I-Joists vs Traditional Timber Joists: What Should You Use for Your Build?

Undertaking any sort of home renovation or home build project means making a decision on the right joists to use. Joists are fundamental to the structure of your building, so it stands to reason that you are going to want to make sure you make the best choice for your needs. Traditionally, the material of choice has been solid sawn timber and that is still a great choice for many projects. However, over recent years engineered I-joists have increased in popularity too.  

Harlow Timber Systems provides end-to-end support for your build, supplying engineered I-joist packages tailored precisely to your architectural drawings. From initial technical floor design to site-ready kits complete with floor decking and fixings, our team ensures your floor system is delivered right on time. 

What Are I-Joists?  

I-joists are lightweight structural members composed of top and bottom timber flanges joined by a central, high-density wood fibreboard web. Supplied by experts like Harlow Timber Systems, ranges such as STEICO I-Beams deliver an exceptional strength-to-weight ratio that optimises performance while minimising material weight. 

Solid Timber Joists 

Solid timber joists offer a familiar, traditional approach that works well for minor repairs and standard, short-span installations. However, natural softwood is inherently susceptible to shrinking, bowing, and twisting over time, which strictly limits allowable span lengths without central support walls. 

Services Integration 

One thing you’ll need to take into account when putting together any project like this is how you are going to route pipes and cable and ductwork.  Routing these through solid timber requires strict compliance with complex drilling and notching regulations that can slow down installation. In contrast, I-joists feature thin webs with pre-stamped knockouts or easy-to-cut holes, letting trades run services smoothly without compromising structural integrity. 

Head-to-Head Comparison 

Building Regulations & Energy Efficiency 

When completing any project of this magnitude, it is important to take UK Building Regulations into account. This doesn't have to be a headache, but you do need a floor system that handles thermal, acoustic, and fire performance like a pro. That’s where STEICO I-Beams from Harlow Timber Systems come in. Because of their ultra-slim wood fibreboard web, they cut down on "thermal bridging" (where heat escapes through solid wood) far better than thick, traditional timber. 

Which Should You Use for Your Build? 

Opt for traditional solid timber joists if you are working on a small, straightforward renovation or minor extension where quick manual adjustments are needed on-site. Choose engineered timber joists (i-Joists) for new builds, timber frame projects, or open-plan designs that demand long spans, high energy efficiency, and silent floor performance. 

How Harlow Timber Systems Can Help 

Working with Harlow Timber Systems means gaining access to a complete, engineered floor kit designed directly from your architectural plans. Our engineering specialists design, cut, and package STEICO I-Beams to your exact spans—drastically reducing on-site waste and cutting installation time down to a fraction of traditional methods.  

Every order is supplied as an organised kit complete with labelled layout drawings, matching rim boards, metal joist hangers, structural adhesives, and weather-protected deck boards, giving builders and self-builders an all-in-one structural flooring solution. 

I-Joists vs. Traditional Timber Joists – FAQs 

Can I-joists span further than solid timber joists? 

Yes. Because of their engineered construction and strength-to-weight design, I-joists can achieve significantly longer clear spans without intermediate supports compared to traditional solid timber of similar depth.  

Are I-joists easy to cut on-site? 

While I-joists are supplied made-to-measure for swift installation, they can easily be cut to length on-site using standard carpentry tools. However, web holes for services must strictly follow design guides to maintain structural strength.  

Do I-joists stop floor squeaks? 

Yes. Floor squeaks are primarily caused by traditional solid timber shrinking, warping, and drying out over time, causing nails and boards to loosen. Because I-joists are dimensionally stable engineered products, they maintain their exact shape, virtually eliminating floor movement and noise.  

Can I-joists get wet during construction? 

Like all timber products, I-joists should be protected from standing water and excessive weather exposure during construction. Harlow Timber Systems supplies complete floor packages paired with weather-protected decking (such as Egger Peel Clean or CaberDek) to protect floors during the build.  

How do I get a quote for engineered timber joists? 

You can submit your structural drawings directly to Harlow Timber Systems, where our engineering specialists will design, specify, and price a bespoke joist package for your project.