Whether you’re building walls on a new home or you’re residing an older one, exterior sheathing has an important role to play. Exterior sheathing is a board or panel that may be made of several different materials.
It’s installed over the exterior walls of the home, and can have several purposes from lending structural support to helping to insulate the home.
Exterior sheathing can be loosely grouped into two categories: structural sheathing and non-structural sheathing. These can be used together or individually depending on the building, with both offering a lot to the overall structure and function of the walls.
What Is Exterior Wall Sheathing For and How Does It Work?
Exterior wall sheathing actually has a few different purposes, depending on the type of sheathing you’re using.
Structural sheathing is first and foremost designed to help strengthen the walls of the home or building it’s installed on. It helps to tie together the wall studs, which in turn increases the strength and the rigidity of the walls.
They also form a solid nailing base for siding materials, giving the siding something to be adhered to, and lending stability to the finished siding. When structural sheathing is installed, the walls are less likely to twist and bend when other forces are applied, such as wind or house settlement.
Structural sheathing is made of a strong, rigid material such as wood or gypsum. When it spans the studs of the walls, it ties them together, making them stronger than they are on their own.
This in turn helps create a more stable exterior that’s better able to withstand both the siding being installed over it, and any pressure or force that may be applied to the property.
What is Non Structural Exterior Wall Sheathing?
Non structural sheathing is the material used when helping to create the tight building envelope that most people want these days to help lower energy bills. Non structural sheathing is applied either to the exterior or interior of structural sheathing and is used to help insulate the home.
If the studs have been supported using diagonal bracing, non structural sheathing can also be applied directly to the studs, rather than being combined with structural sheathing.
All types of sheathing help to keep out things like wind and rain, and non structural sheathing takes this a step further, helping to prevent energy transfer so that the home is more comfortable with lower energy bills. It does this by creating an insulated barrier around the home to help seal up air leaks and to cover the studs and other areas where traditional forms of wall insulation typically don’t offer protection.
Non structural sheathing does not strengthen the walls or lend support on its own, so it is important to use it in conjunction with either structural sheathing or with diagonal bracing.
Types of Exterior Wall Sheathing
There are many different materials that can be used for external wall sheathing. Each has its own attributes, pros, cons, and cost, which may make one the better fit for a specific goal or project than another.
1. Oriented Strand Board Exterior Wall Sheathing (OSB)
Oriented strand board, or OSB, is a popular and frequently used sheathing material. It’s made up of hundreds of thin wood strands that have been pressed into a board with resin and wax adhesives.
- Oriented Strand Board Pros
OSB is incredibly durable. It doesn’t absorb and redistribute water like solid wood, so it stays stable longer than other types of wood sheathing, usually with greater shear strength due to the way that it’s formed. It’s also generally less expensive than other types of sheathing, so it’s primarily used for residential properties where costs may be a factor.
- Oriented Strand Board Cons
OSB is water resistant, but its sides and edges do tend to absorb water if they come in contact with it long term, so the bottoms and edges of the sheathing installation can wick up water, causing it to swell and warp. This can be avoided with sealants, but it is an extra step that needs to be considered.
- Oriented Strand Board Cost
OSB costs roughly $6 a sheet of 4 x 8 sheathing. It can be installed at a rate of roughly 75sq.ft. an hour by a skilled contractor, for an installation cost of roughly $490 for 500sq.ft. and a material cost of $100 for 500sq.ft., for a total of $590, professionally installed, or $100 for a DIY installation.
- How to Install Oriented Strand Board
OSB is installed vertically over the entirety of the exterior. The first panel is installed at the side of the home, with the long edge flush with the corner of the building, and the bottom edge flush with the sill. Do not allow the OSB to extend past the sill plate, as this will cause it to wick up moisture and to potentially swell.
Nail each panel of sheathing into place by driving one, 8d nail every 6-inches along the seams and wherever you find a stud behind its plane. Because OSB can swell slightly on the edges, do not butt edge the panels together when you install.
Instead, drive a nail loosely next to the edge of each panel you install, and install the next panel against the nail. This will create a slight gap for the OSB to swell into. When you’ve hung two panels, remove the nails and use them again on the outside of the second panel before you install the third.
Plan on installing your siding over the OSB as soon as the sheathing is in place to help avoid any unnecessary exposure of the sheathing to rain or moisture.
2. Structural Fiberboard Exterior Sheathing
Fiberboard is an insulating structural sheathing made up of plant cellulose fibers that are mixed with adhesives and given a water resistant coating. Structural fiberboard is often considered a premium material that offers a small measure of insulating and sound reducing properties to the building exterior, along with structural stability.
