A guide to loft or roof insulation

Understanding loft or roof insulation

In this series of ‘understanding retrofit measures’ blogs, we’ll be explaining different retrofit measures which can improve the energy efficiency of homes – reducing energy usage to cut energy bills and carbon emissions, and improve the comfort of your home. We’ll include information on how the measure works, what types of homes it may be right for, what installation looks like, and more. In this post we’re looking at loft or roof insulation.

Want us to cover a particular measure? Drop us an email to info@cosyhomeoxfordshire.org and we’ll see what we can do.

What is loft or roof wall insulation?

In an uninsulated home up to a quarter of heat lost is through the roof. Installing insulation in your roof or loft is a great way to reduce heat loss and make your home more energy efficient – saving money and cutting carbon emissions at the same time.

How does loft or roof insulation work?

Insulating a roof is easiest when there is easy access to the roof space. In this instance, insulation is normally done by using rolls of mineral wool insulation. This material will be laid along the floor and the walls of the roof space.

The thicker the roll of insulation used, the less heat loss there will be. So, even if you already have roof insulation in your home, it’s worth checking if it could be further improved and thickened.

If you want to use the roof space as storage, you’ll then need to lay boards over the insulation material on the floor of the roof. It’s important to leave a gap between the insulation and boards to allow ventilation and avoid damp and mould – as well as ensuring the insulation is not squashed, reducing its effectiveness.

If you want to turn the roof space into a usable attic room or living space it will need further work alongside the roof insulation, ensuring all areas of the walls and ceiling are insulated, and then adding a layer of plasterboard on the inside of the insulation to create the walls of the room.

If your roof space is difficult to access, the best option is likely to be blown insulation. This involved a professional using specialist equipment to blow insulation into gaps in the roof – usually mineral wool fibre, treated cellulose, or polyurethane foam.

If your home has a flat roof it will usually be insulated from above, with a layer of rigid insulation board added on top of the roof. This can be combined with internal roof insulation if the property has only some areas of flat roof, rather than an entirely flat roof.

As with any type of insulation, you need to make sure that the roof is dry and in good condition before any insulation is added. This is not a DIY job and does need a professional and reputable installer to ensure it is done properly and does not cause issues with damp or ventilation down the line. If you work with Cosy Homes Oxfordshire on your home retrofit you’ll have access to our network of trusted contractors, who we will contact and manage for you – so you won’t need to worry about this.

Loft or roof insulation and ventilation

Insulation stops heat escaping from living spaces, so it will make your loft space cooler, which could introduce or worsen existing damp or condensation problems. This means that when you are installing roof insulation you need to also be thinking about how to improve ventilation in the space to avoid issues later down the line.

A professional and reputable installer will ensure that this is taken into account. If you work with Cosy Homes Oxfordshire on your home retrofit you’ll have access to our network of trusted contractors, who we will contact and manage for you – so you won’t need to worry about this.

What types of home does loft or roof insulation suit?

Whether your roof is slanted or flat, used as a loft space or remains empty, roof insulation is suitable for most homes – but the insulation method will vary, as outlined above. Roof insulation may not be suitable for flats within buildings with a shared roof space, as you would need permission of all flat owners within the building.

If you want to check whether you have existing roof insulation or not, and whether this could be improved, the best place to start is by getting a retrofit professional to assess your home. We can help you with this through our home assessment and Whole House Plan service. Simply register your home with us and we’ll be in touch to book your home assessment.

What are the expected costs and savings?

Loft insulation is effective for at least 40 years, so it should pay for itself many times over. 

The Energy Savings Trust predicts costs and savings as below for insulating a previously uninsulated roofspace with 270mm of insulation (table 1) and for topping up a roof space previously insulated with 120mm of insulation to 270mm of insulation (table 2). The date is based on fuel prices as of April 2019.

Table 1

 Detached houseSemi-detached houseMid terraceBungalow
Typical cost (£)£395£300£285£285
Energy bill savings (£/year)£250£150£135£210
Carbon emissions diverted (kgCO2/year)1000kg610kg550kg860kg

Table 2

 Detached houseSemi-detached houseMid terraceBungalow
Typical cost (£)£290£240£230£280
Energy bill savings (£/year)£25£14£12£19
Carbon emissions diverted (kgCO2/year)95kg55kg50kg80kg