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Do I Need Plywood Under Metal Roof

How Many Sheets Of Plywood Do You Need For A Roof

Metal Roof Underlayment

The number of sheets of plywood you will need for your roof depends on the size of your roof. The average sheet of plywood is 4 x 8 foot, with a surface area of 32 square feet.

The average residential roof size is 1,700 square feet, which means a complete set of plywood will count about 53 sheets.

If your property is larger than that, you should expect that you will need more plywood to cover it.

For example, the average roof size for a larger house with a garage is over 3,000 feet, which translates to 93 plywood sheets.

Metal Roof Insulation: Everything You Need To Know

Reviewed by Tomas Kalkys. President. Qualifications: More than 20 years of experience in residential and commercial exterior remodeling. Founding farther of Legacy Service. Written by LegacyUSA Team

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Metal roofing has been steadily increasing in popularity throughout the United States in recent years for many reasons. Not only is it beautiful, but it also has more durability and lasts longer than other types of roofing . But just because its a strong type of roofing doesnt mean that it doesnt need insulation. In fact, insulation will help maximize its energy efficiency.

At Legacy Service, were here to help with any of your home exterior needs. In this article, well discuss the importance of using insulation for metal roofs, your options, and how to get it done. Our team can also do it for you with a roofing installation or replacement. Please feel free to contact us at 215-798-9790 to learn more.

How Much Should A Metal Roof Overhang

A metal roof should overhang the eave end of a roof 1 to 1.5 if you have gutters. If your roof does not have gutters, your roof can overhang up to 3. A minimum overhang of 1 is always recommended to prevent rain and other moisture from blowing up under the metal roof edge.

You should not overlap the rake ends of your roof with your metal panels. While some overhang is acceptable on the eaves, you should never overlap rake edges as too much surface area of the panel would be exposed to wind and you would risk the panel failing in extreme weather.

Read Also: What Is The Cost Of A New Roof

Exterior Sheathing Required Under Steel Siding

BillK said:If I was having it done I would find out who the siding manufacturer is and ask them. They probably have a web site with all of the installation requirements. That way you wont be guessing. That being said, my gut feeling would be that sheathing would give an extra level of strength and insulation. You dont say where you are located but if you are going to be running infloor heat year round I would want the structure as air tight and strong as possible.

Can Metal Roofing Be Installed Directly To Plywood

Do You Need Plywood Under Metal Roofing?

Metal roofing should not be installed directly over the top of bareplywood. You do not have to install roofing shingles or other roofing material, but a felt sheet over the plywood is the bare minimum. You may also want to install a slip sheet to protect the felt sheet from potential damage caused by the metal roofing.

If you install your metal roofing directly on plywood without the protective layers, you greatly increase the odds of the roof leaking. You also run the risk of premature wood rot, as the felt sheet provides a layer of moisture prevention that keeps the wood dry. Even without heavy rain, humidity can build up between the metal roofing and the plywood and ruin the wood.

The slip sheet is also an important layer. This smooth, industrial paper is laid on top of the felt to protect the felt from the metal roofing material. The metal can heat up from exposure to the sun and adhere to the tar-infused felt sheeting. When the metal expands or contracts with changing temperatures, it can tear or wear away the felt sheeting.

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First Two Underlayment Layers

On most projects, there are two types of underlayments needed. The first on the list would be the ice and water shield. This is a roof membrane underlayment made up of either a rubberized-asphalt or butyl-based adhesive with a polyethylene carrier sheet. It has an adhesive backing with a peel and stick feature. This membrane should be labeled high temperature to withstand the surface temperature of the roof on a hot summer day. The heat in hot areas of the country, even here in New England, can exceed the melting point of some of these products. The product should be a premium, high temperature ice and water shield for use with tile, metal, and other roofs with scrim reinforced top surface. It self-seals around nails and provides protection for roof areas prone to ice and water intrusion.

The product needs to be installed on the eave edges up the roof at least two feet inside the face of any exterior wall. The rakes on gable roofs also need treatment to the same standard. All valleys and hips need to be covered. Penetrations such as chimneys, skylights, solar tubes, and vent pipes need to be surrounded with ice and water shield, as well.

If the roof slope is below 3/12 pitch , the entire roof should be covered, but only if the roof is conventionally vented .

Taking Care Of Your Building Envelope

The roof is an important element of the Building Envelope. A Building Envelope is the physical separator between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer. It needs to be addressed with the utmost care and consideration. Be sure that the contractor you choose is trained in the best methods of installation. Having the Right Stuff and not having the skill to do the installation nullifies the benefits of its use.

Also Check: How To Install Snow Stops On Metal Roof

Does A Metal Roof Need Sheathing

5/5metal roofingroofing needsmetal roofs

Thereof, do I need underlayment for metal roof?

The simple answer is yes, your roof does need an underlayment. Traditionally built homes will need an underlayment. If your home is built with joists, insulation between those joists, and sheathing, then an underlayment is needed before you put on a metal roof.

Additionally, can you put metal roof on OSB? A metal roof will outlast a shingled roof. With the metal placed over felt on top of OSB, there will be no condensation.

