Converting an attic space into a functional room often requires modifications to the existing metal roof trusses. These trusses, while designed to provide structural support for the roof, can sometimes obstruct the usable floor area or limit headroom. Altering them effectively and safely involves careful planning, precise calculations, and adherence to building codes. This guide outlines the necessary steps and considerations for how to alter existing metal roof trusses for an attic room, ensuring the integrity of the roof while creating a livable attic room.

What Are Metal Roof Trusses?

Metal roof trusses are structural frameworks made from steel or other metal materials that support the weight of a roof. These trusses are engineered to distribute roof loads evenly to the walls or other supporting structures, ensuring stability and durability. They are often pre-fabricated and consist of a combination of triangular units, which provide strength and rigidity while minimizing material usage. Metal trusses are favored for their high strength-to-weight ratio, resistance to environmental factors such as moisture and pests, and long lifespan. Due to their versatility, they are commonly used in residential, commercial, and industrial buildings, offering reliable support while accommodating various roofing designs and spans.

Why Altering Metal Roof Trusses for Attic Conversion?

Altering metal roof trusses is often essential when converting an attic into a livable space because standard roof trusses are typically not designed with occupancy in mind. These trusses are engineered primarily for structural support, distributing the roof’s weight evenly and resisting external forces such as wind and snow loads. However, their configuration can limit the available headroom and obstruct usable floor space. By modifying the trusses, homeowners can unlock the full potential of their attic, creating a functional room with adequate clearance and structural safety. Proper alterations ensure that the roof remains stable, while also meeting building codes and optimizing the attic’s usability for purposes such as a bedroom, office, or recreational area.

Understanding Metal Roof Trusses 

Metal roof trusses are engineered frameworks that provide support and stability to a building’s roof. Unlike wooden trusses, metal trusses are typically made from steel, known for its durability, strength, and ability to resist warping, rotting, or insect damage. These trusses are designed using a series of interconnected triangular components, creating a structure that distributes weight and forces evenly across the supporting walls.

This triangular design is crucial as it ensures the roof can withstand external pressures such as snow loads, wind, and the roof’s own weight without compromising the building’s structural integrity. However, the same intricate design and load-bearing purpose can make them challenging to alter, particularly when converting attic space. Understanding their function and construction is critical before making any modifications.

10 Methods How to Alter Existing Metal Roof Trusses for an Attic Room

1. Consult with a Structural Engineer

Before beginning any modification, it’s essential to consult with a structural engineer. They will assess the current load-bearing capacity of the trusses and determine if alterations can be safely made. They can also design any necessary reinforcements and ensure that the new structure will comply with local building codes. Having professional guidance is crucial to avoid compromising the overall stability of the roof.

2. Reinforcing the Trusses with Additional Steel Bracing

One of the most common methods of altering metal trusses for attic conversions is to reinforce them with additional steel bracing. This involves adding metal struts or bars to the existing trusses to improve their load-bearing capabilities. These braces can be installed horizontally or diagonally, depending on the specific requirements. Reinforcing the trusses ensures they can support the weight of the attic’s new floor, walls, and any additional load, such as furniture or appliances.

3. Adding a Steel Beam or Header

In cases where large openings are needed (e.g., for staircases or windows), it may be necessary to add a steel beam or header beneath the trusses to redistribute the load. This method requires precise calculation to ensure the beam is strong enough to handle the weight above. Installing a steel beam or header provides structural support and prevents the roof trusses from bowing or warping due to the removal of portions of the trusses for the conversion.

4. Cutting and Modifying the Webbing of the Trusses

Sometimes, alterations to the webbing (the diagonal supports inside the truss) are required to create the space needed for the attic room. The webbing is typically designed to distribute weight evenly, but cutting or removing sections of the webbing can weaken the trusses. If this is necessary, ensure that any removed or modified sections are replaced with steel plates or bars that can bear the weight. This method must be done carefully to avoid compromising the truss’s ability to carry the roof load.

5. Lowering the Ceiling Height

In some situations, lowering the ceiling height within the attic can create the necessary headroom while maintaining the integrity of the existing trusses. By installing a new set of lower trusses or creating a false ceiling beneath the original ones, you can gain additional space for the attic room. This method involves creating a secondary structural system to carry the load, ensuring that the original trusses remain intact while accommodating the new layout.

6. Sistering the Trusses

Sistering is a method where additional metal or steel members are attached to the existing trusses to enhance their strength and load capacity. This involves bolting or welding new members alongside the original trusses. The new members essentially “sister” the old trusses, creating a stronger, more durable support system. This method is useful when the current trusses cannot bear the additional weight of the attic room but can be reinforced by the new members.

7. Adding a Second Layer of Trusses

In some cases, adding a second layer of trusses above or below the existing ones can help redistribute the load. This approach is often used when the existing trusses are too small or weak to support the additional weight of a finished attic. The new trusses are typically placed parallel to the original ones, creating a doubled structure that can handle the increased load. This method requires careful planning and precise measurement to ensure the new trusses align correctly.

8. Using Purlins to Support Roof Load

Purlins are horizontal beams that run perpendicular to the trusses and can help distribute the weight of the roof. If the original trusses do not have adequate support or if additional weight from the attic room is anticipated, adding purlins can reinforce the structure. These beams can be installed along the top chords of the trusses or between the trusses to help with load distribution. Purlins are a practical way to transfer weight to the exterior walls or supporting beams of the building.

9. Replacing Trusses with Stronger Models

In situations where the existing metal trusses are too weak or outdated to support the changes needed for an attic conversion, it may be necessary to replace the trusses entirely. Installing stronger, custom-designed trusses that can bear the additional load of an attic room will ensure the structure remains safe and functional. This method requires removing the existing trusses and replacing them with new ones, which may involve significant cost and labor but will provide a solid foundation for the new living space.

10. Installing a Steel Frame System

For a more comprehensive structural solution, some homeowners opt to install a steel frame system beneath the existing trusses. This method involves building a frame structure that can support the weight of the attic room, which is then integrated with the existing trusses. This system can be custom-designed to match the unique requirements of the attic room, ensuring that it meets building codes while providing a stable foundation for the conversion.

Common Mistakes to Avoid

When altering metal trusses for an attic conversion, there are several mistakes that can compromise the safety and success of the project. Avoiding these pitfalls is essential to ensure the structural integrity of the building and compliance with local regulations:

1. Skipping Professional Consultation 

  Attempting to modify trusses without consulting structural engineers or architects can lead to dangerous outcomes. Professionals have the expertise to assess the load-bearing capacity of the existing structure and recommend safe and effective solutions.

2. Improperly Calculated Loads 

  Neglecting precise load calculations can result in trusses that are unable to support the additional weight of the attic conversion. This can lead to sagging, warping, or even structural failure over time.

3. Cutting Trusses Without Reinforcement 

  Removing or cutting sections of the trusses without implementing proper reinforcements weakens the overall structure. This mistake can cause uneven weight distribution and increase the risk of collapse.

4. Using Substandard Materials 

  Opting for low-quality or inappropriate materials to reinforce or modify trusses may reduce their ability to handle increased loads. Always use high-quality steel or other approved materials that meet building code requirements.

Conclusion

Altering existing metal roof trusses for an attic room conversion is a complex process that requires careful planning and professional expertise. Whether reinforcing the trusses with additional bracing, installing a new steel beam, or replacing the trusses altogether, each method has its advantages and challenges. So, there you have it – a quick and easy guide on how to alter existing metal roof trusses for an attic room.