Roof sheathing? what kind?

I'm going to have to replace some sections of roof sheathing as part of a re-roof project. What is there now is 1/2" plywood. I guess it's been OK because it's lasted almost 30 years. Is 1/2" still OK as far as code goes, etc? The part that is a problem was due to not being vented correctly, which I'm going to fix. It's actually one entire section of roof where that whole section needs to be replaced.
I'm going to get quotes and want to make sure everything is spec'd. What is typically used now for roof sheathing? Is OSB ok? is at as good or better than plywood? Oddly looking at Lowes and HD, it doesn't look like they have sheathing in 1/2". Closest is 15/32. I guess maybe lumber yards have true 1/2"?
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On 2/14/2013 11:58 AM, snipped-for-privacy@optonline.net wrote:

can come up with.
Paul
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On Thursday, February 14, 2013 2:58:20 PM UTC-5, snipped-for-privacy@optonline.net wrote :

ecause it's lasted almost 30 years. Is 1/2" still OK as far as code goes, e tc? The part that is a problem was due to not being vented correctly, which I'm going to fix. It's actually one entire section of roof where that whol e section needs to be replaced. I'm going to get quotes and want to make su re everything is spec'd. What is typically used now for roof sheathing? Is OSB ok? is at as good or better than plywood? Oddly looking at Lowes and HD , it doesn't look like they have sheathing in 1/2". Closest is 15/32. I gue ss maybe lumber yards have true 1/2"?
Nobody has true 1/2" any more. OSB is fine. Stronger and cheaper. OSB is used for almost all new construction. Get the little clips to keep it spa ced properly. Why'd the original fail? Should have lasted longer than 30 years. Get wet?
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because it's lasted almost 30 years. Is 1/2" still OK as far as code goes, etc? The part that is a problem was due to not being vented correctly, whi ch I'm going to fix. It's actually one entire section of roof where that wh ole section needs to be replaced. I'm going to get quotes and want to make sure everything is spec'd. What is typically used now for roof sheathing? I s OSB ok? is at as good or better than plywood? Oddly looking at Lowes and HD, it doesn't look like they have sheathing in 1/2". Closest is 15/32. I g uess maybe lumber yards have true 1/2"?

keep it spaced properly.  Why'd the original fail?  Should have lasted longer than 30 years.  Get wet?
It failed on one section that is a cathedral ceiling. The other two sections have normal attics. And the dumb asses did not vent the cathedral part. I guess I could have put a ridge vent in, but I'm not sure it would have made much difference. I doubt they put baffles in and without them the insulation is likely blocking the air flow all the way from top to bottom in each bay. Fortunately it's only about 900 sq ft.
I did some googling on OSB vs CDX plywood. Seems they are similar. OSB is less expensive, more water resistant. But it appears if it does get wet enough, then it won't return to the same thickness when it dries. Plywood is easier to get saturated, but when it dries out, it's more likely to return close to original size.
Looks like it will be 15/32. I doubt that will make any difference in aligning with any sheets that are still there. It may not matter. I think in the bad section, probably going to have to pull it all to so as to put in the missing baffles for air flow. After tear off, there might be a sheet or two that needs to be replaced on the rest of the roof, so the 1/2 vs 15/32 would only be an issue there and I doubt it matters.
Looking at the cost of various materials, one killer is the ice barrier that I believe is now required by code for the lower areas. And I have long eaves, which requires more of it because as I understand it, the ice barrier needs to extend up 2 ft beyond where the roof meets the heated walls. That means I need two passes, each 3ft wide. That stuff goes for like $79 for a 3ft by 36 ft roll of the product made by Grace. That's $790 just for that. The freaking shingles for the whole 43 sq are only $1400. Maybe there are other products that are less expensive? Ice damming here hasn't been a problem in 18 years....
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wrote:

OK because it's lasted almost 30 years. Is 1/2" still OK as far as code goe s, etc? The part that is a problem was due to not being vented correctly, w hich I'm going to fix. It's actually one entire section of roof where that whole section needs to be replaced. I'm going to get quotes and want to mak e sure everything is spec'd. What is typically used now for roof sheathing? Is OSB ok? is at as good or better than plywood? Oddly looking at Lowes an d HD, it doesn't look like they have sheathing in 1/2". Closest is 15/32. I guess maybe lumber yards have true 1/2"?

keep it spaced properly.  Why'd the original fail?  Should have lasted longer than 30 years.  Get wet?

