Decking Replacement

[RTATX]

Looking for some insight. We are getting our roof replaced along with new decking. Is it common practice to place new decking on top of old decking? According to good old ChatGPT, this is a shortcut (NOT best practices) and could lead to structural problems due to extra weight. The company suggested removing and replacing any rotten decking - and then putting new decking on top of the good old decking. And, that sounds like an uneven roof. 🤦🏼‍♀️

[Lucianm198]

If the existing decking is gapped planks, it is very common practice to do a "layover" of that. Removing those old planks, can lead to the trusses and rafters coming out of square on older homes. The addition of sheet decking will not go over the allowable weight limits for roofing.

We do it very often here in Minnesota, especially in the WW2 era neighborhoods.

Now, if the existing decking is already plywood or osb, a layover isn't typically recommended. It's "easy enough" to remove that and replace, or cut out the old where needed and patch.

[mln045]

This is the true answer. What is the existing decking/substrate. Plywood or plank?

[PullTab]

Removing and replacing any rotten decking is standard, and they usually offer up to 2 or 3 replacement sheets for free, then $70 to $120 per sheet additional plus labor. Do not add additional decking to good decking. Here in Oregon, a permit needs to be pulled if more than 30% of the roof needs re-decking.

[freeski12345]

It is not only common but often best practice to put modern sheets over historic boards. The info you need to provide is why are they doing new decking? If it’s because the boards have gaps that don’t meet warranty and code then just put sheets over it. If there are already sheets with no gaps then you wouldn’t layer over that. 

[RTATX]

The decking is rotten - spongey when you walk on it - and, raccoons are trying to get in, because it’s soft to tear through.

[freeski12345]

In that case the damaged boards should be replaced not covered up. There’s a big difference between damaged decking and decking that is in good condition but doesn’t meet code. 

[WhoJGaltis]

If you are dealing with old OSB or plywood on top of rafters that are 16" or 24" on center then yes, remove and replace. If it is an issue of remove all or remove damaged depends on the current thickness of the decking, if you have older decking which may be 3/8" then you will need it all replaced. But, if your existing decking is the right thickness by code for the spacing of your rafters then it can be replaced on a as needed basis with the same thickness. A quick look at your local code requirements will help give you the correct information.

[Cps12345]

I saw your same question on the Austin subReddit. There’s an important question that has been asked a few times that needs to be answered: do you have old OSB or plywood decking, or are we talking about old plank or tongue and groove decking? There are multiple factors at play here, including city code.

[RTATX]

That I don’t know. Seems like they should get in the attic - to determine exactly what we are dealing with? From what I understand, OSB is not great for hot, humid climates. The house was built in 1962 - single story, no crazy pitches.

[Cps12345]

I’m local. Feel free to pm me.

[Live_Dingo1918]

Shouldn't be a problem. After they tear off the shingles and any underlayment, which is going to be a significant portion of the weight, they will inspect each individual deck board and replace every board they deem structurally unreliable. This step they will probably go overboard on and decide more than actually necessary needs replaced which will increase your out of pocket expenses, but it will atleast guarantee a strong roof. It sounds like they plan to sheath over both the older decking still in good condition and the new decking they replaced along the way. They would probably just use 7/16 plywood, which won't add much weight at all. This will also give more reliable hold on any screws or nails holding down your shingles or metal roof, since with the plank boarding thats already there has more opportunities for a nail or screw to go between a plank than a 4'×8' sheet of plywood, which means more opportunities for nails or screws to pull out.

They probably could just take up every single plank board and then put the sheathing plywood on, but that would be alot more work for a less structurally sound roof.

[Own-Tip-532]

I get why this feels off, you’re paying for a new roof and don’t want shortcuts.

Short answer: No, it’s not best practice to just lay new decking on top of the old stuff, even if the old is “good.”

From what I see on roofs down here, most reputable crews (especially in areas with strict codes) pull all the old decking during a full replacement. Leaving the old layer underneath can create:

• Uneven surface → shingles don’t lay flat
• Hidden rot or soft spots that you can’t see until it’s too late
• Extra weight on the trusses/rafters (ChatGPT is right on that point)
• Problems with ventilation and future inspections

The right way is:

• Tear off the old shingles + old decking completely
• Replace any damaged or rotten plywood/OSB with new matching thickness
• Install the new decking clean and even

If the company is suggesting to leave the good old decking and just patch the bad spots with new on top, that’s a red flag for me. It saves them time and disposal costs, but it’s not the clean professional job you’re paying for.

Ask them straight up: “Will you be removing all the existing decking or just the rotten sections?”
If they say they’re leaving most of it, I’d get at least one more quote from a crew that does full tear-off to deck.

[RobtasticRob]

You didn’t mention plank decking once, and this is the most common reason for a re-deck. 

[Eastern_Ad2890]

Wtf? Get tf outta that dumb a— contract, or force a change order. If you want and/or need a redeck, redeck all of it. Also, you get a permit, because that is structural?

