01664 822 499 info@carbonlegacy.co.uk

Self-Builders and Property Renovators

Many people think that going green is a laborious task that costs the earth. But in reality; altering a few things in your home and the way you do things, will reduce your annual energy consumption costs dramatically. It’s all very well installing a £20,000 heat pump system; but without taking the necessary steps to reduce your home energy heat-loss, it may very well be hot air you’re investing in. Carbon Legacy has put a few things together to touch on certain things, many home owners forget about. Please remember the “Fabric First Improvement “ building philosophy applies to both new and renovated properties. The more you spend on insulation the smaller your heat loss will be and the smaller/cheaper your Renewable Heating system plus you will have lower bills for ever!

Air Leakage

When building new or when carrying out major renovation works, you will be asked by building control to do an air pressure test to show how drafty the building is. This is very important for reasons of energy conservation and also your health. If you make a home airtight with measured results of 3m3/m2 @ 50P pressure or less then it is important to have a ventilation system that will provide fresh air without wasting heat energy. The systems described under ‘Ventilation’ discuss how this can be done.Heatloss
Achieving an airtight property requires a lot of care and attention to detail during building works but figures of 2-3 are achievable without major expenditure as long as all gaps are filled as the works progress with the generous use of expanding foam and careful filling of all joints/service entry points etc. Also wet plastering is one of the best ways to ensure air tight masonry walls. Current regulations ask for a feeble target of 10.

Existing Cavity Wall Insulation – Payback Within 3 Years

New CavityTherm insulationInstalling cavity wall insulation is one of the most cost effective ways of retaining significant amounts of heat and reducing your heating bills as a result.

Many homes built after 1920 were constructed with a cavity between the outer and inner walls, these cavities significantly helped reduce damp and keep houses warmer than the single skinned walls that pre dated them, but there are still improvements to be had.

By filling the cavity with an insulating material such as polystyrene beads or mineral wool you can retain as much as 33% of the heat that would have previously been lost through the cavity, and it’s all relatively simple to do.

A surveyor will measure your walls, deduct the area of the windows and doors resulting in the amount of insulating material that is required.

Holes will be drilled into the wall by the installation team who will then pump the material into the cavity, this all sounds quite a major job but in fact is quite straight forward and a such is a relatively low cost method of gaining significant savings.New cavity-wall 300mm insulation

How Will it Benefit Me?

Over and above the significant savings on your central heating bills you will also notice that your home will be cooler in summer, all due to the improved insulating properties of the walls, it will also help reduce condensation on the walls and ceilings and provide a more stable and even temperature throughout the home.

Is My House Suitable?

There are two steps to see whether your house has cavity wall.  The year that your property was built will give you a good indication:

  • Before 1932 your house is unlikely to have cavity walls
  • Between 1932 and 1982 your house is likely to have cavity walls
  • Houses built after 1982 are likely to have cavity walls as standard

Then, if the configuration of the bricks in your house looks like the ‘Typical cavity wall’ diagram then your house will more than likely have cavity walls.

How Much?

New Celotex cavity insulationA typical house will cost around £350 to insulate which will reduce your heating bills by as much as £90 per year, this equates to a payback of only 3 years, in other words, after 3 years you’ll have an extra £90 in your pocket, every year! You’ll also be helping the environment with a reduction in your CO2 emission of as much as 750kg per year



Self-Builders and new properties

There are several tried and tested high insulation value options when building a new property.

It is false economy to build to British Building Regulation standards. As a minimum you should consider Celotex’s 100mm fully filled cavity option (see picture) but preferably you should go further and use either Xtratherm 150mm CavityTherm (see picture) or a fully filled 300mm cavity with Rockwool or Drytherm 37.

The lower the U value the better the wall insulation. Set your target for new external cavity walls at 0.14 or less.

Ground Floor

Install 120mm Celotex or similar PIR foam-based insulation in new, or when replacing any existing, internal solid floors. Where the internal floors are suspended timber then the same material can be installed between the floor joists and any gaps filled with expanding foam. Do not be tempted to block up the air bricks or you will risk the floor timbers getting a rot infection.
Cleotex-300x224This type of insulation is robust and offers extremely good heat loss prevention. The overall feel of comfort within your home will improve greatly on the completion of the install. There are many manufacturers on the market who claim their high density insulation foam is good, but in our experience, if you don’t fit the best at the start; you may be paying more later down the line; which is why we recommend Celotex as our preferred supplier.

Roof - Attic

Top up existing or install all new glass fibre/Rockwool, preferably within a plastic sleeve such as the Knauf Space Blanket to 300mm. Do not be tempted to take the cheap and easy route of installing under 300mm 400mm in the loft. It costs very little and pays for itself in 1-2 years. In areas where a floor has been laid then lay the insulation on top of any floorboards to allow for future access and get the full benefit of the insulation. There are pre-insulated floor panels that can be bought from some builders merchants which are useful when a large area is required for storage.

Rain Water Recycling

On average, the UK flushes 25 – 27% of our fresh water supply down the toilet; literally.. This includes things like laundry cleaning, showering, car washing and garden watering. Many people haven’t even heard of rain water recycling; and those that do, either think it’s something a farmer only does or don’t really understand the benefits of having a system installed. As we not only see the price of gas and other fossil fuels increase, the price of water is increasing very rapidly. It makes perfect sense to have a rain water recycling system installed, and what a better to country to have it done in; the UK.

