After that use a piece of lumbar strapping to keep the plywood in place until you can get a roofing repair expert to fix it.
Fix sagging roof line.
Unfortunately most roof structural defects don t respond well to homeowner fixes and require professional evaluation and repair.
Check the ceiling for sagging by attaching a string on one end of the beam and run it along the bottom edge of the beam.
When the framing of the roof is put together quite frequently two of the ceiling rafters will be fixed together as this will create a much longer span.
The first step is to the basement first.
Then inspect the metal or plywood gusset plates.
If the sagging roof is due to rotting or warping roof decking the repair will be much easier.
This may be problematic in winter months but allowing the roof to continue to sag can lead to greater problems such as a cave in.
Move the jack in increments of one inch to allow for the roof to be able to move with it without cracking.
Fortunately there are different ways to jack up a sagging roof.
Typically they are lapped and then toe nailed together in its center so that the correct length can be achieved.
A sagging roof line may original from the ceiling s horizontal rafters.
That s how to fix a sagging roof.
The easiest way to straighten rafters is to jack them into position.
Problems with and repairs to a sagging roof should be evaluated by professionals.
Using a flashlight inspect the rafters and decking in your attic especially in the areas where your roof is sagging.
You will need to remove the shingles and the old decking however which means there will be an exposed hole in the roof.
Look for any kind of damage including rot cracks breaks and more.
If the line does not continually follow the bottom of the beam and the bottom of the beam is below the line the beam is sagging.
Push up on the plywood until the foam is touching the underside of the roof decking.
To learn more about roofs and attics see these other blog posts.
This gives your roofer a chance to inspect the flashing and roof underlayment for damage.
Next place your piece of plywood and styrofoam foam side up against the damaged roof decking.
Why is my roof sheathing sagging between the trusses.