Decking and sheathing: the foundation

Everything on a roof fastens to the decking, also called sheathing, the layer of wooden panels nailed across the rafters or trusses that forms the solid surface of the roof. It is the most important material most homeowners never think about, because the finest shingles in the world are worthless if they are nailed to rotten or inadequate decking. The two common decking materials are plywood and oriented strand board (OSB). Plywood is made of thin wood veneers glued in cross grain layers and is prized for its strength and moisture resistance, while OSB is made of compressed wood strands, is a bit cheaper, and is widely used in modern construction. Both work well when kept dry; both fail when chronically wet.

Thickness is a frequent question, and it depends on the spacing of the rafters and the weight of the roofing above. For typical rafter spacing, half inch decking is common for asphalt shingles, while five eighths inch is often specified for heavier materials or wider rafter spacing, and heavy materials like tile or slate may require even thicker or reinforced decking. The key point is that decking must be sound and correctly thick for the roofing it carries, which is why a proper roof replacement always includes inspecting the deck and replacing any rotten sheets before new roofing goes on. That deck repair is the most common surprise cost in a re roof, and skipping it is a false economy, since new roofing over bad decking will fail early. Our parts of a roof guide puts decking in the context of the whole system.

Underlayment: the critical hidden layer

Between the decking and the visible roofing lies the underlayment, a water resistant sheet rolled across the entire deck that serves as a secondary barrier if water gets past the surface. It is one of the highest value, least visible parts of a roof, and the choice of underlayment matters. Traditionally, roofers used felt, an asphalt saturated paper measured in weights like fifteen pound and thirty pound. Felt still works, but it has largely been surpassed by synthetic underlayment, which is a woven plastic material that is lighter, stronger, more tear resistant, more water resistant, and safer to walk on than felt. On most quality roofs today, synthetic underlayment is the standard, and paying the small upgrade over felt is almost always worth it.

In cold climates and in the most vulnerable areas of any roof, a third underlayment material comes into play: ice and water shield, a self adhering rubberized membrane that sticks directly to the deck and seals around nail penetrations. It is installed in the valleys, along the eaves, and around penetrations to protect against wind driven rain and ice dams, exactly the places where ordinary underlayment is not enough. A roof that skimps on underlayment, using cheap felt or too little ice and water shield, is saving money in precisely the layer that prevents the most leaks, which is why an itemized quote that specifies the underlayment is a sign of a quality job.

The surface materials, compared

The visible roofing is where homeowners focus, and the choice drives cost, appearance and lifespan. Here is how the main options compare, each covered in depth in its own guide.

You will also hear the term composition roof, which simply means a roof made of composite asphalt shingles, the standard architectural shingle most homes use, so a composition roof and an asphalt shingle roof are the same thing. For the full detail on each option, see our guides on asphalt shingles, metal roofing, tile and slate, and flat roofing. The right surface depends on your climate, budget, home style and how long you plan to stay.

What is the best roofing material?

There is no single best roofing material, only the best fit for your situation, and any honest roofer will frame it that way. If value and versatility matter most, architectural asphalt shingles are the best all around choice for the majority of homes, which is why they dominate. If you want the longest life and lowest lifetime cost and plan to stay put, metal is often the smartest buy despite its higher upfront price. In hot, sunny or southwestern regions, tile excels and suits the architecture. For a historic or premium home where longevity and appearance justify the cost, slate is unmatched. On a low slope or commercial roof, a membrane system is the only real option.

The decision comes down to weighing four things: your climate and its specific stresses, your budget both upfront and over the life of the roof, the style of your home and neighborhood, and how long you intend to own the house. A material that is perfect for a forever home in hail country may be overkill for a house you will sell in five years. This is exactly the conversation a good roofer has with you before recommending anything, rather than pushing whatever they prefer to install. Our roof lifespan guide and cost guide give you the numbers to weigh these tradeoffs.

