How To – Replacing Old Roof Decking During Re-shingling

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    Most roofs are shingled with asphalt shingles that can last between 15 and 30 years. The length of time between re-roofing your home will be based on many factors: the selection or quality of materials, the methods use to install the shingles, temperature changes and weather conditions in your area and even insulation and venting in your attic.

    Normally roofs can be re-shingled without replacing the plywood decking however small leaks that occur around flashing, ice dams from winter storms and homes located in areas of high humidity may shorten the life of your decking.  When the damage is simple and identifiable dry or wet rot then the decking can be replaced without much worry. The important thing to take note of is if any of your rafters or trusses have also been damaged.

    Bug damage is another way that wood material can be damaged. Normally termites and carpenter ants like to eat 2x material like studs, joists, rafters and don’t normally damage plywood unless they have already eaten their fill of these other items. If you see termite or other bug damage then you need to have a good inspection of not only the adjacent materials but all parts of your structure.

    Determining the amount of decking to replace

    Once you have determined that there is damage you need to decide how much of your decking you will replace.  If you have damage in one specific area you can just replace the decking that is damaged. If you find that a large area or a number of smaller areas are effected you may want to go ahead and replace the whole deck.

    Older roofs that use boards instead of plywood should normally have a large section or whole side replaced to bring the roof up to new material. Although there is nothing really wrong with using single boards for your decking it will be very difficult to match the material and you will most likely end up shimming some plywood to match the height of the old boards.

    Selecting Materials For Replacement

    Your local code will determine the minimum acceptable material you can use and this is usually a 1/2 inch plywood or OSB board with strengthening clips placed between the rafters to increase stability.

    In addition to the actual decking you will need the center clips we just mentioned and if you are doing a full roof deck replacement this is a real good time to look into adding hurricane clips, rafter hangers and metal ties to strengthen your roof system. You may even want to go as far as repositioning your rafters closer together then adding more rafters to get a minimum 24 inches on center.

    Performing the work

    As you can imagine the job won’t be easy and you will be pretty far off the ground so you need to take care when working. OSHA Standards would require that you use a safety harness but most contractors will simply install a pole jack scaffold around the roof to catch anyone that may fall.

    Additionally you should perform as much of the work by standing within the roof on your rafters and not hanging over the edge or depending on a single ladder.

    Make sure that you notify a family member within the home, a neighbor or work with a partner to perform the work.

    An air nail gun will speed your work. Two types of guns will probably be necessary. A clip fed gun for nailing down the decking and a coil fed gun for installing the shingles. Expect to cut your install time in half or more by using a pneumatic nail gun.

    Once the decking is down you want to use Ice Dam Membrane for the first 3 feet of the roof and also around areas such as pipe vents and chimneys. Cover the rest of the roof with tar paper using a chalk string line to snap guides for your shingles.

    Apply your shingles and step flashing to complete the job.

    To extend the life of your roof you can add a ridge vent or gable end vents with an automatic fan.


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