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Re: Ice and Water Shield On Porch?

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Re: Ice and Water Shield On Porch? benick 05-24-2007
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Posted by Don on May 31, 2007, 9:34 am

>> "marson"> wrote
>>
>> > And why aren't manufacturers recommending this? They'd sell more
>> > product.
>>
>> How do you know they aren't?
>> Cause they haven't recommended it to you?
>
> Read the package instructions.

LOL, uh, OK, if you say so.



Posted by marson on May 31, 2007, 4:39 pm
>
>
> >> "marson"> wrote
>
> >> > And why aren't manufacturers recommending this? They'd sell more
> >> > product.
>
> >> How do you know they aren't?
> >> Cause they haven't recommended it to you?
>
> > Read the package instructions.
>
> LOL, uh, OK, if you say so.

Gotcha there. http://www.gaf.com/Content/Documents/20002.pdf .


Posted by Dennis on June 1, 2007, 10:23 am
> And why aren't manufacturers recommending this? They'd sell more
> product.

Manufacturers are manufacturing this product, like all products they sell to
a specific market / end use. This product was designed to comply with a
specific code requirement, as an alternate to two layers of underlayment,
cemented together. It saves time and labor; money in other words.

However, that's the code, and most prescriptive codes are designed as
minimums and are usually exceeded when there is a good reason to do so. The
reason that the manufacturers do not state that it is to be used everywhere
is simple, whatever they put on the package is considered a requirement,
legally binding in court. Any local building official would then be
permitted to make a full installation mandatory. As there is no need to
overbuild anything, there is no need to make such practice a recommendation.

> The answer is probably two fold: it has little or no value in
> practice, and second, ice and water shield is a vapor barrier, and
> unless your ventilation is good, you could wind up with rotted roof
> sheathing.

You're worng on both points. First it has obovious value in offering
additional protection to a roof deck. Only a fool would argue that overkill
has no value. Second, although it does have a specific requirement of 0.01
perms max. it should never cause a roof deck to rot. (Do you think that
standard Type I underlayment overlaid with two thicknesses of asphault
shingles wont retard the passage of water vapor?) Ventilations in al attics
is a must (and a code requiremtnt). The most likely pace you will every find
a rotted deck is low down, near the eaves. Upon investigation we find that
there was little or no air circulation, often that the insulation had been
blown into the area and in contact with the bottom of the roof deck. Proper
ventialltion, and not just the minimums required by the IRC, is an absolute
must. (It's also off topic).

> This is not a standard practice. It is not being done in most parts
> of the country. Go out and look at some roofs, talk to some roofers
> and contractors.

As an inspector (my current position is plan reviewer), I have inspected
hundreds of installations. I have found that roofers vary in their
knowledge, but those highly concerned with doing an outstanding job that
they can be proud of, to those who are looking forward to collecting their
paycheck and getting drunk that evening. (Like any trade). Some even argues
that they didn't need to use underlayment. Many didn't know the proper way
to build a valley and a few could not explain what a stepped flashing was or
what the requirements for it were.

I do agree that it's not standard practice, as most of the public either has
no idea as to what constitutes a good roof verses an outstanding one; and
they will always opt for the lowest price. It's use is really for those who
are building a higher-end home, usually with permanent clay-tile roofs or
long-life asphalt or the like. For the average low-end market, installing
ice-shield at the eaves with regular Type-I underlayment over the rest of
the roof is the only way to maintain competitively and low price.

This by no means ensures that the owner will be getting the best for his
money (for only a modest amount more he could be getting many more years of
roof life compared to the minimum materials). You simply quote minimum code
to get the job and then offer to upgrade the materials (labor will be pretty
much the same in all cases).

The argument isn't whether is costs more or not (it does) or whether is
common practice or not (it isn't). The argument is that it makes a better
roof (longevity and greater leak resistance, especially in high wind zones)
verses one covered with standard Type-I underlayment. (It does).



Posted by Michael Bulatovich on June 1, 2007, 12:48 pm

>> And why aren't manufacturers recommending this? They'd sell more
>> product.
>
> Manufacturers are manufacturing this product, like all products they sell
> to a specific market / end use. This product was designed to comply with a
> specific code requirement, as an alternate to two layers of underlayment,
> cemented together. It saves time and labor; money in other words.
>
> However, that's the code, and most prescriptive codes are designed as
> minimums and are usually exceeded when there is a good reason to do so.
> The reason that the manufacturers do not state that it is to be used
> everywhere is simple, whatever they put on the package is considered a
> requirement, legally binding in court. Any local building official would
> then be permitted to make a full installation mandatory.

That's just not true. Some building officials are power-mad bureaucrats.

>> The answer is probably two fold: it has little or no value in
>> practice, and second, ice and water shield is a vapor barrier, and
>> unless your ventilation is good, you could wind up with rotted roof
>> sheathing.
>
> You're worng on both points. First it has obovious value in offering
> additional protection to a roof deck. Only a fool would argue that
> overkill has no value.

That's plain silly. "Overkill" needn't always be benign. Look at bolt
tortion, for a simple example. Ever heard of "too much of a good thing?"



Posted by marson on June 1, 2007, 5:33 pm
whatever they put on the package is considered a requirement,
> legally binding in court. Any local building official would then be
> permitted to make a full installation mandatory. As there is no need to
> overbuild anything, there is no need to make such practice a recommendation.
>
>

If this is true, then why do they include hips, ridges, and rakes in
their instructions? Ice and water shield on ridges and rakes is not
code in my state. But you are saying that it is considered a
requirement, legally binding in court because GAF puts it on their
instructions?

Regarding ventilation, in the case of new construction, you are
probably right. But it is highly irresponsible to be recommending ice
and water shield over the whole roof to everyone. Lots of old houses
have roofs that are marginally ventilated and have marginal vapor
barriers, as you must know.



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