Thereof, what material goes under a metal roof?

The traditional and most common material used for roof underlayment on a steep-slope metal roof is non-perforated, asphalt-impregnated felt underlayment.

Is roof sheathing necessary?

Roof sheathing is also known as roof decking. It is a crucial part of the entire roof structure as it helps to prevent an array of different issues and damages. In addition to that, sheathing a roof can also help you prolong the roof’s lifespan and make your home more energy-efficient.

Plywood Vs Oriented Strand Board

OSB vs. Plywood: Which Should You Choose for Your Roof Deck?

Strand Board is gaining popularity as a material used for roofing. OSB is a type of wood made up of strands in varying orientations compressed together with adhesive to form a board. This type of wood is typically a cheaper alternative to plywood, but it meets most standards of its alternative.

There are a few disadvantages to using this cheaper alternative to plywood. The most notable ones are the inability of OSB to hold nails as effectively as plywood.

This means that the structure of the roof is compromised ever so slightly. The second disadvantage is the way OSB absorbs moisture.

While it is true that OSB takes a longer time to absorb moisture than plywood, it also takes that much longer to dry.

While plywood dries down evenly, OSB tends to absorb moisture more around the edges, making it swell and dry down with a ring around the edges.

Florida Dade County has prohibited the use of OSB for roof decks because of the effects that Hurricane Andrew had on homes that used the material for roofing.

Read Also: How Much To Build Roof Over Patio

How Much Does A Metal Roof Cost

To the surprise of many, some metal roofs do not cost much more than an asphalt roof. The difference often lies in the installation costs. Simply put, more roofing companies do asphalt shingles. The more competition, the lower the price.

If you are using a commonly found brand and style of metal roofing, then expecting to pay around more than you would for asphalt shingles. Of course, that price can balloon if you want a different color, style, or brand of tin roof.

For instance, one square of asphalt roofing will cost around $100. Metal panels are commonly found in 10, 12, and 16 lengths. A panel that is 10 long and 36 wide would require 3.5 panels to make a square. If one panel is $30, then you are looking at about $115. Of course, that is for the cheapest type of metal roofing.

Can You Install Metal Roof Over Shingles

Yes, you can install a metal roof over shingles. The shingles will act as underlayment for your metal roof and provide a solid foundation provided they are not completely disintegrating.

Some will opt to place battens and underlayment over existing roof shingles. The reason for this is to ensure proper connection of the roofing panels to the roof. Old asphalt shingles may not provide enough holding strength for part of a roof screw, so screwing battens to roof rafters or trusses on top of shingles ensures the integrity of the metal roof.

Read Also: How To Install Metal Roofing Over Asphalt Shingles

Does Metal Roofing Need Underlayment

    There are a lot of decisions to make while going through the process of having a new metal roof installed. What kind of panel are you going to use? What metal gauge are you going to use? What color roof are you going to choose? We understand that it can be overwhelming.

    In the process of making all these decisions, one aspect of metal roofing that gets overlooked is using underlayment. Metal roof underlayment is an important component of a metal roofing system. Some might choose to skip using underlayment to save money. However, the metal roof underlayment acts as an added layer of protection. You can save money by using underlayment because it will help you avoid problems that would need to be fixed.

    The short answer is yes, your metal roof does need underlayment . But like most things in life, it’s not quite that simple.

    At Western States Metal Roofing , we have specialized in manufacturing metal roofing for over 20 years. From our extensive experience, we strongly recommend taking advantage of the benefits of underlayment even if it isn’t mandatory.

    While most building codes require underlayment, there are some instances where underlayment may not be considered necessary.

    We will discuss:

    • Extra Protection

    Metal Roofing With No Decking Or Underlayment

    sheathing: " The contractor has installed new osb over the ...

    Is it generally permissible to construct a SFR dwellings roof with no sheathing? I have seen it done this way on plenty of storage sheds and metal buildings. And I have seen plenty of metal roof coverings on SFR homes but they have mostly been re-roofs over existing roofs with plywood decking, or new roofs with plywood decking. This particular roof has very lightweight metal covering. The gable endwall has plywood sheathing and vinyl cla

    Solid sheathing is only required for shingles. From there, you will have to follow manufacturer guidelines. In my opinion, looks like a fine install from here in GA.

    I bet its gonna get real noisy in a hail storm!

    I bet its gonna get real noisy in a hail storm.!

    not to mention the potential for sweating/condensation.

    Shouldnt your metal roof have underlayment installed, per IBC 1507.4 ? And how about flashing, such as drip edge? I do not think this roof meets residential roof standards.

    Like Larry said, that roof is going to have a big condensation problem, Ive seen it.I would let the buyer know that this roof is not built right, and is likely to have problems that would have been prevented with proper construction.

    Material and procedures that are meant for equipment or storage sheds were never right for a home when it comes to metal. Plywood sheathing has a purpose.

    That is what I see Brian. Underlayments are required for that type of roof covering, which is metal. Hard to do if you dont have a roof sheathing.

