Most homeowners never get up close to their roof. If you're cleaning your gutters, you probably do get a birds eye view, but don't realize there are many layers that make up your roof. All you see when you look at the roof are the shingles, slate or tile on top. You typically aren't interested in the roofing layers that keep your home dry until you have a problem, like light shining into the attic or ice dams in the winter.
Roofs might look simple but they're rather complicated (read: Was Replacement Roof Done Right? to show typical roof installation problems). There are multiple layers of materials, and they have to be installed in the right sequence … and the right way, in order to withstand harsh weather and keep your home dry. For example, there's a starter course of roofing shingles installed at the eaves before the roofing shingles you can see.
Roofing Layers Diagram
So we'll start at the bottom of the deck, and work our way up through all the roofing layers until we reach the shingles and sunshine above your roof. This roofing layers diagram shows the layers that sit directly under the shingles plus the added protection for the edges of the roof.
- Framing – includes the roof trusses that sit at the top of your house and support the weight of all the materials used to build your roof. Some materials like ceramic tile and slate are much heavier than asphalt shingles, so the structure must be designed for the materials used.
- Insulation – in your attic is used to reduce the loss of heated air rising up from your home. Attic insulation will be found on the attic floor or when the attic is finished, between the rafters over the attic ceiling (read: Insulation Doesn’t Work by Itself, to learn how it works with the vents in your roof, necessary for ventilation).
- Ventilation — is critical in attics to rid the space of heat and moisture that enters from the house below. Without adequate ventilation, heat and moisture can cause damage to the framing, insulation and the plywood sheathing that sits on top of the rafters. You may also find yourself dealing with mold and mildew problems.
- Roof deck – is the roofing material that sits on top of the roof trusses. Most roof decking is made from sheets of plywood or OSB. It's also possible to add a radiant barrier to these 4 x 8 ft sheets, as illustrated above (barrier installed facing down).
- Water shield – is the next roofing layer, that creates a water-proof barrier where ice or water can buildup near the roof eaves. It's usually a peel and stick product that adheres directly to the roof deck.
- Underlayment – is usually felt, fiberglass or synthetic rubber (black layer above), that covers the entire roof deck. It is water-resistant to allow moisture to pass through. It will prevent the passage of water in its liquid form.
- Shingle starter strips – are either purchased or created by snapping regular shingles in half. They're installed at the eaves, pointing in the opposite direction to create a first line of defense against wind uplift along the edge of the roof.
Roofing material – is where most homeowners focus their attention with hundreds of materials, styles and color to pick from. The five main types of roofing materials are asphalt shingles, cedar shakes, concrete or ceramic tiles, metal sheets and rubber used for flat roofs.
- Ridge vents – are at the top of your roof, covered by roofing material but with a gap designed to allow warm, moist air to escape from the attic.
- Flashing – is made from sheet metal and used to prevent water from penetrating seams where different materials meet on the roof (and other parts of your home's exterior). Flashing along the roof eaves are called drip edge, and along chimneys it's called step flashing. Flashing is also used around skylights, bathroom vents and any other features sticking up through the roof.
Thank you so much for educating us on this! Great article!
Is it “OK” to use oriental board (OSB) to deck a roof? I have heard that nails/screws will back out of this material over a period of time, therefore, causing trouble with roofing shingles. Thanks!
Joel, OSB is used more than plywood for roof decking as it’s just as strong & cheaper. The one area where plywood is better is how it reacts to moisture but there should be a water barrier over the roof deck to avoid this problem. You can learn a lot more with this article on OSB vs plywood for roof decking from Atlas Roofing.
Apparently my roof deck is made of linear pieces of 1×6 wood. There was quite a bit of damage it seems. The company wants me to pay $3000 for the repairs, but they did the repairs before they told me. My house is older. Was this type of roof deck more common on older homes? Should the sales person have warned me? They only spoke of replacing sheets of plywood as you mentioned and that most homes may need 2-3 sheets, not $3000 in 1×6’s.
This does sound like a scam so I’m happy to give you some ideas. First I must tell you I’m not a lawyer & you probably will need to seek legal advice.
Yes, I have seen boards used for a roof deck but only barn boards in houses built in the 1950s or earlier. I did find an article on roof decks which lists different kinds of roof decking including 2×6 boards but they’re used if they are visible indoors?
Even if the old roof deck was made with 1×6 boards, there was absolutely no requirement to use them again. All they had to do was remove the 1×6 boards and install plywood sheathing on the deck. If they were tongue and groove as the article suggests and they claim they had to remove all the boards just to replace a handful of boards, then they either don’t know what they’re doing … or they were creating more work for themselves which isn’t right, especially if they only discussed replacing sheets of plywood.
Here’s what I would do:
Hope I’ve given you enough ideas to move forward and good luck.
Hello, a teammate in my Facebook master mind shared this with all
of us so I came to take a look. I’m definitely enjoying the info, thanks.
I have a question about the deck part of your roof. Should the plywood be replaced along with the shingles. I just had my roof re-done, but there are areas where the roof sags as if the old plywood wasn’t replaced. What is the rule on the deck of a roof. We paid $16,000.00 for our roof and made the assumption that the old plywood(deck) would be replaced along with the shingles. That’s what we thought we were paying so much money for. Could you help me with my situation as what to do.
Tim, Replacing a roof almost never includes replacing the roof deck. They should inspect the plywood for damage & it is very common to replace several full/partial pieces of the roof decking, just not the entire deck.
A roof job typically starts with the underlayment, a combination of ice & water shield on the lowest 3 or 6 ft, and then a felt type product above this. The metal flashing at the edges of the roof should be replaced, and then the shingles you’ve selected are installed on top of the underlayment … with the lowest row, a double row.