Retrofit Works - An Overview to External Wall Insulation and why you should use it.

If you are thinking about undertaking a retrofit project or looking to self-build a new dwelling, you might be thinking about whether to apply internal, external or cavity wall insulation to the walls in order to improve the energy efficiency. In this post we will explore why you might choose external wall insulation (EWI) over the alternatives and what the various considerations might be for using this approach on your project.

What is External Wall Insulation (EWI)?

External Wall Insulation (EWI) is a way to make a building more energy-efficient by adding insulation to the outside walls of a building, which will reduce heating costs and improve the building's appearance. Insulation boards are simply fixed to the outside of the existing walls and then render or cladding is applied over the top. This creates a high quality and attractive finish.

Woodfibre EWI applied to a passive house project at Wellington Lane

A question we are always asked is whether to apply insulation internally or externally on the exsting walls. EWI is not necessary the right approach for every project but we will explore the potential benefits and the things to consider in deciding whether to take this route.

Benefits of External Wall Insulation over Internal Wall Insulation.

• Increasing the thickness of the wall externally means that you are not loosing valuable space inside your house. As long as you have the room outside then you can make a great contribution to U-value improvement without impacting upon the sizes of rooms.

• Insulating externally brings the opportunity to improve the appearance of a property with an attractive fresh new look.

• Insulation on the outside potentially makes a huge improvement to the internal air quality and health of your building and reduces the risk of mould growth in dwellings. This is because the dewpoint is pushed to the outside of the wall build-up rather than being located somewhere within the building fabric. If you choose to use IWI instead then you need to be really careful about vapour control to avoid condensation forming within the fabric of the wall.

• EWI often provides a much better continuity to the insulation compared to IWI. Often with IWI there are floors or internal walls which are impossible to avoid and creates a cold bridge. With EWI there is opportunity to connect with connect well with "warm roof" buildups.

Considerations and Challenges with EWI

There are some instances where EWI can be more challenging or needs additional work to succeed.

• EWI needs careful coordination with other building elements. Particularly roof eaves, door and window cills. These items should be extended and enlarged to oversail the thickness of the insulation.

• Other building furniture such as gutters, downpipes lean-to structures will need to be removed and then reinstalled, refixed to the outside of the new EWI.

• If you have a cavity wall construction then it is important to make sure that the cavity is filled with a materiel such as cavity wall insulation or the top of the cavity is capped to prevent heat loss through air movement. This can be undertaken during the retrofit.

Lime render finish applied to woodfibre insulation at Wellington Lane

Choosing the Right Insulation Material

There are several types of insulation materials to choose from, each with different benefits. The best option for you depends on your building type, budget, and priorities such as breathability, fire resistance, or affordability. Some common materials are:

• Expanded Polystyrene (EPS): A cost-effective choice for modern homes, lightweight and easy to install

• Phenolic Foam: Offers high insulation performance with a thinner layer, making it ideal for properties with limited space.

• Mineral Wool: Excellent fire resistance and soundproofing, often used in high-rise buildings

• Wood Fibre: A breathable, eco-friendly option that works well for older or heritage buildings. Woodfibre is normally used with a breathable finish such as a lime based render.

 Cost of External Wall Insulation

The cost of EWI depends on the insulation material, wall condition, and project size. The table below provides a general price guide:

Insulation Type	Cost per square metre (including installation)
EPS	£80–£120
Phenolic Foam	£120–£160
Mineral Wool	£100–£150
Wood Fibre	£110–£160
Cork	£130–£180

Designing Woodfibre EWI into a project

How External Wall Insulation is Installed

1. The wall is cleaned, and any loose materials are removed.

2. Insulation boards are fixed to the wall using adhesive and mechanical fixings.

3. A base coat is applied over the insulation, with reinforcing mesh to prevent cracking.

4. A final render or cladding is applied for protection and appearance.

Many considerations need to be made of how the EWI will interact with other building elements such as windows, doors, roof eaves, and the ground.

Is External Wall Insulation Right for You?

External Wall Insulation is a good investment for homeowners looking to improve energy efficiency and reduce heating costs. The best material and approach depends on your property type and budget, as well your sustainablitiy aspirations, . We as architects can help guide you through this process, ensuring you choose the right materials and meet all necessary regulations. Get in touch to see how we can be of help in guiding you through this whole process.

Existing house gets thermal upgrade. Is loft insulation the easiest way to make your home more energy efficient, and save money?

Overview

As architects, we are often working on new build or passive house homes. But we also take on retrofit projects where upgrades to building fabric can make a big difference to the energy performance of dwellings, as well making them healthier, greener and more comfortable to live in. Probably the most effective upgrade is in the loft, especially if you live in one of the many Victorian terrace houses and post war buildings in Bristol or other parts of the UK. 

In this post on how an existing house gets thermal upgrade, we delve into a recent project where we identified a problem with the existing insulation and then calculated the payback period using our passive house PHPP software. We were amazed by how quickly the loft insulation would pay for itself and then continue to save our client money year after year. This is vital at a time when the cost of living, and removal of the winter fuel allowance is pushing energy bills through the roof, with no sign of that changing any time soon.

