Joists are used in floors and roofs to provide essential structural support in modern housing. As with all structural components, they must be capable of meeting the loading demands associated with contemporary house designs. In addition to their structural performance, other factors are considered when joists are specified, such as their durability and consistency, impact on reducing site waste, and any potential energy-efficiency benefits.
Engineered joists, such as I-joists, are composite structural members used in floor and roof systems and are manufactured from engineered wood products. In this blog we will explore the benefits they can offer as an efficient and reliable alternative to help to maximise the efficiency of the housebuilding process.
What are engineered I-joists?
Engineered I-joists are composite structural members used in floor and roof systems. Manufactured from engineered wood products such as OSB (Oriented Strand Board), NFB (Natural Fibre Board) and LVL (Laminated Veneer Lumber), they can deliver consistent load performance and dimensional stability at reduced self-weight.
Engineered I-joists consist of two main components: flanges located at the top and bottom of the “I” shape and a central web that connects the flanges. The flanges are typically manufactured from high-strength laminated veneer lumber or solid timber. The web is made from NFB (a wood-based material known for its high shear strength). The engineered design of I-joists helps prevent warping, shrinking and twisting, ensuring consistent structural performance.
The attributes of engineered I-joists result in a lightweight, high-performance structural alternative to solid timber joists, offering strong load-bearing capacity and enhanced energy efficiency.
Where can engineered I-joists be utilised in housebuilding?
Engineered timber I-joists may be specified in the vast majority of areas that conventional solid timber joists can be used.
Engineered roof I-joists are horizontal or sloped structural members that span between load-bearing walls or ridge beams. Their primary function is to support the weight of the roof and any applied loads, distributing them evenly to prevent stress concentrations that could lead to structural damage. Roof joists can also contribute to the overall stability of the building by preventing the walls from spreading under roof loads.
Engineered I-joists used in both flat and pitched roofs are fundamentally the same, with differences mainly in their required size and strength to suit the specific loading conditions of each roof type. In flat roof construction, the rafters form part of a flat deck with a slight fall to allow for drainage.
In pitched roof construction, roof joists work in conjunction with rafters or trusses to form the structural framework that creates the roof’s slope. In all cases, the essential function of the roof joists remains unchanged, to support roof loads, while the shape of the roof structure above them varies.
Engineered floor I-joists differ from roof joists primarily in their location and orientation. Floor joists are only installed horizontally and are designed to support loads applied to the floor rather than the roof. These loads include the weight of occupants, furniture and other items within the room. In addition, floor joists provide a stable base for the floor structure, whereas roof joists connect with other structural components such as rafters and trusses to form a strong and stable roof space.
Engineered wall I‑joists are vertical structural members used as an alternative to traditional solid timber studs within load‑bearing and non‑load‑bearing wall assemblies. Their primary role is to support vertical loads from floors and roofs above while maintaining dimensional stability and reducing the risk of shrinkage, warping or twisting. The strong flanges and narrow webs of I‑joists also provide improved consistency compared with solid timber, helping to maintain straighter wall lines and more uniform finishes.
In addition to carrying vertical loads, engineered wall I‑joists can enhance the overall performance of the wall system by reducing the impacts of thermal bridging through the wall fabric.
As I-joists are engineered they can be manufactured to suit the majority of applications where traditional timber supports are used, they can also be used as part of off-site manufactured panels. These panels can be insulated in the factory and arrive on site for use as part of wall, floor or roof elements in modern housebuilding.
How do the benefits of using engineered I-joists support efficient housebuilding?
There are several benefits engineered timber I-joists can bring to housebuilding projects that help to make the process more efficient.
The consistency of performance of engineered joists
As engineered I-joists are made under controlled factory conditions they can be monitored and tested to ensure consistency of product performance is maintained throughout the joist. In contrast, although solid timber joists are graded based on their strength, stiffness and quality they are subject to natural variations within the wood that may lead to variable performance in some areas and create issues on site. By specifying engineered I-joists housebuilders are reducing the risk that product variability will affect the structural performance of the homes they are building.
Reduction in site waste using engineered I-joists
Engineered I-joists are manufactured at volume in a factory environment and can be pre-cut to the length required for each house type before being delivered to site. This can save time during construction and may reduce on-site waste.
Increasing energy efficiency using engineered I-joists
The slender profile of engineered I-joists delivers high load-bearing capacity while minimising material use. This significantly reduces thermal bridging and allows for increased insulation thickness. As a result, the use of i-joists can improve the U-value by up to 8% depending on the overall thickness of the structure.
Where can I find out more information about engineered joists?
STEICO has years of experience of making STEICOjoist an I-joist system for roofs, walls and floors. These engineered I-joists feature high-strength laminated veneer lumber (LVL) flanges and Natural Fibre Board webs. The I-joist shape reduces thermal bridging and helps to improve energy efficiency. STEICOjoist is lightweight and offers excellent dimensional stability with minimal shrinkage or twisting[1]. The I-joists include defined zones for easy installation of services, and they are made from responsibly sourced, PEFC-certified* wood.
To enquire about using our engineered timber joist system on your next project, contact us here and our expert team will be happy to help.
[1]https://www.steico.com/fileadmin/user_upload/importer/downloads/4028b6097384810e01749ff1e1ce608c/STEICOjoist_DoP_ETA-20_0995_04-0002.pdf
*PEFC/04-31-2550