Sheathing Buckle
So, you found the perfect home and it even has had its roof replaced within the last 5 years. Most people would not think there would be many concerns with leaks or problems. For the most part, this would be the case, however, there is a concern that many people may not be aware of that is cause for concern when a new roof is installed. The concern is sheathing buckle.
Sheathing is the underlying boards that attach to the rafters or trusses and support the roofing material, most commonly Asphalt shingle. The boards are made from different materials through time, sometimes it is an OSB (oriented strand board) material or plywood. When this material is taken from the manufacturer it contains a certain amount of moisture (4-6%) as most wood will contain some level of moisture. This amount of moisture is not the cause, nor concern! The issue with sheathing boards is how much additional moisture will these boards encounter in the process of being stored or traveling to a job site or when sitting on a roof just prior to being covered with the roofing material.
Recently I came across one of the worst examples of sheathing buckle I have seen. The lift was as much as 3-4 inches in a very short 8 inch strip covering over 3-4 rafters. This buckling causes a visible bulge line on the exterior roof surface (Since this roof was snow covered, the line was not visible, meaning attic inspection becomes even more critical). This condition, although not common, is not unheard of and typically involves a slight gap that you may be able to get flat ruler under to 1 inch lift. Is this cause for alarm, does not have to be. Depends on what is causing the lift. Several factors can cause the sheathing to do this. One such possibility is a lack of proper ventilation and too much moisture in the attic, especially in winter months, causing frost condensation (water) to collect on the sheathing. This will typically cause rot to the sheathing as well. The other contributor to this would be a lack of insulation, allowing hot interior moist air into the attic. However, when a roof is relatively new, there is likely another reason. What could it be? The most likely scenario is that when the roof was being installed, the roofers installed the sheathing firstly without the proper contraction and expansion gap needed to allow for the sheathing to fluctuate as it goes through hot and cold cycles and moisture levels due to humidity (controlled by ventilation and air flow). Secondly, the sheathing was likely left exposed installed on the roof of the home and was exposed to water or rain just prior to adding the shingles. The water would cause the wood to expand and since the board had nowhere to expand too, do to lacking gap, the sheathing begins to bend upward (buckling). If this buckling is severe, it is recommended to have a licensed roofing contractor evaluate and recommend repairs. Typically, this will result in having to remove the section of roof in question and replace the sheathing boards. Consult a contractor is you suspect this condition exists! This is also another good reason hire a qualified home inspector to inspect before any home purchase. You never know!!!
If you would like us to perform an inspection for you or have questions about the article, please feel free to visit us @ www.7countyhomeinspection.com , email : sevencounty@yahoo.com or call us @ 612-919-3844
So, you found the perfect home and it even has had its roof replaced within the last 5 years. Most people would not think there would be many concerns with leaks or problems. For the most part, this would be the case, however, there is a concern that many people may not be aware of that is cause for concern when a new roof is installed. The concern is sheathing buckle.
Sheathing is the underlying boards that attach to the rafters or trusses and support the roofing material, most commonly Asphalt shingle. The boards are made from different materials through time, sometimes it is an OSB (oriented strand board) material or plywood. When this material is taken from the manufacturer it contains a certain amount of moisture (4-6%) as most wood will contain some level of moisture. This amount of moisture is not the cause, nor concern! The issue with sheathing boards is how much additional moisture will these boards encounter in the process of being stored or traveling to a job site or when sitting on a roof just prior to being covered with the roofing material.
Recently I came across one of the worst examples of sheathing buckle I have seen. The lift was as much as 3-4 inches in a very short 8 inch strip covering over 3-4 rafters. This buckling causes a visible bulge line on the exterior roof surface (Since this roof was snow covered, the line was not visible, meaning attic inspection becomes even more critical). This condition, although not common, is not unheard of and typically involves a slight gap that you may be able to get flat ruler under to 1 inch lift. Is this cause for alarm, does not have to be. Depends on what is causing the lift. Several factors can cause the sheathing to do this. One such possibility is a lack of proper ventilation and too much moisture in the attic, especially in winter months, causing frost condensation (water) to collect on the sheathing. This will typically cause rot to the sheathing as well. The other contributor to this would be a lack of insulation, allowing hot interior moist air into the attic. However, when a roof is relatively new, there is likely another reason. What could it be? The most likely scenario is that when the roof was being installed, the roofers installed the sheathing firstly without the proper contraction and expansion gap needed to allow for the sheathing to fluctuate as it goes through hot and cold cycles and moisture levels due to humidity (controlled by ventilation and air flow). Secondly, the sheathing was likely left exposed installed on the roof of the home and was exposed to water or rain just prior to adding the shingles. The water would cause the wood to expand and since the board had nowhere to expand too, do to lacking gap, the sheathing begins to bend upward (buckling). If this buckling is severe, it is recommended to have a licensed roofing contractor evaluate and recommend repairs. Typically, this will result in having to remove the section of roof in question and replace the sheathing boards. Consult a contractor is you suspect this condition exists! This is also another good reason hire a qualified home inspector to inspect before any home purchase. You never know!!!
If you would like us to perform an inspection for you or have questions about the article, please feel free to visit us @ www.7countyhomeinspection.com , email : sevencounty@yahoo.com or call us @ 612-919-3844
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