Plans showing proposed building in Chester

EnerPHit Retrofit 2: Why step-by-step plan rather than a “one-hit” retro-fit?

Posted on 08/06/22

Our Passivhaus Designer Matt has recently bought a new family home. He is retrofitting various elements to a high standard of energy efficiency, and he intends to carry out the works to EnerPHit standards. In his latest blog, he explains his thinking behind undertaking the work step-by-step, rather than all at once.

Retro-fitting a property to a high level of thermal and airtight performance is not cheap. It is one thing if you are starting from scratch as you don’t have any walls and floors etc. However, when you have an existing building, with a complete envelope, essentially adding in extra elements, such as walls and a roof (to either the inside or the outside) of the existing one is going to require significant extra investment.

Furthermore, it is critical to ensure that the process of retrofitting the building to EnerPHit standards will not adversely impact the existing structure which, in turn, could cause significant defects. If we take the existing walls as an example, this may require further investment in measures such as specialist tapes, membranes or other solutions and their related labour charges, to create an effective and robust solution.

All these considerations mean that the costs do add up to a substantial figure. When it comes to my own project, we have a finite budget to work to, so doing the work incrementally is the only viable way for us to complete the project. A bonus for me, as an Architectural professional, is that by doing a great deal of the work myself I will have a far better understand of the principles and also the realities of the works – understanding how systems work together, what may not be practical as a solution and what considerations need to be made to achieve effect results. There are some further considerations that have led us to opt for the step by step retrofit route: 

Limiting disruption to family life

It has always been our intention, as far as possible, to limit the negative impact of the project on family members and our precious family time. We have purchased a great plot and we think we’ll be very happy living here for a very long time. However, the property does need a lot of work; a lot of very noisy, dusty and disruptive work. My wife and I have full time jobs and we have a nine year old and a seven year old to look after. As we will be living in the property throughout the works, the scale and, just as importantly, the duration of any disruption needs to be managed so that it is tolerable, and we can hopefully maintain our sanity during the process.

Lifespan of existing elements and preventing waste

A great thing about the EnerPHit retrofit Plan (ERP) is that it includes the function to assess the existing elements of the property and assign a useful life and renewal date to them. This function is called the “Scheduler”. This means that funds can be directed to those elements that will most effectively improve the performance of the building whilst not removing or altering those elements that can still serve a reasonable purpose.

For example, we have a mixture of single, double and triple glazed units installed at the property. I want to replace the single glazed units as soon as I am able to. However, whilst some of the double-glazed units don’t appear to be performing well, others, and the majority of the triple-glazed units do appear to be functioning well. This means I don’t need to replace these elements yet. In fact, I have a specified date on the ERP that I can work to before I need to consider replacing them. This helps to spread the costs. It also prevents undue waste by prematurely scrapping elements that have been manufactured, have embodied carbon, that can still serve a useful purpose.

Compromised Damp Proof barriers and uneven flooring

Before moving in, we knew that some of the floors needed replacing as they had settled and become uneven. This in turn has led to the integrity of the Damp Proof barriers being compromised. It is now apparent that all the floors have settled and been re-levelled (to various levels) over the years. As they all need replacing in any case, we’re seeing this as an opportunity to improve the performance of the building. We also understand that the additional cost of higher-level upgrade is nominal on top of the base costs. We have to dig out the ground in any case to remove the soft clay that is present and replace it with a suitable depth of DoT type 1 sub-base. We also need to install some insulation and a new concrete floor slab. We have to install new damp proof membranes too and then tie these back to the existing DPC’s in the walls; so to increase the amount/depth of the insulation will only result in a nominal increase in the cost of the process.


I have to bear in mind that undertaking some of these works will trigger the need for others to be carried out too. One example is with airtightness and ventilation. Once you get to a figure of about three air changes per hour, ventilation becomes critical if you are to avoid detrimental knock-on effects caused by moisture build up etc.

There are other “triggers” or interrelations that the ERP helpfully lists so that critical/important consequences can be reviewed, and potential issues avoided by design. For example, when considering the installation of external wall insulation, one must also consider such things as preparing for the later installation of windows and doors in a thermally optimal position and the creation of penetrations in the existing exterior wall for fresh air and exhaust air ducts.

Planning Approvals

We want to make some changes to the building to improve the living spaces and add a bedroom/ensuite. The planning process is likely to take nine to twelve months, so doing things step-by-step allows me to complete a large amount of the required internal works without needing to wait for receipt of Planning Approvals first. We want to get works started where possible and improve the building’s performance before next autumn / winter because March and April were very cold with the electric panel heaters only on just enough to take the edge off the cold. Ideally, by this autumn we will have substantially improved the thermal envelope of the building and installed a new air source heat pump based heating and hot water system. So, these are the reasons why we’re choosing to employ a step-by-step approach for the retrofit of our property. If you’re considering a renovation of your own, you may well have different reasons and priorities. Hopefully my experience demonstrates that the reasons for choosing to undertake a retrofit on a step-by-step basis are not as important as just appreciating the fact that it can be achieved and is often the most suitable method to opt for. In my next blog I’ll be discussing why EnerPHit is the best solution for what we want to achieve for our home.

To find out more about EnerPHit and Passivhaus design, contact our team.

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