Office-to-residential conversions have seen a sharp rise in popularity thanks to a subdued office market, demand for housing, and an amendment to the General Permitted Development Order 1995 which enables change of use without Planning Permission.
Department for Communities and Local Government (DCLG) figures show that between April 2015 and March 2016 new dwellings achieved through ‘change of use’ numbered 30,600 units, compared to 20,650 the year before.
Many office blocks ripe for conversion were built in the 1960s, and have since become unsuitable for modern commercial use – in fact they will require very specific treatment in order to make them suitable for use as modern dwellings. From an energy efficiency point of view, there are some particular steps that should be taken with office-to-residential conversions in order to ensure both compliance and householder comfort:
Determine the thermal performance of the existing fabric
The first task is to determine the thermal performance of the existing fabric of the building, so that the requirements for any insulation upgrades can be specified. This requires some local opening-up works to determine current wall, floor and roof insulation provision, and confirming any cavity widths. An assessment of the existing external windows and doors will also be needed, to determine whether replacement with new double-glazed units, or secondary glazing, would be the best option.
It’s worth bearing in mind, at this early stage, that historic building significance or Listed status may affect opportunities to upgrade insulation.
Review against Part L requirements
It’s important to undertake a Part L assessment early on, so that any impact compliance might have on internal design can be considered. Particularly relevant to this kind of project is the insulation requirement between the dwellings and any unheated communal corridors or stairwells, both for thermal and acoustic purposes.
Ascertain any changes to ventilation
Some office buildings may have been designed to have sealed facades with mechanical ventilation and air conditioning, so this aspect needs to be considered when converting them into apartments. A simple ventilation strategy, with local extracts to bathrooms and kitchens, and openable windows in habitable rooms, would normally be the preference. However, you may need to consider mechanical heat recovery and ventilation (MVHR) or even comfort cooling in buildings with sealed facades.
Consider the energy efficiency of the electric-only option
There is a perception that conversion schemes are ‘new build’ schemes, but they don’t have to meet the same stringent energy efficiency standards as actual new builds. A lot of conversion schemes are fitted out as electric-only, due to the attractively low construction costs involved – especially if the previous office use may mean there is a larger electricity supply to the building. But the money-saving is short-term, and electric-only central heating may result in poor EPCs, and high running costs for occupants.
More and more homebuyers are considering energy efficiency when making offers on properties these days, so an EPC rating of X or above is not just good practice, it’s a good marketing tool. It’s also worth carefully considering the minimum EPC ratings for renting, since many such conversions are intended for the landlord market.
Investigate centralised heating and CHP feasibility for large schemes
For schemes of more than 100 units, it may be feasible to consider centralised heating plant, potentially with CHP. The capital costs of these systems are significantly higher than individual gas boilers or electric heating, but provide significantly lower carbon emissions, and lower running costs if designed, installed and managed correctly – which will not only assist with compliance, but also potentially could be a selling point for the finished dwellings.
To find out more about how we can help maximise energy efficiency in office-to-residential conversions, please call us on 01206 266755 or email mail@ajenergy.com.