The answer to 'roof replacement sagging' is that a sagging roof is often a sign of structural issues that require professional inspection and repair. Roof sagging can be caused by factors like inadequate roof framing, water damage, or excessive weight from accumulated snow or debris. Symptoms may include visibly uneven roof lines, cracks in the ceiling, and doors/windows that no longer close properly.
While some minor sagging can sometimes be addressed with DIY repairs like reinforcing roof trusses or replacing damaged shingles, significant sagging is a serious issue that requires a professional roofing contractor to assess and fix. Attempting major structural repairs without the proper expertise and equipment can be dangerous and may cause further damage. It's best to have a qualified roofer inspect the roof and recommend the appropriate solution, which could involve full roof replacement if the damage is extensive.