    Read Also: What Is A Hail Resistant Roof

    Three: Install Flashing And Gutters

    Use the tape measure to determine the length of the roofs edge. Cut the flashing material to size using the metal snips and install along the roofs edge with ½ roofing nails.

    If you need to install gutters in any of the valleys, cut the gutters to size using the snips. Then secure the gutters in place with the ½ roofing nails.

    What Underlayment Is Best For A Metal Roof

    There are three main types of underlayment for metal roofs. They include felt, synthetic sheet, and self-adhering membrane. Although there is no superior type, wed like to help you find one that works best for you since they each have their own advantages and disadvantages. Weve included some of the pros and cons in the sections above under Underlayment Materials, but its best to consult a professional to determine which type would actually be best for you.

    At Legacy Service, weve been in the industry since 2005, and weve helped a countless number of customers install or replace their roof and build the home of their dreams.

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    Install Edging And Underlayment

    Install the underlayment as per the instructions by the manufacturer. If you are installing edging, which is essentially flashing that works with your metal roof panels, then you should first install the eave edging.

    When installing your eave edging, youll fit it to the underside of your eave and onto the face it should cover the entire face of your eave. Screw the eave edging to the underside of the eave, through the lip of the flashing. Then nail the faces with stainless steel finishing nails of the same color as your flashing.

    Then install your underlayment so that it covers the eave edging edge. Install the rake edging over the underlayment. It attaches in the same way as your eave edging, except that you use roofing screws to face screw the rake flashing. Ensure the eave end of the rake edging goes over the eave edging.

    Note that some rake edging may go over the installed metal panels, not under. In that case, install the metal panels first and the rake edging afterwards. It depends entirely on the manufacturer of your metal roofing panel.

    When You Need Roofing Underlayment

    Metal Roof Underlayment – Delta Trela Review

    If you have a new construction home and your metal roof is not going to be installed immediately, then synthetic underlayment is necessary. The synthetic underlayment can remain exposed anywhere from 2 months up to 30 months, depending on the brand, and will still remain watertight. It will not be harmed from exposure to weather conditions. Since the material doesn’t absorb moisture, it keeps from wrinkling which would ultimately compromise the finished look of the metal roof.

    You must also keep your roof slope in mind. If you have a low-sloped roof, underlayment needs to be used as your metal panel will be at a higher risk for water damage, especially in areas with higher rainfall. The low slope does not allow water to run-off as quickly as higher-pitched roofing and can accumulate on the roof, potentially resulting in leaks. The underlayment serves as an extra layer of protection from water damage.

    Additionally, any home built with joists, insulation between those joists, and sheathing, needs to use underlayment material.

    Also Check: How Often To Get Roof Replaced

    Do You Need A Vapor Barrier Under A Metal Roof

    Vapor barriers are used to reduce the amount of condensation that can move through a material. When theyre installed properly, they can help reduce any problems that you have with condensation as well as air leakage on fiberglass-insulated walls. Without one, water can get trapped in the wall, which will produce moisture and ultimately other issues like rot, mold, and trouble with thermal performance. Vapor barriers are recommended for under metal roofs.

    Prepare The Roof Surface

    You can use metal roofing over old shingles. If you opt to do this, youll benefit from using furring strips and a waterproof barrier first. If you think that is overkill and youll have an unheated shed, then you can screw directly through the shingles.

    Again, if you opt for battens, then you are reducing the weight of your structure and increasing the likelihood of condensation beneath your roof surface. Battens, however, are cheaper than solid decking and totally adequate for a simple, unheated shed.

    Underlayment is not necessary, as mentioned above, for an unheated shed. You can screw your metal panels directly to the surface of your sheathing.

    Finally, as you prep the roof surface for underlayment and/or your metal roof panels, plan out any roof venting that you intend to install. Mark it out but do not cut a hole yet. You will make your cut after the roof is installed to ensure the sheathing and metal roof panel cut align perfectly.

    Recommended Reading: How Long Does A New Roof Usually Last

    Do You Need Plywood Under A Metal Roof

    metal roofingrequire plywoodyouplywoodroofingmetal roofs

    The simple answer is yes, your roof does need an underlayment. If your metal roof is going on top of asphalt shingles, then there is already an underlayment, and it likely doesn’t need another. Keep in mind, however, that expansion and contraction of the shingles could cause damage to the back of the metal over time.

    Beside above, how do I stop my metal roof from sweating? Traditionally, condensation is managed by insulating the metal roof so that the panel temperature never reaches the dew point. This is often accomplished using vinyl-backed fiberglass insulation to prevent humid air from coming into contact with the cooler metal roof .

    Beside this, do you need a vapor barrier under a metal roof?

    Traditionally, we‘ve insulated the roof panel to try and keep the temperature on the panel FROM reaching the dew point. We‘ll add a vapor barrier so the moist air does not flow up through the insulation and condense on the roof. But a preinstalled membrane may be even more effective at removing condensation.

    How do I keep my metal roof from sweating?

    The five key points to stop your metal roof sweating are

  • Good roof ventilation. The key to getting condensation to evaporate is air flow.
  • Roof pitch.
  • Keep the inside of the shed dry.
  • Insulation.
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