENTS.


RIDGE VENT AFTER FRESH 6" SNOW FALL


HIP VENTS ON SAME HOME AFTER 6" SNOW FALL


FULL HOUSE VIEW OF RIDGE VENT AND HIP VENTS.
SEE HOW THERE IS NO SNOW AT THE EXHAUST AREAS?

THIS HOUSE ALSO HAD 100% EAVE INTAKE VENTILATION PROVIDED FOR BY THE SMART VENT FROM DCI PRODUCTS INC.
THE RIDGE VENT BRAND IS THE SHINGLE VENT II FROM AIR VENT CORP.

NEIGHBORS HOUSE.


OTHER NEIGHBORS HOUSE

DrewD

Well Ed, I'm and engineering student and vented roofs are becoming a big debate issue especially with closed cell spray foam. I would say that since there is no ice hanging off your eaves you don't have a heat loss like the other house's. That is a direct sign of heat in a roof and the cause of ice daming. I personally don't agree with cold vented roofs and would rather see the under side of roof decks filled with spray foam. It adds 60% structural integrity, is water proofs, you don't stand the chance of having a heat loss and also you don't expose your attic to extreme temperatures ( cold in the winter, hot in the summer). Unfortunately code in many states require a vented roof. Hope this helps.

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oldfrt

I can tell you one thing about those last two houses,they are a PITA to ventilate properly.
They are very close in design to my first home,which was built around the late 1800's.
It had balloon framing and the exterior walls were not insulated,so all the heat that escaped into the walls shot directly up to the attic causing massive heat loss through the roof.
The attic had 2x6 floor joists under T&G,which was a bear to insulate.
The over hang was at such an acute angle that it was hard to cut the soffit out for venting.
Those two homes need some major work($) for the proper ventilation.
Not only is there this heat loss problem,but there is probably major condensation problems in those attics.

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neolitic

Okay then, so now you're heating/cooling your attic space as well
for free?
Then what happens to the gallon or two of water vapor
produced by each person in the house every day?
Still migrates through the lid into your un-vented attic?
Okay now you retro-fit an active ventilation system
for the whole house, and an air-to-air heat exchanger
to feed it.
For free?
Then someone still has to convince me that a shingled roof
isn't going to get fast cooked with out under deck venting.
(i.e. the heat is trapped in the shingle)
Suppose we could all switch to slate and metal roof,
that won't add any cost will it?
All this may be great in the long run,
but I'm not sure I can be the only kid on the block...

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oldfrt

I've got to agree with neolitic here.

Until the verdict is in on the close cell insulation installed in the rafters,I'll stick to what I know works.
Seeing that the shingle manufacturers recommend the proper ventilation for warranty reasons,there is no way I'd insulate this way.
I'm still replacing decking from the old style of putting fiberglass between the rafters because of moisture problems.
You car argue that the closed cell doesn't allow the transfer of vapor to the underside of the decking,but,as neo said,it's going somewhere.That somewhere is the attic area,trapped.Possible mold growth and /or moisture damage isn't a chance I'd be willing to take.
The thing about learning from books is that anyone can have opinion and print it,but what you see in the field is not always going to be what you were taught.
Hope this helps!

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DrewD

I can see where you guys are coming from and I've worked in the field on both, vented as well as unvented roofs. Most log homes have large open cathedral ceilings which consist of 2x6 T&G nailed to the top of log rafters followed by a 6 mil or greater poly vapor barrier and then foil faced insulation panels. The whole thing is sandwiched on top buy 5/8 to 3/4 CDX and then Roofguarded. There is no venting in this style of roof. You don't have massive outbreak of mold growth in these homes. If proper vapor barriers are in place (6 mil poly) along the bottom chords there should be minimal vapor transfered to the attic. This site has some good points on this topic http://www.advancedinsulationinc.com...am/default.htm.

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neolitic

Many houses are not log construction.
Most of them have drywall or plaster/blueboard ceilings
and separate attic spaces.
"Aye, there's the rub!"

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oldfrt

Hey Drew,
I looked over that site and I see where this has to be a system of components and restrictions;
Proper roofing material
Vapor barrier paint
Ventilation System
No walk in Attic or storage spaces
It sounds like it would be better for new construction,where all these factors can be taken into consideration in the cost analysis,but in older applications it would add too much to the cost because of the other factors that have to be addressed.

