In a previous blog topic, I identified what a sheathing or roof deck is, and identified that it is commonly plywood or oriented strand board (OSB). I am going to delve a bit deeper; what is OSB and why is it superior to wood planks? Also what makes OSB different than plywood? OSB is relatively new to the building market, coming only into common construction uses, including sheathing or roof deck, since approximately 2000. While plywood is made up of several plies that are veneered and glued together with wood grain oriented in specific directions, OSB is specifically engineered and made up of wood strands hot compressed with adhesive. While those strands may look random, the directions of the strands are strictly controlled in the manufacturing process. Plywood may have 5-7 layers; OSB may have 50 layers. In the plywood blog I identified that the plies in different directions increase the strength of plywood vs. wood planks, with OSB this benefit is magnified somewhat as the engineering and manufacturing controls can result in product where the strands are oriented in many more directions. For structural grade plywood, we already identified that there could be knots and defects, and this could result in voids internal to plywood sheet where you cannot inspect the product. OSB is compressed and will have no voids; further demonstrated by OSB weight (a sheet of OSB will weigh more than the same size sheet of plywood). Since OSB is a more highly processed and engineered product, it will be more consistent than plywood. As with structural grade plywood, since OSB used as sheathing and roof deck will be covered, appearance doesn’t matter. Which is a good thing, OSB does not have an attractive finished surface. It was engineered as a structural product though, and for that purpose it works admirably. As a specifically engineered product serving a specific purpose, it is definitely superior to wood planks.
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In a previous blog topic, I identified what a sheathing or roof deck is, and identified that it is commonly plywood or oriented strand board (OSB). I am going to delve a bit deeper; what is plywood and why is it superior to wood planks? Which do roofing companies prefer to use? Have you ever seen a Martial Arts demonstration that included breaking wood planks? Perhaps using feet, hands, or even their head? Have you ever inspected the planks themselves? It is easier to split a board with the grain than it is across the grain. Had those boards been cut differently, the Martial Arts demonstration might look somewhat different. Wood structures and wood furniture take advantage of this strength as the any loads or forces acting on the wood support the load itself. However for sheathing or roof decking, what is the direction of the force acting on the wood planks? Plywood is made up of many thin “plies” of wood veneer that are glued together. Each “ply” is laid out so that the grain is oriented in a different direction. This is called “cross-graining”, and among other things it contributes to dimensional stability, reduced potential to split when nailed close to the edges, and makes the strength of the panel consistent across multiple directions. The thin layers result in a product that is stronger than a single layer of wood, even if the single layer of wood may be thicker. These factors taken together are why plywood is superior to wood planks as a sheathing or roof deck material. Plywood is graded based on appearance and defects in the plies. For sheathing and roof deck plywood, since it will be covered by roofing materials to the outside and not visible to the inside, the important issue is structural and not appearance. There is no need to purchase Grade A (surface veneers free from all defects) and instead we use CDX (face has knots, defects, not appearance grade, not sanded). CDX is some pretty rough appearance plywood, but for a structural purpose it is more than sufficient. The important factor for sheathing or roof deck uses is that the plywood be exterior grade. Now then, next time I see a Martial Arts demonstration that involves breaking wood planks, I want to slip in a plank or two made of plywood. That will result in quite the headache… As a roofing contractor, I field a lot of questions about different components of a roof. Enough so that I think a series of blog topics to educate on all the parts would be useful for my prospective clients (and honestly for any homeowner, even if you don’t call me). Let me know if you find these useful. Asphalt shingles need to be installed over continuous wood decking; this wood decking is commonly referred to as sheathing or roof deck. In the ancient past, this may have been wood planks. However plywood and oriented strand board (OSB) have long since replaced wood planks, and as engineered wood products these are both superior options to wood planks. When we say, “They don’t build them like they used to,” in this situation I must admit the buildings are superior with engineered wood as the roof deck. Asphalt shingles are flexible and will telegraph any imperfections in the roof sheathing itself. The most common areas of imperfections in roof sheathing take place at the joints. Plywood or OSB come in four (4) foot by eight (8) foot sheets; these will have much fewer joints than wood planking, greatly reducing potential for imperfections at the roof joints. Wood is what is known as a “hygroscopic” material => this means that variations in relative humidity can impact its dimensions. As moisture content in the air increases (high humidity), the wood sheathing can absorb some of this water from the air, and this causes the wood to swell and the dimensions increase. As moisture content in the air decreases (low humidity), the wood sheathing will dry out and this causes the wood to shrink and the dimensions to decrease. The wood sheathing is exposed in the attic space; a properly vented roof will have the wood sheathing exposed to