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Why is Retrofit, Passivhaus, energy efficiency and embodied energy important?

The UK government has signed into law a commitment to bring all greenhouse gas emissions to net zero by 2050. The UK Green Building Council estimate that the built environment accounts for 40% of all carbon emissions. This means that the construction industry as a whole has a large part to play in contributing towards the goal of net zero. 

The Building Regulations are being updated in a series of phases to require improvements to the energy efficiency of buildings however there remains the question of whether the step changes go far enough, quickly enough. This is where Passivhaus and other energy standards come in. 

What about existing buildings?

80% of the buildings that will be around in 2050 have already been built. This means significant upgrades will be required to most existing buildings, they will need to undergo improvements to their energy efficiency and change the type of energy supplied (no more gas).

There is no mechanism within Building Regulations to encourage or force building owners to upgrade these buildings unless they are extending or converting them. Even then the regulations don't go far enough with no requirement for a full house integrated plan, or forced upgrades to existing walls, floors or roof etc.


This leaves a significant portion of the building stock without a considered plan for how they are to be upgraded to meet the standards required as part of the net zero 2050 ambition. 

What is retrofit?

Retrofit and deep retrofit are construction industry terms for projects that make significant energy efficiency improvements to an existing building, even if it is to be phased


A retrofit project will be informed by an energy assessment and a thorough appraisal of the existing building construction. The plan will follow the Retrofit Principles and be informed by Passivhaus Enerphit techniques and advice from LETI, AECB and The Retrofit Academy. 

What are the other benefits of retrofit?

A by-product of retrofit design is the high level of thermal comfort will be provided to users. There won't be any cold drafts, there will be no condensation, there will be good air quality and the building will maintain a steady temperature through-out the year.

A completed retrofit project will also reduce the impact of fuel costs rises as the building will be less fuel dependant. This helps to reduce ongoing costs and reliance on the energy grid and wherever it is sourced from. 

What is Passivhaus?

Passivhaus is a German energy efficiency standard for how much energy a building uses for heating (and cooling). It requires a very low energy demand; approx. 90% less than current UK Building Regulations. It can be understood as the gold standard for energy efficiency. Thorough testing has proven that the as built results meet those predicted by the design, which isn’t the case with other design standards.


What is fabric first?

Fabric first is a key approach to providing sustainable energy to a building. The principle is to ensure that as much of the heat added into a building is retained within the building rather than relying just on a sustainable energy supply.


This means that the priority in a retrofit is ensuring a good level of thermal performance for the walls, roof, floor, windows and ventilation (both intentional and unintentional). 


Only once a fabric first approach has been taken should the energy supply and technology (solar panels etc) be reviewed. 

What about ventilation, airtightness and drafts?

Heat is lost from a building through two types of air movement, controlled ventilation, which we need to ensure that we have adequate air quality, and infiltration which is a result of gaps in the building structure and experienced as draughts. 

The retrofit plan should seek to reduce the amount of infiltration by improving the airtightness of the structure through reducing air leaks while also ensuring that the amount of controlled ventilation meets agreed standards. This is often not the case with older housing which rely on draughts to provide the ventilation required for adequate air quality. 

Without proper ventilation moisture will build up within the home resulting in high humidity which can lead to condensation forming on and within the building structure and the formation of damp spots / mould growth or even rot. Poor ventilation will also lead to a build-up of pollutants such as carbon dioxide, VOCs, radon, smoke etc all of which have a negative effect on the inhabitants of a dwelling. 

What is PHPP and SAP

PHPP and SAP are energy assessment software tools. PHPP comes from Passivhaus and SAP is the standard used for UK Building Regulations

Both of these pieces of software model the energy performance of the building by balancing the heat lost through the walls, roof, floor, windows, drafts and ventilation with the heat gained through the heating system, solar gain and other gains from people and computers etc.  

By modelling individual buildings it is then possible to develop a bespoke retrofit strategy that responds to that individual building which is far more likely to result in a successful result.  

How does retrofit work with traditional buildings?

Traditional building techniques often use materials such a lime that are vapour open, or often thought of as ‘breathable’. It is very important that a retrofit assessment understands this type of construction so any proposed upgrades can be sensitive to this type of construction. Introducing the wrong kinds of insulation or membranes that are vapour closed can cause unintended consequences, forcing moisture into other areas and causing damp and or deterioration of the structure. 

What is embodied energy?

Embodied energy accounts for the energy taken to build, produce, manufacture and deliver the materials and products selected. The importance of looking at embodied energy comes not just when selecting materials and construction methods but also when considering demolition or re-use. 


How far should a retrofit go?

There is no one prescribed standard for retrofit projects as each building will have it's own set of constraints, depending upon the building construction, budget, or if the building is Listed etc etc.


LETI, AECB, The Retrofit Academy (RA) and Passivhaus (Enerphit) all provide advice or their own standards with Enerphit being the 'gold standard'. LETI, AECB and RA generally agree that on average a 70% reduction in the energy demand is an appropriate ambition that balances cost and positive impact. 

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