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  • Writer's pictureGlenn Thompson

Are You Considering Installing Spray Foam Insulation in your home!?

Here is an impartial guide for homeowners. I'm sure many of us have seen spray foam being advertised. If you are considering installing spray foam please read the following guide very carefully.


Thermal improvements can be made to many homes. If you want to reduce your carbon emissions and keep your energy bills low, installing insulation, draught-proofing can reduce heat loss, your energy needs and bills.

Installing spray foam insulation in your home. | An impartial guide for homeowners.
Spraying between roof rafters in an existing attic.


Spray Polyurethane Foam (SPF) spray foam, is a form of insulation material that can be applied to roof spaces, walls and floors. It is installed by spray gun application, which can seem advantageous.

However, there is often limited understanding among homeowners regarding spray foam modification to their property and its impact on valuation, home surveys and lender decisions. Moreover, Trading Standards and various media reports highlight issues with ‘cold-calls’ or unsolicited offers to sell or remove spray foam installations.

Spray foam insulation may seem like a simple way to reduce heat loss in your home, but it should be viewed as a serious modification. This guide aims to inform you as a homeowner on the ways in which spray foam insulation could impact on your property.

Installing spray foam insulation in your home. | An impartial guide for homeowners.
Spray foam insulation installed between rafters in an existing attic.


This guide applies to alterations and modifications to existing roof structures in lofts where homeowners are considering the application of or have already had spray foam retrospectively applied between rafters.

Spray foam changes an existing roof from ‘cold roof’ into a ‘warm roof’.

Installing spray foam insulation in your home. | An impartial guide for homeowners.
Cold Roof (Insulation at ceiling level)

Installing spray foam insulation in your home. | An impartial guide for homeowners.
Warm Roof (Insulation at roof rafter level)

Spray foam is an insulation material that is applied to homes to offer thermally efficiency. However, like all insulation, its material properties, design and installation need to be considered very carefully before application to ensure it is suitable for your home.

This is particularly important when retrospectively installing in an existing property. Buildings are a combination of individual component parts, designed to work together. Introducing new materials can have an impact, both positive and negative, on how your building performs. For example, sealing hot air inside can keep you warm but can also seal water inside and make roof repairs much more difficult.


Homeowners may want to increase insulation levels within their homes to improve thermal performance and reduce energy bills. However, insulation of all kinds can also negatively impact how other parts of the building perform depending on its form, position and most importantly, the condition of the existing materials. Incorrectly installed insulation can negatively impact ventilation and result in moisture damage.

Firstly, your property needs to be wind and watertight before spending money on improving its energy performance. If a property is not maintained, it will be vulnerable to rainwater getting inside. Adding insulation to a poorly maintained roof will increase this vulnerability and accelerate the decay of any untreated timber roof structures.

Secondly, all changes need to be considered in the whole. A typical pitched roof loft void is designed to have ventilation to balance water vapour in the air, reducing the risk of condensation.

Traditionally insulation is laid above habitable rooms at ceiling level. This is called a ‘cold roof’ because the loft is a cold space. Installing spray foam to the underside of a roof structure is known as a ‘warm roof’ because the roof space becomes warm. The combination of two different insulation locations is a fundamental change from how the roof was originally designed to perform. Changes may lead to unexpected problems if the original design requirements are negatively impacted by the change, which can result in newly installed spray foam not meeting expectations or installers claims.


There are different types of spray foam, with different performance properties, and once applied, they are not easily reversible. Homeowners should carry out appropriate checks on the material, its properties and to be aware of the risks involved by using independent experts, commercially and independently separated from the installer and manufacturer.


Some spray foam insulation can make it difficult to identify problems to the roof because it restricts the view from within the roof space. If the timber roof structure is covered with spray foam it cannot be fully seen or inspected.

Climate change science indicates more frequent extreme weather events will occur, such as multiple severe storms, one after another. Storms can damage roofs and the presence of spray foam can, in certain circumstances, make repair more difficult.

If there’s a roof leak behind spray foam insulation, you may not notice it. An undetected roof leak can lead to rotting timber. It is important to look after your roof, be proactive by regularly inspecting and maintaining it to keep it watertight.

If you already have spray foam installed in your roof you may not see a problem developing until it is too late.

