Headers make the openings of windows and doors. They perform an essential structural function of collecting and distributing the weight above windows and doors to nearby studs because they cannot support weight other than their own.

Headers maintain the structural integrity of the building, so it is critical to size the header correctly. Let's look at how we can select the correct header size for our windows.

 Different Sizes Option(in")
Width Height Size
24 24, 36, 48, 60, 72 24x24, 24x36, 24x48, 24x60, 24x72
30 30 30x30
32 36, 48 32x36, 32x48
35 35 35x35
36 24, 36, 48, 60, 72 36x24, 36x36, 36x48, 36x60, 36x72
40 60 40x60
48 36, 48, 60, 72 48x36, 48x48, 48x60, 48x72
60 36, 60 60x36, 60x60
72 36, 72 72x36, 72x72



What Is A Window Header?

The top of the window casing has support called a window header. Typically it is twice the thickness of the framing components of the window.

The header provides additional support by spanning horizontally across the top of the window casing, preventing the wall's entire weight from resting on the window casing. These structural components let us add windows and openings without weakening the walls.

Headers act as bridges. The king studs and jack studs (trimmers) are the vertical pillars at each end of the header.

Most wood-framed buildings use dimensional lumber installed on the edge for the headers. The trimmers that butt immediately below the header and the king studs fastened into each header's ends create a solid vertical support column.

Together, the headers, king studs, and trimmers carry weight from the ceiling to the floor and foundation below and around window and door openings. They take the weight of the materials above them to the floors and foundations below via the trimmers.

Larger headers are needed for longer apertures. Small headers will bow downward, making it challenging to operate windows and doors. They will also damage trim and crack drywall.

Common Window Header Sizes

Getting the correct size of the window header is essential for ensuring the structural integrity of your building and for a smooth window opening. Its size depends on what the header needs to support.

If your header is different from the suitable size, it could be challenging to open and shut the window, and if you frame glass, there's a danger that it will break.

Window headers are often made of 2 segments of dimensional sawn lumber, such as Laminated Veneer lumber (LVL) or Glued Laminated Timber (Glulam). Window header thickness, similar to components utilized in wall systems, is constrained by the wall's depth.

In most wall systems, 2-by-4-inch thick lumbers are used, which are 3-1/2 inches wide. You can obtain more strength by employing thicker beams, but it is not practical as the wall's 3-1/2 inches depth needs to be maintained, so instead, we have to use higher and broader pieces of lumber.

Window Span: 3 Feet

Two 2-by-4 or one 4-by-4 piece of lumber is used for approximately 36 inches or less spanned windows. A 24-inch to 34-inch range of windows is typical; it is the size of most used window headers.

Window span: 4 Feet, 6 Inches

Two 2-by-6-inch sides of window header are used for more expansive windows that span 4 feet, 6 inches, or less. It is a quite often used window span as many are in the 45-50 inch range.

Window Span: 5 Feet, 9 Inches

Two 2-by-8 pieces of lumber are used for windows that span 5 feet and 9 inches.

Factors That Change Header Sizes

These guidelines for the sizes of window headers are for single-story buildings 20 feet wide. More expansive facilities have shorter window header spans.

Window header sizes can also change due to heavy snowfall or other circumstances. Because of this, it's crucial to follow all development to local codes.

The following factors should be considered that can affect the header size:

• The door or window opening’s length

• The weight of the walls, floors, and roofs above

• The width of the building

• The amount of snowfall in the area

• Whether it is a non-bearing wall (having parallel running rafters, beams, and trusses) or a bearing wall (having resting rafters, joists, and trusses)

• Whether the wall is an exterior-bearing wall or an interior-bearing wall

• Type of wood used

While framing a window, calculating the header size becomes more challenging. To be extra cautious, some contractors would overbuild the window header. For French doors or 6-foot patio and 4-foot wide window openings, a pair of 2-by-12 placed side by side is customary.

Over-building will marginally raise the price. The increase in thermal bridging between the inside and the outside is one drawback.

Using Laminated Veneer Lumber (LVL) For Window Headers

Laminated veneer lumber (LVL) is a composite wood product made from many thin layers of wood stacked together. Edge-forming material, rim board, beams, and headers are usually made from it.

Larger beams are produced with laminated veneer lumber by layering thin veneers together. The layers are bonded together, and intense pressure is applied in the machine until they connect. As a uniform and dimensionally stable building material, LVL is suitable for bearing and non-bearing walls.

LVL has several benefits over standard milled lumber. It is straighter, more uniform, and stronger. It is far less prone to twist, warp, shrink or bow than regular lumber because of its composite structure. It has more significant permissible stress than sawn lumber.

Glulam beams are another kind of LVL. The full-sized lumber is bonded under tremendous pressure to create beams in Glulam. LVL can also be utilized with Glulam as an outside glulam tension lam to strengthen the glulam beam.

LVL is a very dependable building material that offers many of the same qualities as large-sized timbers. LVL is stronger and more rigid than typical sawn dimensional lumber. When there are vast spans, as there are for garage door headers or French doors, LVL is valuable.

LVL is more expensive, so it is preferred for wide window headers, i.e., 6 feet or larger. Sawn lumber can easily bridge smaller windows, which is cheaper than LVL.

Final Thoughts

Correct sizing and selection of material for headers are essential to ensure the strength of walls.

Local factors that affect the sizing should be considered to make headers long-lasting. Larger windows need larger and stronger headers and vice versa.

February 27, 2023 — Della Wang