Spray Foam For Under Floors

About Spray Foam For Underfloor Voids

Cold draughts and a lack of insulation generally make ground floors very cold and unbearable during winter months.

Either Sucraseal Open Cell or Nexseal LE Closed Cell are viable spray foam solutions to insulate the underside of the suspended floor system. The airtight insulation will stop draughts rising through the floor whilst mitigating heat loss from inside the house.


Spray Foam will eliminate cold draughts entering your home


Spray Foam has excellent thermal performance per inch


Spray Foam uses recycled plastics with no harmful VOC’s or HFC’s

Where To Use Spray Foam For Floors/Under floors

Unlike pre-manufactured materials which are difficult to transport into an underfloor crawlspace and fix into place, spray foam offers the perfect solution. Spray-applied directly to the underside of the sub-floor deck, between joists, spray foam will adhere to the surface meaning that no mechanical fixings are required. The seamless, airtight and monolithic structure of spray foam helps to completely eliminate cold draughts whilst retaining the heat within the property. Both Sucraseal or Nexseal LE are suitable for under floors of all shapes and sizes. The process involves sending an installer into the underfloor void or where access is particularly tight, a Q-bot could be considered.


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Use one of our ThermoFoam-approved installers


Once installed, we provide a 25-Year Product Warranty


Check out our Gallery where you will find some photographs of installations we’ve completed in the past. Whilst spray foam is insulation and not decoration, our experienced installation teams will always endeavour to provide a neat and tidy finish to the insulation. Nexseal LE closed cell is easier to achieve a neater finish whereas Sucraseal Open Cell expands at a faster rate to leave an undulated finish.


Why Insulate a floor void?

During winter months, dense, cold air tends to linger at floor level and can make for a very cold space. With underfloor voids generally ventilated via air bricks, cold draughts can then be pushed up through the floor, requiring additional heating to combat the impact. Spray foam insulation can be applied to the underside of the floor in crawl spaces.

Why can’t you fully fill a floor void?

This is not a recommended practice because the insulation can allow damp to track up from the ground which in turn could hold moisture and rot the floor deck. It’s also important to maintain the cross flow of air so that moisture can escape. The airflow is created by air bricks that are intermittently located under the damp course in the lower walls.

How Long Does Spray Foam Last?

Pre-manufactured insulation materials can shrink, slip and degrade, especially with gravitational pull. Spray foam is entirely different because it is manufactured in-situ, therefore spray applied to the underside of the floor deck. The spray foam itself remains in an inert, unchangeable state once applied and it will therefore last with the life of your property.

How much space do I need underfloor?

We tend to send installers into the floor void crawl space as this represents the best chance of getting a monolithic airtight coverage of insulation. A general rule of thumb requires a minimum of 450mm clearance from the bottom of a floor joist to the ground in order for an installer to manoeuvre underneath the floor.

How Long Does The Process Take?

Provided there is pre-made access to the underfloor crawlspace, the process is usually carried out within a day for up to 150m2. The tighter the space, the longer it will take an installer to move about underneath the floor. A team of two is usually always present when underfloor voids are insulated due to health and safety reasons.

What About Dampness In Under floors?

Under floor voids are generally well vented through ventilated blocks which promotes airflow under the floor. An installation of spray foam should not heighten any damp issues provided cross-floor ventilation is present. We run hygrothermal assessments on every project to ensure that the insulation design will perform adequately and without causing damage to the underfloor structure.

Our Products

Check out our BBA Certified Spray Foams

Our range of open and closed cell spray foams are industry-leading, BBA-Certified, use recycled materials and contain water-based blowing agents.

Nexseal Closed Cell

This low exothermic, high-lift closed cell foam boasts a fast installation time, offers incredible thermal performance and improves the structural integrity of a building. Loved by installers for its fast rise, Nexseal is ozone-friendly and is pending BBA certification which is due in June 2022.

Sucraseal Open Cell

The leading open cell foam now available in the UK. Sucraseal combines peace of mind British Class 1 fire safety with exceptional thermal performance and is pending BBA Certification which is due in June 2022. Sucraseal is installed exclusively by ThermoFoam-approved contractors only.

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