Just found out the Owens Corning has an ice barrier product that is less than half the cost of the Grace one. A lot more reasonable at $330.
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You gotta wonder if the $330 product is a good as the $790 product. I know that price isn't always an indication of quality, but that's a huge difference.
I picture a $15K Ford vs a $36K BMW. Same uplift as yours - 2.4X. That extra $21K isn't going to be just for the name.
Maybe you don't need whatever the extra $460 is going to get you, but is it really apples to apples with that big of a price difference?
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I looked into them some more and the essential difference seems to be that the Grace product is breathable and the OC product is not. I guess the Grace product must be like Gortex, in that it keeps water out, but allows air in. That then leads into a debate about the importance of it being breathable. The issue is if the wood does somehow get wet, if it's not breathable, then the sheathing has to dry from the inside, which takes longer, leading to potential long term wood damage.
The two sides of this and their points:
Breathable is very important group:
Sheathing being able to dry from both sides is better
Normal roof construction with felt and shingles allows for some air flow to get down to the sheathing to dry it out, if it gets wet, so ice dam barrier should do the same.
Every roof eventually has some leakage, so some will get behind the ice dam at some point.
Breathable not so important group:
Sheathing still dries effectively from one side, provided that the side away from the shingles is properly vented as it should be. If it's say a cathedral ceiling that uses spray foam and has no venting, then you could have a problem because it can't dry out from the inside.
Properly installed ice barrier sticks and seals so well that it's very unlikely any water is ever going to get behind it.
Any water that gets behind shingles, felt, etc on any roof is going to dry mostly from the inside, because not much air gets through the layers of shingles, etc.
Currently given the big price difference and that OC makes both the less expensive ice barrier and the shingles I'm probably going to use, I'm leaning toward that option.
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On 2/14/2013 6:14 PM, snipped-for-privacy@optonline.net wrote:

I am curious as to why you are paying so much. Nobody I know would ever pay that high of a price for work like that around here...
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I haven't paid anything yet. I'm trying to look at the key issues so when I get quotes I know what I'm getting and know how much it costs. And I can make sure that the quotes spec equivalent grade materials.
After making that post, I found that Owens Corning has a similar ice barrier product that is less than half. And since I've had no problems in 18 years with no ice dam product on there now, seems like it;s mighty fine to me.
That brings the material cost to around $2500 for a 4,000 square foot roof. Shingles are $32 a square. Sound about right?
And for the section that probably needs all new sheating, I'm going to get it quoted for replacement of that whole section of roof and on a per sheet basis. That way depending on what we find when we start taking it off, I won't get hosed.
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On Thu, 14 Feb 2013 14:10:57 -0800 (PST), jamesgang

re-roof project. What is there now is 1/2" plywood. I guess it's been OK because it's lasted almost 30 years. Is 1/2" still OK as far as code goes, etc? The part that is a problem was due to not being vented correctly, which I'm going to fix. It's actually one entire section of roof where that whole section needs to be replaced. I'm going to get quotes and want to make sure everything is spec'd. What is typically used now for roof sheathing? Is OSB ok? is at as good or better than plywood? Oddly looking at Lowes and HD, it doesn't look like they have sheathing in 1/2". Closest is 15/32. I guess maybe lumber yards have true 1/2"?

