Technical

There is a wealth of information available about home energy efficiency measures. This page summarises some of the measures that are likely to be necessary for your home, and points to further more detailed information.

Retrofit

General questions about retrofit and the whole-house approach.

The rating system on your EPC is based on cost of energy and not carbon savings. Your EPC is based on average data for a home like yours, not on your actual home. Whilst there is some good advice in the EPC recommendations section, the methodology for data collecting is generic, and lots of assumptions are made. For example, it may recommend solar pv when your property is not suitable because there is significant overshading from trees or buildings or your main roof faces north.

An EPC does not recommend new technologies such as heat pumps because although much more efficient, heat pumps use electricity, and electricity is currently more expensive than gas. The EPC does not take into account how you and your family live in in your house, nor does it look at the amount you spend on energy. Additionally, the EPC does not advocate airtightness, or recommend additional ventilation.

Retrofit is a whole house methodology. The last 30 years have provided a lot of information about the do’s and don’ts of insulating, including why some insulation fails and how it can cause other issues such as damp and condensation. A retrofit assessment looks at everything that affects your energy consumption, from lack of insulation to the construction type of your property and how you and your family live in it. Insulation is a significant part of retrofitting, but if it isn’t installed correctly there will be a ‘performance gap’ between what is expected and what actually happens. Consequently areas that have been traditionally overlooked, such as window reveals, will be included with your retrofit plan.

Retrofit starts with the ‘fabric first’ approach. By ensuring that the fabric of your property (roof, walls, floor) is dry and in good repair, and then adding extra insulation, you can reduce the energy demand for heating your property. It makes sense to tackle air tightness at the same time as insulation, as you will be uncovering your walls, floors and ceilings, and membranes and tapes are simple, less expensive and less disruptive to install concurrently. When you know the heat demand of the insulated property you can size a suitable heating system; smaller systems cost less to purchase, install and run.

Finally we look at renewables. When your home is well insulated then more energy is used to heat hot water than heating the house. You can look at renewable options to offset the energy demand for your hot water, such as solar thermal or solar pv with a diverter to your hot water cylinder.

Whole House Eco-Retrofit – Centre for Alternative Technology (cat.org.uk)

Energy saving retrofits – Centre for Alternative Technology (cat.org.uk)

The cultural heritage of our country is signified through specific buildings and areas and retrofit is careful not to disturb or damage historically significant building fabric. When a building is listed or within a Conservation Area extra thought is given to what types of interventions are appropriate and achievable.

All retrofit work on listed buildings needs to be approved by the local Conservation Officer, and sometimes Listed Building Consent will be required. However, there is always something that can be done to improve the energy efficiency of these houses. The retrofit plan will take the special requirements into consideration.

Responsible Retrofit Guidance Tool (responsible-retrofit.org)

Repair and maintain

Simply maintaining your home is the first step to increase both your own comfort and the fuel efficiency of the building, as it allows the building to work as effectively as possible. For instance, rotten windows will be letting draughts in and heat out, whilst cracks in the guttering or render may contribute to damp, which in turn makes a home harder to heat to a comfortable temperature.

Maintenance makes your home ‘retrofit ready’ and should always be done before undertaking larger measures.

Properties that are in a poor state of repair lose energy rapidly. The condition report looks at issues surrounding damp within the building fabric, and the causes of that damp. This could be via cracks in the walls, leaking roofs and rainwater grounds, or via broken drainage. Often vapour open buildings have been repaired with non-permeable materials, such as gypsum plaster and concrete, and this can lead to more issues with damp. Damp in the building fabric is associated with greater heat losses through that area. Damp air in the property also takes more energy to heat up.

Existing ventilation is recorded in the Condition Report. When insulation is added to roofs and floors care needs to be taken to ensure that there is adequate ventilation in place to avoid condensation. For example, an insulated suspended timber floor needs to be ventilated below to avoid condensation build up in the timber floor structure so before suggesting insulation, attention is given to ensure that there is sufficient ventilation flow in the sub-floor. This may be difficult in terraced or semi-detached properties, and sometimes might mean that laying a solid insulated floor is preferable. Using the right materials, it is feasible to install a vapour open insulated solid floor.

Insulate

The inclusion of the correct form of insulation is likely to be the single most important measure in reducing your home’s energy consumption.

Most UK homes now have loft insulation, and cavity wall insulation if the home has cavity walls. Additional insulation needs to be carefully selected for the construction and particular features of your property, and installed with proper consideration for ventilation.

The home assessment will examine the original construction of your house, and your Retrofit Plan will include details of the right materials to use, and where and how to apply them.

