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?