How To Fix A Roof
This roof deck looks rough, but doesn't look like it is is hiding anything terrible until you take a closer look. The board ends are rotten and, more importantly, the roof rafters are rotten. This is a major structural issue and can be dangerous to the homeowner. Fixing a rotten roof is tricky business as this is a very expensive and time consuming process.
Exposing The Rafters
In order to assess the damage to the rafters, the decking has to be removed. Rip off the decking boards starting at the top and working down to the eaves. This will give you a good idea of how bad the damage is and help you formulate a plan to fix the rotted rafters.
Repairing The Rafters
For this project, the rafters were 2x6s 18 feet long. This is undersized by today's standards, but was common for homes of this era (1930s). In order to strengthen the roof and repair the rafters, 2x4s were used on each side of the rotten rafters. Any of the rafters that were not rotten had a 2x4 attached on one side for added strength (See picture below).
Planing Out The Roof
In order to make sure that the new roof sheathing installs properly and the roof surface is flat, the new boards should be planed through to make the roof surface true. This means relatively flat. This is performed using a string line and a 6 foot level. The longer the level, the better. Remember that you are not looking for level. You are just making sure that all of the rafters are the same height after the initial height has been established by the string line.
It is important to give a roof like this as much structure as possible. For this reason, using 3/4 inch tongue and groove 4'x8' sheathing will lock the entire roof surface together, making the roof extremely strong. This also eliminates the need for sheathing clips and prevents joint swelling and de-lamination. The sheathing is nailed down with 8 penny nails typically by a pneumatic nail gun.
Now that the roof deck and structure are repaired, the roof can be properly water proofed and shingled. This is an inexpensive way to turn a nightmare repair project into a manageable fix that is also relatively inexpensive. One very important aspect of any roofing project is to make sure that you are careful to operate in a safe manner when on the roof. If you are uncomfortable with heights, this may not be a project you should undertake on your own.