We are using Passivhaus approaches to help us design for energy efficiency on a wide range of projects. Even where Passivhaus certification is not sought, the application of the same principles can achieve substantial inexpensive improvements to building energy performance.
Considering and designing out thermal bridging at an early stage can reduce the need for other more costly improvements required to achieve energy efficiency targets. Reducing the heat lost through element junctions is typically achieved by simple and cost-effective adjustments to construction details. With the improved detail potentially then being used multiple times across a development; a small amount of early design work can result in significant savings.
The Passivhaus standard requires the almost total elimination of thermal bridging. This is done by ensuring a continuous insulation layer around the building including all structural connections. A Passivhaus level of thermal bridging performance can result in up to a 15% improvement in CO2 emissions over the 2013 Building Regulations targets and up to a 20% improvement in Fabric Energy Efficiency (FEE).
Figure 1, below, shows a typical timber suspended ground floor junction with medium dense inner leaf blockwork.
Figure 1: Detail to be Improved
By replacing the two highlighted courses of blockwork with an aircrete equivalent, the predicted heat loss can be reduced by over 70%. This simple change improves the performance of a standard terraced house by around 2-4% over the Building Regulations Target Emissions Rate (TER). This could mean that instead of air testing to less than 3m3/hr. m2 a less onerous air tightness standard of 5m3/hr. m2 could be used.
Figures 2 (before) & 3 (after) are outputs of our thermal bridging analysis software for the detail shown in Figure 1.
Figure 2: Heat flow before Improvement
Figure 3: Heat Flow after Improvement