used for almost all new construction. Get the little clips to keep it spaced properly. Why'd the original fail? Should have lasted longer than 30 years. Get wet? The reason OSB is used instead of plywood is price.. Most "half inch" ply today is closer to 12mm -the international rather than US standard. 5/8" is better but not used very much. I've seen 3/8 used but I'd never use it - particularly in OSB here in snow country. (even though it's been years since we've had a real winter)
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On Thu, 14 Feb 2013 14:10:57 -0800 (PST), jamesgang

re-roof project. What is there now is 1/2" plywood. I guess it's been OK because it's lasted almost 30 years. Is 1/2" still OK as far as code goes, etc? The part that is a problem was due to not being vented correctly, which I'm going to fix. It's actually one entire section of roof where that whole section needs to be replaced. I'm going to get quotes and want to make sure everything is spec'd. What is typically used now for roof sheathing? Is OSB ok? is at as good or better than plywood? Oddly looking at Lowes and HD, it doesn't look like they have sheathing in 1/2". Closest is 15/32. I guess maybe lumber yards have true 1/2"?

used for almost all new construction. Get the little clips to keep it spaced properly. Why'd the original fail? Should have lasted longer than 30 years. Get wet? The major disadvantage of OSB is that if it gets exposed to significant amounts of water or moisture, the edges expand by up to 15%. . . especially if they are cut edges. This swell will then telegraph onto the shingles or some flooring. When plywood gets wet, it expands evenly throughout the panel, dries more quickly and shrinks down to its original size more rapidly than OSB.
The "little clips" are definitely not used to keep the sheathing "spaced properly." They are to provide additional support between the rafters when using minimum code sheathing.
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Trader4:
If I were you, I would phone around to some of the roofing supply companies and roofing contractors in your area and see what their opinions are on OSB versus plywood and the Dow Corning Ice & Water Shield versus the Grace product. The people that sell and use those products every day would be the most knowledgable as to whether they're much the same thing, or completely different in terms of quality, and where you need to spend the extra money now to avoid spending even more later.
--
nestork


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Since you must go with 1/2", I would go with 1/2" CDX, 4 ply. Don't go with a 3 ply, even tho you could save a few pennies. And yes, get it at a real lumber yard.
I have 20+ years in construction, from my younger days. Check out Certainteed ice/water guard. We always used the sanded, which basically is a non-slip surface so you can walk on it b/4 the roof covering is down. We used to start the roll on one end, and be able to roll across the edge without cutting it into 10' pieces. Most manufacturers recommend to use 10' pieces because the product is virtually stuck once it is applied. On Certainteed, you are able to lift it back up if it's not going on straight. It also has a split back instead of one solid backing, which makes it easier to apply. I may not explain this very well, but if you applied the different barriers, you would see the plus side of it. Word of caution, if using Certainteed, you must apply mechanical fasteners (staples, nails, etc) on initial installation b/4 walking on it. The adhesive takes a while to stick, so the fasteners hold it in place so there are no WHOOPS.
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Thanks for the info. And I understand your points. I watched a video online of one of the ice barrier products being applied. It had the split backing and I could see the advantage to getting it positioned and applied.
Looks like the CT product is similar to the Owens Corning in that it does not appear to be breathable and is priced similarly. The 1/2" CDX is probably what I'll go with for' sheathing. My main purpose was to learn enough about the various issues so that I get the right stuff quoted and don't wind up with a quote that just says "4x8 sheathing".
What do you think about the breathability issue of the ice barrier products?
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snipped-for-privacy@optonline.net wrote:

I never heard of a breathable ice barrier, felts yes (and I believe all felts are). I don't see how an ice/water barrier could be. Thinking about ice barriers, they have adhesive, there's no way to control the adhesive, unless it's not sticking thoroughly.
Maybe I'm missing something. But, have been away from construction for awhile.
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wrote:

Sometimes just 2 rows of shingles installed bottom side up under the finish layer. I know of some areas where 3 feet of galvanized steel was used along all the drip edges as an ice barrier, with a coat of tar to seal the nail holes.
Today's self stick polymer products are much better, simpler to install, readily available, and even reasonably priced. They are impervious to moisture, so you want to install them on a dry roof. A friend was doing his own roof - over a period of days, and to be sure the house stayed dry if it rained before he was done, without having to tarp, hu used the stick-down blue ice-guard product on the whole roof. I think it was Henry Blu-skin.

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