Installing new windows in your home can make a huge difference in energy efficiency, noise reduction, and aesthetics. One important consideration when replacing windows is selecting the proper header size. The header is the horizontal structural element above the window opening that bears the weight of the wall above. Choosing the right size header ensures the structural integrity of the wall and a secure, long-lasting window installation.

How to Determine the Correct Header Size

Selecting the appropriate header size for a window involves considering several factors:

Window Width

The width of the window rough opening is the starting point for header sizing. As a rule of thumb, the header should extend 6-12 inches beyond the width of the rough opening on each side. For example, if the rough opening width is 36 inches, the minimum header size would be 48 inches (extending 6 inches beyond the opening on each side). A larger 12 inch overhang would require a 60 inch header (36 inch opening plus 12 inches on each side).

Wider windows will need wider headers. A good general guideline is to add 1 foot of header width for every 2 feet of window width.

Wall Construction

Wall construction plays a key role in header sizing. The header must be sized to carry the load of the wall and roof above the window opening. This load will vary based on wall materials and building codes.

For standard wood frame construction with 2×4 stud walls, typical header sizes are:

Up to 4 foot wide openings: Use double 2×8 or 2×10 headers
5-6 foot openings: Use double 2×12 headers
7-8 foot openings: Use triple 2×12 headers

Other heavier materials like masonry, brick, or stone will require a larger header to carry the increased weight. Consulting local building codes is recommended to determine the proper structural header size.

Building Codes

Most areas require headers to be sized according to regional building codes. These codes provide specific structural requirements for headers based on opening width, wall construction, and roof load.

Always check with local municipalities and obtain any required building permits when replacing windows. Using a qualified contractor familiar with local codes is also a smart idea.

Load Bearing or Non-Load Bearing Wall

Headers in load bearing walls near the middle of the home must carry more weight than those in non-load bearing exterior walls. Load bearing headers may need to be sized 2 inches thicker than non-load bearing headers in the same opening width.

Roof Type

The type and span of the roof will impact the structural loads on the wall and header. A large roof with trusses spanning 40 feet will exert higher forces than a smaller roof framing system. Regional snow loads must also be considered.

Number of Floors Above

The number of floors above the window affects the header load. A header on the first floor of a 2-story home will need to be larger than a header in the same location on the second floor.

Structural Engineer

For large window openings, unusual load conditions, or multi-story homes, consulting a structural engineer is a good idea. They can analyze the specifics of your project and determine the proper header size and reinforcements required. This will ensure the structural integrity of the building is maintained.

Standard Header Sizes

While the factors above impact header sizing, there are some typical standard sizes that are used in conventional wood frame construction:

2×4 – 3 1/2″ wide x 1 1/2″ tall
2×6 – 5 1/2″ wide x 1 1/2″ tall
2×8 – 7 1/4″ wide x 1 1/2″ tall
2×10 – 9 1/4″ wide x 1 1/2″ tall
2×12 – 11 1/4″ wide x 1 1/2″ tall
3-ply 2×12 – 11 1/4″ wide x 3 1/2″ tall (3 boards laminated together)
4-ply 2×12 – 11 1/4″ wide x 5 1/2″ tall (4 boards laminated together)
Laminated veneer lumber (LVL) beams are also commonly used for headers. They are available in depths up to 20 inches and can span greater distances than conventional dimensional lumber.

In general, a good guideline is to use a minimum double 2×8 header for openings up to 4 feet wide. Increase to a double 2×10 for openings 5-6 feet wide, and a triple 2×12 header for larger openings.

Installing the Header

Once you’ve determined the proper size, the new header can be put in place. This involves the following steps:

Removing interior wall finishes like drywall to expose the existing header and framing.
Temporarily supporting the weight above the opening. This is often done by installing double jack studs on each side of the window.
Removing the old header. This is usually done by cutting it in the center and prying each half out separately.
Measuring for the new header length.
Cutting the new header to size from dimensional or engineered lumber.
Installing the new header on top of the jack studs and securing it with nails/screws.
Applying additional support like cripple studs above and trimmer studs on each end.
Replacing any insulation or vapor barriers.
Refinishing the interior wall surfaces.

Proper safety precautions must be taken when removing load bearing walls and headers. Using equipment like temp support posts, jack studs, and headers with pre-cut kerfs can make the structural work easier and safer.

When undertaking any major structural project, experienced contractors should be consulted to ensure codes and safety practices are properly followed.

Different Header Options

While dimensional lumber is the most common material, there are several other header options available:

Steel Headers

Steel headers provide maximum spanning capacity with minimal thickness. They are often double L or box-shaped for strength. Available insulated for energy efficiency. Used for large openings.

