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What is the difference in the thermal performance of off-site and on-site constructed passive houses?

Emily Charles

Test Methods
Case Study
Psi-Therm Software 

For copy of full dissertation, contact:

Olivia Golden 
Darren Bergin 

This study consists of a comparative analysis between off-site timber frame construction and on-site masonry construction focusing on the key junctions where thermal bridging can occur. 

There is a significant gap in the construction industry for off-site constructed passive houses. 7-10% of the construction industry are off-site or modular constructions 1. This study was carried out as a comparative study of off-site timber frame construction and on-site masonry construction of a house, built to Passive House standards. The most commonly used construction methods for passive houses in Ireland are timber frame and masonry constructions 2. This research highlights that the same thermal performance can be achieved using both construction methods. This study suggests that timber frame construction performs slightly better than masonry construction, although the difference isn't significant. Timber frame off-site construction has a slightly quicker timeframe which could help the housing crisis in Ireland today.
This research was carried out using a case study of a closed panel timber frame off-site constructed Passive House and compared it to an on-site cavity wall masonry constructed Passive House. Through the proposed research, three key junctions where thermal bridging commonly occurs in both construction methods were investigated and compared to results generated from PsiTherm software. The results were then evaluated to determine which construction method has a better thermal performance.

In terms of thermal bridging, it is evident to see that timber frame off-site construction performs well and is a viable option instead of masonry construction and in some cases proves to be a better option for construction of a Passive House. Timber frame construction also has a slightly quicker time frame, for example a 204sqm Passive House built using off-site timber frame construction has a turn-key finish time of 6-7 months, where as a cavity wall masonry Passive House of the same size has a turn-key finish time of 8-9 months. 

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