Would you like to know how to make your home more eco-friendly? Get in touch with us to discuss our sustainability assessment which identifies key areas of the home that could be improved to offer an enhanced level of comfort and energy efficiency. 

You can read a detailed overview of the sustainability assessment here.

Case Study

The owners of a 1960s dwelling in Bristol recently approached us to better understand how they could improve the thermal efficiency of their home using our sustainability assessment service.  We surveyed the building and identified a large loft space where the insulation was very poor and had compressed and degraded to the point where it really wasn’t working effectively. The client had also reported condensation and mold forming on the upstairs room ceiling close to the rear wall, likely to be a cold spot. We found that the insulation had been pulled back away from the eaves in the loft. Whilst this has the benefit of maintaining ventilation at the eaves, it was the source of condensation in the upstairs rooms.

A row of 1960s housing in Bristol. We helped the owner of one of these houses thermally upgrade the building fabric.

Thermal Analysis

We modeled the existing dwelling in PHPP, which is the software we use for passive house projects. Whilst we are not hoping to achieve anywhere near passive house level on this project, the software is still useful for estimating the energy loss over the course of the year, using historic weather data and an estimation of insulation levels in the buildings.

The results were fascinating. The as-existing dwelling was estimated to have an annual heating demand of 8770kwh, which means that building owner is spending over £480 a year on just heating the house with their gas boiler. This will be rising to £550 when the energy price cap rises next month in October 2024. A whopping 15% rise, at a time when people are still suffering from the cost of living and pensioners are losing their winter fuel allowance. The cost of heating is likely to get substantially higher in the future when gas starts to become phased out.

A technical detail showing the amount of insulation added to the loft

Savings

So how much money could loft insulation save? By increasing the thickness of insulation to the minimum level required by building regulations when upgrading your roof (U value of 0.16 W/m2K) it will reduce our client’s annual heating demand to 6686kwh per year, an impressive 25% saving. This would lower the annual heating bills to £420 from October, saving £130 per year.

So how much does the insulation cost? Knauf loft roll from B&Q currently costs about £7m2 for the 270mm thickness that is needed. So covering the client’s whole loft would cost only £250. So the client will have made their money back by the end of the second winter! If the house was heated by electricity then the client would be making their money back in a matter of months!

Ease of Installation

Unlike external wall insulation or floor insulation upgrades, it is actually relatively easy for people to add new insulation to their loft, saving on the cost of installation. Make sure that it is safe to move around in your loft and wear protective equipment as certain insulation materials can be an irritant to the skin. Do look closely at the installation instructions for the insulation materials that you are using.

Other Considerations

When upgrading the insulation in your loft, you need be aware of the increased risk of condensation. By making your house warmer, you are actually making the loft colder which can cause condensation to form in certain conditions. The best way to prevent this is to maximise the ventilation in the loft as much as possible. If you still have an old fashioned roofing felt which has a high vapour resistance, then you need to use felt lap vents. You will also need to make sure that there is a clear gap between the roofing felt and the insulation at the eaves in order to maintain a through ventilation.

We are here to help

On this project we were able to advise the client on the design and specification of their roof upgrade. In this instance the roof had clearly not been renovated since it was constructed in the 1960s, and so the client decided to undertake a full renovation by replacing their roof tiles, some of which were old and damaged. At the same time they could replace their old felt with a ‘breather membrane’ which helps with ventilation. Replacing the tiles would also allow for installation of an eaves ventilation system which would make sure that the ventilation gap between the insulation and felt would be maintained for years. Finally we suggested the use of loft stilts so that the loft space could stay usable for storage, even with a substantial amount of new insulation installed.

Are you thinking of upgrading your loft? Get in touch with us to see how we can help?

Barn Conversions in the UK are easier than ever

Gatcombe Barn under construction.

We worked with the client from his initial idea of conversion and look forward to seeing the finished dwelling.

With the relaxation of planning legislation, there has never been a better time to convert a barn into your dream home. Recent changes to the General Permitted Development Order (GPDO) 2015 have simplified the process, making it easier to transform agricultural buildings into residential properties without needing full planning permission. These changes allow homeowners to bypass the complex and often lengthy planning system, opening up more opportunities for rural development.

However, while the process may seem more straightforward, the expertise of an architect is invaluable. Navigating building regulations, structural considerations, and design challenges are crucial steps in ensuring your barn conversion is both compliant and functional. We as architects can help you optimise the layout, enhance energy efficiency, and ensure your new home blends seamlessly with its surroundings while maintaining the charm of the original structure.

If you're considering a barn conversion, get in touch with us. We can guide you through each stage, from initial concepts to completion, ensuring that your vision is realised in a way that respects both your budget and the unique character of your property. We are experienced in agricultural barn conversions of different shapes and sizes. You can read about our recent barn conversion projects in the links below.

Gatcombe Farm / Glebe Barn / Dundry Barn / Bell Farm / Scatterleigh Barn /

King Nymptons Barn / Mariansleigh Barn