Plans showing proposed building in Chester

EnerPHit Retrofit 5: Passivhaus Planning Package Results

Posted on 09/11/22

In my last article I explained the Passivhaus Planning Package (PHPP) software package and how it accurately calculates a property’s heating load and its performance. I also detailed what standard I am aiming to achieve with the retrofit (EnerPHit Plus) I am carrying out at my family home. In this article I will cover the steps you need to take in broad terms to achieve that standard.

Raising the performance of the house

In order to achieve the standard, we need to improve the thermal performance and airtightness of the entire house.
As our home is a bungalow, it has a fairly poor Form Factor, which means we’ll have to go to greater lengths than we would with a property of the same size, but of a better form factor. In simple terms, this means improving U values of the thermal elements to a higher level than might otherwise be necessary.

What work needs to be carried out? 

Eventually we’ll be upgrading all the thermal elements of the property to include:

 · New ground floors
 · Upgraded walls: the existing, defective, mineral wool cavity wall insulation has just been replaced under guarantee with EPS Bead. External Wall Insulation will be installed following a future planning approval
· Windows and doors: the existing windows and doors are a mix of single, double and some (poorly performing) triple glazed units. All will be upgraded to meet the performance requirements of EnerPHit
· Roof: the current, rather badly installed, loft insulation is only 200mm thick and it will be upgraded to 500mm, once all the existing / redundant services have been resolved or removed and the new elements have been installed 
· Mechanical heating and ventilation will also be installed. Black mould was rife when we first purchased the property. The house currently has no mechanical extraction, so we still suffer from high moisture and condensation at times. A new balanced system, with controlled extract and the introduction of filtered clean air that has been pre-heated by the unit will make a significant difference to the air quality of the house and associated issues such as moisture and mould. This system will retain approximately 90% of the heat from the air being extracted from the house so we won’t lose hundreds of litres of warm air by opening a window every time we have a shower or bath or do any cooking.

Minimising ventilation heat losses

As the works progress, we will be doing all we can to make the house airtight to minimise ventilation heat losses. This includes ensuring continuity of the airtight layer as we patch and re-plaster rooms, sealing any junctions for instance, between new slabs and the walls, and stopping air movement through service locations, such as socket back boxes. Another critical element will be the installation of new windows and doors and ensuring that each opening is taped and finished well.

The PHPP package has allowed me to balance the performance of the above elements, while factoring in both the Mechanical Ventilation with Heat Recovery (MVHR) and airtightness of the completed building. This means I won’t over-specify any element and incur unnecessary costs. I’ve made no bones about the fact that this isn’t going to be a cheap process. So ensuring that it can be done as efficiently as possible, in terms of financial costs as well also sequencing, is really important.

The “plus” bit of EnerPHit plus

EnerPHit plus requires improved standards/performance over the standard EnerPHit standard. The Primary Energy Demand of the building must be less than 45 kWh/(M²a) as opposed to 60 kWh/(M²a) – a reduction of 25%. Renewable energy generation is required and, for the “Plus” standard, this must exceed 60 kWh/(M²a). To achieve this, and in addition to the existing 3kW solar panel array, I will be adding an additional 5.3kW array.

I have also allowed for a 3kW wind turbine currently to generate electricity in the winter half of the year, when solar generation will drop off substantially. This is subject to planning and practicality but will go a long way to providing off grid year-round electricity. Supporting these additions will be a battery for storing energy and two solar thermal panels to generate the majority of the hot water requirements for about six months of the year. These will be covered in future blogs.


So far in these articles I’ve talked a lot about how great the Passivhaus and EnerPHit standards are. The following results show the incremental gains of each step very clearly.

Energy demand and generation

The planned changes will significantly reduce the energy requirements of the house. Each step improves the performance of the building in a clear and demonstrable way. For future steps I may be better to replace the remaining windows first, and then insulate the external walls, however, there is a greater cost associated with this. I’ll need to weigh up the difference and determine the payback of both.

Generating energy all year round

The figures confirm a significant reduction in the Primary Energy Demand of the house. Even with the 9.5kW battery I intend to install in the next few months, I will be generating additional energy at times in the sunnier months that we cannot store or utilise. I’ll want a full year of data to confirm things but my expectation is that we should not be paying for any of the electricity to operate the house once the works have been completed. This is for heating or any other tasks, for the remaining 13 years of the FiT agreement. This is taking into consideration the FIT tariff payments we receive for the existing 3kW array, the ability to take discounted energy from the grid at off-peak times and then store it in the battery for later use, and the Smart Export Tariff for any spare electricity generated by the PV panels.

Not only will we have significantly reduced our energy requirements by meeting the EnerPHit Standard, but we will have, by achieving the EnerPHit Plus standard:

a. significantly increased the amount of energy generated from sustainable means on the premises

b. reduced our reliance/demand on the grid

c. shielded ourselves from the costs of energy.
As we will still be grid-tied we will have to pay the daily standing charge for our electricity connection and time will tell if this is also covered by the income generated from the system.
I am currently in the process of completing the many necessary documents for pre-certification on the Passivhaus Portal and await feedback from my certifier. In the next article I’ll start to cover the practical side of making the changes. To find out more about Passivhaus, get in touch with our team.
Image: an image of the results page from the PHPP software, confirming that Matt's home, as designed will achieve the EnerPHit Plus Standard

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