whatever seasonal weather fluctuations occur. In my service area of Jackson County, Missouri, our seasonal fluctuations are significant and range from very cold dry air in the winter to very hot humid air in the summer. And if you have a roof leak, the sheathing is exposed directly to water and not simply humidity in the air, making this problem even worse. While any individual component of the roof sheathing dimension may change only marginally; over a space as large as your roof the changes are cumulatively significant. With our local climate, a 4x8 sheet of plywood or OSB may expand and contract as much as 1/8 inch. This expansion and contraction itself leads to imperfections in the roof sheathing that will telegraph through the asphalt shingles. To compensate for this, when roof decking is installed it includes gaps to account for the seasonal fluctuations. This is usually measured and consistent by using the shank of a nail used to secure the roof sheathing as a guide. I already identified that the most common areas of roof imperfections occurs at the joints, and here we are required to make imperfect joints to account for the wood to expand and contract, so minimizing joints is important. In addition, both plywood and OSB are much more dimensionally stable than wood planks. Wood planks, when they were used, had to have larger gaps. Again, imperfections at the joints are where asphalt shingles will telegraph imperfections in the roof sheathing; wood planks have many more joints and the joints are larger. They don’t build them like they used to, and as a roofing contractor I am certainly glad they don’t!!! One of the topics I frequently get when talking to people about roof repairs is when is it better to replace vs. repair your roof? Clearly if you have evidence of a roof leak, missing shingles, deteriorated shingles, your roof warrants a repair. But as with many things, you have to ask yourself when to repair and when to replace. I recommend consideration of five (5) factors when it comes time to replace your roof. The first is that you have repeated or frequent leaks that need to be repaired – this is indicative that the roof is nearing the end of its useful service life. The second is age – as an example you wouldn’t typically replace a 5-year old roof, but if you have 15-20 years on your composite shingle roof then the repairs are going to get more frequent. The third is storm damage – we are coming into severe weather season in the local Lees Summit, Missouri area and all of Jackson County, and one severe hail storm can significantly reduce the remaining service life of your roof. The forth is homeowners insurance discounts – if your roof is over ten (10) years old, you will likely qualify for a pretty significant discount that may make it cost effective to replace your roof even though it isn’t failing. And last is pure aesthetics, you simply want to change the color of your roof, which is no different than painting your house a different color. Obviously the first three (3) reasons are critical decision factors as your house is likely your single largest investment and you need to protect it. Aesthetics and how our house makes us feel perhaps seems superfluous, but your roof makes a big difference in perception and curb appeal. When you couple aesthetics with potential homeowners insurance discounts for new roofs, this ultimately may not cost much amortized over several years of homeowners insurance discounts. A good local roofing company should be willing to work with you to discuss these factors and whether your roof warrants repair, or replacement should be a consideration. Don’t assume that repairs are automatically cheaper option, as often times there comes a point when repairs simply exceed replacement, not even accounting for homeowner’s insurance discounts you may be eligible for. A good roofing contractor will present options so that you can make an informed decision. There are many roofing materials to pick from, and many people prefer the aesthetics of natural materials. Natural materials include wood, clay, and slate. And while many of our local homeowners associations in Jackson County Missouri used to require natural materials, more and more of them are changing this restriction to allow my choice of materials; architectural composite shingles. It used to be that composite meant only three-tab shingles, and these were definitely the “budget” solution for roofs; which is why homeowners associations did not allow their use. However, composite shingles have come a long way and architectural composite shingles are being embraced by more builders and homeowners associations at all price points. The reasons for this transition are simple. Architectural composite shingles are available in a variety of styles and colors to complement any style home and offer a variety of aesthetics beyond any of the natural materials. Do you like the aesthetics of wood shingles? I can’t blame you, they look great. However we can get architectural shingles that mimic new cedar or weathered wood (depending on your aesthetic preference), something natural wood as a material cannot provide. And we can do so with less cost, less maintenance considerations, longer life, and a number of other benefits. Do you have a house with stucco finish that would look great with clay tiles? Again we can get architectural shingles that mimic clay tiles and do so with significantly less cost, less weight (clay tiles are heavy and need substantially stronger roof structure to support the weight), and less maintenance issues. What about a brick house that would look great with slate roofing? One more time, we can provide architectural shingles that mimic slate roofing and do so at significantly less cost, less weight, and less maintenance issues. Both clay and slate are brittle, so access for maintenance becomes challenging in addition to these materials also breaking. And the biggest advantage of architectural composite shingles vs. natural