Solid Wood Headers

These can be made by laminating multiple layers of dimensional lumber together for built-up strength. Allows wider headers using common lumber thicknesses.

Structural Composite Lumber

Materials like laminated veneer lumber (LVL) or parallel strand lumber (PSL) are engineered for higher strength. Used as headers for long spans and heavy loads.

Insulated Headers

Combination headers made with plywood/OSB skins over foam insulation provide energy efficiency. Used to reduce thermal bridging in exterior walls.

Concrete Lintels

Common over openings in masonry or brick construction. Pre-cast or formed onsite. Very heavy duty but limited insulation value.

Steel Lintels

A steel angle iron or plate used as a structural lintel over windows and doors in masonry walls. High strength and spans but lower insulation value.

The right option will depend on structural requirements, energy codes, type of construction, cost, and local availability of header materials. A qualified contractor can recommend the best type for your specific project.

Structural Reinforcements

In addition to an adequately sized header, the opening may require extra structural reinforcements like these:

King Studs

A king stud is a full length stud extending from the bottom plate up to the header. King studs are placed on each end of the header and provide required support.

Jack Studs

Short studs that span from the bottom plate up to the header. Used to temporarily support the load above while replacing the header.

Cripple Studs

Short studs placed above the header to transfer load into the jacks studs below. Provide stability and strengthen the surrounding framing.

Trimmer Studs

Vertical studs that attach to the ends of the header. Help transfer load from the header into the jack studs.

Additional Jacks

Extra jack studs placed between the king studs help share the weight load on very wide windows.

These reinforcements properly distribute structural stresses around the header for maximum performance and longevity of the opening.

Key Takeaways on Header Sizing:

Size the header so it extends 6-12 inches past the rough opening width
account for the wall construction, roof type, building codes, and load paths above.
Use a double 2×8 header for small openings up to 4 feet wide.
Increase to double 2×10 for openings 5-6 feet wide.
Use triple 2×12 headers for very large openings up to 8 feet wide.
Structural reinforcements like jack studs, cripple studs, and king studs help strengthen the header.
Consider insulated or engineered headers for higher structural capacity and energy efficiency.
Always follow local building codes and obtain permits.

Properly sizing the header for replacement windows ensures the structural loads are carried safely for the life of the building. Taking the time to analyze the building specifics and consult experienced contractors will guarantee a code-compliant and durable window installation.

Frequently Asked Questions on Header Sizing for Windows

Replacing the header over a window opening involves important structural considerations. Here are answers to some often asked questions on selecting the right header size:

How big does a header need to be for a 4 foot wide window?

For a 4 foot wide window in a standard 2×4 wood frame wall, building codes typically specify a minimum double 2×8 header size. The two 2×8 boards laminated together provide sufficient strength to carry the roof and wall weight over openings up to 4 feet wide.

What size header do I need for a 5 foot wide window?

Most building codes require stepping up to a larger double 2×10 header for window openings spanning 5 feet wide. The extra depth provides more structural capacity over the wider opening, especially important in load bearing walls on lower floors.

What size header for a 6 foot wide window?

For rough openings 6 foot wide, a double 2×12 header is typically required. Some codes may even specify a 3-ply header using three 2×12 boards for added strength over openings this large. It’s a good idea to have a structural engineer analyze the loads and specify the proper header size and reinforcing method.

Should headers match stud size?

Not always. Headers are designed to carry much greater loads than vertical wall studs, so they often need to be a larger dimension for required strength. For example, 2×4 stud walls will commonly have 2×8 or 2×10 headers while 2×6 stud walls may use 2×12 headers over large window openings.

How big of a window can a 2×8 header support?

A typical double 2×8 header can safely span window openings up to 4 feet wide in conventional wood frame construction. For anything larger than that, you will need a wider 2×10 or 2×12 header to provide sufficient structural strength and code compliance.

How far should a header extend past the window framing?

Standard building practice is to size the header so that it extends past the actual window frame opening on each side by a minimum of 6 inches, and up to 12 inches for larger windows. This added width provides required bearing surface on the studs and allows for shimming/insulating around the window during installation.

Do I need a header for a small bathroom window?

Even small windows in non-load bearing walls require a proper structural header. The header transfers the weight of the wall above down into the studs at each side. Most codes require at least a double 2×4 header over bathroom or kitchen windows to provide needed support.

When should I replace an old window header?

Signs that an existing header may need replacement include sagging, sloping or dryrotted wood, cracks in brick/stone headers, or if you’re looking to expand the opening width. Replacing an undersized or deteriorated header ensures the structural integrity around the window is restored.

How much does it cost to replace a window header?

