This isn't about saying one system is always right or wrong. It's about being honest about what each one is good at, where the limits are, and what to expect in five or ten years' time. If you want a room that feels like part of your home, a SIP build is usually the most sensible starting point - but it's your money and your decision.
| Aspect | SIP garden room What I build | Cabin / shed kit | Timber frame | Steel system |
|---|---|---|---|---|
| Core structure | Structural insulated panels - structure and insulation in one. | Interlocking boards, often thin, with add-on insulation. | Stud frame with separate insulation, boarding and sheathing. | Steel frame skeleton with insulation and cladding built around it. |
| Insulation & comfort | High, predictable performance when detailed properly. | Variable - can feel like a posh shed, not a room. | Can be excellent if specified and installed well. | Depends heavily on build-up and installer - can be great or poor. |
| Typical lifespan | Decades when protected from moisture and UV. | Shorter - movement, weathering and joints working loose. | Long, similar to traditional building if detailed well. | Long, but needs correct detailing to avoid corrosion and cold bridges. |
| Running costs | Low when built as a "proper room" - easier to keep warm/cool. | Higher - more heat loss, more swings in temperature. | Depends on insulation spec; can be low or average. | Varies - can perform well with good insulation and airtightness. |
| Upfront build cost | Mid-high. You're paying for performance and detailing. | Lower ticket price, but usually with compromises. | Anywhere from mid to high depending on spec. | Often higher at small scale; can be efficient on big projects. |
| Maintenance | Mostly external finishes and normal housekeeping. | More painting, sealing and seasonal "fettling". | Similar to a small extension - check paintwork and seals. | Exterior cladding and joint sealing; structure itself is low maintenance. |
| How "solid" it feels | Like a small extension - solid, quiet, stable underfoot. | Can feel light, with more bounce and noise. | Close to extension feel when done well. | Very solid structure, but acoustic feel depends on build-up. |
| Best suited to | Year-round offices, gyms, studios, serious hobby spaces. | Occasional use, seasonal rooms, storage, hobby sheds. | Complex shapes, traditional-style buildings, linked extensions. | Bespoke, engineered projects, larger spans or unusual designs. |
| Spec transparency | Should be fully documented - panel thickness, U-values, details. | Often vague: "insulated", "double glazed" with little detail. | Can be well documented; depends on builder and drawings. | Usually documented, but smaller projects can be under-specified. |
| Typical UK price band (guide only) | 1,450-2,000+ per m2 for a proper build. | Lower headline price - but closer to ext. costs once upgraded. | Broad range - similar or above SIPs at like-for-like performance. | Often higher at small scale; can be efficient on big projects. |
These are broad, honest generalisations based on real projects I've seen and worked around. There are brilliant and terrible examples of every system - the key is how clearly the structure, insulation and detailing are specified.
If you want something that feels like a real room of your home - not just in the first summer, but on a damp Tuesday in February - then a properly detailed SIP build is usually the most sensible balance of performance, speed and cost.
Cabins and lighter structures absolutely have their place. I just don't pretend they're the same thing as a SIP room, and I don't sell them as if they are.