What I would really like to see is a chart of the cost/benefit over the long term as apposed to conventional fiberglass insulation.

That site only says:

So the question that needs to be asked, is do the benefits of the foam outweigh the additional expense? We believe so, when you consider the lower utility bills, increased comfort reduced amount of dust being driven through attic vents and into the house, and a healthier home.

If they" believe so",show me the monetary savings.

The extra cost of construction with recommended components,the added heated area,loss of a walk in storage area,so another storage area would be needed,have to be taken into consideration.

I can be sold on this system if I have all the facts.

Number one is $$$$!

Show me the money!!!

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theroofinggod

Then someone still has to convince me that a shingled roof
isn't going to get fast cooked with out under deck venting.


the above is true,the shingles will bake faster,and not last as long that way,as most shingles are bare asphalt underneath,and not protected from the heat which reflects back up under the shingles

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neolitic

I'm betting that this thread isn't headed where Ed intended

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Teetorbilt

My take is that if it's below 60*s and white crap is falling on you or your house, you should really think about moving somewhere else.

Tomorrows high is expected to be 78*. I'll be in my shorts, T-shirt and flip-flops. I may go wet a line, the Flounder are in and the Pompano are on the way.

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Ed the Roofer

Neolitic,

I had absolutely no intentions of anywhere this thread was going when I posted it.

Look at the time stamp. I was just getting done finding out what bugs my office computer picked up and could not gain access into any of the START Menu items.

3:19 am this morning.

I was bored.

Plus, I thought the picture, especially showing how the freshly fallen snow has instantaneously melted along the ridge vent profile, would be informative to many people who are always curious if the ridge venting works in the winter when it snows.

It positively and conclusively does. The old circa 1900 home in the photos just had 12" + of snow freshly fallen the day before, yet all of the ridge vent troughs are melted away cleanly for the proper exhaust flowage to be maintained.

The first pictures, where from a home I did a little over 1 1/2 years ago, which also had the uniqueness of Hip Ventilation added to the scope of work, along with insulation baffle vents and 100% continuous Smart Vent along all of the perimeter eave edges, and also with the jack rafters requiring to be notched for vertical air movement between each encapsulated rafter bay.

While I took those photos, I also took photos of neighboring houses, which were not properly ventilate, hence the extreme snow melting and radiant heat loss from those home photos.

Ed

edit:
This is not the forum I posted the circa 1900 home in. Thats how tired I was, that I couldn't even remember. Ed

Ed the Roofer

Here is the other house I was speaking about:

Ed



I have another home recently completed which has the Shingle Vent II Ridge Vent and the DCI Products, Smart Vent installed.

This one had a 12" snow fall on top of the roof.

If you enlarge the photos of the areas by the gutters, you will be able to make out the 7/8" high filtered portion of the Smart Vent Intake Ventilation System.

People unknowingly express concern about this detail, wondering if the vent will get clogged by ice and/or snow. This shows how the snow melt and potential ice damming effects are minimized.

For comparisons sake, I took a few photos of some neighbors roofs too.

Ed

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NOTICE HOW THE SNOW IS ALL MELTED BY THE RIDGE VENT UP TO THE POINT WHERE THE SOFFIT OVERHANG IS? THE RIDGE VENTILATION PRODUCT IS STILL RUN ALL THE WAY TO THE END FOR CONTINUITY AND COSMETIC PURPOSES THOUGH.


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Ed the Roofer

I notice that you only referred to vapor transmission. To be fair, I didn't have the inclination to check out that link yet, but I have done significant research on "Unvented Roof Assemblies" and icyene foam insulation applied directly to the underside of the sheathing, and I am not convinced.

Studies that these manufacturers and their legions use for justification, tend to talk about roof surface shingle tenperature and orientation of the sun and colors of the shingles being more important than a proper balanced attic/roof ventilation system being in place.

What they do not address, is the frying of the asphalt in the shingle from being super heated. Their is a specific temperature range, that becomes unacceptable for shingle life longetivity, which I believe is around 160* to 180*, but I would have to look it up to be accurately certain.

I just see it way too often, how the short sightedness of the HO and their previous roofing contractor left either the intake ventilation or the exhaust ventilation substantially inadequate.

Even if the roof top exhaust ventilation system is provided for correctly, it is the rule rather than the exception, that the intake is woefully inadequate. Without the proper balance and the washing effect from the air flowage from bottom to top, the underside of the deck sheathing and the interior attic temperatures will escalate.