materials is the adhesive bond between shingles. Wood, clay, and slate shingles are loosely attached and as natural materials will have slight movement. Composite shingles have an adhesive strip on the underside that allows the shingles to bond together when exposed to heat from the sun. This provides an extra level of protection against wind driven rain. While natural materials such as clay and slate typically have higher wind resistance, a properly installed composite shingle roof can also meet the same hurricane standards (that don’t apply here in Missouri, but demonstrate wind resistance). Ask your roofing contractor if architectural composite shingles are the right choice for you, and the advantages to composite. With architectural composite shingles, you can have your cake and eat it too. You can get a roof that complements any architectural style of house, and do so with less cost, easier maintenance, and other benefits inherent in composite shingles. Many roofing contractors will tell you that the purpose of roofing felt or underlayment is temporary waterproofing to “dry-in” the structure before the roof shingles are installed. They identify that any secondary waterproofing the roofing felt or underlayment provides is entirely negated by the numbers of nails pushed through it. This makes some sense when you realize that roofing felt or underlayment is nailed or stapled, and then a typical architectural shingle roof takes ~800 nails for every 100 square feet of roofing area. If you use a high-wind nailing pattern, that roofing felt has ~1,200 nails for every 100 square feet of roofing area. That is a lot of “holes” in something that provides secondary waterproofing is what these contractors will tell you. They will tell you that you can get by with no felt at all, or at a maximum they will install a 15-lb. felt. If you read any asphalt roof manufacturer’s warranty literature or installation criteria, you will note that universally they specify minimum underlayment requirements. Vary from this installation procedure, and the warranty isn’t valid. Those contractors that tell you roofing felt or underlayment isn’t necessary will also maintain that of course any company that manufactures and sells roofing materials wants to sell you more product, and they also manufacture and sell roofing underlayment that they specify for installation. The roofing contractors that tell you this tend to be low bidders, and are often high-pressure storm-chasers that descend on areas after hail storms or other wind events that cause widespread roofing damage. A 30-lb roofing felt costs about $7 for every 100 square feet and 15-lb roofing felt costs about $3.50 for every 100 square feet. In comparison, architectural shingles are about $100 for every 100 square feet, so this savings amounts to mere pennies on a replacement roof. As your home is likely your most valuable asset, do you really want these contractors working on this when you know they are cutting corners that required by the manufacturers that make and offer warranties on their roofing materials? That sounds penny wise and pound foolish to me. Find a local roofing contractor who has been in business in your locale and has a proven reputation. Have you ever watched one of your neighbors get a new roof? Wow, that house always looks so much better with a new roof than it did with the old roof. There is much more to a roof than just new shingles though; but shingles are the only part you see from the ground. Architectural shingles sure look nice though. Flashing, while critical, isn’t something homeowners are likely to think about. Do you have a fireplace and associated chimney? What about a gas furnace or hot water heater? Do you have indoor plumbing? What about skylights? Do you have a valley where different roof pitches meet? What about areas where a wall meets a roof? What all of these have in common is that metal flashing is used to seal these areas. Without proper use and installation of this metal flashing, you are likely to have roof leaks. Your home is your most valuable asset, and your roof is your first line of defense to protect this asset. Leaks due to improper flashing is not how you protect this asset. Drip Edges are installed at eaves and gables, and prevent any moisture exposure to the exposed edge of the roof decking material (either plywood or oriented strand board – OSB). They also deflect rainwater from the exterior surface, such as your fascia board and into your gutter. There are different profiles of drip edge, depending on application and how much protection you want and how much you want to spend. A lot of roofing contractors will use an L-shape drip edge of the cheapest material, because that is all that is required by code (drip edge is a recent addition to the International Residential Code, depending on the age of your roof you may not hava a drip edge at all). I like to install a DL-lip type overhang profile drip edge. Also, there is some discrepancy on proper installation of drip edge; I install drip edge under the overlayment at the eave, but use drip edge over the underlayment as the gables. The price difference between a stick (10 linear feet) of L-shape drip edge and the overhang profile is about $0.50 more per stick. On a typical house, the cost increase between minimum flashing and drip edge vs. upgraded flashing and drip edge is negligible; but it is the minor details that ensures your new roof will be trouble-free for a very long time. Ask your roofing contractor about flashing and drip edge details before, not after, installation of your new roof. In Lees Summit, this has been a most unusual winter. We have warm days approaching 70-F, and yet only a couple of days later we have high only approaching 30-F. And the see-saw continues. These wide variances in weather conditions make me wonder what the severity of our spring storms might look like. Hail, wind driven rain, tornadoes; all widespread will damage a lot of roofs and create needs