Retrofit Projects& case studies

We created a retrofit plan for a whole house retrofit aiming for an 85% reduction in space heating demand. This involved using PHPP and thermal bridge modelling, along with creating a window schedule and work sequence. The plan for the internal wall insulation was diathonite followed by wood fibre, with thicknesses based on u-values similar to another sandstone house in the region that had had WUFI hygrothermal analysis done. Here the sandstone walls were very thick, which created a challenge for insulating the window reveals to ensure no condensation risk (when doing internal insulation, the thicker the wall gets, the more problematic the reveal) – in our case it was possible to solve but only by using custom window frames (giving us more to insulate onto). The plan for the roof was to insulate using wood fibre from inside. For the floors, some could be insulated within an existing void, while others would need digging up and re-laying.

This was a two-storey oblong L-shaped solid-walled sandstone house with 10 different types of wall build-up (based on the existing construction). We made a whole house phased retrofit plan based on PHPP, carried out thermal bridge modelling, devised a work sequence and checked the window schedule before the order was placed. Since internal wall insulation was being proposed and the house was in a reasonably exposed location, we felt it would be sensible to get some WUFI hygrothermal modelling done to assess moisture risk and how much insulation we could safely apply (this is so that solid walls can still dry out as fast as they get wet, which might not be the case if you add too much insulation internally). This analysis (done by Greengauge Building Energy Consultants) concluded that 15mm of diathonite followed by 80mm of wood fibre with lime plaster internally would be safe, as long as there was an MVHR system installed – the analysis also checked relative humidity levels at joist ends where these entered a wall (maximum allowed was 87% relative humidity).

The first phase of the retrofit was carried out by Haus Martins and involved both storeys being insulated at one end of the house, and also the single storey utility room at the other end – as well as the walls, this involved putting wood fibre in the pitched roof from inside, and also digging up some of the existing floors and relaying glass aggregate overlaid with a lime screed. During this work, the walls were allowed to dry out after the diathonite was applied, which involved finding out the source of two patches of moisture on the walls – once these were resolved, Calsitherm was put on the bottom metre instead of wood fibre, just to be sure. When all phases will be completed in future, we envisage a 63% reduction in space heating demand (with a final demand of around 71 kWh/m².yr).

Further info about this project has been detailed in one of our case studies.

We helped carry out thermal bridge modelling of a few junctions – these were for cantilevered balcony connections and parapet roof junctions.

We carried out thermal bridge modelling for 29 different junctions for a new build concrete house in Portugal that was in the process of being constructed and aiming for the Passivhaus standard. In the end, it wasn’t certified but in effect it’s very close to a Passivhaus. The homeowners moved in at the end of 2024, and without heating it was 14 deg C inside while being -4 deg C at night outside, which after a day or so of running the heat pump, got the internal temperatures up to a constant comfortable internal temperature, after which the heat just needed topping up. In the summer, experience so far is that the house stays cool, especially downstairs, with a bit of thermal gain upstairs – the MVHR system helps to cool things down when running in summer bypass mode, and the heat pump can also run in cooling mode if needed.

For this project, we did not carry out a whole house PHPP model but only advised remotely on specific u-values and build-ups, as well as on details for window junctions based on thermal bridge modelling. This top floor apartment had a few challenging issues including a dense concrete roof that was prone to overheating in summer, along with limited space for internal insulation. The solution for the walls was to use aerogel bonded to magnesium oxide boards to save space – in this case, the client had problems making the gypsum plaster stick to the boards despite using an aggregate primer, but a second attempt using lime plaster worked well. There were also a couple of odd areas that also needed insulation and airtightness detailing (e.g. a services shaft within the flat connecting the different floors in the building). We also put the client in contact with Luft MVHR who carried out the ventilation design and supplied the equipment.

