Ice Gaurd membrane

[Ed Fako]

The aluminum nail that pierced the copper flashing is lower on the galvanic chart and would chemically break down instead of the copper flashing behind the new siding, fyi.

But, the course of siding material would now lose its hold onto the structure due to the fasteners breaking down. The corrective action would be to advise the usage of copper nails wher they piece through the copper flashings.

Typically, there should not be a difference of greater than .15 in the anodonic chart to prevent galvanic corrosion from occurring.

Ed

Galvanic Corrosion Chart


Galvanic corrosion is the corrosion that results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte.
A difference in electrical potential exists between the different metals and serves as the driving force for electrical current flow through the corrodant or electrolyte. This current results in corrosion of one of the metals. The larger the potential difference, the greater the probability of galvanic corrosion.
Galvanic corrosion only causes deterioration of one of the metals. The less resistant, active metal becomes the anodic corrosion site. The stronger, more noble metal is cathodic and protected.
Galvanic corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly. Metals close to one another on the chart generally do not have a strong effect on one another, but the farther apart any two metals are separated, the stronger the corroding effect on the one higher in the table.
This table lists the potential differences for various metals in water. The order of the series can change for different electrolytes (for example, different pH, ions in solution).
I have omitted Stainless steel alloys from this table as they can significantly change their potential and become much more active if exposed to stagnant or poorly aerated water.

Electrode Potential at 77 F (25 C)
Anodic end (this is where the corrosion occurs)
Element
Standard Electrode Potential (Volts)

Lithium

-3.045

Potassium

-2.920

Sodium

-2.712

Magnesium

-2.340

Beryllium

-1.700

Aluminum

-1.670

Manganese

-1.050

Zinc

-0.762

Chromium

-0.744

Iron; Mild Steel

-0.440

Cadmium

-0.402

Yellow Brass

-0.350

50-50 Tin-Lead Solder

-0.325

Cobalt

-0.277

Nickel

-0.250

Tin

-0.136

Lead

-0.126

Hydrogen reference electrode

0.000

Titanium

+0.055

Copper

+0.340

Mercury

+0.789

Silver

+0.799

Carbon

+0.810

Platinum

+1.200

Gold

+1.420

Graphite

+2.250
Cathodic end, passive - (no corrosion here)

[Peter C. Russell]

Ed, nice point about all the technical data but the facts remain that deck attachment failure is a direct result of improper fasteners and connectors being used and my point was to bring this subject up to reiterate what Marcel said about one trade not knowing or even caring how their work effects the overall quality of the house being built.

[Ed Fako]

Originally Posted by Brian A. MacNeish

I'm thinking that virtually no one on these boards have ever had a subscription to the newsletter Energy Design Update or if they had they did not believe what they read. In the July 2006 issue (I believe;can't find my copy at the moment), a Building Science Corp reseacher measured roof temps of dark roofing materials in Jacksonville, FL during the month of August. Yes, he found that the unvented roofs had higher temps at their surface (the hottest part of the shingle since the sun hits there) but over the month the average temp rise on the unvented roof surface was something like .2 degrees F, not likely to cause shingle failure.

Brian,

If I remember my readings correctly, that paper was written regarding unvented "cathedral or vaulted cieling designs", which have a completely different trapped air containment than the typical attic structure.

Ed

[Ed Fako]

Originally Posted by Brian A. MacNeish

Robert Cramer:

"I read the article that Brian was referring to....."

This is just the beginning of articles I will supply on these issues that I have been fighting since 1983. The first partial one was to Roy Cooke about a weeek ago concerning the origins of the 1:300 attic venting rule.......it has no scientifically proven basis yet it is in codes everywhere. It was derived from a single lab experiment in 1947-8 at Penn State University on vapour barriers in flat roof assemblies. They weren't even testing for attic venting but derived a number due to having an incomplete understanding of how these systems truly worked back then.

If we really knew the building science of moisture movement in houses then (98-99% is air movement; the rest is vapour diffusion), vapour barriers would not be installed in homes but they would be built more airtight (as is happening now). If you put in a loose, unsealed vapour barrier, you are attacking 1-2% of the problem and the other 98% defeats you at every receptacle/switch box and unsealed joint!! Make the drywall airtight and leave out the vapour barrier and now you have hit the real problem- air leakage. Same as with attic moisture from condensation- have an airtight ceiling so that house moisture does not migrate by upward air leakage and the need for venting goes way down to about what's naturally left in the attic anyways.

