As with all low energy retrofits, there are site specific issues for ground floor flats, and important issue is whether the floor is solid or suspended timber and the degree of work being planned - often dictated by whether you'll be living there whilst the work is being done.

Whilst double glazing and carpets are a good start, draught proofing and insulation of suspended floors will be a benefit and for solid floors, the addition of thick underlay and/or insulation. Internal or external solid wall insulation are required to make flats really low energy and will make them really cosy and eliminate many of the condensation and mould issues associated with cold walls, but this should be considered as part of a comprehensive low energy strategy, that includes heating, ventilation, lighting, appliances and renewable systems.

Cavity wall insulation can lead to damp issues in rare cases. For example, the insulation could offer a path for wind driven rain if the external wall is highly porous, poorly pointed or cracked, or the building is extremely exposed. This risk may be reduced if bead insulation is used instead of fibre, but there isn't much research on this.

In buildings where part of the wall is solid, for example in ring beam construction, the warmer insulated walls may accentuate condensation at the corner of the wall with the floors and ceilings. Finally, the insulation may reveal building faults such as blocked weep holes or missing cavity trays.

Modern condensing boilers can achieve efficiencies of over 90% in ideal conditions, while old boilers range from 65% for really old boilers to about 80% for the best non-condensing boilers. So replacing an old boiler for a new condensing model of the same output would save 28%. For a 24kW boiler, that's 10kwh per hour of operation.

Accurate assessment the trade off between embodied energy of products depends of the materials used to make them, how they are processed and how they are delivered. This is a complex analysis, however, a rough estimate can be based on the embodied energy of the materials used. Some of the materials in modern boilers like the aluminium heat exchangers have a high embodied energy of 200 MJ/kg whilst the steel body has an embodied energy of 32 MJ/kg. If we assume that the average is somewhere in between, that's an embodied energy of 120MJ/kg, This means that for a typical system boiler with an output of 24 KW, the embodied energy is about 1,200 kWh.

Even when you take manufacturing energy into account, it's worth replacing an old boiler as soon as possible.

At 5 hours operation per day, this will mean a carbon pay back of about 24 days. So even when you take manufacturing energy into account, it's worth replacing an old boiler as soon as possible. It can be argued that their long life of up to 20 years compared to modern boilers with a 12 year life lock people into a high level of emissions.

Perhaps the most cost effective way of minimising draughts from a disused chimney is to use a chimney ballon. Ideally the the top of the chimney should also be caped with a rain proof ventilated cowl to minimise the risk of damp. That said, the manufacturers of chimney balloons do not call for cowls to be fitted and claim that there is usually sufficient ventilation passing the balloons to prevent damp.

While external wall insulation is easier where there is a rendered finish, internal wall insulation is quite possible for solid walls finished in brick or stone.  Fit 2-4 inches of insulation combined with breathable membranes and cover with plasterboard or fibre board.  Radiators and electricity sockets will need to be moved and window sills extended internally.  

One advantage of internal wall insulation is that you can fit selected rooms only. It seems counter-intuitive, but you should insulate the warmest, most lived-in rooms first, since these are losing most heat.  The saved heat will then spread to other rooms.

A professional specification from an architect or insulation expert is necessary to avoid the risk of moisture being trapped between insulation and wall, a problem specific to internal wall insulation. If you cannot obtain a specification locally, we may be able to help depending on your location.

I would first fit chimney balloons to the unused chimneys. Then tackle the floorboards and skirting boards using deck caulking from yachts, which is expensive but is designed to expand and contract a lot and stand the test of time. Skirting boards can be sealed using decorator's caulk. Bear in mind that old properties need some ventilation, but there should still be some from doors and electrical sockets (sounds mad but sockets are a big contributor to draughts!).

After that you have a choice with the attic rooms.  If you never use them, then you can lay 300mm loft insulation on the floors.  If you do use them, then use Thermal Laminate Boarding (TLB) or natural insulation boards such as Pavatherm. The latter is more environmentally-friendly and eventually bio-degradable. The former is more efficient per inch of thickness.

We're planning to do more of these 'ask an expert' features in future – which piece of the carbon-cutting puzzle should we focus on next? Let us know on the 10:10 Facebook page.

Further reading

• How old homes can conquer climate change
• The 10:10 guide to insulating at home
• Case study: 18th century cottage gets a 21st century makeover
• Case study: the Lawrence Family Part 1 | Part 2
• Three ways to fix the Green Deal
• Low energy superhomes: looks can be deceiving