- Structural Fiberboard Exterior Sheathing Pros
Structural fiberboard is dimensionally stable. Unlike OSB, it doesn’t warp or swell with moisture, and you don’t need to take care to space the boards. Because it’s also insulating, it can potentially help lower energy bills, and many people use it for exterior sound control to help reduce noise on the interior. It’s also fairly easy to cut, and doesn’t require specialty materials
- Structural Fiberboard Exterior Sheathing Cons
While fiberboard is dimensionally stable, it isn’t as strong as other materials. Depending on how and where it’s used, you may need to include additional bracing in the application to help make up for the lack of strength in the fiberboard. The panels are heavy and difficult to move, and they also don’t handle screws well. It’s possible to easily strip the screw holes when installing, so installation can be harder for DIY. This is also a fairly expensive material. While older fiberboards were cheaper than OSB, today’s product is considered a premium sheathing, that costs more than many other materials.
- Structural Fiberboard Exterior Sheathing Cost
Structural fiberboard has a range of costs depending on its other benefits, and the range of insulation it has. It can cost $12 to $30 a sheet, so assuming a 500 square foot installation, it can cost $690 to $990 for materials and installation.
- How to Install Structural Fiberboard Exterior Sheathing
Fiberboard is heavy, so plan on having at least two people to install each panel, as it may be necessary to have a second person to hold it in place while nailing. Like OSB, it can be installed vertically, beginning at the edge of the home or building with the long edge flush to the edge of the studs and the bottom edge reaching to the top of the sill.
Depending on the fiberboard, you may be able to nail straight through, taking care not to nail flush to the board, every 6 inches around the perimeter. For some specialty boards, you may need to drill pilot holes to make the installation easier. Avoid using screws whenever possible, as the material often strips out screw holes quickly.
The material does not swell, so it can be installed butt-edged across the installation.
3. Plywood Sheathing
Plywood is a frequently used material for external structural sheathing. It’s made up of several thin layers of wood, or plys, which are laid in opposite directions to one another. This creates a much more stable and structurally sound sheath that can be used over the exterior.
- Plywood Sheathing Pros
Plywood is fairly easy to install, mostly because it’s very lightweight, weighing roughly 15% less than OSB. It’s also very dimensionally sound and is less likely to swell or warp than other materials. It has good moisture resistance, and dries quickly so it stays stable long term even in wet climates.
- Plywood Sheathing Cons
Plywood is not as uniform as some other materials. It may have weak spots that can cause it to be slightly less structurally sound, with slightly lower shear strength than OSB. It’s also more expensive to purchase than some other materials, although it has similar costs for installation.
- Plywood Sheathing Costs
Construction grade plywood costs roughly $10 for a 4 x 8 sheet, making a 500sq.ft installation cost roughly $650 installed, or $490 for installation and $160 in material.
- How to Install Plywood Sheathing
Plywood is very straightforward and fairly easy to install. Place it vertically, lined up flush with the edge of the building, with the short bottom side installed above the sill plate. Use 2-inch nails roughly 6-inches apart on the edges and no more than 12-inches apart on the center. Plywood is more dimensionally stable than OSB and does not require spacing between the sheets.
Start your next row of sheathing at least 3 stud bays off from the first, rather than lining up the sheets directly on top of one another. Mark door and window openings with tick marks so they’re easy to cut when you reach this step. For best installation practices, be sure to use house wrap over the plywood prior to installing the siding.
4. Foam Board Wall Sheathing
Foam board is a non structural sheathing designed to help insulate the home and create a tight building envelope. It’s normally installed after structural sheathing, but may also be installed over existing siding before new siding is put on, or it may be used on its own if the studs have been diagonally braced for stability first.
- Pros Foam Board Wall Sheathing
Foam board can help make the home more energy efficient, reducing thermal transfer, and helping to cover areas where air leaks are common, such as over the studs. It can be used in place of house wrap when installed on the outside of structural sheathing, helping to reduce building costs. Because it helps insulate the home, it will also result in lower energy bills over time, which can essentially mean that the material pays for itself.
- Cons Foam Board Wall Sheathing
Foam board has tight tolerances for installation, which means that if it isn’t installed properly, it won’t be as efficient an insulator. Likewise, if it isn’t sealed properly at the edges, it can allow moisture to infiltrate, causing problems for the sheathing behind.
It has little to no structural integrity of its own, so it must be combined with other sheathing or bracing. This will mean that using it can dramatically increase the cost of the project up front, even if you expect to recoup costs over time.
