Rotted plywood cannot support the weight of a roof the way healthy wood can nor can it safely grip the nails put into the roof and keep them held firm.
Roof change plywood.
If your roof carries a heavier load like if there s less pitch and or it snows in your area a roofer may recommend the use of the inch variety.
Moisture causes wood to rot and rotten wood absorbs water even more readily than fresh wood.
This is a popular option because it presents homeowners with functional but affordable roof sheathing.
Inspect the underlying roof sheathing for damage and make any needed repairs.
Start from the top of the roof and remove the old shingles along with the flashing underlayment and vents.
Most roofs will be sheathed in plywood at least 3 8 inch thick.
A half inch cdx plywood is often used with rafter with 24 inch spacing.
Hammer down any large nails that are exposed by the removal.
Place a new plywood board in the same location ensuring the ends align over roof rafters.
Step 6 unroll new roofing felt over the new plywood and extend it at least 3 inches over each edge of the new plywood.
Loads will vary with the pitch of the roof.
That will suffice on a roof with rafters set 16 inches apart with minimal roof loads.