13/06/2026
High-Performance Engineering: Inside Our Latest SIPs Garden Annexe
When building a premium garden annexe, achieving ultimate thermal efficiency is only half the battle. You also have to design how the building breathes.
Here is a technical look at how we achieved an incredible, ultra-low U-value of just 0.14 W/m²K on our latest Edinburgh project using Structural Insulated Panels (SIPs), and why a dedicated MVHR system is vital to a high-performance build.
By utilising high-density SIPs panels, we’ve created a continuous, high-performance thermal envelope.
A U-value of 0.14 means virtually zero radiant heat loss through the walls and roof!!
Incredible energy efficiency, drastically reduces heating costs, and a space that stays naturally warm in an Edinburgh winter and cool in the summer.
SIPs builds are so structurally precise that they are completely airtight.
Traditional, drafty buildings rely on accidental ventilation (leaky windows and doors) to move air. In an airtight SIPs structure, that doesn’t happen. Without controlled airflow, stale air, VOCs, and moisture from breathing or cooking get trapped—leading to condensation and poor air quality.
To solve this, we integrated an EnviroVent energiSava 200 MVHR (Mechanical Ventilation with Heat Recovery) system (shown in the install photos):
1. Fresh Air, No Heat Loss: The system continuously extracts stale, humid air from the annexe and replaces it with fresh, filtered outdoor air.
2. Heat Recovery: Before the indoor air is expelled outside, a high-efficiency heat exchanger strips the thermal energy from it and pre-warms the incoming fresh air.
3. The Result: Total air changes every few hours, pristine indoor air quality, zero condensation risks, and all without losing the heat we worked so hard to keep inside.
A premium build isn’t just about looking good on the outside; it’s about smart, mechanical engineering on the inside.
