The Importance of Material Selection in Thermal Bridges
Energy efficiency is a primary concern in modern building design, particularly for new builds where sustainability and performance are key. One aspect that significantly influences thermal performance is the choice of materials at thermal bridges. While lightweight thermal blocks are commonly used in wall constructions for their superior insulation, dense concrete blocks continue to be the standard choice below the Damp Proof Course (DPC) due to their structural benefits. However, recent energy consultancy work suggests that this conventional practice should be reconsidered for improved thermal efficiency.
Investigating Ground Floor Psi Values
We recently studied the thermal performance of different ground floor junctions, specifically the E5 - Ground Floor (Normal) junction, comparing two construction methods. Both employed the same block and beam floor construction but differed in materials below the DPC:
Standard 7N Dense Concrete Blocks with a thermal conductivity of 1.59 W/m·K.
7N Lightweight Aircrete Blocks (Thermal Blocks) with a significantly lower conductivity of 0.19 W/m·K.
The results were striking:
Psi Value for Standard Concrete Blocks: 0.137 W/m·K (shown left above)
Psi Value for Lightweight Aircrete Blocks: 0.064 W/m·K (Shown right above)
The images above are the Heat Flux diagrams for each version, these show the thermal energy (heat transfer) of the materials within the model. The red signifies the areas with the greatest heat loss. It is clear to see the model (left) with dense concrete blocks is significantly worse.
Understanding the Impact
These calculations highlight the considerable influence of material choice. The lightweight aircrete blocks demonstrated a superior ability to retain heat, reducing thermal bridging significantly. Temperature and heat flux diagrams further validate these findings, showing improved heat retention and lower energy loss.
Despite the traditional preference for denser concrete blocks below the DPC due to their structural strength, the research indicates that, in many low-rise residential buildings, replacing them with lightweight 7N thermal blocks is not only feasible but also beneficial. This change can enhance the Psi value at critical junctions, directly impacting the overall energy efficiency of a dwelling.
Structural Considerations & Regulatory Compliance
Transitioning to lightweight blockwork requires collaboration with structural engineers to ensure no compromise in integrity. However, for most low-rise structures, the switch is practical and aligns with modern building regulations.
Part L 2021 Building Regulations emphasize energy efficiency and reduced carbon emissions.
SAP10 Requirements push for improved thermal performance.
The Notional Dwelling Psi Value target is 0.16 W/m·K, which lightweight aircrete blocks significantly outperform at 0.064 W/m·K.
Why This Matters for Your Project
Achieving a lower Psi value than the Notional Dwelling standard contributes to a better SAP rating, leading to:
Lower Dwelling Emission Rates (DER)
Reduced energy costs
Increased occupant comfort
A smaller carbon footprint
Conclusion: A Step Towards Sustainable Construction
By re-evaluating the choice of materials at crucial thermal bridges like the ground floor junction, we can enhance both structural integrity and environmental performance. As the industry moves toward more sustainable building practices, incorporating lightweight aircrete blocks below the DPC represents a forward-thinking, energy-efficient approach.
Need Expert Guidance?
If you're looking to optimize thermal performance in your next project, get in touch with us at 01489 565920. Our expertise in energy efficiency can help ensure compliance with regulations while maximizing sustainability and cost-effectiveness.Enhancing Thermal Efficiency: The Impact of Lightweight Blockwork Below DPC
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