Elm Avenue – Monmouthshire Housing Association ORP 3.2

Introduction

Elm Avenue flats are a block of 4 Gregory type, non-traditional ‘system built’ flats constructed in 1956. The external walls consisted of two in-situ poured concrete leaves with a 50mm unfilled cavity tied together with galvanised steel wall ties. The external concrete was finished in traditional spar render and the roof was traditionally constructed with interlocking concrete tiles. The ground floor is the original uninsulated concrete slab with traditional screed. One of the ground floor flats is occupied by a leaseholder who had installed a conservatory off the living room to the rear of the building. The remaining flats are all social rental. The property was selected for consideration under the ORP scheme as it matched the criteria in terms of delivering a fabric first retrofit approach and providing challenges to enhance our knowledge and learning. A retrofit assessment was carried out to the building and the following work was determined:

• Extend Gable ends of roof to accommodate the additional thickness of the EWI and still maintain roof overhang
• Remove soffits to enable continuous external wall insulation from minimum 150mm below DPC to roof insulation
• Check External wall cavity and cavity wall ties and install additional ties where required
• Install carbon bead cavity wall insulation and EWI system to achieve a minimum external wall u value of 0.21 W/(m²K). The cavity wall insulation was installed to prevent convection currents from the ventilated roof circulating and cooling the inner skin
• Replace the existing aluminium windows with new A rated double glazed windows, u value of 1.3 W/(m²K).
• Take down masonry external steps and landing to first floor flats and replace with purpose made freestanding metal steps and landing
• Install on roof PV system to each flat
• Upgrade ventilation including providing undercuts to internal doors where required
• Install LoRaWan environmental monitoring and gateway. The existing gas combination boilers were retained as they were not due for replacement. The work was to be carried out in compliance with PAS2030/35 design/installation standards as well as being eligible to be registered with TrustMark

Project learning

This project has given us valuable experience of working with Gregory Type non-traditional buildings including how to deal with their cavities, fixing EWI to their rendered external faces and the unusual external staircases. The original intention was to install a 2KW array to each flat as part of the work which would enable the property SAP Band to rise from a Band C to a Band A. MHA also intended the tenants would receive the full benefit from the electricity generated and not used by selling back through the Smart Export Guarantee (SEG). Unfortunately, after the DNO application was submitted, we were informed that the properties could not be connected to the grid as there was no spare capacity on the existing network and no timescale could be provided. We countered this by requesting a larger array of 3.52KW consisting of 8 x 440W panels with zero export from the inverter which they agreed to. The benefit of export limiting is that it overcomes the immediate problem where we cannot export electricity, but we are free to use whatever is generated. The limiting can be easily removed or changed when the network is upgraded. The oversized array will also make up some of the losses that would have been gained from exporting via Seg in the meantime. This experience has taught us not to take no for an answer and also highlighted the need to submit a DNO application earlier in the process to gain a better understanding of what we are able to generate/export from the start. This experience has benefited us substantially on subsequent schemes. The project also gave us a better understanding of the range and coverage of LoRaWan equipment which is much lower and sparse than originally thought. The assistance given by our monitoring equipment supplier has been invaluable to the success of this and other ORP projects.

Project innovation

The property had two exterior staircases which were built into the external fabric of the building providing access to the first-floor flats. Two options were considered to minimise cold bridging in these areas: 1. To maintain the structures and insulate the internal walls to the kitchen and living room on the other side. 2. To remove them, make good the external leaf and continue the EWI over the whole external elevation, providing a safe temporary access incorporated into the scaffolding and installing a new freestanding prefabricated stairs and landing on completion. Both options would present inconvenience to the tenants particularly as the first option would require significant work in their homes including the removal and replacement of their kitchens. It would also make the rooms slightly smaller. Following consultation with the residents it was decided to undertake option 2 and use the experience gained as a test bed for other similar projects in the future. The timing of the works posed a challenge, but it was not substantial, and the tenants could see the long-term benefits of the solution and were prepared to put up with the inconvenience of having to leave their homes for two mornings to complete the work.

Challenges

The most challenging aspect leading to change was the decision of where to locate the PV inverters in the property. MHA traditionally located inverters in the attic space, but this would require installing two inverters (one for the ground floor and one for the first floor) in the same roof space. This was deemed unacceptable as only the first floor had access to the roof space. Therefore, it was decided to install the inverters in the pantry cupboards located in the kitchen. The only issue with this approach was that during the Fire Risk Assessment it was deemed necessary to replace the existing pantry doors with 30-minute fire rated doors and the provision of an additional smoke alarm, adding unforeseen costs to the project. As a result of this MHA will in future be utilising micro-inverters integrated with the PV array on similar installations, eliminating the need to find a suitable location for the inverter inside the property.