roof decking bubbling up

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#1

Originally Posted By: pk richardson
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i am new here and have a question for the experts. i recently looked at a house that was around 50 years old and had the ashphalt shingles and all decking replaced 1 year ago. the decking was plywood. i noticed in several areas averaging about 1-2 foot in diameter that the decking was “bubbling up” for lack of a better term. i confirmed this from the attic as well, sorry i have no pics to offer. Georgia Pacific says it is because the roofer did not space the sheets of plywood when applying allowing for expansion of the sheets. the roofer says that the plywood seemed “green” when he applyed it. and that he has never spaced decking when applying it and never had this happen before. this might seem obvious to many of you but have you seen this happen before or could shed any light on it for my education. thanks

#2

Originally Posted By: psabados
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PK


First off, GP requires H clips to be installed for expansion. The contractor thought the plywood looked green. Looks like the contractor may have a slight problem by not adhering to the manufactures installation specs. The contractor should have known better. The shear nature of wood is that it will expand and contract during the seasonal changes.

You confirmed the bubbling from the attic. Did you see gaps between the rafters and the decking? Or something else? How about a little more information. Roof style, pitch, rafter size and spacing, plywood thickness. Where is the bubbling taking place? Top, center, bottom, edges, near a dormer or valley?

A few of roofers in my area use OSB and do not use spacers. Most start showing a problem within a short time of the installation. I guess that's the difference between a 6000.00 job and a 5500.00 job.

Paul

#3

Originally Posted By: pk richardson
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gable style of roof, 2x6 rafters 16" on center, 6/12 pitch, 15/32"decking.


areas of bubbling are in random places on the roof. it is 49 square.


from the attic perspective the bubbled areas are in some places over the rafters and in some places between them. there doesn’t appear to be a pattern. 7 different areas all together, roof installed 18 mos ago. hope this sheds more light on it. it would seem to me that the decking was improperly applied by the roofer any other ideas or amplification would be appreciated, thanks.

#4

Originally Posted By: Blaine Wiley
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It sounds like differential warping of the plywood. But, was this new sheathing also, or did they just replace the shingles. Did you see spacer (H) clips between the sheets?


I once ran across a roof something like this, and the "bubbles" were where they ran out of nails, had to refill their nail gun, and didn't start back where they left off. The shingles were applied in the summer, so they adhered to each other quickly, but weren't held down to the sheathing.

Blaine ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

#5

Originally Posted By: nlewis
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Are you sure the H spacers are required for stick framing with rafters 16" oc.


I have only seen them used for engineered trusees with 24" oc.

#6

Originally Posted By: pk richardson
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this is all brand new decking underneath new shingles, applied at the same time. there are no h brackets and the ga pacific rep said that they were not required for this type of roof as their primary purpose is for structural integrity on truss style roofs with a greater span between trusses. it would seem to me that if this problem were caused by expansion of the individual sheets of decking that the whole sheet would raise up or warp not just a small area within the sheet(its not at the corners) but i don’t have the experience to know for sure? what do you think bad wood or bad installation and after 18 mos is this as bad as its going to get or are there problems down the road. the casual observer might not even notice them. the roofing contractor has offered to come back, remove the shingles in the affected area and nail the decking down to fix the problem.

#7

Originally Posted By: rmeyers
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PK,


Did you confirm that it was a GP product or is that just who you spoke to?

Had similar problem on 1 year warranty inspection for Architect's residence where 5/8" plywood was requested in lieu of 1/2" OSB. Installation was on 24" o.c. trusses, spaced and clipped.

In speaking to local lumber supplier I was alerted to the fact that there are some "Mill Certified" plywood products on the market well below the normally expected prices for the typical "APA Certified" products. With this (red flag) comment in mind I recommended that the Architect confirm the source of the material that was thought to be an upgrade (additional charge) but is now presenting problems.

Still waiting to hear back from the Architect on who made the extra money on the plywood and who's going to pay now! ![icon_cry.gif](upload://r83gSGUzNOacIqpjVReDwcR83xZ.gif)

Just another avenue to explore! Isn't this fun!!

Have a great day!

--
Russ Meyers

#8

Originally Posted By: lfranklin
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Just thinking out loud here. But was the attic ventilated properly?


And could this be causing the problem?

#9

Originally Posted By: Blaine Wiley
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Larry,


Proper ventilation could certainly be a problem, if for nothing else than heat build up. I see bad ventilation down here, and it usually manifests itself with mildew or mold growth.

The wonderful thing about this business is that we just have to report the problem, recommend an expert, and figure it out later on a wonderful board like this.

