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TRJ CONSTRUCTION · STRUCTURAL INSULATED PANELS
A warm garden office. A comfortable annexe. A carefully planned extension. Understand the panel system behind the space, and the details that make it work.
Discuss your SIP building ↗
SIP annexe wall layout viewed from above
BEHIND THE FINISHED ROOM
A SIP combines two structural OSB board faces bonded to a rigid insulation core. The panel works as a composite element: the faces and core act together, rather than structure and insulation being separate layers.
SIP panels can form the floor, walls and roof of a building. Their layout, connections and openings are designed together, with the complete structure confirmed for the project.
TRJ focuses on the complete building envelope: the panels, glazing, joints, membranes, cladding and internal linings. Each part contributes to the finished building’s performance.
Read our detailed SIP guide ↗THE DETAILS THAT SHAPE THE RESULT
These six subjects explain why a specification should be considered as a complete building, rather than a panel thickness or a single insulation figure.
01 · SIP DESIGN DETAIL
The structural OSB faces and rigid insulation core are bonded into one composite panel. Their combined action is central to how the SIP system works.
The panel layout, connections and supporting members are designed together for the proposed building. The illustration introduces the forces and layers within the system.
Understand the panel system ↗02 · SIP DESIGN DETAIL
Our typical specification uses 125mm structural wall panels and 150mm roof and insulated floor systems. The final specification depends on the design, loads and intended use.
Thickness matters, but it does not determine performance by itself. The insulation material, complete build-up, junctions, openings and installation all influence the result.
Explore panel thickness ↗03 · SIP DESIGN DETAIL
EPS is widely used in SIP systems. Foam-injected PUR/PIR systems can offer different thermal performance for a given thickness. TRJ’s stated foam-injected specification uses PUR insulation.
Compare the actual product data and complete build-up. Thermal conductivity, structural properties and fire classification are specific to the product and tested system; one core name does not guarantee every performance measure.
Compare insulation cores ↗04 · SIP DESIGN DETAIL
Panel joints, openings and the connections between floor, wall and roof need careful sealing. Uncontrolled air leakage can undermine a well-insulated panel specification.
Membranes and vapour-control details are coordinated with the build-up. Airtightness needs appropriate ventilation, so the room remains suitable for its intended use.
Understand airtightness ↗05 · SIP DESIGN DETAIL
The bonded panel faces and core work together as a structural system. The design establishes the spans, openings, supporting members, connections and load paths.
Garden annexes and extensions require the structure to be designed for the proposal. The panel specification alone is not a substitute for the necessary structural assessment.
Read about structural design ↗06 · SIP DESIGN DETAIL
Insulation, airtightness, glazing, heating and ventilation work together to support more stable internal conditions. The aim is a usable room through the seasons.
Surface temperatures and moisture management matter as well as heating demand. Condensation risk and acoustic performance depend on the complete design and room use.
Explore thermal comfort ↗Both approaches can be used to create a carefully designed building. The comparison should cover the project specification, workmanship and the finished envelope.
| Design point | SIP construction | Timber-frame construction |
|---|---|---|
| Structure and insulation | Bonded structural faces and insulation core form a composite panel. | The frame and insulation are specified as coordinated components. |
| Junctions and sealing | Panel joints and openings require designed connections and airtight sealing. | Studs, insulation continuity, membranes and openings require careful detailing. |
| Design flexibility | Panel layout and openings are planned around the structural system. | The frame can be adapted around the proposed form and structural design. |
| Programme and value | Prepared panels can support efficient assembly; the full project scope determines time and cost. | Time and cost depend on the chosen system, preparation and project scope. |
SEE THE CONSTRUCTION DEVELOP
Drag each comparison control, or use the arrow keys, to reveal the two stages. Open either photograph to see the full image.
See the SIP wall layout develop into a weather-protected shell with glazing.
BeforeAfterCompare the structural assembly with the completed annexe exterior.
BeforeAfterThe original project photographs show the SIP extension structure and finished exterior.
BeforeAfterCompare the SIP wall structure with the completed timber-clad garden building.
BeforeAfterSee the house before and after the extension work.
BeforeAfterTake a closer look at the panel structure and openings, then explore the full construction process and standard specification.
We develop the layout and specification around the site and the intended use, from a garden workspace to a self-contained annexe or house extension.
A place to work, exercise or create, with the openings, electrical provision and comfort systems planned for the room.
Explore garden rooms ↗Plan independent living facilities, including the kitchen, bathroom, drainage and any required approvals.
Explore granny annexes ↗Coordinate the structure and connections with the existing house, site conditions and project design.
Explore SIP extensions ↗A SIP has structural OSB board faces bonded to a rigid insulation core. The faces and core act together as a composite panel, which can be used within a coordinated wall, roof or floor system.
TRJ typically specifies 125mm structural wall panels and 150mm roof and insulated floor systems. The final thicknesses and structural details are confirmed for the building design and intended use.
No. The core materials have different product properties. Compare the manufacturer’s data and complete construction build-up for thermal performance, structural requirements and fire classification. TRJ’s stated foam-injected specification uses PUR insulation.
Yes. Airtightness and ventilation should be designed together. Sealed joints help control unwanted leakage, while suitable ventilation supports the intended room use and moisture management.
Yes, SIP systems can be used for these building types when the structure and envelope are designed for the proposal. Foundations, openings, services and applicable planning or building-control requirements are assessed for the project.
No single panel name guarantees whole-building performance. The insulation material, thickness, complete build-up, junctions, glazing, workmanship and use affect the result. Confirm the values and specification for your own project.
Share your postcode, approximate size and intended use. TRJ works across North London, Hertfordshire, Buckinghamshire, Essex and surrounding areas.
Discuss your SIP project ↗See completed projects ↗TRJ Construction Ltd is a specialist Structural Insulated Panel (SIP) construction company delivering high-performance garden rooms and granny annexes across North London, Hertfordshire, Buckinghamshire and surrounding counties.
We design and build engineered living spaces using 150mm roof and base SIP systems, 125mm structural walls and professional K-Render finishes — creating buildings designed for durability, efficiency and long-term value.
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