SIP vs Pre-Insulated Timber Frame: What’s the Difference

When it comes to choosing a structural solution for your build, understanding the differences between SIPs (Structural Insulated Panels) and pre-insulated timber frame systems is key. While both offer significant advantages over traditional building methods, they perform differently across several important parameters such as thermal efficiency, structural integrity, build speed, and long-term value.

There is no one choice – the difference between the two can help guide your choice of materials to fit the needs of your build. 

Thermal Performance

SIPs stand out when it comes to thermal efficiency. They have a BBA-approved PUR core, which provides very low U-values without needing extra layers of insulation, which is particularly useful where space or wall depth is limited. U-values are a measure of the thermal transmittance, so a low number means better insulation performance without compromising on thickness. 

Because SIPs don’t include repeat timber studs throughout the panel, unlike timber frame systems, they significantly reduce thermal bridging. That means fewer weak points where heat can escape, helping the building perform closer to its design targets.

Another key point is compliance. High-quality SIP systems come with pre-calculated PSI values, which are essential when calculating overall fabric performance under SAP10. This is an efficiency methodology that measures energy efficiency, and is looking to assess how well a building keeps in heat. In an assessment, it’s useful that we know this for sure so that we don’t have to pay an extra cost to find this out, or rely on default figures that might negatively affect the ratings. 

Structure

From a structural point of view, SIPs and timber frames work very differently. SIPs are self-structural panels consisting of a PUR core and OSB facings, meaning they don’t need internal studwork to support loads. The panel itself acts as the structure, opening up more flexibility in design and simplifying the construction of features like vaulted ceilings or habitable roof spaces.

In contrast, timber frame panels rely on regular internal studs for strength. These must be factored into the layout, and the panels may also require additional elements like glulam beams or steelwork depending on the spans involved.

Another key difference is settlement. Timber frames naturally shrink and settle as the structure dries and beds in which often require an allowance of 15mm per floor. Over a three-storey building, that’s 45mm of movement to plan for. SIPs are much more dimensionally stable, with only a small allowance (around 2mm per floor), which makes them well suited to lightweight finishes like render and reduces the risk of post-completion issues such as cracking or joint movement. 

Cost

Ultimately, a standard timber frame may often be less expensive than a SIP system. A SIP system is a high-end solution that is superior in quality both structurally and thermally than a standard Timber Frame Product. If your goal is simply to meet regulatory standards and deliver quickly at minimal expense, this system can be a practical choice.

However, SIPs offer more than just compliance. With higher thermal performance, faster weatherproofing, and improved dimensional stability, they can reduce long-term costs, improve build quality, and minimise snagging later in the project.

Programme

Both SIPs and pre-insulated timber frames offer faster installation than traditional methods, in some cases SIPs can provide additional efficiencies

For example, a SIP roof system not only provides insulation and structure in one, but also creates a weather-tight shell quickly. This allows internal and external trades to begin work simultaneously, reducing downtime and helping the programme stay on track. In comparison, pre-insulated timber frame systems often use more traditional roof structures like trusses, which need to be insulated on-site by follow-on trades. This can leave the structure exposed for longer and slow progress, particularly in unpredictable weather conditions.

Windows and doors can also be ordered in advance with greater confidence, as SIPs are manufactured to tighter tolerances than traditional timber systems, which helps prevent delays.

The predictability of installation for both systems is a great reason to choose these over traditional methods, as the systems are installed quickly and accurately in conditions where more traditional methods may have to stop. For any project both systems help to minimise risk of variables and delays to programmes which often then incur cost.

Accreditation

Whatever system you choose, working with an accredited supplier is critical.

We always recommend choosing a provider who is a Gold Standard Member of the Structural Timber Association, and whose products carry independent third-party certification such as:

• BBA Certificate
  
• ISO9001 Quality Management
  
• Fire performance testing to EN1365-1 (30- and 60-minute standards)
  
• NHBC Accept or other major warranty approvals
  

Our SIP supplier includes all of the above along with acoustic data, standard construction details, and pre-calculated PSI values. These documents help ensure smoother approvals with building control, warranty providers, mortgage lenders, and other regulatory bodies.

Both SIPs and pre-insulated timber frame systems have a place in modern modular construction. The right choice depends on your project priorities.

If budget and simplicity are key, a pre-insulated timber frame may suit your needs. But if you’re looking for high performance, speed, stability, and long-term reliability, SIPs provide a clear edge. If you’d like to learn more about how we plan and build our modular buildings, speak with a member of the Qube team today.