What is a nailable roofing surface?
In this slideshow we are attempting to illustrate what the bottom of the roof decking would look like after four roofs had been installed. What you are seeing are the shingle nail lines that repeat approximately every six inches all the way up the roof of course in an actual scenario most of the roofing nails get removed after each re-roof. However, in an effort to fully illustrate this for the camera, we decided to leave the nails in place. Also, we painted the nails to make them stand out. We also painted the back side of the OSB decking white, so that the nails would stand out even more. How safe do you think it would be to walk on the surface of a roof deck with this many holes? Well, it is actually much worse in reality as we did not use any roofing felt because we wanted to make the view of the nail lines clear and distinct for the camera.
How many nails are too many?
Using the nailing patterns recommended by some felt manufacturers, you would use almost as many nails as we used to apply the shingles. Now imagine what that decking would look like with all of the nails from the felt in place as well. Now add in even more nails for the ridge shingles, the hip shingles, valley metal, step flashing, drip edge, and more. Composition shingle nail lines repeat up the slope of a roof approximately every six inches. This means that there would be a horizontal row of nails every six inches all the way from the bottom to the top of the roof plane.
Once the old roof has been torn off, the new shingles would be installed beginning at the eve of the roof as were the shingles of the original roof. All things being equal, the nail lines for the new shingles would fall in the same place approximately every six inches as they did on the original roof. Most of the time the nails would find good solid decking, but occasionally the nails would be driven directly into a prior nail hole or close to a prior nail hole. Through an experiment performed entitled “roofing nail pull force testing”, it was found that many of the nails that were driven within a half of an inch of a prior nail hole seemed to hold with only a fraction of the strength of a nail that is driven into decking that has no nail hole around it. Of course, if it is driven into or just to the edge of a prior nail hole, there will be almost no adherence to the decking at all.
10% are driven in the same holes
With every roof that is torn off, the rows of nail lines are increasingly populated with prior nail holes, and the risk increases that you will have shingles that are more easily blown off. At four nails per shingle, it has been calculated that on the very first re-roof as much as 10% of all the nails driven into the shingles would be driven within a half inch of a prior nail hole. For each re-roof thereafter; the percentage rises exponentially. Almost all roofing contractors are now utilizing nail guns to fasten roofing shingles. When using a nail gun, the roofer would likely have no indication whatsoever that a nail had been placed in a weak spot or directly into a prior hole. By hand nailing the shingles, the roofer might have a good idea that a nail had gone directly into a prior hole, but it might not be altogether clear if it was in a spot that was merely weaker due to being near a prior hole.
It will be ok – right?
Your insurance company may tell you that they might have considered paying to re-deck your roof if you were on your third or forth re- roof, but since it is your first re-roof then “it won’t be that bad”. The problem is the next time you replace your roof, what if you don’t have insurance or the cause of the damages excluded for one reason or another? Then you might be on the hook to pay for the decking that your insurer talked their way out of on your last roof replacement.
Indemnification is a four letter word
It is our position that the reuse of roof decking is not indemnifying policyholders to a pre-loss condition.