One step at a time: Retrofitting to EnerPHit Plus

Longstanding PHT Patron & Passivhaus Architect, Eco Design Consultants, walk the talk with an aspirational phased self-build retrofit aiming for EnerPHit Plus.

This Buckinghamshire home is currently being retrofitted in stages, aiming to achieve the EnerPHit Plus standard. The owner-occupiers (Alan and Donna) from PHT Patron Eco Design Consultants have future-proofed the design to allow the house to adapt to the changing needs of the family over time. Although retrofitting a home whilst living in the property may present challenges, they are completing the work through an extended construction program, moving furniture between rooms and a touch of DIY.

Key stats

Construction: Traditional masonry cavity construction
Occupancy: 3
TFA: 164 m² (including accessible loft storage)
Build start date: May 2021
Expected completion: The project has no specific completion date as the homeowners are retrofitting one room at a time.
Certification: Aiming for EnerPHit Plus

Parklands aiming for EnerPHit Plus Image credit Eco Design Consultants

Not only is Alan the Passivhaus architect on the project, he and his wife Donna are also carrying out most of the work themselves. They are sensitively updating the home to remain in keeping with its leafy surrounds while offering an aspirational prototype for other self-builders.

So far, the renovation phases have involved enhancing the house's form factor with a modest extension and minor reconfiguration to the first floor. These changes have enabled the addition of a mezzanine in the loft and a new bay window on the ground floor. The old roof was replaced with a new airtight membrane topped by a panelled PV solar roofing system. They've also installed a modern MVHR (Mechanical Ventilation with Heat Recovery) system.

On the first floor, they've upgraded to triple-glazed windows, complemented by an airtightness membrane and external insulation. Currently, work is underway on the ground floor to add floor slab insulation, and they are internally insulating the walls to maintain the exterior's brick appearance, ensuring consistency with the surrounding homes in the estate.

Completing a retrofit in stages is useful when either it’s not practicable to carry out the whole retrofit at once or when all the necessary funds are not immediately available to do so. In this case, cost and time were the key reasons for carrying out the work in phases.

We kept putting of the retrofit until everything lined up, but there was always something which stopped it being the ideal time and the costs just kept rising. So, we decided to just start going for it, doing just the first step. Taking a staged approach has also allowed us to get involved in every stage, which is very satisfying and educational. It’s also allowed a lot of the team to come along and experience the process first hand.

Alan, Client & Architect, Eco Design Consultants

A radical whole house retrofit is likely to achieve the best results both in terms of energy reduction and comfort. However, this is a significant undertaking which could take place over several years. Getting the sequence right and decisions in the early phases are critical to ensure that the full potential of the retrofit is realised and that the project doesn’t inadvertently result in ‘carbon lock-in’.

Passivhaus step by step retrofit

Alan and Donna have chosen to pursue a final EnerPHit assessment rather than following the precertified EuroPHit path. To secure certification, they developed a comprehensive house plan using the Passive House Planning Package (PHPP), which has steered the entire EnerPHit retrofit process. This initial planning is critical to ensure that every step is well understood and properly planned out right at the start of the project. Throughout the retrofit, Alan has consistently referred back to this plan to confirm that any adjustments still align with their certification goals and to minimise risks. For the certification process, the homeowners are working with PHT members Mead Consulting. Together, they have explored the most effective options for this retrofit.

Parklands EnerPHit Plus, Client quote - Image credit Eco Design Consultants

Construction

Alan and Donna are also trying different approaches including external insulation and cladding to the first floor. Some of the work is being carried out as a DIY project such as internal insulation to the ground floor using 175mm of high-performance mineral wool and an innovative one-directional vapor permeable airtightness membrane.

Many of the elements, including the GRP brackets supporting the EWI and external cladding will and have been reused on future projects, also the thicker IWI made possible with the one-directional vapor permeable airtightness membrane. The prefabricated roof cassettes are also being developed further harvesting heat as well as electricity from the roof

Alan, Client & Architect, Eco Design Consultants

U-values

Floor: 0.34W/m²K

50mm 0.019W/mK Phenolic + 22mm chipboard replacing screed.

Wall Ground Floor IWI: 0.14W/m²K

Ground floor 175mm 0.032W/mK Mineral wool with offset timber stud wall, vapour control membrane, 25mm service void and plasterboard.

Wall 1st Floor EWI: 0.13W/m²K

200mm 0.032W/mK Mineral wool in timber framework held off wall with GRP Brackets, and plank cladding.

Roof: 0.15W/m²K

300mm 0.032W/mK Mineral wool between LGS studs & 70mm 0.045W/mK mineral fibre inside between rafters.

Embodied carbon

Alan and Donna are considering embodied carbon throughout the retrofit as they believe it is important to ensure that they are not using more carbon that they are saving. This has provided some challenges due to costs and availabilty. They are reusing exisitng loft insulation and recycled timber, they have also opted for lower density mineral fibre insulation where suitable.

Predicted building performance

Space Heating Demand (≤ 25 kWh/m².a)	24.9 kWh/m².a
Heating Load	12 W/m²
Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)	66
Primary Energy Renewable Generation (PER)	90

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Services

To achieve EnerPHit Plus the clients opted to integrate a “Power-roof” panelled roofing system with integral PV. The prefabricated roof cassettes are being developed further harvesting heat as well as electricity from the roof.

Parklands EnerPHit Plus Power-roof

Key team

Architect & M&E consultant: PHT Patron Eco Design Consultants
Contractor: Vangard Construction, EMC joinery, Mango Projects (MVHR)
Structural engineer: Allan Consulting Engineers & Kirkwood Structures
Passivhaus Certifier: MEAD Consulting

It is the first project for the contractors and they have now moved on to other EnerPHit projects. Alan from Eco Design Consultants is an experienced Passivhaus Architect and has been involved with very popular Passivhaus events and workshops including the NSBRC and the International Passivhaus Open Days. We can’t wait to see how this project progresses.