When it comes time for a roof replacement, there’s one hidden component that often surprises homeowners: roof foundation replacement.
Although common for homes with undiagnosed roof leaks, homeowners tend to be surprised by the cost of replacing the lowest layer of their roof. While necessary, it’s known to be a pricey fix. Not only that, but usually you won't know you need the foundation replaced until the old shingles are removed.
At Linta Roofing, we like to be transparent about the costs associated with replacing all parts of your roof before a contract is signed. But in the event that you’re not aware of the price, we’re here to break it down.
So, how much does it cost to replace the foundation of your roof?
Let’s get into it.
What is the Foundation of a Roof?
Roof decking is the foundation of your roof. Roof decking is the layer of wood beneath your shingles and underlayment that provides structural support for your roofing system. It’s usually made of OSB (oriented strand board) or plywood. If this wood is rotted, sagging, stained, or damaged, it must be replaced to prevent detrimental roof issues down the road.
How Much Does it Cost to Have the Foundation of Your Roof Replaced?
While the price can vary some from roofer to roofer, this is the general breakdown:
- Average Cost Per Sheet (4’x8’ sheet): $75 o $95 (including labor and materials)
Some roofers in the area may provide a sheet or two for free and charge this price for additional sheets as needed.
You may be wondering, why is a sheet of plywood so expensive? It all boils down to the labor that goes into replacing roof decking.
This labor includes:
- Tearing out damaged decking
- Removing nails
- Cutting new boards
- Hauling off debris
Although a single OSB sheet may cost only $10–$12 at a hardware store, the real value lies in the skilled labor involved. Roofers are working at heights, removing and replacing boards in often difficult conditions. This is a service-based cost more than a material-based one.
Does the Entire Foundation of My Roof Need Replacing?
Most roofs need little to no decking replaced, especially if they’ve been regularly maintained. In fact, at Linta Roofing, we find that only a small number of homes require more than 4 or 5 sheets.
However, there are exceptions. Some rare cases require over 10 sheets due to widespread rot or structural issues. For example, one homeowner in our area had significant sagging over a large roof area, ultimately requiring a major repair.
These photos show the damage we uncovered when we removed the shingles and underlayment on their home.
Can you Tell if Your Roof Foundation is Failing?
There are a few telltale signs that may indicate your roof foundation might be failing:
- Leaks inside your home – water stains on ceilings or walls are a red flag.
- Visible sagging areas – if you spot dips in your roofline from outside, that could mean the decking underneath has rotted.
- Attic inspections – if safe to do so, look for dark stains, water damage, or visible sagging from below.
Keep in mind that many roof foundation issues are hidden beneath shingles. It’s not always possible to know the full extent until the shingles are removed during the replacement process.
Frequently Asked Questions about a Roof Foundation Replacement
Q: Do you have to replace an entire sheet of roof decking?
A: Not always. We typically replace decking over at least two rafters to ensure structural stability. If a section is only partially damaged, we don’t necessarily remove a full 4x8 sheet—but we make sure the repair spans enough area for strength and safety.
Q: Can I request a roof foundation inspection before deciding on a new roof?
A: You can request one, but remember: even the most thorough inspection won’t reveal all hidden issues until the shingles are off. We’re upfront with homeowners and never promise that no decking replacement will be needed.
What Homeowners Should Expect from a Roof Foundation Replacement
Your roof decking is a crucial element for your roof to perform its best. Reliable roofers will not replace your roof if you are not willing to have your roof decking replaced.
But fear not. As it’s not incredibly common to have a lot of roof decking replaced. Usually underlayment, ice and water shield, and roof flashing do a great job of protecting your roof decking when they’re applied properly.
If you have additional questions about the integrity of your roof, don’t hesitate to reach out to us at Linta Roofing. We’re happy to answer any additional questions you may have so you can get the peace of mind you deserve.
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