- Foam Board Wall Sheathing Costs
Rigid foam board sheathing installation comes in at around $2.50 a square foot for material and labor costs. This makes installing 500sq.ft. of sheathing about $1,250 total, with labor costing about $350, and the materials costing around $900.
- How to Install Foam Board Wall Sheathing
Before you install, you will need to determine whether or not the foam board is foil faced or not, and what type of siding you will install over it. Some materials require the foil to face out, such as brick, and other materials require it face in, such as vinyl. Make sure you follow the instructions of the manufacturer for the foam board to determine which direction to face the foam board.
The foam board should be installed directly over the sheathing, or if you are using bracing instead, it can be installed directly to the studs. In rare instances, it can also be used to cover up existing siding, in which case it should install similarly to other types of sheathing.
The material is installed vertically, and screwed directly to the sheathing or studs underneath, keeping to within ⅜-inch of the edge, no more than 6-inches apart around the perimeter. It should be butt edged, with each row above being offset by one stud length.
After the sheathing has been installed, cover the seams with the recommended tape for that specific foam to help seal the boards properly and prevent any moisture infiltration between the boards.
5. Gypsum Exterior Wall Sheathing
Gypsum sheathing is a type of sheetrock meant to be used in exterior applications. It may be combined with fiberglass or it may simply be made of gypsum and given a waterproof exterior finish. While not as popular as other types of sheathing, this material does have some particular uses that keep it in business.
- Gypsum Exterior Wall Sheathing Pros
Gypsum sheathing is completely fireproof, which makes it an excellent material for use on the exterior of homes and buildings located in areas prone to wildfires and natural disasters. It’s very strong and durable, holding up better than fiberboard, without the issues of swelling and warping that OSB is prone to, and without the weak areas of plywood.
- Gypsum Exterior Wall Sheathing Cons
Gypsum’s biggest con is its inability to flex, which means that it can’t be installed around curves on an exterior the way that OSB or plywood could be. It also means that if the sheathing were to be struck or impacted by something hard, it would crumble or crack easily, rather than absorbing the blow with flexibility.
- Gypsum Exterior Wall Sheathing Costs
The costs of installing gypsum sheathing is around $2 a square foot installed, which makes a 500 sq.ft. installation cost roughly $1,000 when complete. This includes both labor at roughly $700, and materials at roughly $300.
- How to Install Gypsum Exterior Wall Sheathing
Gypsum sheathing has slightly more flexibility in installation than other materials. It can be installed either vertically or horizontally, and the edges can be butted together without a spacer or gap. The boards should be laid and installed so that there is a minimum number of joints. Keep the gypsum roughly ¼ inch away from other materials and around openings.
The material can be cut by scoring and snapping ahead of time, then fitting it around the various openings. It can be screwed down using 2-inch long screws, 6-inches apart around the perimeter.
6. Diagonal Tongue And Groove Exterior Wall Sheathing
Diagonal tongue and groove sheathing is not very common today, but prior to World War II, it was the standard way to sheath an exterior. By installing tongue and groove boards diagonally across the studs of the home, you can create an extremely stable and strong exterior perfect for covering with siding. A vast number of woods can be used for this type of sheathing including fir and pine, so the overall cost of material can be relatively low.
However, not as many installers know how to work with diagonal tongue and groove sheathing, so it can be difficult to find someone who can install it. It’s also more difficult to find the materials for, as it’s not nearly as common a building material as OSB or plywood.
Installation can also take longer, because each board must be fitted into the one before it, then nailed into place on the studs. So, while the materials may be less per square foot, installation can often be considerably higher than with other materials, and the total time to install can also be much longer.
Making Sense of Your Options
Exterior sheathing is integral to every home exterior. Whether you’re adding it for strength and stability or to increase the energy efficiency of the home, sheathing is the right material for the job.
Structural sheathing adds stability and durability to the walls of the home, and in the case of some types of fiberboard, may also add some degree of insulation as well. Non-structural sheathing is designed to work with structural sheathing to help create a tight building envelope that can lower the home’s energy costs.
Exterior sheathing comes in several different materials. And although most are installed in a similar fashion to one another, there is enough variation between them that special care should be taken each time to get to know the recommendations for that specific material and its best uses.
Regardless of what type of architecture the home has or what type of siding will be installed over it, sheathing can improve the function, comfortability, and strength of the whole structure. Make sure you understand the options open to you to ensure that you’re getting the right type of sheathing for every project you undertake.