The typical price range to replace a window header is $800 – $2000, with an average cost of about $1300. Prices vary based on location, header size, accessibility, and finish work needed. Replacing a header is a structural job that requires proper building permits and experienced contractors.

Conclusion

Installing properly sized headers is one of the most important steps in successfully replacing windows. Take the time to analyze the building’s structural requirements, consult local codes, and work with qualified professionals to select the ideal header size and installation method. This will guarantee your new windows have a secure, long lasting, and structurally sound framework that will provide comfort and performance for decades.

How to Measure for the Correct Header Size

Determining the right size header for your window replacement project involves carefully measuring the existing opening and calculating required spacing. Follow these steps for measuring correctly:

1. Measure the window rough opening width.

Measure across the horizontal space between the framed opening at the top of the window.
This is called the rough opening width and determines minimum header span.

2. Add desired overhang space.

Headers should extend 6-12 inches past the rough opening width on each side.
For example, 6 inch overhangs would add 12 inches total to the rough opening measurement.

3. Account for any sizing ups.

Building codes often require upsizing the header 1 size for spans over 4 feet.
For example, rough openings over 5 feet may need 2×10 rather than 2×8 headers.

4. Consider header thickness.

2-ply headers are 3 1/2 inches thick. 3-ply headers are 5 1/2 inches thick.
Make sure the new header will fit in the existing wall framing depth.

5. Determine header overhang.

The header ends should extend past the outer edges of the window framing.
Make sure to account for this required overhang size when taking overall measurements.

6. Consider exterior finishes.

If siding, stucco or other exterior finishes need to be removed and replaced, factor this into the total header length.

7. Use an existing header as a template.

For easiest measuring, use the old header after removal as a template for the new size. Trace the outline onto new material.

Accurate measurements are critical for proper structural performance and a successful window header installation. Take precise measurements and calculate required overhangs to determine the optimal header size.

How to Install a New Window Header

The proper sequence of steps for professionally installing a new structural header over a window:

1. Prepare the work area.

Protect floors, furnishings with drop cloths
Ensure sufficient work space for demolished materials
Gather tools: pry bar, hammer, saw, utility knife, etc.

2. Remove interior finishes.

Take down drywall, trim around entire window area to expose studs and existing header.

3. Add temporary support posts.

Install temporary support posts below header area on each side of window to carry weight above.

4. Remove exterior finishes.

If necessary, remove exterior siding, stucco, etc. surrounding the window.

5. Cut old header in half.

Using a Sawzall or hammer and chisel, cut old header down the centerline into two pieces.

6. Pry out old header halves.

Use pry bar to carefully pry each half of old header material from opening. Remove any nails or screws.

7. Vacuum debris.

Use shop vac to clean out old insulation, debris from header area after removal.

8. Install king studs.

Cut and install new king studs same length as rough opening on each side of window.

9. Install jack studs.

Cut and install jack studs above and below opening to support header load during installation.

10. Measure and cut new header.

Place old header on new material and trace cut lines. Cut new header 1/2″ shorter than rough opening.

11. Install new header.

Place new header on top of jack studs, match ends to king studs. Nail or screw in place.

12. Add trimmer studs.

Install new trimmer studs at header ends if required for extra support.

13. Install cripple studs.

Cut and install cripple studs above header between top plates or rafters.

14. Replace insulation and vapor barriers.

Insulate header area per code. Install vapor barriers and seal appropriately.

15. Replace finishes.

Refinish interior and exterior surfaces, install window per manufacturer instructions.

16. Remove temporary supports.

Once fully installed, carefully remove temporary posts and jack studs.

Follow proper safety procedures and building codes at all times. Take care when removing and installing load bearing elements.

Common Code Requirements for Window Headers

Window header sizes must meet minimum requirements set forth by building codes. Here are some of the most common code specifications:

Minimum Header Depth

2×4 minimum for openings up to 4 feet wide.
2×6 minimum for openings 5-6 feet wide.
2×8 minimum for openings 6-8 feet wide.
2×10 minimum for openings 8-12 feet wide.

Minimum Bearing Length

Headers must extend at least 3-1/2 inches past window jambs.
Increased 1 inch minimum bearing length required for each foot of opening width over 4 feet.

Approved Header Materials

Dimensional or engineered lumber.
Prefabricated metal or composite headers.
Solid wood headers of laminated 1x material.

Fastener Schedule

16d common nails every 16 inches for built-up 2x lumber headers.
10d common nails every 12 inches for 1x laminated wood headers.

Height Above Opening

Bottom of header must be within 1/2 inch of top window framing.
Maximum 1/4 inch gap permitted between header and top jamb.

Insulation

Headers in exterior walls must meet minimum insulation values per energy codes.
Insulated headers, sill seals required in many areas.

What Size Header Is Needed for a Window