08:53PM | 07/05/04
Member Since: 07/05/04
1 lifetime posts
I am purchasing a home. After the purchase offer was accepted, the physical inspection revealed that portions of the roof sheathing were delaminated and the rafters were discolored due to significant moisture in the attic caused by a bathroom exhaust fan which was venting into the attic. I agreed to continue with the purchase after the owners agreed to an addendum to the purchase offer requiring them to install a new roof to include sheathing/decking. I recently got a copy of the contract with the roofer and discovered that new plywood will be installed over the existing damaged plywood. The damaged sheathing will not be replaced. Is this an adequate repair for this problem. What plywood thickness should be used. I am very concerned. The roof is due to be installed in 1 week. Help! I know nothing about these things. I'd appreciate any advice.


06:21PM | 07/06/04
Member Since: 01/28/03
693 lifetime posts
I agree with Grumpy's advice to correct the ventilation problems and address any mold problems, but...

And while it is probably best to remove the old sheathing before installing the new...

That does not really address the question of adding new plywood over old.

As long as your building code permits its and it does not add too much weight to the existing roof rafter system, there is no reason I can think of that would prevent the addition of a new roof deck over the old.

As long as the new plywood itself can span the distance and carry the roof, wind, seismic and snow loads for your region, adding new ply over old is just fine.

The new plywood thickness should be at least equal to the exusting plywood thickness.


01:03PM | 07/08/04
Member Since: 01/21/03
66 lifetime posts
It is relatively common practice to lay new sheathing over old, but I don't like it, and whenever we are faced with this, we remove the old and install the new. I'm going a reroof in two weeks time, where we are removing all the old roof covering, and the old sheathing (delaminated and rotted 3/8 plywood) and replacing it with new 5/8 T&G plywood.

My reasons were: 1) the old stuff has no more structural integrity, and at best, it is a spacer between the new sheathing and the rafters onto which the new sheathing is fasted. 2) The old stuff is full of mold. Why build a new roof with the mold-starter built in? 3) If and when you will sell the house, someone will go into the attic and see all the old rotten and delaminated wood. How are you going to convince them that you've got good stuff hidden away behind it?

While we've got the sheathing off, we are also going to ensure that the ventilation channels (from soffits to the main attic area) are clear and open. The homeowner wanted to have a proper solution, since the two roofs he installed in the twenty years he's lived in the house have failed prematurely.


07:54AM | 07/11/04
Member Since: 11/06/02
1281 lifetime posts
You have two reasons for replacing the plywood. One is the structural failure you see in the de-lamination. The other is that there is undoubtedly mold damage and mold spores in not only the sheathing but in other places also. Has your inspector raised this concern? I would expect from seeing this problem a dozen times ( why don't people hook up their vents and kleep them clean?) that you have mold problems in the attic insulation as well. You need to be sure that the vent is correctly installed, and ANY material harboring mold is replaced with new.

As to the structural issues, There may be local jurisdictions - mostly in seismic zones and hurricane zones that would have specific issues with nailing new over old that would probably be adressed with increasing the number of fasteners to overcome the lost shear strenth in offsetting materials like that. Other places might reject that option outright, requiring direct application to satisfy requirements for shear.

Here is another hint for your negotiations, If the current roof sheathing has only 3/8", they may be considering the same for replacement. that is still acepted in some places but is woefully inadequate for roof loads if you still want it to look good in a few years to avoid sagging between rafters. depending on the area of the country you are in, you would want 1/2" or 5/8" sheathing

Excellence is its own reward!


10:52AM | 09/04/13
"and the old sheathing (delaminated and rotted 3/8 plywood) and replacing it with new 5/8 T&G plywood."
Question? When you put tongue and groove on, what happens when the sheathing expands? I have seen some pretty bad damage from this type of installation in the past(torn shingles, plywood raised on all edges, nails pulled out of decking) has wood changed over the years or does it still expand abd contract. If it still expands get ready for some serious problems.
El Dude erino


11:34AM | 09/04/13
Member Since: 01/24/06
1548 lifetime posts
Replace the entire roof and use CDX or other treated 3/4 Ply wood


Post a reply as Anonymous

Photo must be in JPG, GIF or PNG format and less than 5MB.


type the code from the image


Post_new_button or Login_button

If you are interested in more about fans and air conditioning, consider: How To: Install a Ceiling Fan How To: Choos... It turns out that many bath and kitchen cleansers contain chemicals that are dangerous to the skin and eyes, and often pro... So often we paint tiny nooks white to make them appear larger, but opting for a dark, dramatic wall color like this one—Be... Chocolate-colored walls and large window frames allow the exposed wood beams to take center stage in this small screened p... If you're not crazy about the idea of commingling plants and pool, this modern variation may be more to your liking. The s... Yes, a freestanding garage can become its own tiny house. Artist Michelle de la Vega has all the comforts of a modern resi... There’s nothing like a new set of cabinet hardware to refresh a room. The possibilities are endless: Go modern, rustic, or... Pursue what's known as the stack effect. To achieve it, open the windows on both the upper and lower floors, and as warm a... Like no other floor type, a checkerboard design works wonders to underscore the retro kitchen theme. Vinyl flooring, ceram... Twine lanterns add pops of crafty—but sophisticated—flair to any outdoor setting. Wrap glue-soaked twine around a balloon ... When securely fastened to a tree or the ceiling of a porch, a pallet and some cushioning make the ideal place to lounge. V... Incorporate nature into your lighting scheme by securing a dead tree in a concrete mold and draping your pendant lamp from... For the cost of a can of exterior paint , you can totally transform your porch. Paint the floor a hue that complements yo... In this urban apartment, a standard-issue patio became a serene and green perch by replacing the typical concrete with gro... If you put the washing machine in the mudroom, you can stop the kids from walking through the house in dirty, grass-staine...
Newsletter_icon Google_plus Facebook Twitter Pinterest Youtube Rss_icon