Installing is a simple operation when building a new property or refurbishing an existing property. It is relatively cheap to do for a local builder/ground worker and plumber for the internal separate distribution pipe work. It pays for its self over 2-5 years by cutting water bills in half. Make sure you tell your water company as they will reduce your standing charges as well. If you need further information and would like to discuss the matter in depth, please give us a call.


With new homes or when considering replacement windows, spend wisely. Triple glazing such as Viking Windows of Estonia or “The Green Building Store” range can now be supplied and fitted for roughly £390/m2 including VAT. They will provide a long life (30 years+) solution with tremendous improvements in energy losses with U values of 1.0 W/m2K or less.

If you have to fit double glazing then make sure the completed windows come with whole window insulation values. The target should be no more than 1.8U. Be very careful you are not just quoted the glazing only figure which may sound good at 1.6U. Ask for warm edge spacers, argon filled 16mm cavity and Pilkington Optitherm soft low-E coating.

On buildings where the original single glazed windows must be retained due to listed building status, then secondary glazing can be used and we advise the use of double glazed secondary glazing to give significant improvements in heat loss reduction. The same specification should be used as that suggested above for double glazing.

Solid Wall - Internal

Minimum Specification – dryline on the internal face with 62mm laminate insulation board
(50mm foil backed PIR or Celotex insulation with bonded on plasterboard), mechanically fixed to
the wall then skim with plaster (3mm). Budget cost about £30/m2 of wall.

Medium Specification – 92mm dry-lining installed as above.

DryliningZero Carbon Insulation Specification  – 152mm drylining.
Note, depending on how flat the walls are and how damp, they may need to have treated timber
batons with plastic spacers to give a level surface to fix the insulation panels to. It is worth foam
filling all joints and the top and bottom of the insulation panels to improve air tightness for all of the
drylining solutions above.

One way to approach internal wall insulation is to have it done on a room by room basis starting
with the north facing, coldest rooms or the most frequently used rooms first. You can then progress to
do the rest as time, disturbance and budget allow.

Solid walls: (no cavity) External

Where it is possible to change the look of a building on the outside or where the property already
has a rendered finish, then an external insulated render system (eg. Weatherby, Stow or Weber) will
provide the best possible reduction in heat loss. As this solution is only likely to be done once, it is
well worth going for at least the minimum solution suggested below. Do not be tempted with a lower
specification or thinner insulation solutions. The additional cost for the thicker solutions is minimal and the results well worth the small extra cost.

Minimum Specification:

100mm PIR high density foam/Celotex with reinforced self coloured acrylic render finish. Target
whole wall U-value 0.18 W/m2K.
An example cost for a 120m2 GIFA 3-bed detached is £14,500. Payback in as little as 5 years with
the savings made from lower fuel bills.

Zero Carbon Specification:
150mm PIR high density foam/Celotex with reinforced self-coloured acrylic render finish. Target
whole wall U value 0.1 W/m2K.
External IRS have a dramatic effect on the heat loss as they avoid most structural cold bridging effects
and easily improve air leakage heat losses.

Thermal Mass

Thermal Mass & night_flushing_-_revisedConserving energy and controlling its use with thermal mass is one of the simplest and most rewarding energy conservation techniques you can use to improve comfort levels and reduce energy costs.
By building it into new and existing homes you can provide a passive heat/energy store that will absorb excess heat during the day and release useful heat in the cooler evenings and night time.

Examples of thermally massive surfaces include hard dense surfaces such as tiles, stone floors, dense plastered/rendered walls, exposed brick work/stone work. Please speak to us to understand the full benefits for this passive system. It will never break down or wear out, but will help to keep you cool in the summer and reduce the time through the year when you need to use your heating system.

Underfloor Heating - UFH

U.FUFH is a brilliant solution to include in new build and in homes undergoing extensive renovation to save energy and increase comfort levels. It also removes the need for radiators. Most plumbers will supply and fit and it works best in new insulated solid floors but can also be used in some timber floor structures. Costs are very similar now to radiator based systems and it comes with the added benefit of reducing running costs.U.F timber structure

It works extremely well with heat pump heating systems by allowing the heat pump to run at lower flow temperatures of 35-40 ° which is when they are most efficient. Speak to us about your home and we will talk you through the entire process of what to use, and where to use it; including time and budget.


Install heat recovery fans in the bathrooms and kitchen (approximately £300 each installed). Vent
Axia Solo is a good example:
Consider the addition of a humidistat in the kitchen unit and a recirculation kitchen hood with carbon filter if you go for a cooker hood.

Mechanical Ventilation with Heat Recovery (or MVHR) is an essential part of Passivhaus low energy building design.

Carbon Legacy has developed specialist technical expertise in delivering MVHR systems for ultra low energy/ Passivhaus buildings. We offer a full design & commissioning service to ensure the optimal efficiency and quietness of our MVHR systems. Carbon Legacy ensure the optimal efficiency and quietness of our MVHR systems, with recovery rates of up to 95% as standard.  If you are building a new house or carrying out major renovation works then consider a whole house ventilation unit with heat recovery (WHVHR). An excellent manufacturer is ITHO of Holland who make various best in class units at reasonable cost. It is important to have an air tight structure to make this work. Carbon Legacy have installed many ITHO heat recovery systems; and we know exactly what works.