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Roof sheathing disintegrating

mikeingp's picture

We had an addition built in 1980. Just recently, we've found a few rather good size "soft spots" in the roof. On inspection, it appears the plywood has just disintegrated (one of the areas seems very dry, although we do have some moisture in another area). You can very easily push a screwdriver through the plywood, and nails don't hold very well.

My question is how is this typically repaired? Can we just put new sheating on top of the old roof shingles (one layer) and all? Or do we remove the shingles, and put the new sheathing over the old, or (least desirable), remove the old sheathing?

Any advice would be welcome!

(post #101594, reply #1 of 18)

"Can we just put new sheating on top of the old roof shingles (one layer) and all?"

How in the world is that a fix?????

""Or do we remove the shingles, and put the new sheathing over the old,""

How in the world is that a fix also????

""or (least desirable), remove the old sheathing?""

Least desirable!!............You have no choice but to do this.

You have to find the problem first and then remove the shingles and what's left of the sheathing and replace the sheathing and shingles, period! How else would you expect to fix this?

This has nothing to do with you being a homeowner or not, it's just common sense and don't try to be cheap, fix it right!

Joe Carola


Edited 7/3/2006 5:45 pm ET by Framer

Joe Carola

(post #101594, reply #2 of 18)

Thanks for your response, but I'm thinking maybe I wasn't clear. I'm 99% sure the problem is a Fire Retardant sheathing issue, not something like water damage. Would that make a difference in your response? I'm not likely to do this work myself ('fraid of heights), but it seems like putting new sheathing on top of the old would be a lot easier and safer.

(post #101594, reply #3 of 18)

you are one step ahead of my responce. In the late seventies, the chemical used for making plywood fire retardent was later found to cause the plywood to disintegrate due to reaction with the temperatures in attics. It is ironic that what was intendd to prevent oxidation of the wood actually caused it, though over a long period of time instead of in an hour or so.

The only solution you have is to remove the shingles and the sheathing down to the rafters and replace the sheathing. I would use Advantech - far better stuff than plyuwood.

Then roof away!

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #101594, reply #4 of 18)

I'm now wondering if FRT had anything to do with it. Is it possible for 26 year-old sheathing to just disintegrate from heat, and moisture from the house? One of the worst spots is above a bathroom, and there's a skylight that blocks the air flow from the soffit to the ridge (this is a cathedral ceiling). I don't think the problem is moisture from the outside, because a) the roof is in very good shape, and b) the soft spots are all over the roof, and I don't think I could have that many leaks.

(post #101594, reply #5 of 18)

""I'm 99% sure the problem is a Fire Retardant sheathing issue, not something like water damage. Would that make a difference in your response?""

No, it wouldn't change my response.

""I'm not likely to do this work myself ('fraid of heights), but it seems like putting new sheathing on top of the old would be a lot easier and safer.""

Yes, putting new sheathing on top of ROTTED out sheathing would be easier, but it's WRONG!.

That wouldn't solve a thing doing that. How can you possible think that nailing a new piece of plywood to the top of a rotted piece of plywood would even be the right thing to do? You’re just putting a band aid on it.,

Let's see, after you take the existing shingles off and nail the new plywood down on top of the old rotted plywood, what will you do with the difference in height where the old plywood makes it stick up higher then the rest of the roof and then shingle over that with a nice big hump in your roof???

Joe Carola
Joe Carola

(post #101594, reply #6 of 18)

I'd think that the worst problem is that he would lose any shear strength in the rafter/roof assembly as the rest of the old gradulayy disintegrates

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #101594, reply #7 of 18)

 


 Would you not also think you might have some damage to the rafters that need to corrected also  


What is the chemical going to do to the rafters if the old ply is left in place and if you just add new deck on top old with time? 


Was this chemical add after the construction or was it included into the ply in the manufacturing process ?

(post #101594, reply #8 of 18)

At time of manufacturing. It was not some aftermarket spray-on. I think it was injected same as pressure treated against rot. I know it left irritating crystals on you some times

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #101594, reply #9 of 18)

fire treated ply "fell" apart all the time... the stuff from the '80's seemed to delaminate before it was unbunked... the fire treat broke down the glues... nailing the sheating on was the fix till the crew could collect and clear the site.. a word never spoken about the problems... major law suits against the mfgr's too....


he's in for a 100% new roof....


Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming


WOW!!! What a Ride!


Forget the primal scream, just ROAR!!!

"Some days it's just not worth chewing through the restraints"

(post #101594, reply #11 of 18)

Yeah, I had read something about class action lawsuits, but thought opportunity to collect was gone long ago. Maybe there is something still active.

As I remember, it not only interfered with the glue between plies, buty that it actually broke down the wood cell structure like mold does, but without acting like a visible parasite

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #101594, reply #18 of 18)

> I'd think that the worst problem is that he would lose any shear strength in the rafter/roof assembly ....


In addition to that, he's putting more weight up there than the rafters or trusses were designed for.  If seismic loads are a consideration, that's a real bad thing. 


Weight is bad, weight up high is worse.  In an earthquake, the weight of the roof uses the whole height of the house as a lever arm.  It's like the difference between swinging a hammer, and swinging a hammer handle without the head.   


 


 


-- J.S.


 

 

 

-- J.S.