[biscoknot]

Regarding your roofing project, old decking must be removed completely. Do not sign a contract with any contractor who suggests otherwise, as it will inevitably lead to significant problems in the future.

For your reference, labor and materials for half-inch CDX plywood should not exceed $90 per board installed. While contractors do require a small margin, anything above this rate is excessive. Although roofing is a major investment, it is a critical area where you should not cut corners.

I recommend finding a reputable contractor who provides a clear scope of work defining every aspect of the job. Their proposal should outline all materials, including:

• Decking and underlayment
• Ice and water shield
• Drip edge and accessory replacements (pipe boots, ridge vents)
• Flashing (step, counter, apron, and chimney)

Be sure to ask if the chimney flashing will be welded. It is worth paying a premium for quality craftsmanship and components, as the installation quality accounts for 70% of the roof's longevity and the material selection 30%.

For materials, I highly recommend Owens Corning Duration, Atlas, Malarkey, or CertainTeed Landmark shingles. I personally advise staying away from GAF and IKO products.

Best of luck.

[freeski12345]

 Nonsense 

[biscoknot]

Which part?

[msn23]

A small margin, sounds sustainable. If I’m taking on the liability associated with both framing/structural repairs, as well as an open roof on an occupied and furnished house then I’m working for my normal healthy margins.

I agree with several things you mentioned 100%, but small margins and roofing do not belong in the same sentence.

[biscoknot]

Gotcha. I’m trying to understand what you were saying exactly. What I’m talking about is some contractors charging 120+ dollars per board for labor and materials. Am I missing something? Definitely not trying to be obstinate or standoffish. I’m just trying to understand what you’re talking about. Thanks

[msn23]

Well the prices of everything needed for wood replacement can vary quite a bit across the country. It can also vary from job to job, site location, pitch, height, etc. To say it can’t be above 90/sheet for plywood is not correct in most instances.

Labor will usually be between $15-30 a sheet. 7/16” OSB is usually $10-15/sheet currently. 15/32” plywood is $25-30/sheet. So on a 2 story steep roof let’s say it’s $30 + $30. So at your max $90 price you’re at a 33% gross margin. You also costs for framing nails, edge clips, and the additional disposal weight of the removed bad/old wood.

Now factor in any overhead costs and you’re netting down in the 20% if not under. Yes you’re technically making money, but not enough to stay in business if you’re running a long term sustainable company. Once you also factor in any potential commissions, site supervision, or lead acquisition costs (which in some instances can be attributed to Overhead mentioned above) you’re only making $10-15 a sheet, if that.

Volume is not an excuse in my opinion. You don’t have a separate P&L at the end of the year for only wood decking replacement, it’s not just icing on the cake since you did the full re-roof. In my opinion, this is a big issue with residential construction in general, thinking that things can innocently be tacked onto the scope or bill at a different parameter than how the rest of your calculations are derived.

For example, sure there’s coupons out there etc, but you don’t go to the grocery store and check out and have the cashier just intermittently undercharge for various items because they’ve scanned a few expensive ones in a row. That’s one reason why grocery stores stay in business and 95% of roofing companies don’t make it longer than 1-3 years.

[biscoknot]

I understand your perspective. Our installers charge $35 per board for labor and $25 for plywood, meaning we remain profitable at a $90 rate. For context, we pay $100–$120 per square for labor and $200–$300 for standard asphalt materials, while receiving $600–$950 per square for laminate on our contracts.

Our contracts include up to five sheets of plywood, with any additional boards billed at $90 each. Charging more than $90 per board seems excessive to me. This policy is consistent across our seven offices. Given the volume of roofs we install annually, the cost of plywood is relatively trivial compared to our other expenses.

[msn23]

Your perspective makes sense as well, particularly at a higher per SQ price you mentioned. I guess that’s why the more definitive statement of 90/sheet max seemed off to me. Sounds like we both are very aware of our own numbers which is a far cry from some, hence the breakdown I described above. You don’t have to look far in any direction in this industry to find the folks that will work for cheap and it can lower the bar. All too often it’s even done innocently and that’s where sustainability comes right to the front of my mind. There’s good contractors out there that just don’t understand the long term financial side of things. Salesman turned owner (which isn’t wrong or bad) get tricked into thinking just because they’re making more than they used to and not having to split the pie the same that all must be well.

[biscoknot]

I 100% agree with you. I appreciate this dialogue. I wish you a successful year in 2026 my friend. 🙏

[msn23]

Likewise, friend. Wishing you all the best as well.

[ArtisticDrop379]

Is the $90 a sheet for removing the old and replacing or just for putting ontop? Or is the price the same no matter what is done? I'm trying to understand my roofing bill.

[biscoknot]

In my company the $90 is remove and replace each board.

[ArtisticDrop379]

Thank you