OSB Roof Sheathing, Windstorms, and Your Roof
Windstorm certification of your roof is a big deal in coastal areas, and it can be important for your insurance.
I actually enjoy going in behind another inspector, doing my own analysis, and then hearing what they stated. Most of the time different types of inspectors come up with the same findings, because we are looking at the same things. Sometimes the analysis and the significance may differ though. There are times that I am left scratching my head. Today was one of those days after I discovered that my roof inspection was dealing with a windstorm certification, and the findings of another inspector.
I do not perform windstorm certifications, so I cannot speak to the standard that those inspectors are required to abide by. I have been involved in a few inspections where windstorm certification for a roof was needed, and generally I did not have moments where I was in disagreement with these inspectors. Mainly I find if the inspector does not walk the roof, and I do, I may see something differently, because I have gathered more facts. They may have gathered more facts than I did on another part; however, I usually go beyond what many inspectors do, so I have helped clients dealing with insurance agencies or builders in the past. I do not know what this inspector did (did he go up on this roof?) or what he stated (I did not speak to him or see if he produced a report), but there is one statement from the homeowner which has me wondering.
Many inspectors that I have encountered do not go up on roofs. I am sure that they would not go on much of the roof that I was on today; it is not safe. I coud not find anything wrong with the install from being on the roof. In fact, the roofer had done quite well compared to others. One thing immediately bothered me though. The old vents had been reused. They were plastic vents, and they already had problems. The roofing contractor said that the family did not want them changed out, but I told him that these were already primed to leak. What also bothered me was the ventilation for the attic. The flow would have been bad. The contractor said the family did not want a ridge vent. I do not know if this is true, but if you are planning on having your roof redone, you may want to learn about things to consider: vents are great leak points; metal vents are better than plastic; air ventilation for your attic can effect the life of your roof and the energy efficiency of your home; and the type of roofing material is dependent on your roof slope. You may also wish to be aware that the type of roof covering can effect your energy efficiency. This homeowner may have been trying to save money. The contractor may have wanted his bid to be the lowest. You can cut corners, but understand the consequences, and contractors should educate you instead of letting you compare apples to oranges.
Here is where the issue that left me wondering comes into play, and it has to do with OSB sheathing. OSB is a perfectly fine roof sheathing material, and it is used quite often. OSB has a problem though when used in areas where it may be exposed to moisture: the strands are glued together, and they can delaminate when the board has moisture. OSB stands for oriented strand board. If you have hammered a nail through this board, you may know something else about the way the material behaves. The nail does not always go cleanly through. Small strands can buckle out. This happens more often when using a nail gun, but it can happen with a hammer. Why is this significant? The board has a greater weakness at that point. If the shingle is loose, the wind could rip the shingle away from this damaged sheathing with a greater possibility than from other spots where the sheathing was not damaged in this fashion. There are some factors which we have to consider for this to happen. Is the roof covering loose where it can fly up during the windstorm? (Asphalt shingles have a glue strip which glue the different shingles together, and then the asphalt itself melts into one piece). How much of the OSB came off with the nail? (Nail into any wood product and you will often have some slivers break away from the main board). Does the manufacturer state that nail guns should not be used with his shingles? (You have to check the packaging for this one, but many manufacturers do not place a prohibition against nail guns on sheathing or roof coverings). Did the nails damage the shingles when they went in through the face? Were there enough nails in the shingle? Where they nailed into the correct location? (This can only be checked if the shingles can be parted with breaking them. Also, I am writing nails, but there are various fasteners which could be used).
My dilemma is that this first inspector apparently stated that 80% of the roof was installed incorrectly, because of this problem with the OSB. He may also have stated that a nail gun shoud never have been used. I am not a building code official, but I do read building codes, and you will see the statement that a product has to be installed according to manufacturer’s specifications. Unless there is evidence from the manufacturer that the nail gun should not be used, you cannot condemn its use. There is an exception, if building code for a certain area has a rule about the sheathing and about how it is to be installed, you can make the broad statements that the nail gun shoud not be used, or that the OSB is incorrectly installed due to these pop outs, but you have to be certified by the building code provider to do so. All other factors to me indicate that this roof will hold up in a windstorm. I have no evidence that the manufacturer has instructions against nail guns or that the OSB manufacturer indicates that its product is irreparably damaged by these pop outs. In fact I do not know if the contractor used a nail gun (he never said that he did, but I had the feeling that he may have used one). So this first inspector will not give the windstorm certification, but I feel that he may be in the wrong.
So is OSB sheathing bad? My prefence is not to use it for roof sheathing, because a leak is possible, which can damage the product. In fact, I would not use the product in any situation where there is a concern with moisture. However, the OSB used may be designed to handle that scenario. I may also consider cost. Going with another product may cost far too much. I would not say that OSB is bad. There are OSB sheathing pieces manufactured by responsible methods (think green here). I mean the product on a normal basis is using material which otherwise may have been wasted. It is engineered for strength. Moreover, the binder holding the strands together can be low VOC. Also, the material used for the strands could have come from sustainable forests. Unless I can find a report stating that these nail pop outs in OSB severely weakens the material, I cannot believe that they do weaken the board. As I wrote, OSB is engineered. The strands are aligned to give strengh, and that may not have been weakened in this situation.
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