T1-11 Plywood Siding

All homes have siding of some sort or another. That siding might be brick, stone or adobe, even though we don’t think of those materials as siding. But most of the time, when we talk about siding, we’re talking about a wood product, aluminum or vinyl. In those last two cases, aluminum and vinyl, they are often installed over the original siding, when a home needs a face lift.

Wood siding in the USA goes all the way back to the earliest sawmills. Clapboards, slabs of wood, cut from a tree, were used in place of logs as early as the 1700s. But the clapboard was reinvented in the early 1800s, giving us the clapboard we know today.

Aluminum and vinyl siding were invented as a lower-cost alternative to clapboard siding; but clapboard wasn’t the lowest cost building material to use as covering for a home. That designation belonged to T1-11 (sometimes written as T-111) siding, a plywood product which was commonly used in the 1960s through 1980s.

What is T1-11 plywood siding? Is it worth using for a home or outbuilding? This wood-based siding product isn’t as popular as it used to be, but it still has quite a few good uses. If you’re wanting to build an outbuilding for your home and don’t want to spend a lot of money, you definitely need to take a look at T1-11 siding as a possible option.

T1-11 Siding Basics

You’ve probably seen T1-11 siding at least a few times in your life; perhaps without even looking at it. This handy engineered wood product was very popular throughout the 1960s, 70s, and 80s, but fell out of favor as aluminum, vinyl, and composite siding gained popularity. Luckily, manufacturers still make good quality T1-11 siding. It might not be your first choice for building a home, but it could be ideal for finishing up a shed, chicken coop, or other outbuilding in an inexpensive, yet attractive way.

There are two T1-11 plywood siding panel grades: OSB and softwood plywood. The OSB version is usually a bit cheaper than the plywood, but has an inherent downside: OSB doesn’t normally last as long, it’s easier to damage, and it can’t be finished in as many ways as plywood T1-11 siding.

As originally designed, T1-11 siding was made from Softwood plywood. The addition of OSB was made as a cost-cutting measure. But the best T1-11 siding is still made of softwood plywood. OSB is much more susceptible water soaking in and swelling the sheet, especially at the edges. This is because of the large number of layers included in the average panel.

The best T1-11 is pressure treated T-1-11 plywood siding. The process of pressure treating it injects rosin and other chemicals into the wood fibers, under pressure, making it virtually waterproof. It’s more expensive than other versions of the siding, but it will last considerably longer, even without painting or staining it.

Other Plywood Siding Projects

While T1-11 siding is the most common plywood siding, it is not the only plywood siding style. You can also find V-groove and beaded panels. While these are more likely to be used indoors, especially the beaded panels, they can be used just like T1-11 panels.

One of the configurations that Hardi board comes in is visually almost identical to T1-11 siding. Although wood fibers are used in the construction of Hardi board, it is not normally thought of as a wood product. The combination of cement fibers with sand water and cellulose from wood make a very dense, durable product. It comes pre-primed, with instructions that it must be finish painted within 180 days. However, it cannot be stained.

T1-11 Plywood Siding Specifications

Most T1-11 siding products come in sheets measuring 48×96 inches, although it is possible to find it in sheets that measure 48×120 inches. Just like plywood, T1-11 siding comes in a variety of thicknesses. The most common T1-11 siding sheet thicknesses are 11/32”, and 19/32”. For most applications, you only need the thinner versions, as you won’t need the structural strength that ¾” siding imparts.

The grooves in T1-11 siding may be four or eight inches apart, depending on the mill that made it. Some companies also offer a pleasing reverse board and batten design. There’s no structural difference here; the main factor is aesthetics, and this decision is a mere matter of personal preference.

Depending on the manufacturer and supplier, you may find T1-11 siding in a smooth finish, or in a rough, more rustic finish. Both types are acceptable, with the rough, rugged surface providing a more rustic, natural appearance.

Plywood T1-11 siding can be stained with oil-based exterior stains, or it can be primed and painted. The choice is yours. However, if you opt for OSB T1-11 siding, you will need to prime and paint it with an opaque finish such as exterior grade paint. Staining is not an option because the OSB strands show through the surface.

How to Install T1-11

Before you get started with T1-11 siding installation, note that this type of siding should never be installed in contact with the ground. Always be sure to install it high enough above the ground, that standing water will not be able to reach the edge. The edges of the panels are highly absorbent, and contact with moisture will lead to swelling and/or separation of the sheets. When this happens, T1-11 siding becomes susceptible to mold, meaning it will need to be replaced long before its expected lifespan has come to an end.

One truck that you can use, if you are planning on painting your T1-11 siding is to seal the edge with caulking, before installing. Standard painter’s caulking, rubbed into the edge with your finger, will seal the end grain much better than paint can, helping to prevent water from soaking in. Do this before starting to install the siding, allowing the caulking time to dry, before installation, so you can reapply if the edges are not fully sealed.

