How can PSI values support retrofit?
Calculating psi values to work out the heat loss through existing and improved junction details is an essential part of delivering high-quality retrofit in homes and buildings. Without carrying out an appropriate PSI value calculation, it can be impossible to know whether the retrofit work being undertaken is delivering the hoped-for improvements.
In particular, when looking to meet a standard such as EnerPHit, it is necessary to ensure performance is met for the purposes of certification. Calculating PSI values helps to demonstrate that a junction detail will perform as required and that the surface temperature at the junction will not support condensation and risk mould growth.
Read on to learn more about the importance of accurately calculating PSI values for retrofit projects.
What is retrofit?
Retrofit is the widely-used term for construction works carried out on an existing building with the aim of improving its energy performance and comfort and reducing its carbon emissions. Typically, retrofitting implies a deeper, and often more intrusive, level of work.
‘Refurbishment’, for example, can be thought of as surface-level improvements primarily designed to improve aesthetics.
‘Maintenance’ can be small or large-scale, but suggests the intended outcome is for something to perform the same as it did originally, rather than being an improvement.
Considerations for retrofitting
There are logistic and economic considerations to retrofit. Highly invasive work on existing fabric on buildings can be time-consuming, expensive and messy.
A retrofitting programme can be carried out by itself or as part of extending or remodelling a property. It might seek to tackle just one area of the building or look to improve the entire property (which is referred to as ‘whole-house retrofit’).
There are logistic and economic considerations to retrofit. Highly invasive work on existing fabric on buildings can be time-consuming, expensive and messy.
It may be desirable to tackle the entire property in one go, but where that is impractical or would cost too much, then a retrofit plan can be designed to be completed in stages over a number of years.
Why carry out retrofit?
The motivations for carrying out retrofit can be many and varied. There might be a single, isolated issue, such as temperature factors, that needs tackling, or a building owner might have much broader ambitions. Reasons for pursuing retrofitting in construction could include any or all of the following:
- Improve the thermal performance of the building fabric to reduce energy use.
- Reduce heat losses and draughts to make the property more comfortable.
- Tackle structural issues, or building fabric problems such as damp.
- Reduce the environmental impact of the building, including relying less on fossil fuels for heating and hot water.
- Combat issues like dampness, condensation, mould and poor air quality to create a healthier home.
Undertaking work on a property, particularly extensive and invasive work, requires building regulations/standards approval. However, not all of the above is covered by building regulations.
Retrofitting Challenges
There are requirements relating to thermal performance, energy efficiency and ventilation, but those requirements are not necessarily ‘joined up’.
As a result, it can be hard to know if the proposed work will generate the desired outcome. How can you be sure that insulation, airtightness, and energy efficiency improvements won’t make air quality worse, for example?
Retrofitting an individual area of building fabric might not have those kinds of consequences. However, the advice of expert retrofit professionals should still be sought – especially as the process of uncovering parts of the property might highlight other issues that need attention.
But undertaking a whole house plan, especially one done in stages needs careful consideration to define an overall outcome.
In that case, it can be helpful to aim for a standard like the AECB Retrofit Standard or EnerPHit U-values (the equivalent of the Passivhaus standard for existing buildings).
Why do thermal bridges need attention in retrofit?
When carrying out retrofit measures in an existing property, it’s just as important to pay attention to junction details and thermal bridges as in a new-build property.
If building fabric elements like floors, walls and roofs are insulated, made airtight, and otherwise upgraded, then a failure to give the same attention to thermal bridges or assuming default values can risk creating or worsening existing problems.
If an existing thermal bridge is poorly insulated and/or not very airtight, then improvements to the surrounding fabric will drive issues towards the thermal bridges.
The role of thermal bridging in heat loss
The thermal bridges will be responsible for a greater proportion of total heat loss. If warm, moist air can escape at a thermal bridge, then there is a risk of condensation as the air cools when it comes into contact with the cooler surfaces.
What makes junction details particularly tricky to deal with in retrofit is that they can be very hard to get at. Many thermal bridges are the result of how the building structure bears loads and transfers them to the foundation.
The reason thermal bridges generally lack an insulation layer is that a thermal insulation material would not be strong enough to bear the loads present at the building junctions of thermal bridges.
Adding insulation to a building element to improve its U-value is relatively straightforward compared to improving the PSI value of some thermal bridges. For that reason, thermal bridges in retrofit need careful thought as to how they can be improved sensitively.
Energy Analysis for Retrofit in Construction
While it is not necessary to pass a SAP assessment for retrofitting, it’s still important that your site uses thermal modelling software to perform an energy analysis of your current ratings. While the site may have previously passed the SAP assessment, your business cannot assume that the new renovations will maintain the low-energy status of your site.
Default values were previously included in the junction details according to common construction types in Part L compliance of the Accredited Construction Details (ACDs). Even though retrofit doesn’t require SAP assessments to meet a building regulation, your business still cannot rely on default values to accurately measure heat loss. An energy analysis for retrofit is essential to ensure the extensions still account for potential additional heat loss.
Though a U-value calculation can be helpful for measuring heat losses, U-values alone cannot account for linear thermal bridging. For a precise reflection of your energy efficiency, an accurate PSI value, rather than a U-value, is required. Construction companies can now determine heat loss with the inclusion of thermal bridging and linear length with construction PSI values.
These values consider multiple important factors that are crucial for a positive energy rating after retrofit changes, such as heat flows and U-values
With accurate PSI calculations in construction projects, we can now calculate a precise value to replace the default y-value (the total loss from thermal bridging) with a thermal transmittance calculator.
Optimising thermal bridging with building thermal analysis software
Existing buildings – and older buildings in particular – require bespoke detailing and calculations to address the specific constructions encountered. BRS Technology’s AutoPSI thermal modelling tool can help with that. The easy-to-use drag-and-drop interface allows customisable junction details to be created and calculated quickly and easily.
The online building thermal modelling software works to the relevant standards and calculates both the PSI value and surface temperature factor instantly. It’s therefore possible to experiment with different ways of treating a difficult thermal bridging detail to see what solution can deliver the desired result – especially when aiming for a particular certification.
This technology is especially useful for retrofit projects where changes to the existing structure need to be carefully reviewed and considered.
AutoPSI: Innovative PSI Calculation Technology
Founded in 2019, AutoPSI has created innovative building software to make calculating linear thermal transmittance efficient for the construction design industry. Our software for PSI value calculations is primarily used by SAP assessors, housebuilders, technical teams, and architects.
A PSI calculator is necessary to support optimal retrofit efforts in construction, pass regulations, ensure BR497 compliance, and improve energy performance. Our online PSI value calculation software makes thermal modelling in construction efficient by helping you accurately calculate PSI values.
Our innovative PSI software for PSI value thermal bridge calculation makes your PSI measurement easy to customise for retrofit in construction. It’s extremely simple to add or delete data in our whole-house retrofitting calculator, allowing you to find the most optimal ways to reduce heat loss with ease.
Many of our clients aiming to calculate a PSI value have succeeded in reducing heat losses in materials and improving energy efficiency.
Now that you understand the importance of calculating PSI values for retrofit projects, why not sign up for a demo of AutoPSI’s PSI value calculator software. See how you can improve the energy performance of your building.
Find out more by visiting the AutoPSI website or our LinkedIn page.
