Can I-joists be used for roof structures?


At RML we originally specialised in roof trusses, however our expansion into joists over the years has meant our expert team of designers are able to utilise I-joists for both floor and roof structures. Although many buildings require a specific type of truss to suit the traditional roof structure, many building types are suitable for the use of I-joists for the roof.

We carry out flat roof designs on a variety of buildings such as apartment blocks, garden summer houses and extensions to existing properties. This shows the versatility of I-Joists for a wide range of building types.

I-joists enable greater spans and are simple to handle and install – making them ideal for roofs. The composition of I-joists means they resist shrinking and warping and have an excellent strength to weight ratio. As they are half the weight of equivalent solid timber, I-joists are light to handle for builders and therefore pose less risks in installation.

A quicker installation is also possible due to the skew-nailing of soft wood flanges, meaning less metalwork such as Z clips are required. I-Joists can also be tailored for various design challenges, such as roof lanterns and sky lights. The loadings required for these features are taken into account during the design process, without the need to double up joists and create additional costs. An example of this is portrayed in our 3D layout below:

Furthermore, sustainability is an important aspect of production for us. As the I-joist components are grown and manufactured in the UK, during their use they have a negative carbon footprint. I-Beams are cut to size in our factories and delivered to customers so do not require any cutting on site, resulting in less waste. In addition to this, we convert any off cuts to heat our working areas through a biomass, maintaining renewable energy sources.

Our teams carry out a wide range of work involving I-joists for roof structures and are experts in creating innovative solutions for any design challenges. If you would like to enquire around our products for your next project, please contact us on 01933 279597 or email us at

If you have a development project you’d like to talk to our timber frame team about, email or call us on 01933 279597.