Joe Lstiburek (Phd., P. Eng.) of Building Science Corporation (www.buildingscience.com) promotes a basement wall system that has no vapour barrier on the warm side of the wall behind the drywall.

Brian,

Here is some wonderful archived history regarding where and when ventilation history came from. The 1/300 was a HUD guide from 1942.

http://www.buildingscienceconsulting.com/resources/presentations/Roof_and_Attic_Ventilation_Issues_in_Hot-Humid_Climates.pdf

Keep throwing links my way too please. I thrive on seeing both sides of the issues.

Ed

[Brian A. MacNeish]

Ed:

"Here is some wonderful archived history regarding where and when ventilation history came from. The 1/300 was a HUD guide from 1942."

This presentation is quite interesting since it uses Bill Rose's presentation materials, is given by Armin Rudd from Building Science Corporation headed by Joe Ltsiburek. Let's look at these folks 1-by-1.

The Energy Design Update (EDU) article (January 1993) titled The Mysterious Origins of the "1:300" Rule quotes Bill Rose saying it's origin was from a lab experiment at Penn State performed by Ralph Britton. Now that article was 14 years ago and Rose may have changed his views on this by finding more archived materials. Maybe Britton was testing the numbers in the HUD paper??

Originally Posted by Brian A. MacNeish
I'm thinking that virtually no one on these boards have ever had a subscription to the newsletter Energy Design Update or if they had they did not believe what they read. In the July 2006 issue (I believe; can't find my copy at the moment), a Building Science Corp reseacher measured roof temps of dark roofing materials in Jacksonville, FL during the month of August. Yes, he found that the unvented roofs had higher temps at their surface (the hottest part of the shingle since the sun hits there) but over the month the average temp rise on the unvented roof surface was something like .2 degrees F, not likely to cause shingle failure.

Armin Rudd, the presenter to the NRCA conference in the web address you give, was the Building Science Corp (BSC) researcher in my above post. I mentioned Joe Lstiburek since he is the principal of BSC. I first met him at a large 1985 building conference titled Avoiding Failures; Learning From Experience in Ottawa, Ontario. From what I know, Joe's take is that venting does little, if anything, to improve shingle life. He's the big proponent of the sprayed foam, conditioned attics being used in the "Build America" program where they spray foam right onto the underside of the roof sheathing. This does not allow any ventilation whatsoever and makes sure that virtually all the heat buildup at the shingle surface never gets into the attic. This should be the worst case scenario for having no venting. At least with an unvented regular attic, heat coming through the sheathing can heat the attic air and be radiated down to the insulation or ceiling thus bringing the roof surface temps down a degree or so.

It was interesting to see some of the early assumptions in which air leakeage, the largest mover of moisture into the attic and walls, is given virtually no consideration since they didn't fully understand all processes/phenomena involved. The emphasis was on vapour barriers and vapour diffusion, missing 98-99% of the problem.

I'll have to read the presentation more in depth and get back later to start a list of facts/research contrary to the street knowledge on attic venting. May be a few days as from 9:30 AM on 'til Wed morning, I'm fully booked with various items

[Ed Fako]

Brian,

I was hoping to get you back into the discussion relating to the pros and cons about attic ventilation, and for you to have come up with the links that disapeared when your previous posting went haywire and did not allow you to send your lengthy response.

Since our last discussion, I have been adding to and editing my links page into a Word Document in the event anyone wanted a mother load of roofing and ventilation information.

Hope to hear back from you with your response and links if you are not too busy.

Ed

[Kenton H. Shepard, CMI]

http://www.coolroofs.org/aboutthecrrc.html

History
The Cool Roof Rating Council was created in 1998 to develop accurate and credible methods for evaluating and labeling the solar reflectance and thermal emittance (radiative properties) of roofing products and to disseminate the information to all interested parties.
Mission
The CRRC is incorporated as a non-profit educational organization for the following purposes:

• To implement and communicate fair, accurate, and credible radiative energy performance rating systems for roof surfaces.
• To support research into energy related radiative properties of roofing surfaces, including durability of those properties.
• To provide education and objective support to parties interested in understanding and comparing various roofing options.

Also... Somwhere on BSC I remember reading that ventilating attics is about 5% effective while shingle color can be up to 25% effective for white shingles.