phi Low Carbon was established in 2021 by Jeremy Poulter and Sara Darwin to specialise in the design and delivery of low energy, low carbon buildings with a value over £1 million

Both Jeremy and Sara have run their own successful architectural practices, Poulter Architects and phi Architects and both are Certified Passivhaus Designers.

phi Low Carbon offer the full architectural service on projects where clients are looking to achieve Passivhaus or EnerPHit levels of energy use as well as low embodied carbon.

For large residential and mixed use schemes we are also able to act as consultants to clients, contractors and architects, supporting them in achieving Passivhaus, or close to Passivhaus, and advising on low carbon materials and construction.

phi Low Carbon are members of the Passive House Trust and the AECB.

Jeremy Poulter


Jeremy is a chartered architect with 18 years post qualification experience, in a wide variety of project types, through all project stages from inception to completion.

Jeremy founded Poulter Architects in 2010 and has delivered numerous small scale residential and commercial projects.

In 2018 Jeremy qualified as a Passive House Designer. reinforcing his commitment to delivering low energy, low carbon buildings and the importance of accurately calculating energy demand at the design stage to improve building performance. In 2023 Jeremy obtained the supplementary Passivhaus qualification of PHPP Expert which covers more complex buildings such as schools and apartments as well as more in-depth analysis of topics such as occupancy, multiple MVHRs, shading, internal heat gains, variants and step by step retrofit.

An advocate of the use of BIM (Building Information Modelling) Jeremy has contributed a case study to the book BIM in small practices published by RIBA Enterprises which charted how BIM was used to great effect on a residential project in Knutsford.

Prior to establishing his own practice Jeremy worked for both PRP and Levitt Bernstein, two leading housing practices where he was involved in the design of a number of large scale housing and regeneration schemes.

Sara Darwin


Sara formed phi architects after qualifying as a European Certified Passivhaus Designer, to build upon her background in low energy sustainable design.

In previous practices, Sara gained a great breadth of experience and expertise in education, housing and sustainable design. During this time Sara has worked on buildings that have achieved a BREEAM ‘Excellent’ rating and a Green Apple Award ‘Gold’ standard for sustainability.

As an Associate at Walker Simpson Architects, Sara was involved in a number of education buildings, including Manchester’s largest Sure Start Centre, a Primary School in Withington and a Staff Resource and Training Centre for a campus of Special Schools and an extension to an Independent Specialist School for Students with Autistic Spectrum Conditions (ASC).

Other experience includes establishing a National Strategy for Supported Living Accommodation for an International Charity and was the project architect for a sustainable Visitor’s Centre in Stoke on Trent featured in international magazine, Detail as an exemplar sustainable building type, built using straw bale walls and incorporating a water source heat pump for heating.

Whilst working in London and as an Associate at ECD Architects, Sara was responsible for the realisation of a number of schemes at all stages in the areas of social housing, residential care, community buildings and urban regeneration. Low energy and environmentally friendly buildings were at the core of all the work of this practice. Projects included a timber frame 50 bed elderly persons’ care home with two Day centres, a residential home for young adults with behavioural difficulties and a housing scheme in Hulme, Manchester, short listed for RIBA Housing Design Awards and published by CABE as a design guide for urban housing.