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Room-by-room DIY retrofit

An unassuming detached house in Chorley Lancashire has been transformed steadily over 4+ years into an eco exemplar retrofit project, thanks to the steady DIY efforts of its occupants. Diana & John Holland have undertaken a methodical room by room retrofit of the house, following advice from eco building consultant Eric Fewster at ColdProof UK, who developed a whole house plan for the retrofit.

All of the retrofit work has been undertaken by the Hollands themselves, with guidance and support from Eric Fewster along the way and the involvement of local builders, electricians, plumbers and plasterers when needed.

21° supplied the triple glazed timber windows and doors and MVHR system for the project, as well as offering some consultancy advice at the outset of the project.


The Hollands were inspired to undertake the retrofit to reduce the carbon emissions from their home.

We face a climate emergency and we are very scared for the future of our children and grandchildren, but turning that fear into action on the things over which we have control has given us hope. We continue to reduce our carbon emissions as we progress with our retrofit and have the bonus of creating an extremely comfortable home. At the start the challenge seemed overwhelming but nibbling away at it bit by bit, room by room has made it manageable. We feel very lucky to have had the time and resources to be able to carry it out.

Diana Holland


The home is a detached house built in 1991 with cavity wall construction with ‘dot and dab’ plasterboard internally.

The Hollands started improving the house in by installing solar thermal and solar PV systems on the roof between 2006-10.

We started the wrong way around by installing renewables and ways to generate energy, instead of thinking of fabric first options to minimise energy use in the first place.


After a visit by 21° Director Bill Butcher in 2013 the Hollands realised that they had to take more drastic action to improve the energy efficiency of their home by undertaking an energy efficient retrofit, including removal of plasterboard and addition of internal wall insulation and airtightness measures.

Eric Fewster subsequently helped draw up a whole house plan after modelling the house in Passivhaus Planning Package. This gave a strategic direction to the overall project. Eric also offered practical step-by step advice as to how the Hollands could undertake the retrofit on a room-by-room basis.

The Room-by-Room approach

Undertaking the retrofit themselves on a room-by-room basis was a practical and affordable way of making it happen, helping to spread the cost over several years.

This was the only way we could afford to do the retrofit and it meant that we didn’t have to move out. Another positive has been that the mess was also only confined to one room at a time.


The Hollands started out on the utility room as a practice run. They hacked off the dot and dab plasterboard and installed 140 mm wood fibre internal wall insulation (IWI) with Intello membrane added on top as the airtightness layer. Green Building Store’s triple glazed timber windows were installed mostly on a room by room basis as well. with the IWI wrapping the frame to help reduce thermal bridging.

As they have moved through the rooms in the house over the last few years they have gained in confidence with their retrofit skills. The retrofit has involved mainly wood-working, screwing the timber insulation into the walls and then adding timber batons for service voids.  John  Holland was already a competent amateur carpenter so has been able to build on that for the project.

The Hollands have tried as far as possible to re-use materials during the retrofit. When they retrofitted the kitchen they managed to remove and re-instate their existing kitchen units, which had, coincidentally, been made out of reclaimed timber from a ship-yard. They replaced the conservatory with a garden room and managed to re-use some French Doors from another room for that. The floor in the garden room is reclaimed wood from a school gymnasium.

By the summer of 2020 the Hollands have only got 2 more rooms to retrofit before the project will be completed. The bathroom is one of the last rooms to go because it is potentially expensive as it could involve replacing the bathroom suite. Insulating the ground floor has been missed out of the retrofit, so far, as it its very challenging and would involve substantial disruption, including removing and re-installing an oak floor. By not being able to tackle the floor the project will miss out on the chance to go for EnerPHit (Passivhaus retrofit) certification but it feels just a step too far for the Hollands after their epic retrofit efforts.

The retrofit has made a huge difference already and the house feels cosy and comfortable.

The Hollands

Joined up thinking

By doing the retrofit on a room-by-room basis the Hollands have also needed to be aware of avoid ‘unintended consequences’. For example, with some rooms insulated and others not there could have potentially been a danger of condensation and mould growth in the uninsulated rooms, which would have been acting as ‘thermal bridges’ for moisture-laden heat from the insulated rooms. Fortunately, the Hollands had the foresight to install an MVHR system for ventilation in the middle of the retrofit work which has helped keep the air fresh and avoided any mould and condensation issues.

Another important consideration was the need to ensure that the insulation and airtightness strategies continuous between the separate rooms. The whole house plan developed by Eric Fewster was essential for this, knowing that every element of the retrofit was contributing to the whole. For example, cutting back the ceiling in the downstairs rooms to allow IWI to be fitted between the joists and up to the floor of the room above. Then covering the IWI with Intello with enough spare to pull through to the upstairs room when the  floor is cut back and the IWI is fitted.

Triple glazed timber windows & doors

The Hollands chose triple glazed timber windows from 21°, which have been installed in four phases as the retrofit has progressed. The project has included 21°’s former Ecoplus3 range and more recent PERFORMANCE triple glazed range.

The windows and doors are fabulous and they feel very warm. There are no draughts or down-draughts coming from the windows and we get no internal condensation – only external. The noise reduction is very good too. We like the way you really get looked after by the 21° team throughout the process. There have been a small number of snagging issues but they’ve always been dealt with by the aftersales team. Over the long process of the retrofit we really feel like we’ve got to know the 21° team – from Jason the surveyor who comes to measure the windows to Chris and the fitting team and everyone in the office.

Diana Holland

MVHR heat recovery ventilation

21° supplied and designed the MVHR heat recovery ventilation system at the project. The system will be finally commissioned when all the retrofit work has been completed.

The MVHR system is really good. We have constant fresh air inside and it has helped prevent any condensation issues while the house is still half-completed. The MVHR system is also very quiet – it is located in the utility room and we only ever hear it when we are in there or when we need to boost the system after cooking.

Diana Holland

More information

Eric Fewster, ColdProof

Project details

Case study


Life changing homes