All types of T1-11 siding have outer edges with 3/8-inch wide lips on the long sides, designed to overlap the piece that was installed previously. This is not a tongue-in-groove joint, but rather a lap joint. Panels are always installed with the grooves running vertically.

When installing, the edges should be positioned over a stud and nailed into place together, with one overlapping the next, rather than being nailed separately. The secret to this is nailing in this order:

  1. Cut your first piece, which should be mounted to one end of the wall. If you need to cut it to width, so that the edge falls in the center of a stud, cut the excess material from the corner side of the sheet, not the side which will join up with the next sheet. Note that this sheet should be mounted so that the lower side of the lap is the joining side.
  2. Mount the first piece, nailing it first to the corner of the building, then across the top, then to the center studs, and finally the bottom, leaving the joining side free. Double check as you are working, to ensure that the sheet is both plumb and aligned properly with the adjoining stud.
  3. Cut the next piece (if needed) and align it with the first, overlapping the joint and nailing that side of the sheet first, to keep it from sliding. Then follow the same nailing pattern as the first sheet, leaving the lap joint free for the mounting of the next sheet.
  4. Continue in this manner, always leaving the lap joint to be nailed when the adjoining sheet is attached.
  5. Add corner and any other trim. It is common to add a 1”x 2” trim board at the top, where the sheet butts into the soffit or gable end.

As always, the rule is to measure twice and cut once. If you make a mistake and have to remove a nail or two, you’re likely to damage the siding. Use a circular saw to cut the siding to fit around windows and doors. Allow a ½-inch expansion gap in these places. Don’t worry though, it will be hidden by the trim.

Depending on building codes in your location and the type of project you’re working on, you may be able to use T1-11 siding alone, without any other sheathing beneath it. This is a very economical way to go for sheds and other outbuildings, but keep in mind, your building will be stronger if you use plywood sheathing in the corners. Typically, this is 1/2” sheathing, with Styrofoam sheathing used throughout the rest of the structure.

Adding sheathing underneath your T1-11 siding also provides you with the opportunity to cover the structure with Tyvek house wrap or tar paper (roofing paper). This gives a moisture barrier underneath the siding, so that the structure is protected from the rain, even if the siding becomes damaged. It is possible to do this without the sheathing, attaching the moisture barrier directly to the studs, but there’s a good chance of it becoming damaged over time.

t1-11, board, wooden house, plywood
T1-11, Carl Bengtson

As with any project, you will want to apply 1”x 4” lumber trim pieces to the corners, at the joint between the siding and the soffits and around any windows. You’ll also want to apply Z-flashing to any upper joints to prevent water from leaking under the top edges of your sheets.

After installation, finish T1-11 siding with your choice of exterior stain, or go with a primer and paint combination that suits your budget as well as your sense of taste. Be sure to paint or stain well in the grooves, as it is easy to miss spots there, leaving someplace for moisture to seep into the wood. Please note that it is important to repaint or restain from time to time, in order to protect the wood from moisture.

If you are using pressure-treated T1-11 siding, you will need to wait before either painting or staining it. Staining is not normally recommended for pressure-treated wood products, as the finish tends to end up sloppy. For painting, you should wait for six months, allowing the chemicals in the wood time to dry thoroughly. Failure to wait for this time will cause the paint to flake off.

It’s worth noting that T1-11 siding is fairly easy to install. Many guides recommend hiring a professional to do it for you, but considering that part of this product’s appeal is its inexpensive price tag, you may want to spend some time planning your project carefully, and then hang the siding yourself. It’s a fairly forgiving product – you simply need to ensure that you follow guidelines for overlapping edges, measure carefully, and ensure that all your lines are straight.

How to Maintain T1-11 Siding

There’s a common misperception that T1-11 siding always fails… eventually. This doesn’t have to be true. Just like other forestry products, T1-11 benefits from plenty of TLC. Protective finishes go a long way. As with any other wood siding, T1-11 requires a fresh coat of stain every three to five years. Do not skimp on the finish, and consider applying new stain before the wood starts to look like it’s showing some wear.

If you have painted T1-11 siding, you’ll find that the look is less natural, but the upkeep is a bit more forgiving. In general, T1-11 siding that has been painted needs to be refinished every ten to fifteen years or so, depending on factors such as weather conditions and the type of paint that was used in the original project.

Is T1-11 Siding Worth It?

If you’re looking for a fairly attractive product that you can install yourself at a lower price than many other popular siding types, then go for it. T1-11 siding has pros and cons just like any other building material. When properly installed and maintained, it offers an attractive appearance and provides your building with protection from the elements.

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