Ed

POOLMANinCT

well?????? should I be proud I'm the last roof to loose the snow, on my side of the street.

I was reroofed last november, cobra ridge vent was installed.... should I have the old louvers (sp) open or closed?

ty
ray

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Ed the Roofer

Ray,

I am not sure what you are referring to when you said "old louvres".

Do you mean the old mushroom vents, (turtle vents), or do you mean the gable louvred vents in the upper apex of the siding, or do you mean the turbine whirlybird vents?

If any of those are being used as an exhaust vent, then you should seal them.

If you ar speaking about under soffit eave intake vents, then leave them open.

Yes, the snow on your roof means that your attic is providing the cold roof/attic assembly needed to minimize ice damming problems. It also probably means that you have good insulation, minimizing your heat loss from the internal conditioned living environment.

Ed

DrewD

I have a link to a study done in Las Vegas Neveda. In the study the maximum measured temperature of the plywood was 126 F well below the 180 F limit.
The article also has some very good data on temp in the unvented attics.
http://www.buildingscienceconsulting...ted_attics.pdf

Another very good article I believe should answer your questions is here.
http://www.homeenergy.org/archive/he...99/991111.html
It talks about unvented roofs in cold climates. In it he talks about asphalt shingles having a 2%-3% absolute temerature increase. While this will shorten the life cycle of the shingle, a 10% reduction in heating costs I believe would be a worthy trade off. Also the author talks about the disadvantages of shingles. I don't see where you get that you can have attic storage, if anything you have attic storage that is now inside your building envelope, warm in the winter, cool in the summer. The biggest problem with fiberglass batt insulation is the air leakage which directly results in heat/cooling loss. In a vented attic any air loss through duct work is lost the outside air. By bring the attic and the ductwork inside the building envelope that air leakage is still inside the occupied space. I can see where the upfront cost would scare most people, but with the rising heating costs wouldn't lowering heating/cooling energy consumption by at least 10% eventually offset the initial cost?

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Ed the Roofer

Before you posted this, I was researching this subject earlier today, but dang-it, my home printer is not working and I didn't save the link, since I figured I would be able to find it once I got into the office.

It was from some site that ended in .....NaturalVentilation.com or something similar.

The article dealt with shingle and attic temperatures also, but was even more specific about the break-down of the structural wood components in actual recorded testing due to the unventilated or under ventilated attic/roof structures.

Happy hunting if you can find it before I do. I like to collect as much information from both sides of the debate as possible, especially when they are from unbiased resources.

But, I looked up something I posted in the DIYchatroom forum last May 3rd and found this:

from buildingscience.com

Ed

Effect on Shingle Life


In general, shingles installed on unvented attic assemblies operate at a slightly higher temperature. This has impacts on the durability of roof assemblies. A 2 or 3 degree F. rise in average temperature is typical for asphalt shingles and a corresponding 10 degree F. rise in average temperature for sheathing (Parker & Sherwin, 1998; Rudd & Lstiburek, 1998; TenWode & Rose, 1999)

All other things being equal, applying the Arrhenius equation (Cash et.al, 2005), a 10 percent reduction in useful service life should be expected. This is comparable to the effect of the installation of radiant barriers. What is more significant to note is that the color of shingles and roof orientation have a more profound effect on the durability of shingles than the choice of venting or not venting (Rose, 1991) – double or triple the effect of venting/non venting.



P.S. I know what it says at the end, but the important related information is at the beginning of the first paragraph and the 10 % reduction statement.
Ed

Pavola

This article brings up a good point, though its one that the author leaves as kind of a side note. The dew point temp. and maintaining the relative humidity at 35% at 70 degrees F so that no condensation occurs.

Interior humidity levels are critical to avoid condensation under the roof plywood with un-vented roofs.
What happens when, and this is very common in cold weather climates, the interior humidity reaches humidity levels that are much higher than 35% and condensation begins to occur. How will it be dried out in such cases. HVAC systems along with humidifiers/dehumidifiers, air exchangers, etc. are all preventative measures then in this case and leave a biig unanswered question for the drying action needed if needed. I happen to think it's "when needed".

A W Smith

I have been to Las Vegas Nevada. I didnt see a single asphalt roof there. All tile.

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