Blaine ![nachi_nachi.gif](upload://uHOMNyaTr9Egc1VkzoQvcptyboG.gif)

#10

Originally Posted By: psabados
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PK


Could definitely be a moisture problem too. Did you happen to see any water stains on the underside. Another thought, was felt paper installed over the entire roof? A little extra moisture penetration and the plywood is delaminating.

What area of the country are you in. Bubbles weren't occurring in the area of bathroom vents by any chance? All vents to the exterior


Paul

#11

Originally Posted By: jburnell
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PK


It sounds like the roofer used 3ply cdx and it probably wasn’t dry when he installed it. I’m guilty of this myself, I found out the hard way that it’s not worth saving a couple bucks a sheet for cheap plywood. He could try placing some nailers in the bad spots and drawing it down with screws, but if it’s warped too much it will probably just pull thru the screws anyway. If that doesn’t work, it’s time for a new roof with 4ply cdx this time.


John

#12

Originally Posted By: jfarsetta
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I’m having a bit of a problem with the statement someone made toward the beginning of this thread with regard to the use of H-clips and GP roofing products.


As the framer is unaware what roofing product will be used, and so are many clients/builders until a decision is made, how is anyone supposed to ensure thast the plywood was installed to a specific roofing material manufacturer's specs. What about existing homes?

The roofer's job is to dry-in the roof, and to apply materials. The roof is alwais sheathed prior to the roofer's coming on site. They cant even put a tape on it until its sheathed. Most roofers wont provide a price or order material until they actually measure the roof, despits everything the plans may say.

I'm with Neal on this one. I believe the placemant of h-clips are more of a construction requirement. Or are we stating that GP wont warranty their materials on existing roofs, where h-clips aren't installed in 90% of the applications?

Something else is going on here. H-clips are a red-herring, IMO

--
Joe Farsetta

Illigitimi Non Carborundum
"Dont let the bastards grind you down..."

#13

Originally Posted By: pk richardson
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here is some more info…


the roofer installed the decking and the shingles and used heavy felt over the entire roof. the decking is 3 ply plywood, it has the GA Pacific barcodes still attached to the plywood with its specs. the old deck that came off was completely delaminated throughout. thought to be defective La. Pacific plywood of early 1960’s vintage. no signs of moisture. i felt the roof was inadequately vented when the roof was installed, i.e. not enough intake capacity. 4 gable vents only. the roofer installed 2 electric exhaust fans when he installed the roof. the owner had soffit vents installed 1 year after the roof went on. do you think this was a heat problem that caused this or impropery applyed or defective (uncured) plywood? i am in atlanta,ga. thanks for all of the responses. also the roofer called Ga Pac.


and had their rep meet him at the house to look at the problem.


the rep said that there was not enough space provided between sheets and that was causing the problem. the roofer says its bad wood and he has never spaced decking in the past with no problems…

#14

Originally Posted By: jburnell
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PK


Definitely looks like a combination of problems here.
Homeowner vented the soffit a year after the roof was installed, a lot of the damage has already been done by then, were the soffit vents installed properly - free air flow to the attic.
Gable vents defeat the purpose of soffit vents, air will take the path of least resistance, it won't draw from the soffit. Electric roof vents are OK, but ridge vents are much better if possible to use them.
I've never spaced plywood sheathing either unless we were using H-clips with 24" OC rafters - I could be wrong on that one, check the GP specs.
3ply vs 4ply sheathing....that extra laminate is worth the cost, I don't have any proof on why it's better, just my own experiences.
I'm surprised there was no moisture evidence in the old delaminated sheathing.
I know we are way beyond the scope of HI here, but keep the questions and replies going - I'm here to learn from the pros. ![nachi_nachi.gif](upload://uHOMNyaTr9Egc1VkzoQvcptyboG.gif)

#15

Originally Posted By: rhinck
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PK,


I think everyone in on the right track- but you have not disclosed the species of wood the plywood is made of. In our area the "cheaper" plywood is made of Yellow Pine. I have used this on occasion and if any moisture comes in contact w/ it and it in not spaced correctly - large areas of expansion or heaving up will occur. I'm curious if this decking is yellow pine. Just my thoughts



Rick

#16

Originally Posted By: pk richardson
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thanks for all of the feedback. i guess time will tell.

#17

Originally Posted By: ekartal
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Not having roof vents could also add to the problem. Soffit and roof or soffit and ridge vents are most effective. But I’m not sure if this would be a problem after only one year. Guys what do ya think icon_question.gif



Erol Kartal
ProInspect