Rotted plywood can cause a number of issues.
Roof change plywood.
Install a layer of roofing insulation as recommended by the roofing manufacturer.
A half inch cdx plywood is often used with rafter with 24 inch spacing.
This is a popular option because it presents homeowners with functional but affordable roof sheathing.
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.
Step 6 unroll new roofing felt over the new plywood and extend it at least 3 inches over each edge of the new plywood.
Place a new plywood board in the same location ensuring the ends align over roof rafters.
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.
Inspect the underlying roof sheathing for damage and make any needed repairs.
Most roofs will be sheathed in plywood at least 3 8 inch thick.
That will suffice on a roof with rafters set 16 inches apart with minimal roof loads.
Secure the plywood by inserting six penny nails along the rafters spacing them every 6 inches.
Moisture causes wood to rot and rotten wood absorbs water even more readily than fresh wood.