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Old 01-21-2014, 09:58 AM   #1
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What does underside of #30 felt look like?


Let me start by saying that I'm very ignorant about building materials. I was in my attic the other day and I noticed that on the plywood sheeting (sheating?) there were many missing knotholes; looking through these knotholes I could see some kind of material that looked to me like the underside of shingles, but should be (according to my contractors specifications) #30 roof felt. So, my question is, is the underside of roof felt hard and grainy? I'm seriously thinking and hoping that I'm not looking at shingles, and its far enough up the roof that I don't think it's the ice/water shield.

All advice appreciated.

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Old 01-21-2014, 10:10 AM   #2
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What does underside of #30 felt look like?


should be smooth and black

hard and grainy sounds like a an upside down shingle

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Old 01-21-2014, 10:18 AM   #3
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What does underside of #30 felt look like?


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Originally Posted by NWIndiana View Post
Let me start by saying that I'm very ignorant about building materials. I was in my attic the other day and I noticed that on the plywood sheeting (sheating?) there were many missing knotholes; looking through these knotholes I could see some kind of material that looked to me like the underside of shingles, but should be (according to my contractors specifications) #30 roof felt. So, my question is, is the underside of roof felt hard and grainy? I'm seriously thinking and hoping that I'm not looking at shingles, and its far enough up the roof that I don't think it's the ice/water shield.

All advice appreciated.
Ayuh,.... Unless I'm missin' something,....

When ya see a knot hole in a sheet of plywood, you should be lookin' at the next ply in the sheet, 'n Not clean through the Whole sheet of plywood,...
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Old 01-21-2014, 10:21 AM   #4
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What does underside of #30 felt look like?


Post a picture.
There's no way if it's really plywood you could be seeing any of what's on top of the sheathing from below or have a knot hole that goes all the way through to the outside.
It's made in layers called ply's so if one layer had an unfilled knot hole all you would see is another layer of wood.
Far more likely your seeing something like 1 X 6's. Commonly done in older homes.
Often times in those old style roofs the knots would fall out. If it's the lower part of the roof you may be feeling Ice and water shield.
(just a guess)
Depending on the condition of the old 1X's it's common to go over the old sheathing with new plywood for more nail holding power.
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Old 01-21-2014, 12:27 PM   #5
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What does underside of #30 felt look like?


I've uploaded some photos, so you can see what I'm looking at. Is this just another layer of ply? If not, what is it? It's hard and bumpy/grainy to the touch, and seems to go too far up the roof to be ice/water shield. The roof was put on just over a year ago.

Thanks
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Old 01-21-2014, 12:33 PM   #6
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What does underside of #30 felt look like?


That is just the plywood.
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Old 01-21-2014, 01:39 PM   #7
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What does underside of #30 felt look like?


+1

Nothing but a small part of one of the layers coming off there. Shouldn't be an issue.
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Old 01-21-2014, 01:54 PM   #8
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What does underside of #30 felt look like?


That second picture has me worryed.
That looks like a whole section of plywood is missing and I'm not seeing any H clips.
http://tecotested.com/techtips/tt_edgeclips
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Old 01-21-2014, 03:55 PM   #9
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What does underside of #30 felt look like?


Looks to me like the plywood is missing a small section of the outer ply. The black you see is the glue that is used to adhere the plys together.
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Old 01-21-2014, 08:08 PM   #10
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What does underside of #30 felt look like?


You're all set. Those are normal voids that are found in today's plywood. Back in the day even C-grade plywood, like CDX for instance had voids filled. Today's C-grade plywood looks like the stuff we rejected years ago.
If I were to guess from that picture I would say you have CDX pine. I prefer CDX fir. I believe there is one more ply and all of the voids are filled. At any rate the fir plywood they sell around my area is much better than the pine.
In case you're wondering CDX = one side is C-grade, the other is D-grade, and the glue is rated for eXterior use.
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Old 01-21-2014, 09:15 PM   #11
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What does underside of #30 felt look like?


Thanks for all the replies. I'm a little less ignorant about about plywood thanks to you guys. In answer to a couple of points raised, there are H clips, just not shown in those pictures. The plywood should be 3/4'' Douglas Fir according to my contractor's estimate.
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Old 01-21-2014, 10:07 PM   #12
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What does underside of #30 felt look like?


If your rafter spacing is 16" or even 2' on center with 3/4" sheathing, h clips aren't necessary anyways.
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Old 01-24-2014, 01:35 PM   #13
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What does underside of #30 felt look like?


The designation of CDX was dropped a very long time ago. The designation for plywood used in roofing is usually CD/ Exposure 1. CD indicates the face veneer (Grade C) and D indicates the Back veneer. Fir plywood is always better on roofs due to its superior dimensional stability, when compared to pine. Full Dimensions like 1/2- 5/8- 3/4 were replaced with 15/32-
19/32-23/32 some time ago also.

FYI the X in CDX used to indicate exterior glue. They only use exterior glue in plywood since about 1968. Thats when the designation was dropped, I think, but a lot of people still use the term.

Better veneer grades can obviously be used, but they usually arent, due to cost.

By the way, I did not see very many nails through your deck. Maybe its just the size of the area.

If you want to see if you have felt, look up from under the deck by a vent pipe.

Also, most roofers do not use No. 30 below asphalt shingles, and most do not use ASTM D-226 felt, they use cheapo shingle underlayment. WAY less asphalt, thinner, and nowhere near as good as D-226
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Old 01-24-2014, 06:01 PM   #14
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What does underside of #30 felt look like?


http://www.performancepanels.com/sin...pp_pp_atr_dur1

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PS. http://www.strongtie.com/products/co...pscl-psca.asp#
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Old 01-25-2014, 11:32 AM   #15
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What does underside of #30 felt look like?


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Originally Posted by jagans View Post
The designation of CDX was dropped a very long time ago. The designation for plywood used in roofing is usually CD/ Exposure 1. CD indicates the face veneer (Grade C) and D indicates the Back veneer. Fir plywood is always better on roofs due to its superior dimensional stability, when compared to pine. Full Dimensions like 1/2- 5/8- 3/4 were replaced with 15/32-
19/32-23/32 some time ago also.

FYI the X in CDX used to indicate exterior glue. They only use exterior glue in plywood since about 1968. Thats when the designation was dropped, I think, but a lot of people still use the term.

Better veneer grades can obviously be used, but they usually arent, due to cost.

By the way, I did not see very many nails through your deck. Maybe its just the size of the area.

If you want to see if you have felt, look up from under the deck by a vent pipe.

Also, most roofers do not use No. 30 below asphalt shingles, and most do not use ASTM D-226 felt, they use cheapo shingle underlayment. WAY less asphalt, thinner, and nowhere near as good as D-226
Look who came out of the wood work....?



They might see I/W if they look around the plumbing vent as well.

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