Tell us a little about open web joists?

Open web joists – or Posi Joists – have seen a considerable increase in demand in the past few years. This product is a common way to structurally frame an upper floor in a residential building. They comprise TR26 structural-graded timber for the flange and steel webs forming an open web design, which provides the lightness of timber with the strength of a steel web.

What are the benefits of using open web joists?

The primary benefit of Posi-Joists compared to other engineered timber joists is that they allow for longer clear spans or shallower depths. They are ideal for floors or flat and mono-pitched roofs in domestic, industrial, and commercial applications.

They’re particularly popular when aiming for a sustainable build as they help to cater for thicker insulation and mechanical heat recovery and ventilation (MHRV) systems; both of which assist in the creation of more energy-efficient buildings with low U-values. The open design also allows for insulation or MHRV systems to be placed wherever they are needed, so builders don’t need to compromise.

Open web joists also bring the benefits of engineered timber – cut to size, factory manufactured with precision, and delivered ready for installation, they shorten build times and minimise on-site waste. Plus, timber is an environmentally-sound building material, so increasing the amount of timber in a build helps with sustainability credentials.

In addition to creating energy-efficient buildings, Posi-Joists are also easy to handle and install. Their precision manufacturing means there is a reduced need for site alterations, and they also create minimal vibration and improved acoustic performance. Plus, the open web design means that they eliminate costly cutting and drilling when installing services, and it offers a flexible solution for building contractors during any future internal building layout modifications.

Why has there been such an increase in demand for open web joists?

The main reason is the increase in sustainable building. Posi-Joists are the far superior option when incorporating MHVR systems. With the 2025 Future Homes Standard, and likely all future homes standards, calling for heat recovery systems in new homes to support energy-efficiency, Posi-Joists will be the most cost-effective solution.

Are open web joists a new product?

No, they’re not - people across the UK have been building with Posi-Joists for decades, and at DTE, we have made significant investments in our own Posi-Joist manufacturing capabilities at multiple times over the last 10 years to ensure we can meet demand with technical capability and the necessary capacity.

What difference will the 2025 Future Homes Standard make?

From 2025, newly built homes will need to be ‘zero carbon ready’, with a 75% reduction in carbon emissions to 2021 levels in England and Wales, and a 57% reduction in Scotland.

Reducing the requirement for energy in the home is the first step, before introducing low and zero carbon energy sources to provide heating and power. Fossil fuel heating is likely to be banned in new homes, with a shift to new heating systems like air source heat pumps. Combining an MVHR system with an air source heat pump is a super effective energy-efficient solution to heating and ventilation, and this is likely to be commonplace in houses being built to this standard.

Posi Joists remove the need for additional drilling when installing MVHR systems, which can create time delays and additional expense; and they also minimise dust caused by drilling and cutting on-site during installation. Many housebuilders are taking the 2025 Future Homes Standard seriously and expressing a desire to understand how this will affect the industry, and how to adapt future projects and processes. Many notable projects have already taken place with Posi-Joists used as the product of choice to achieve these standards.

What impact will this have on engineered timber product specification?

With the long-term goal of achieving Net Zero, and the ever-changing sustainability and energy efficiency specifications, this will no doubt put more and more emphasis on the use of robust and diverse products to accomplish these targets. The technical strengths of Posi-Joists will play a big part in raising the standard, while being able to meet the demand for new UK homes for years to come.

What is the alternative to building with open web joists?

Many builders continue to opt for more traditional I-joists, which are a viable option for some projects. While I-joists are by no means obsolete, we see Posi-Joists taking a leading role in the future.

What advice do you have for people considering open web joists?

We see Posi-Joists as a key to the future of housebuilding in the UK, and encourage the industry to take note now, and be ready to adopt them into their plans for the next five years and beyond.

If you would like to find out more about open web joists, contact your local sales team.