for both repair and replacement. My roofing company, as with most established roofing contractors, maintains crews based on work we have available. Following storm or natural disasters, there is far more roof work than local roofing contractors can support. This leads to an influx of migrant roofing contractors, swooping in to grab storm-related insurance work, and they will certainly move on once a larger storm happens elsewhere or once the roof replacement work dries up. I encourage you to hire a local roofing contractor for roof repairs. Your house is likely your single largest investment. And the roof is your first line of defense in protecting your house. With some types of shingles, a roof may last 25-30 years, or even longer. The reasons to select a local roofer are many: 1) The roof being installed comes with a manufacturer’s warranty. That warranty is only as good as the manufacturer that stands behind it, but proper installation is also crucial to ensure the manufacturer honors the warranty. When you select a local roofing contractor, you can ensure that the installer is available later. How are you going to get support from a migrant roofing contractor? 2) It isn’t just the roof shingles; these are only one part of a bigger system including underlayment, ice and water shield, flashing, and venting. While you only see the shingles, every component is critical. Migrant roofing contractors are chasing money only, and are likely to cut costs in ways you cannot see. Local roofing contractors that rely on referrals don’t have that luxury. 3) We are properly licensed by the state of Missouri, and even the localities we do work in. 4) We are insured, for your protection. 5) We have a proven reputation within the community; this is among our most valuable intangible assets. While I agree that there will be more work following storms than local roofing contractors can handle, and it may take some time to get a new roof, we can install a short-term solution such as a properly secured tarp roof. This may not be the most attractive, but it is likely at least some of your neighbors have these as well. A properly installed and secured tarp will provide 90-120 days of protection, which gives local roofing contractor time to schedule a proper roof replacement. Your house is your largest asset. Are you willing to trust a transient roof contractor to provide the first line of defense and protection? After the last show event in Lees Summit, I went out into the neighborhood and snapped some pictures to illustrate some common roofing problems you may want to address with your roofing contractor next time you need a new roof. You may want to look at your own roof and snap some photos even if you don’t need a new roof, because you eventually will and this data is perishable and will be long lost when you eventually replace your roof. See the lines on this roof? Why is it that the snow melts and leaves a pattern of perpendicular lines? This is called “thermal bridging” and illustrates the location of individual framing members. This pattern would be particularly pronounced for light-gauge steel framing (which may have been used in residential construction prior to steel prices increasing), but is still visible in wood-frame construction. Since the insulating value of you framing members is less than the insulation, each framing member acts as a thermal bridge directly to the outside. This provides a conduit to transfer or leak heat, which melts the snow into this interesting pattern. Note on the left side of the photograph where this doesn’t happen? Same roof slope, same sun exposure, the difference is that the left side is the roof over an unheated garage; minimizing the heat escaping into the attic and also the thermal bridge from the roof framing. In the Lees Summit locale, this generally isn’t or doesn’t lead to a roofing problem. If the pattern is reversed however, where the snow melts between the roofing members, this indicates too much heat loss and can lead to ice damming. After the last snow event in Lees Summit, I went out into the neighborhood and snapped some pictures. This one shows how well a ridge vent works and is something your roofing contractor should install when you do need a new roof. In a previous blog on ice dams, I identified that one of the ways to prevent ice dams was better roof and attic space venting. While this roof has an inadequate amount of ridge vent (typical of a hip roof), and is relatively low pitch (~4:12), it does show the effectiveness of ridge vents in our locale as the vent itself is completely clear and working well (and thus minimizing potential for ice dams). People tend to think that ridge vents will get blocked by snow, closing the vent and rendering them completely ineffective. However note that the snow is even coated on the roof, but the ridge vent remains completely clear. This is actually a GAF Cobra Snow Country Vent, but other roofing manufacturers have their own equivalent ridge vents that are comparable. Now then, what if you see the ridge vent blocked? This would be a problem. Ridge vents are the exhaust vents, the intake vents or in the soffits, or roof overhangs. If there is insufficient intake venting, there is not going to be enough airflow out the ridge vent to keep it clear. Inadequate venting can lead to ice jam problems. In the picture, the ridge vent is accompanied by a continuous soffit vent which offers more than adequate airflow. Again, following a snowstorm is a great opportunity to snap some pictures of your roof that will be valuable later when you need your roof replaced. Your roofing contractor won't see what snow patterns you have on your roof when they are replacing it in much more pleasant weather conditions, and you can share y our winter pictures with them. |
Bobby WilliamsWe are an experienced Lees Summit roofing company with over 15 years experience in repair, service and installation. Archives
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