The fabric of your house is designed to be either ‘vapour open’ or ‘vapour closed’, sometimes known as ‘breathability’. Generally houses built before 1920 are vapour open and use lime and clay based products for render, mortar and plaster. Later builds tend to be vapour closed, with cement mortar, concrete render and gypsum plaster.

Traditionally, solid masonry wall constructions allowed an element of rainwater absorption, vapour movement and evaporation from both inside and out, and consequently are self-regulating. Increasing insulation and air tightness levels (and thus the internal temperature) means that the moisture movement qualities of the structure can be compromised and care must be taken choosing the right materials to allow that to continue.

Insulation can also be vapour open or vapour closed. Natural insulation products (like wood fibre, hemp or cork) allow the fabric to continue to ‘breathe’, and this can help prevent excess moisture, condensation and mould within the property. When breathable insulation products are used then plasters, renders and decorative paints should also be breathable.

Ventilate

When insulation is added to roofs, walls and floors, care needs to be taken to ensure that there is adequate ventilation. Poor ventilation is likely to result in condensation, which can lead to damp, mould and failure of the insulation. ‘Interstitial condensation’, ie unseen condensation underneath wall insulation is a particular problem when the wrong insulation is used together with inadequate ventilation. Hence the slogan ‘insulate tight, ventilate right’.

Your Retrofit Plan will avoid these risks by specifying the right insulation and ventilation for your particular home.

The simple answer is yes, opening windows is part of ventilation (we call it purge ventilation). But when the weather is cold or if your windows are on a ground floor or easily accessible from outside you may not want to rely on opening your windows to ventilate your property.

Moisture is all around us in our homes, within the air and the building fabric. There are hidden dynamics at work when we occupy a building which, when unchecked, will eventually lead to problems, both with our health, and with the longevity of the buildings that we occupy.

Ventilation is needed when you insulate your property and make it airtight. Older houses were not built air tight and so there was plenty of fresh air moving through the property. Once that air movement is halted then stale, warm, damp air is trapped in the building, and it will condense on the coldest surfaces. This can cause damp patches and mould. The internal air quality of your property becomes stuffy, and can cause health problems for you and your family.

Measures can be taken to introduce better air quality in your home. Ventilation can be a simple, mechanical extract system from your ‘wet’ rooms (kitchen and bathrooms) or it can be a more complex whole house system, like a Mechanical Ventilation Heat Recovery (MVHR) system, which recycles the heat from your home. It really depends on how airtight your property is, whether there are suitable air inlets (for example, trickle vents in your windows) or what type of insulation you have in your property. A ventilation strategy is an important part of the retrofit process to ensure that insulation doesn’t cause unintended consequences.

Once a property has been insulated, a large proportion of remaining heat is lost through draughts and gaps in the building fabric. If this is addressed at the same time as insulation, through special air tightness membranes, tapes, mastics and grommets, then costs for heating your home are significantly reduced. Air tightness is not just about tapes and membranes though, 3mm of plaster is also air tight, so a good finish to your walls and ceilings can help improve heat losses. Air tightness membranes can be vapour open, so although they prevent excess draughts and air leakage, moisture can still move through them.

Heat

Unless your current heating system is near the end of its life, decisions about installing a new low-carbon heating system should be taken after repairs, insulation and ventilation have been addressed. This is because if these efficiency measures have been taken effectively, much less energy will be needed to keep your property warm.

Your Retrofit Plan will make recommendations about the most suitable low-carbon heating system, which will depend on your property, its size and age, and how much outside space you have.

Ground or air source heat pumps using renewable electricity are currently the most efficient low-carbon option. This is because they can generate over three times as much heat energy as they consume. Installation can be costly: the pumps cost more than a standard gas boiler and existing central heating systems may need adaptation to the lower water temperature of heat pumps. Until 31 March 2022 the cost will be offset to some extent by the government’s Renewable Heat Incentive scheme.

Heat pumps are, on their own, rarely suitable for homes that are less well-insulated. Hybrid systems, which use heat from a pump and from another source, such as a biomass boiler or electrical immersion heater, or a standalone biomass system may be more appropriate for these properties.

IMAGE OF HEAT PUMP OR HEAT STORE OR SIMILAR

Generate

Many people are chosing to generate their own electricity, usually with solar panels. In recent years the price of panels has dropped dramatically, and the bulk of the cost of installation is now labour and scaffolding rather than the panels themselves.

A typical 12 panel 4kWp installation can cost as little as £4,000, and depending on orientation of the roof will generate between 3 and 4 MWh per year, some of which can be sold back to the grid.

Bruton and Castle Cary Town Councils have teamed up with installer IDDEA as part of the Solar Streets initiative. £50 will be donated to a community initiative for every installation.