Four Walls retrofit

Four Walls retrofit with PERFORMANCE triple glazed windows and doors
Green Building Store’s PERFORMANCE range was by far the most cost-effective of all the quotes we received. They were of a high quality and the U value fitted the bill for the level of retrofit that we were aiming for.

Ian Mawditt

As a result of good planning and installation, the MVHR system was successfully installed exactly as designed…and the delivered air flow rates easily meet their design values, and achieves a very good system balance.

Ian Mawditt

Green Building Store’s windows and MVHR system specified for ambitious ‘deep retrofit’ project.

Building performance researcher Ian Mawditt has recently undertaken a ‘fabric first’ deep retrofit of his 1960’s home in Bristol. Although the project did not aim to achieve EnerPHit certification, Ian wanted to see how far he could go with improving his home’s thermal performance and comfort levels, given the constraints of the site and budgetary considerations. The retrofit strategies for the project have been well documented in Ian’s regular Fourwalls blog and have included extensive insulation and airtightness improvements as well as replacement of the existing windows and doors with Green Building Store’s triple glazed PERFORMANCE timber range. Green Building Store also supplied the MVHR system for the retrofit.

Triple glazed timber windows & doors

Ian commented: “We wanted to improve the thermal performance with triple glazed windows and approached a number of companies for quotes. We looked at a range of windows and Green Building Store’s PERFORMANCE range was by far the most cost-effective of all the quotes we received. They were of a high quality and the U value fitted the bill for the level of retrofit that we were aiming for. Had we wanted to go down the Passivhaus route we maybe might have chosen windows with insulated frames, but the PERFORMANCE range suited the needs of the project perfectly.

We have been very happy with the windows. There are no draughts and they have contributed to increased comfort levels considerably. The thermal images of the house, before and after the retrofit, show how well the windows are performing compared to the original windows. The aesthetics of the windows are also very pleasing and they always attract interest when we do OpenHomes events etc.

We have also been very happy with Green Building Store’s after-sales service. There were no quibbles when we needed to replace a failed glazing unit and, while they were replacing it, the team also helped us adjust some of the doors in the house (fitted by another company).”

The original house also had a large amount of thermal bridges, which Ian aimed to reduce or eliminate wherever possible. This involved the removal of concrete gutters and a balcony, and wrapping the house in 120mm of external wall insulation. The new windows and doors were positioned at the centre line of the external wall insulation layer so as not to compromise the new thermal envelope. A comprehensive airtightness strategy meant that airtightness improved from the original 18.4 down to 1.4 m3/hr/m2@50Pa following the renovation works.

MVHR heat recovery ventilation

Good indoor air quality is maintained by the heat recovery ventilation system, ducted to each room in the house. The project has a PAUL Novus 300 MVHR unit, with rigid steel ducting, supplied by Green Building Store.

Ian commented: “I am convinced of the importance of heat recovery ventilation for airtight buildings: it is a sound principle. However through my work I come across a lot of examples of where MVHR installations have gone wrong. Although not a new technology, MVHR is becoming increasingly popular in new homes in the UK. There are numerous under-performing systems, largely due to the inexperience of many of those involved with the design, installation, and commissioning of MVHR systems. I wanted to see first-hand the hassle-factor and complexities involved with installing an MVHR in a retrofit, as many say this strategy is only suitable for new builds.

MVHR design & performance

As a former building services engineer, I was able to design the MVHR system myself, but still felt it was important to engage Green Building Store’s MVHR design service to produce the fabrication drawings. Green Building Store’s Andrew Farr also offered some useful feedback on my original designs, resulting in a few tweaks and improvements. The installation of the MVHR was carried out by our main contractor, Greenheart Sustainable Construction, who are used to installing rigid steel ducting systems and take pride in quality and workmanship. As a result of good planning and installation, the MVHR system was successfully installed exactly as designed”

Ian added “I commissioned the system myself, and the delivered air flow rates easily meet their design values, and achieves a very good system balance. The MVHR unit is located in a cupboard in my office in the house and you really can’t hear it unless it is in boost mode, which is only used on occasions during cooking. The commissioned air flow rates during normal speed are more than sufficient for removal of moisture in the bathroom when using the bath or shower.

MVHR & Indoor Air Quality

Anecdotally, there has been a marked improvement in my wife’s allergies and hay fever – she now no longer needs to take daily anti-histamine tablets. The combination of fabric airtightness and the MVHR filters are significantly reducing the particulates and pollen entering the home, which means that her immune system is better able to cope with a smaller amount of pollutants that might still enter the house”.

Throughout 2015-6 Ian is undertaking some further Indoor Air Quality research and monitoring on his home, comparing it with homes using ‘natural ventilation’, which he will be sharing later in 2016. Watch this space!

More information

Ian Mawditt, Director, fourwalls Tel: 08456 804802 email: ian@fourwalls-uk.com www.fourwalls-uk.com/blog/
SuperHome listing: www.superhomes.org.uk/superhomes/bristol-pitchcombe-gardens/
Contractor: Greenheart Sustainable Construction, Tel: 07766 395 386, email: info@greenheartuk.com, www.greenheartuk.com
Design detailing & thermal bridge calculations: Ruairi Kay, Taylor Kay Architects www.taylorkayarchitecture.co.uk 020 3794 5945

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