See photos below:

Spray foam insulation can make it difficult to identify problems to the roof because the timbers can be ‘dry’ on their exposed, visible surface but ‘wet’ behind the spray foam

Installing spray foam insulation in your home. | An impartial guide for homeowners.
Dampness Reading 15.2

Installing spray foam insulation in your home. | An impartial guide for homeowners.
Dampness Reading 23.6 (Wet behind the spray foam)


There is a risk that energy saving claims are not achieved if installations are not planned correctly. Spray foam insulation is a better thermal insulator than the same thickness of standard mineral wool loft insulation, however, existing loft mineral wool insulation can be topped up to modern standards of current building regulations resulting in better thermal performance than the typical maximum of 100mm of spray foam installed between the sloping rafters.

Before introducing spray foam, thermal calculations and condensation risk checks need to be undertaken by a qualified professional who has surveyed all parts of the roof. This documentation should be kept by the homeowner for future reference. Some calculations may show that the mineral wool insulation above the ceiling needs to be removed, i.e. you may not be able to have both ceiling and insulation between rafters.

Removing existing insulation from above the ceiling and changing the position of the insulation may make you use more energy compared to a property well-insulated at ceiling level (because you have to heat the roof space before heat will be retained in the living space below). With some roof spaces being relatively large, e.g. in a bungalow, this may not be cost effective.


Polyurethane spray foam is typically a flammable material. Building materials are tested using British European Standard BS EN 13501-1 with typical polyurethane rating as Class E – Combustible, which ‘will only resist a small flame for a few seconds’.

You should be aware of the increasing risk to your property when using polyurethane spray foam as insulation. While uninhabited loft spaces do not require protecting from fire, in the event of a fire in your home, spray foam is flammable and will increase the likelihood and extent of damage to your property and any adjoining properties.


As with all types of insulation, poor installation can lead to unintended and adverse consequences. Incorrectly installed insulation can lead to dampness, such as uncontrolled condensation and damage to parts of the property.

Consider the following matters before spray foam is installed at your property:

  • Is your roof reaching the point when it will soon need to be replaced? If so, spray foam will not be cost effective.

  • Is the roof free from defects and damp?

  • How is ventilation to the roof structure to be controlled, as required by the manufacturer?

  • Will any existing insulation need to be removed to control condensation risk?

  • Will the spray foam applied require additional materials such as a vapour control layer?

Seek independent expertise, commercially separated from the installer and manufacturer, to advise if spray foam is appropriate for their property.

Most pitched roofs on houses and bungalows are designed to be ventilated and spray foam is a change to the original design.

A draughty loft above ceiling level insulation is generally a dry loft. Air circulation balances moisture vapour to manage condensation risk within acceptable limits. Spray foam creates a warm roof void. It seals the gaps to prevent draughts and retain heat but will also seal in moisture unless adequate precautions are taken. Seek professional advice on how to manage any moisture risks.


  1. Most insulation products should not be applied directly to the back of tiles / slates or be applied to remedy leaks or damage.

  2. Some products must not be applied to waterproof roof underlays such as bitumen sarking felts and unventilated plastic sheets because they do not let water vapour through and therefore require ventilation to remove water vapour and condensation. These roof underlay materials go under the roof tiles and above the roof structural frame.

  3. Some products must not be installed against roof underlays at all and must have a dedicated ventilation channel installed behind the foam to control condensation risk.

  4. You will need documentation that demonstrates the system was designed and installed to manufacturer’s guidance, particularly if a warranty is provided only for the insulation material and not the installation workmanship and design.


The presence of spray foam insulation is a factor that could affect a surveyor’s professional opinion of value. If a surveyor encounters spray foam insulation during their inspection, they may request an independent specialist report – the results of which could impact on their opinion.

If spray foam has been applied incorrectly, or say to a listed property without prior consent, this will be reflected in the surveyor’s valuation. The surveyor will also have to conform to the instructions and any policy provided by their lender clients.

Make sure your installer provides you with all the relevant documentation including the installation contract, relevant calculations, works carried out to the roof, any guarantee or warranty and any independent test certificate, for example, a BBA or Kiwa certificate.

If you are purchasing a property with spray foam insulation already present, ensure this documentation is available as this will assist in any queries received from the valuer, lender or legal representatives.

Hope this article has been helpful and thanks to the RICS for their advice. My opinion remains the same, I would not be recommending spray foam, there are other methods of insulating a home. If you have any questions please feel free to contact me and thank you for reading this article. Glenn

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