Many Portland homeowners don’t know what to answer when I ask if they want their estimate to be for a roof tear off or a roof recover.
When there is no compelling reason for a recover, a tear off should be chosen. A tear off allows for your new roof’s felt underlayment to be installed directly on top of the sheathing. Since the sheathing is a uniform, rigid surface, this is going to allow for better life expectancy for the new roof. Being installed on top of the old roof (a recover) does not provide the same consistency. Some roofing material manufacturers will not extend the same warranty if the new roof is installed over an existing roof. Generally speaking, a roof that is torn off down to the sheathing will last longer.
That being said, a recover does have its benefits. Mainly, cost savings. While the saving may not be as high as you think, when every dollar counts, there is money to be saved with a recover. When a house has two roof layers or less, current Oregon code allows for one more layer. A recover is sometimes chosen when a house will be put up for sale very soon after the project and the owner is less concerned about buying the new owner extra years of roof life. However, a recover often is visible to the experienced eye and it could result in a slightly lower sale price.
This photo of a recent roof replacement shows an interesting side issue. Sometime when we tear off the roofing material, we uncover what is called OSB (Oriented Strand Board) instead of plywood for the sheathing. Many homeowners wonder if this is a cause for concern. Likely not, especially if an experienced and reputable company is performing the re-roofing project. Ideally, All Surface always chooses to use a 4-ply plywood for the sheathing when we are installing it from scratch. The main reason that plywood is preferred is its performance in moist environments. OSB, while cheaper and actually stronger than plywood in terms of shear strength, it can expand much more than plywood if wet, particularly on any cut edges.
Expansion of a roof’s decking (another name for sheathing) is not a good thing. It can cause lifting and buckling that can cause further, serious problems. Of course, a good roof should ideally never let water penetrate the sheathing. But over the life a roof, there are a multitude of unexpected occurrences that can allow moisture it (deteriorated pipe boots, dislodged flashing or vents, falling limbs, etc.)
However, if we our inspection of the existing OSB determines that it is in fine shape, the cost of removing it and replacing it with plywood is usually just not justified. A proper job of covering it with underlayment, flashing and new shingles will keep it from moisture exposure and any of the negatives that can occur.
If you are ready to have your upcoming roofing project done right, call All Surface today!