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Discussion Starter · #1 ·
I know this must of been discussed but i cant find anything. The fact that Deck Armor is breathable, does that make it more prone to water getting through? I know vapor and moisture are have different sized molecules but if water sits on deck armor long enough will it eventually get through quicker than a synthetic that isnt breathable?
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It's actually a good thing, especially if it's going to sit exposed for any period.

If any moisture or condensation gets under the underlayment, it will vent out and remain dry. I have seen two underlayments I will not use anymore because they trapped moisture under it and the deck was soaking wet merely because of this. Really opened my eyes to possible problems with the synthetics. DeckArmor is one of the few underlayments that will keep the moisture from penetrating from above but still allow it to escape from below. Very good product.
 

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Discussion Starter · #3 ·
Renegade
What is your feeling on Deck Defense ? Its technically not breathable.
Keep in mind, we are installing shingles the day of or day after the deck defense( non breathable) is installed.
 

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Housewraps and other vapour permeable sheet goods are considered to be 'water resistant', so yes water would probably get through a eventually. However, that's not a problem with the underlay, it's a problem with the roof.

Here's an interesting article on permeable underlays.
http://www.rci-online.org/interface/2011-12-Lstiburek, Karagiozis, Gassman.pdf
Basically it says that the asphalt shingles, once bonded, aren't very permeable (aka they don't breathe). With a typical vented attic space there's isn't a need for a breathable underlay. The decking will dry into the attic.
 

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Discussion Starter · #5 ·
I just had a long conversation with technical reps from both owens corning and gaf.
My conclusion from their candor is breathability sounds good but after a vapor barrier such as the shingles themselves are installed, breathability kind of becomes a moot point. It really doeant mean much. Although owens corning deck defense is slightly breathable.
Both reps dint really put the other company's product down. The GAF rep said owens corning Deck Defense was very strong and very resistant to water. The owens corning rep said deck armor was a very good product as well but said the breathability is kind of misleading because of the shingles being a vapor barrier and attic ventilation.
Another interesting fact about Deck Armor by gaf was this : the perm rating / breathability was tested WITHOUT any shingles over it.
I would like to see what the perm rating would of been with shingles applied over it, that would make much more sense and would be much more realistic.
 

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Renegade
What is your feeling on Deck Defense ? Its technically not breathable.
Keep in mind, we are installing shingles the day of or day after the deck defense( non breathable) is installed.
My opinion of underlayments in general can be found in other posts over the years and that is pretty much the underlayment is inconsequential once the roof is installed.

The reps are correct in the same respect. Once the shingles are installed the only thing underlayment does is act as a slip sheet between the shingles and the deck. People put way too much emphasis on underlayments and some of us know that with a properly installed roofing system the underlayment doesn't much matter.

Only on roofs left open for any amount of time I have seen a great importance in a good underlayment. I would rather have 30# felt on the roof as it allows any condensation or moisture that may get underneath to dry out. Some synthetics will trap that moisture, keeping it laying on top of the deck which is not good. Might as well throw 6mil visqueen up there. Does about the same thing.

If you are roofing it in a timely manner, ice/water at the eaves and valleys and 30# felt in the field is going to get you the same result as anything more expensive.

I personally like the synthetics for the ease of transport and installation and that's a great reason to use them. Beyond that there is no benefit to the homeowner or the contractor, only to the mfrs pocketbook.

In your situation it sounds like there will be no detrimental impact on using either one. DeckArmor is pricey but it is the best out there. OC makes some products I love, some I hate. Defense is one that I do happen to like also.
 

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Underlayment is important. Breath-ability is another question.. I use Deck Armor on all roofs because I only use Gaf shingles. Every Gaf product used is covered under their warranty, its mostly a selling point.
Once you put shingles on they are not sealed to driven rain, or ice and water damming. Thats why we use I&W for 2 rows now. If any water does happen to get under the underlay then a poly-synthetic will not release it, if the attic isn't properly vented will cause deck rotting. The breathable deck armor is supposed to give a chance to release.. but like others say who knows if it does with shingles over top of it. Everyone will have problems with either product.... Use what makes you money
 

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I have seen the same thing deck being wet with some synthetics.
With that said, they had been at times when even the ridge venting opens were covered waiting to be opened up.

I have always said the synthetics need to have the correct amount of ventilation to not retain moisture in the building.

Am also currently considering going to Deck Amour because the sight of the wet deck concerned me and to be perfectly honest, the condition of the deck and moisture, after the roof is on, remains an unknown.

There is another breathable underlayment I have always been interested in its called Vapor Shield or something like it. Breaths like nobody's business. Pretty pricey though.
 
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