# Sealing Cuts on OSB?



## echase (Mar 10, 2010)

Getting ready to cut in a ridge vent, and I'm concerned about the oppressive southern humidity damaging the decking once the sealant is cut off of the edge. What's the proper material to seal this edge? 

I was thinking Killz on a roller, but spray paint is also an option... I don't need to be neat, as a new roof will be installed right after this is cut and sealed. 

Any roofers have recommendations here?


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## AaronB (Jan 29, 2005)

I have been roofing 20 years and never knew this had to be done...


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## echase (Mar 10, 2010)

I'm sure it doesn't *have to* ... but I know that edges are OSB's achilles heel, that's where the moisture tends to get in and do it's dirty deeds. 

I'm sure it's overkill, but that's why I like DIY... I can afford to take the time to overdo details like this. 

In your experience, have you noticed if OSB failures tend to occur around the edges?


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## AaronB (Jan 29, 2005)

I have noticed that OSB failures occur under roof leaks.


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## echase (Mar 10, 2010)

That was good for a LOL. 

Nothing like the voice of experience to point out what should be obvious. So, you think my overkill is ridiculous? If you've not seen humidity cause problems at ridge vents, etc I'll leave well enough alone. 

I really do appreciate the advice from those who know better.


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## AaronB (Jan 29, 2005)

I have never seen it myself.


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## Gary in WA (Mar 11, 2009)

And well you should worry: "Performance is similar in many ways, but there are differences in the service provided by osb and plywood. All wood products expand when they get wet. When osb is exposed to wet conditions, it expands faster around the perimeter of the panel than it does in the middle. Swollen edges of osb panels can telegraph through thin coverings like asphalt roof shingles.
The term ghost lines or roof ridging was coined to describe the effect of osb edge swelling under thin roof shingles. The Structural Board Association (SBA), a trade association that represents osb manufacturers in North America, has issued a technical bulletin outlining a plan to prevent this phenomenon. SBA correctly indicates that dry storage, proper installation, adequate roof ventilation and application of a warm-side vapor barrier will help prevent roof ridging.
Irreversible edge swelling has been the biggest knock on osb. Manufacturers have done a good job of addressing this issue at the manufacturing facility and during transportation by coating panel edges. But the reality is that builders don’t limit osb use to full-sized sheets. The edges of cut sheets are seldom if ever treated in the field. Houses under construction get rained on. And if you use osb in an area of very high humidity, like over an improperly vented attic or over a poorly constructed crawlspace, you are asking for trouble." http://bct.nrc.umass.edu/index.php/...ing-between-oriented-strandboard-and-plywood/ http://www.rd.com/19557/article19557.html
Other problems with OSB: http://www.gp.com/build/PageViewer.aspx?repository=bp&elementid=6132

Be safe, Gary


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## echase (Mar 10, 2010)

Thanks for the links. This renews my concern that this potential issue may be more of a real-world problem in the humid south (where my house is) than in the environment where AaronB has extensive experience. 

So, anyone know how I can seal the cut edges?


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## MJW (Feb 7, 2006)

If you are seriously concerned about this, you better tear off the entire roof and seal the edges of every sheet.

IMO, it's a ridiculous thought to even consider.


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## echase (Mar 10, 2010)

The factory already sealed the edges on the uncut sheets (that's what the paint is for) ... but I think I found the evidence I needed to sleep tight with unsealed edges: the cut at the existing power vent, which has been pumping out humid Atlanta air for 20 years shows no significant swelling. 

I'm gonna pass on the paint. 

Thanks everyone for your advice on this!


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## Jim F (Mar 4, 2010)

One more thought to consider. Is ridge venting the optimum way for you to go with your roof. There are many thoughts and opinions pro and con about ridge venting.


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## echase (Mar 10, 2010)

Uh oh... Tell me why NOT to ridge vent.


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## Scuba_Dave (Jan 16, 2009)

Strong winds can blow rain into a ridge vent
We've had some really strong rainstorms & I haven't had a problem
But it can happen - poorly designed/installed model
Some roofers will say that any roof pentration will eventually leak


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## echase (Mar 10, 2010)

I thought about the wind-driven rain... the prevailing wind blows parallel to my ridgeline, so I think that will help minimize that problem. I'm using Cobra Rigid Vent III, seems like a decent design, but I don't have experience with these. 

Cutting as soon as I post this, installing Friday afternoon.


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## Scuba_Dave (Jan 16, 2009)

Yeah most of the wind blows parallel to my ridge vent too
We have trees pretty much all around the property that helps cut down the wind too


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## Big N8 (Oct 28, 2009)

I have never heard of the osb being sealed in anyway shape or form. I would think the paint that comes on the edge from the factory is nothing more then paint not really a "sealed" edge. I the worry is there i would just replace all the top sheets with plywood and be done with it.


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## MJW (Feb 7, 2006)

echase said:


> The factory already sealed the edges on the uncut sheets (that's what the paint is for) ...


If you've ever looked at a roof before without shingles, you'd notice that not every sheet is a full sheet. Every vent hole ever cut was never sealed with any paint or anything that I am aware of.

Looks like you answered your own question.


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## JAX27332 (Feb 7, 2018)

I just had a fight with a roofer over this same problem. He cut the OSB without my permission and didn't seal the edges. On the cut OSB he didn't put up moisture got into the OSB and messed it all up. So I would suggest sealing ALL edges of OSB for roofing. And trying not to cut as much as possible.


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## Nealtw (Jun 22, 2017)

Anyone care to show some photos of problem caused by anything being talked about here.
We have OSB sit out in the rain sometimes for a week, the edges get wet and swell. Sometimes we have to use bigger H clips. and on a big house it may take a week in the rain to get all the sheeting on. Yes it swells up more on the edges but with OSB we never had to replace sheets on 16/12 because of ply separation. 
I have never heard of a mold problem in even the wettest house when done.

Let's not confuse humidity problems with insufficient venting.


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## jlhaslip (Dec 31, 2009)

Neal,

Must be a regional thing. I have ever seen or heard about sealing cut edges, and you live in a far more humid zone, but without the heat issues they have down south.


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