 

(post #101594, reply #10 of 18)

To add to what Piffin said, I used to live in Fairfax County VA.  There the building inspections department required the use of fire retardant plywood in certain situations, and specifically on townhouse roofs.  I remember because I was on the roof installing it in the 70s...  Anyway, later, it was found, as Piffin says, that the fire retardant plywood deteriorated relatively rapidly.  My wife owned one such townhouse - before we got married.  It was built in 1984.  We got married (1989) and she sold the townhouse a few years later and was forced to replace the entire roof - plywood and all, at a cost of $thousands for a relatively small roof.  The funny thing was that the county basically disavowed all knowledge and (obviously) responsibility- and none of the builders could be found although personally I think it was the counties fault for requiring it and more so the lumber manufacturers.

Matt

(post #101594, reply #12 of 18)

I have an old stone farm house and moisture would come in the basement and have no where to go -- it went to the attic and stayed there -- roof got spongy and not only had to replace the shingles (only 10 yrs old) but also the sheathing -- roof now had a thermostatically controlled roof vent and it makes all the difference in the world because the moist air is sucked out -- how is the cathedral cei.ing vented?

(post #101594, reply #13 of 18)

It's a shed roof, and the both ends have soffit vents. In theory, it should be enough venting, assuming the vents haven't been painted over, and there is some provision for keeping the insulation from filling the entire area between the rafters.


There's a skylight that blocks the airflow between the rafters in two places. I suppose I should have a roof vent installed above the skylight?


I appreciate all the feedback. There doesn't seem to be any alternative but to rip off all the shingles, see what we see, and work from there. I like the idea of the Advantech sheathing.

(post #101594, reply #14 of 18)

I'm gonna stick my nose in here and risk annoying my honoured friend and mentor Piffin by suggesting you skip the Advantech and go with standard exterior-grade plywood.


Here's the blurb from the Advantech website about the composition of their product:


AdvanTech engineered wood panels are bonded with an advanced resin technology system. Tests by  U.S. Forest Products Laboratory and Oak Ridge National Laboratory have found formaldehyde emissions from panels bonded with phenolic resin to be nonexistent or negligible. The Federal Department of Housing and Urban Development (HUD) has exempted wood panel products bonded with phenolic adhesives from all formaldehyde testing requirements.


This is just an example of the general reason I hesitate to use new 'engineered-wood' products. I don't claim to have an opinion on the formaldehyde issue, but I'll bet that fire-retardant additive was approved by some government department before it was marketed, too.


Government approval is not an assurance of problem-free performance.


Neither is the 50-year guarantee the manufacturer offers. In most cases, a long-term guarantee like that is just fancy marketing razz-a-ma-tazz unless (a) the product has actually been in use for the last 50 years, and (b) you have a reasonable expectation that the company will be around to honour that guarantee for the next 50 years.


The issue with these new high-tech building products is, to a great extent, one of chemical interactivity. Possibly the formaldehyde/phenolic resin used in this particular product is stable in a neutral environment, or even in contact with any of the other commonly used 'engineered' building products in use today.


But what new type of methyl-ethyl-badsh!t will some bright boy come up with in ten years? Will the glue in Advantech (or the cross-linked polyethelyne in PEX, or the binders or colouring agents in Hardiplank, or...) co-exist happily with the next whiz-bang chemical soup...or will it start to degrade?


There's no way of knowing.


There have been too many high-tech product failures in recent memory. I take a very conservative approach to using these products as a result.


MikeSmith, Piffin--I know you guys disagree with me on this; go ahead and make your own cases to this poster. I've said my piece.



Dinosaur


How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....


Dinosaur

How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....

(post #101594, reply #15 of 18)

I bow graciously to the extrememly civil manner in which you have presented your case. It seems to perch precariously on the limb that "we don't know how long new stuff will last" and then you recommend plywood instead. ( when I posted my recommendation for Advantec, I saw that limb and ducked under it, but now that you have waved it at me...)

I would point out that in the approximately ten years Huber's product has seen service, it has not failed and has won the confidence and trust of thoise who use it, even to the point of sometimes paying more for it, than for similarly rated plywood. I admit that We don't know whether some extreme situations might at some point in the future lead to failure of the product - that is true, but for the life experience we do know of, it out preforms typical exterior rated plywood

But by comparison though, we do know that an inconveniently large percentage of the supplies of CDX plywood currently available do fail in that delamination of plies is a regular occourance. On the average job, I fully expect to have to return culled out three or four sheets if I am using plywood.

So we are faced with the quality control question "Shall we use a sheathing product that is winning the loyalty of users wherever it is available by virtue of its apparant percieved quality or shall we use the previous generation of sheathing in full knowledge that some of it fails and that we may need to replace a sheet or two of it within a year or two, making this choice primarily because it has a sixty year track record so we know how it will perform?"

So here we are, in a free land, making choices based on freely available information, to work in a free market, to pursue happiness and a dry roof. May we all be happy with the choices we make!

and now Mon Ami, shall we retire to the Tavern for a round? First one is on me.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #101594, reply #16 of 18)

If you have FRT then there is a reason and you will need to fire rate your roof assembly differently than FRt provided. We remove the plywood, nail a 1x4 cleat 5/8" lower than top of truss chord, cut  5/8" sheetrock in 22 1/2" strips and nail ply over this assembly.


 

 

(post #101594, reply #17 of 18)


I'll get the next one....



Dinosaur


How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....


Dinosaur

How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....

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