When building a passive house the first thing you will have to choose is a foundation. The Irish standard for a traditional foundation is a u value of 0.21 W/m2K whilst the Passivhaus standard is between 0.10 – 0.15 W/m2K. This simply means that there is less heat loss through the passive foundation.
When we examine the traditional strip or raft foundation we can discover thermal bridging in the structure; where heat will be lost.
A passive foundation differs in the sense that it has no thermal bridges and is very well insulated to minimise heat loss; an example of this is Integrated Energy's Passive Strip Foundation.
There are many other foundation systems used for Passivhaus construction. In Ireland there are three main insulated foundation systems that are commonly used.
1. Viking House
These three insulated foundations are based on a similar concept; each uses a permanent expanded polystyrene (EPS) former to enclose the foundation. This prevents heat loss (thermal bridging) through the structure by eliminating any contact between the foundation and the cold ground.
The insulation used in these foundations is called EPS and comes in different strength grades; mainly EPS300 and EPS100. This is of a much higher compressive strength than traditional expanded polystyrene insulation; with EPS300 being able to support loads of up to 120kN/m2. This is more than adequate with typical loads from a two-storey dwelling being 45 – 55kN/m2.
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