Flashing, drip edge and fasteners

Beyond the big three layers of deck, underlayment and surface, a roof depends on a set of accessory materials that punch far above their cost. Flashing, the metal that seals joints at walls, chimneys, valleys and penetrations, is where most roofs leak, and using quality flashing installed correctly is essential, as our flashing guide explains. Drip edge, the metal strip along the eaves and rakes, directs water into the gutters and protects the edges from rot. Starter strip and ridge cap shingles seal the edges and peak. And the humble roofing nail matters more than you would think: the right length, material and quantity, driven correctly in the nail zone, determine whether shingles stay put in a storm.

These accessories are small line items, but skimping on them is exactly where cheap roofs go wrong, because they are the details that make the difference between a roof that lasts and one that leaks. When you compare quotes, the presence of quality flashing, drip edge, proper underlayment and the right fasteners in the scope is a strong signal of a job done right, while their absence is a red flag no matter how good the shingle brand sounds.

Material cost versus the whole job

A common misconception is that the roofing material is most of what you pay for. In reality, on a typical shingle roof the materials are often only around forty percent of the total, with labor, tear off, disposal, permits, overhead and warranty making up the rest. This is why upgrading from a basic shingle to a better one usually adds a smaller percentage to the overall bill than people expect, and why the cheapest material paired with a poor installation is a bad deal, since you are still paying most of the cost for the labor and getting a roof that fails early. It also explains why premium materials like metal and tile cost so much more overall: not only is the material pricier per square, but they take more skill and time to install correctly.

The practical lesson is to think in terms of the whole system and the whole cost, not just the sticker price of the shingle. Spending a little more on quality underlayment, flashing and a better surface material, installed correctly, protects the much larger investment of the labor and your home beneath it. Our roof replacement cost guide breaks down exactly how the total is built, so you can see where materials fit in the bigger picture and judge a quote fairly.

OSB versus plywood: which decking is better?

Since decking is the foundation of the whole roof, the plywood versus OSB question is worth understanding. Plywood is manufactured from thin sheets of wood veneer glued together with the grain alternating in each layer, which gives it excellent strength and dimensional stability. Its key advantage for roofing is how it handles moisture: when plywood does get wet, it tends to dry out and return to shape, and it holds fasteners well. OSB, oriented strand board, is made from compressed wood strands bonded with resin, costs a bit less, and is engineered to be strong and consistent, which is why it is extremely common in modern construction.

The practical difference shows up with water. OSB is more prone to swelling at the edges if it gets and stays wet, and it dries more slowly than plywood, so chronic moisture is harder on it. In a well built, well ventilated roof that stays dry, both perform their job for decades. The takeaway for a homeowner is less about picking a side and more about keeping whichever you have dry, through good flashing, underlayment and ventilation, and replacing any sheet that has been compromised by a leak rather than roofing over it. When a roofer specifies new decking in a quote, it is fine to ask which material and thickness, and a good one will match it to your roof and local code.

Energy-efficient and sustainable materials

Roofing materials increasingly compete on more than just cost and looks, and energy efficiency and sustainability are worth factoring in. On the surface side, lighter colored and specially coated cool roof materials reflect more solar energy, keeping the attic cooler and trimming summer air conditioning costs, an effect strongest with reflective metal and cool roof rated shingles. Metal roofing also stands out for sustainability because it is highly recyclable and often contains recycled content, whereas asphalt shingles are a petroleum product that mostly ends up in landfills. For homeowners who want the roof itself to generate energy, integrated solar options exist, which we cover in our solar roof tiles guide, and a living or vegetated roof is another sustainable option we explore in our green roofs guide.

Underneath, better underlayment and proper ventilation contribute to efficiency too, by protecting insulation and keeping the attic dry and moderate. If lowering energy bills or reducing environmental impact is a priority, mention it to your roofer early, because it can influence the material recommendation, from a reflective surface to a recyclable metal system, and some efficient materials qualify for utility rebates or tax incentives that improve their value. As always, the best choice balances these benefits against your climate, budget and how long you will own the home.