Deep Retrofit: Giant steps to energy efficient, warm homes

A webinar by Liam Schofield from the Carbon Coop

This session was the next in the progression of these fantastic webinars by the Carbon Coop from Draughtproofing to Airtightness and now some practical steps with case-studies of people who have made these energy efficient changes to their homes.

And these examples were not for the faint-hearted, most took several weeks and cost many pounds but effected huge changes to the homes. There was a lot of detail covered but the key steps are:

  • Survey
  • Plan & Budget
  • Design
  • Maintain high standards



Detailed building surveys generally look at the condition of the house, examining the condition of roof, walls, windows etc, suggesting further investigation for structural defects, damp and infestations. They will often suggest that you can make energy upgrades but very few provide detailed energy retrofit advice. So, consider doing a specific energy report. It is costly but if you want to make energy saving improvements this will give the head start required and will pay for itself in time


Plan & Budget

Decide what you want to achieve and how much you have to spend. The aim of retrofitting is to make your house more energy efficient and warm in winter, it is not to make it perfect! Balance energy efficiency with retaining original any features you want (or are required to by conservation/listed building consent) and your budget. Be as clear as possible about what you want to do and where you want to put things from the start, any alterations will expand the timescale and the price. You also need to fit it in with your daily life. If you want to do a major retrofit (over 50% of the house) it will be more cost effective and MUCH less stressful to move out completely.

In terms of budget, you need to do a good job for the money you have – cutting corners can result in higher costs later down the line e.g. with damp problems. Lowest price is not always a guarantee of quality, likewise highest price will not necessarily give you the best installation. Its recommended to get three quotes which will give you a better understanding of the likely cost.

Liam also recommended having a contingency in your budget of between up to 20% for those pieces of work you cannot plan for depending on the scale and complexity of the project.



This is crucial. Making your home air-tight and installing insulation sounds pretty basic but it can be really complicated so get some proper designs drawn up that your builder can understand and work with on site. The clearer you are at this stage the easier the work will be to price up and manage on site. The best way to do this is to use an architect with specialist knowledge in domestic retrofitting. These designs will enable you to sequence the work, making sure that different tradespeople are engaged at the right time and the work progresses. You don’t want to go back and fit a Mechanical Heat Recovery unit, for example once you have completed all the airtightness and insulation work because this will require undoing work and may compromise the end result.

There are a wide-range of products out there including sustainable materials, if you want to use these make sure they are specified at the design stage.

Even small pieces of work need a design, for example insulating timber suspended floors is fiddly and hard to do properly, even with a design.

Ensure the design is correct for you and you understand it, but do not micro-manage the contractors, you need to trust them!


Maintain high standards

Ensure you have a retrofit coordinator on-site, to provide support to your main contractor. This should not be the site-manager as they will already have a lot to do, but someone who can check the work against the designs and ensure that all tradespeople on site are clear about what you are trying to achieve.


Practical Tips

Make sure your insultation layer meets or overlaps with other insulation layers eg walls with floor, in the industry jargon: A deep retrofit should ensure a fully thermal envelope to your property. For example, if you are going to insulate your walls, do not leave any uninsulated walls as this will lead issues on the walls where insulation has not been applied. If you are intending to do work over a period of time, factor this in.

Make sure you retain ventilation where it needs to be eg in the eaves of the roof or under a suspended wooden floor with airbricks.

Use appropriate internal wall insulation and install it correctly or you can get condensation and damp building up behind it.

Before installing internal wall insultation ensure your walls are repaired with a like-for-like material, or you may get gaps which can bridge the insulation, causing cold spots, draughts and may result in damp.

If your retrofit project includes an extension, keep it simple, as close to a box as possible because it will be more energy efficient and easier to insulate and seal up (and therefore cheaper)! because there are fewer thermal bridges.

Reduce the number of thermal bridges (cold bridge, heat bridge, or thermal bypass). These are found where there is a direct connection between the inside and outside through one or more elements that are more thermally conductive than the rest of the building envelope. For example, a gap in the insulation, around pipework, ducting or where the joists sit on the supporting wall. They will need to be sealed to be air-tight and insulated separately.


Timescale estimates for a 3-bedroom house

  • Uncomplicated re-roof: 4 days.
  • Floor insulation: if it is a timber suspended floor and is stripped of carpet and furniture, it can be stripped, insulated and have a new floor installed by 2 workers in a week



The type of materials will be specified by your architect, but do some research about what you want


  • Jute from recycled coffee bags which has a high thermal value
  • Most roofing materials is now permeable, it used to be non-permeable felt so would need a ventilation gap to stop condensation on the rafters
  • Celotex and earthwool (standard insulation)
  • Woodfibre board – internal or external
  • Hempcrete – external. IT has a low thermal value but can be build up into thick layers and is breathable
  • Dianthonite is a really good breathable layer for stone walls


  • Vapourblock creates an air-tightness layer and help strengthen up a structure.
  • Air-tightness tapes eg Proclima have been stress-tested to 100 years, if installed correctly
  • Test air-tightness post-retrofit using an air-leakage tester fan eg Minnesota.


Where to find help in Bristol & the West of England

The FutureProof service (managed by the Centre for Sustainable Energy) provide advice, support and access to builders who are trained in the principles of whole house retrofit, as well as specialist installers for items like (cavity wall insulation, air/ground source heat pumps, solar PV etc.).

They can:

  • Provide in-depth advice on how best to approach your retrofit – assessing your property, understanding your requirements, advising on best approaches to suit your budget, retrofit timescales (all in one go or incrementally), and a whole host of other associated parameters.
  • Arrange a whole-house survey to find what will work best for you – to better understand the cost benefit savings in terms of money and energy of installing different improvements.
  • Help you find a builder or specialist installer in your area that you can trust – connecting you with builders who have undertaken training to understand the principals of whole house retrofit and who have the skills to deliver high-quality work
  • Help with reviewing quotations – to maximise your investment.
  • Provide referrals to qualified Retrofit Coordinators who are able to provide quality assurance – ensuring works are carried out correctly, to a high standard and will deliver on energy savings.
  • Provide advice on a range of materials and techniques appropriate to your home.

Check out their website or contact them by email   or phone 0800 038 5007.


There are a number of specialist deep retrofit building firms operating in the Bristol and wider region, most of whom can be recommended through Futureproof. Retrofit specific qualifications are limited in the building sector; the training provided to Futureproof builders provides a bridge to fill this gap. If you are intending to complete a whole house retrofit and are looking for a very good level of airtightness, thermal efficiency and low running costs from your home improvements there are two codes that may help you meet your requirements. The Association of Environmentally Conscious Buildings (AECB) has a ‘Building Standards Framework’ setting out minimum standards in principles of retrofit. In addition, the Passivhaus institute has the Passivhaus standard (aimed primarily at new build) and the Enerphit standard that is designed specifically for retrofit of existing houses.

The Green Register has twenty year’s experience training building professionals on the best approaches to energy retrofitting. They have a ‘find an architect’ search function that will help you identify someone with appropriate skills to help you design your project. Alternatively look for an architect with either the AECB building standards qualification or who has the Passivhaus certificate. Not all of these will be on the Green Register list. In addition, review their past work and where possible see if you can speak to or visit the property of someone who has worked with the architect.

If you want to DIY, there are lots of Green building forums and website but people often have opposing views. It is important to understand the fundamentals of building physics and whole house retrofit to ensure that you do not unintentionally create problems that will need to be addressed in time. Forums are useful for getting a good baseline of knowledge, however with all specialist activity you are likely to get a better result by consulting professionals before undertaking any work yourself; and of course a fee will be attached to that professional advice.