When we talk about retrofitting a home, we mean improving the energy efficiency of a home by upgrading parts of it. This could include insulation, double glazed windows, generating electricity from solar panels on your roof, heating and hot water or ventilation systems and draught proofing. You can find detailed information on different retrofit measures on the energy at home page on the Energy Saving Trust website.

The retrofit upgrades presented vary across any of the priority options, depending on what is feasible for your home, what the system knows of your home, and the budget you set. The priority options are:

• reduce my CO2 emissions - provides a combination of options for reducing the use of gas for heating and hot water and improving energy efficiency to reduce energy bills
• reduce my fuel bill - provides options that prioritise energy efficiency to reduce energy bills (reducing carbon emissions is not prioritised)
• target zero C02 emissions - provides options for eliminating carbon emissions, moving completely away from fossil fuel use

In some cases, depending on the home, the options can be the same or similar. In other cases, and with a larger budget, bill cost reduction and carbon reduction options may be very different, such as replacing a gas or oil boiler with a heat pump.

Plan Builder uses a range of public data sources, including the EPC (Energy Performance Certificate) database. If the EPC was recently produced it should accurately describe how your home is constructed and what heats your home and hot water. If there is no EPC, the system models your home, based on other houses in the neighbourhood. If this is not accurate you can edit the information, if you register your email and login.

Specifying the heating energy source, (for example, gas or electric), is very important in getting the most useful results. Knowing what type of heaters or boiler you have is much less important.

The options Plan Builder provides you with are a guide for comparison between the different upgrades you could make. You can turn options off and on to see the effect they make. Different homes and occupant usage will greatly impact costs and benefits.

We expect them to be most relevant where the system has the most accurate understanding of your home, your motivations (what you want to achieve) and budget available. We recommend professional advice is sought before committing to any works.

An EPC will also give you home improvements suggestions you could make to reduce the cost of energy, rather than reducing carbon emissions.

If you wish to obtain an Energy Performance Certificate, you'll need to pay for one provided by a domestic energy assessor. A search engine will give you options for local providers. We recommend you shop around. You could expect to pay in the region of £50 to £100. You only need a valid EPC if you are renting or selling your home.

The costs are as accurate as possible, based on market research and updated through the year. Grants may be applicable and, in some circumstances, reduce the cost of retrofitted items and services.

We recommend seeking at least three quotes where possible for any work being considered.

Professional advice is available from recognised professions such as retrofit coordinators, retrofit assessors and retrofit designers. Further information is available from:

• Trustmark - Find a tradesperson
• Elmhurst energy assessor or retrofit professional - find an assessor
• Ecmk
• Stroma
• Quidos

The costs Plan Builder provides are offered as a reasonably realistic guide. The cost of building work and allied services and trades has risen over recent years as well as the cost of materials and transporting them. Quotes and estimates for works will vary.

As energy prices have risen in recent years, this increases manufacturing and distribution costs, in turn increasing costs of goods and services.

Homeowners and landlords may have equity in their homes and may have the opportunity to access this. Some mortgage lenders have arrangements or products to support retrofit of homes. It may be more cost-effective to do some retrofit upgrades at a suitable point in time, such as when the heating and hot water system replacement is due. Independent financial advice should be sought regarding any financial arrangements or financial products.

Grants may assist some owners and tenants in certain circumstances. For more information visit our home energy webpage.