This was a whole house retrofit done in one go, which was certified to the AECB Carbonlite Retrofit Standard. The final space heating demand according to PHPP was around 30 kWh/m².yr (representing an 86% reduction from baseline), and the team managed to get a good airtightness result (1.015 ACH). The contractor for the job was Jon Day from Myzsa Group, who was responsible for coordinating most of the work. For the walls, this involved insulating the external walls using EPS which required the rafters to be extended at both the eaves and gables, as well as requiring a reconfiguration of the garage roof and a couple of other external structures so that the insulation could pass behind. The cold loft (insulated at ceiling level) was converted to a warm roof that was insulated over / between / under rafters with wood fibre (for which a structural engineer had recommended strengthening a couple of the purlins), the floor had phenolic added over the existing slab, and new windows and doors were installed (which were set on brackets fixed to the outer leaf to ensure no thermal bridging).

Thermal bridge modelling was carried out on all junctions to minimise heat loss and check condensation risk. As always with retrofit, there can be some tricky details to resolve in terms of either insulation or airtightness continuity, and in this case the junction between external wall insulation and the pitched roof was a challenge for both – we have written about the airtightness challenge here and our specific solution on a Linkedin post. A heat pump was installed by Integrated Energy which had an operating COP of 4.4, and the MVHR ventilation system was designed by Luft MVHR.

Further info about this project has been detailed in one of our case studies.

We helped optimise u-values for internal wall insulation planned on a rear façade (upstairs & downstairs, through the floor void) – due to space limitations some walls had to have aerogel / magnesium oxide boards, while the other walls had wood fibre and airtight chipboard. As it was a phased retrofit, the contractors (Bradley Hope and Reece Dalton) had to ensure that the airtightness would be sealed back to the solid wall and floor at all the perimeters – this involved adding flaps of membrane at the perimeters which were taped in place before the insulation went on, which were then brought round the insulation to be taped to the airtight layer afterwards.

Several thermal models were also done to minimise heat loss and ensure no condensation risk at junctions (floor to wall, wall to window, door threshold, party wall to external wall) – the perimeter and door threshold junctions entailed ensuring continuity from the existing EPS insulation under the floor to meet the new internal wall insulation. We also helped specify what triple-glazed windows to order in.

We created a retrofit plan for a whole house retrofit aiming for near EnerPHit standard (a 94% reduction in space heating demand). This involved using PHPP and thermal bridge modelling, and in this case liaising with an architect who had previously been appointed to produce plans for an extension and loft conversion.

We created an initial PHPP energy model for a whole house retrofit aiming for the EnerPHit standard, along with thermal bridge modelling for 10 junctions. We also helped coordinate getting the MVHR design done. Following our involvement, this project was taken forward by HEM Architects – due to a few needed compromises along the way it didn’t quite reach EnerPHit standard, but it still ended up being certified to the AECB Carbonlite Retrofit Standard, which is a great result with a final space heating demand of around 42 kWh/m2.yr (representing an 87% reduction from baseline). This project has been written about here: https://www.hemarchitects.co.uk/2024/01/28/retrofit-projects-were-working-on/

This was a detached house from the 1960s that had had an extension added in 2001. The job started through the need for an immediate look at the roof to wall junction prior to part of the house being re-roofed – very sensibly, here the clients had wanted to ensure that anything that needed to happen at the eaves took into account any possible subsequent insulation work. This then was followed by a request to do the whole house retrofit plan which included PHPP analysis, thermal bridge modelling and help with the MVHR design.

We created a PHPP energy model for this house as the start to creating a retrofit plan. We also helped to manage various initial jobs on the house including repointing (which was a nightmare – work done by first contractor was of such a poor quality it had to be completely raked out and redone!), the bathroom wall insulation with airtightness as part of a bathroom refit, and work on the roof (roof tile replacement and repairs to the chimney stack and flashing).

We helped create a whole house retrofit plan based on a PHPP energy model as well as thermal bridge modelling. Although this house had been built relatively recently, there was still a lot of heat loss that had to be sorted out. The cavity walls had not been filled, which ended up making up 59% of the proposed savings in space heating demand (the retrofit plan was for an 83% reduction in space heating demand to around 47 kWh/m2.yr). We also organised the MVHR design together with Luft MVHR, and got the window schedule put together.