Foam applicator gun
Foam applicator gun
~ unit cost £30 + installation £30 = £60

Page summary…

Successfully draught proofing a home by preventing uncontrolled air ingress/egress is essential to improving comfort, reducing energy costs and managing moisture… damp.

We’ll look at some common appropriate and inappropriate voids, questioning their objectives and whether they are achieved. We’ll ask if they are functioning correctly and being operated appropriately before considering what practical affordable improvements are possible.

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Related on another page…

  • Doors
  • Windows
  • Paper and paint



Aims – Draught-proofing is perceived as easy and affordable, something a homeowner might tackle themselves following a visit to a hardware store to purchase a few low-cost products. [Ref – DECC] Improving the performance of doors and windows is of obvious concern, however, our existing homes have become perforated with a history of inappropriate and often hidden holes that go undetected. The current approach to draught-proofing fails to deliver successful results.

Objectives – Air moving through a building takes the path of least resistance. When air ingress/egress is restricted at one point in the fabric the air pressure will increase the rate of air passing through at other locations.

Hypothesis – When blindly installing draught-proofing product the results are more often disappointing. Is it possible to achieve better results with a more thought-through methodology? Start with larger to expose the small. Success comes from being universal.



Does it work and is it used appropriately?

  • Don’t beware the temporary measure
  • Start with the large
  • Expose the small
  • Be universal
  • Managing moisture


  • Chimney voids – both top and bottom
  • Kitchen and bathroom – dysfunctional vents and service voids
  • Floors and ceilings – gaps and cracks
  • Miscalanus  holes – obsolete unimpeded vents and unnecessary air-bricks

Common voids…

Chimney voids


Chimney pots


Sub-floor voids


Gaps in floorboards


Roof and ceiling voids

Attic spaces

5mm continuous gap

Hairline cracks


Service voids

Kitchen and bathroom


The following projects are intended as a means of developing transferable skills, understanding the objectives and applying the principles required to achieve successful results. They are not intended as a comprehensive how-to instruction manual.

Expanding foam applicator gun

Foam applicator gun

Expanding foam filler is an invaluable material for sealing up draughts and a versatile adhesive for securing things in place without the need for mechanical fixings such as screws and nails.


Don’t beware of the temporary measure

Foam filler is ideal for preventing uncontrolled air ingress/egress “draught-proofing”. It is a good insulator, preventing the conduction of heat and also preventing moisture vapour from migrating to cold surfaces causing interstitial condensation.

Historically, Polyurethane foams (PUFs) are manufactured from petrochemical-based products and use potentially toxic blowing agents. Understandably, there has previously been some resistance to the use of PUFs, however, much improvement has been made. Polyurethane Foams: Past, Present, and Future

A more pragmatic approach recognises that when used in moderation a small amount of Expanding Foam can be very beneficial and therefore an immediate game-changer for reducing energy consumption, lower heating bills and improved comfort.

Essential around the frames of windows and doors, or when assuring insulation board is airtight. Expanding foam filler is also invaluable as an easy win or temporary work or temporary measure.


Always read the instructions

Unlike disposable canisters, a foam applicator gun provides full control. The application can be in moderation and the canister can be closed off and reused on another occasion to avoid waste.

Expanding polyurethane foam is essential for installing doors and windows. When a frame is airtight, constructed to a good standard or improved with secondary glazing air will more easily be sucked around the frame which will cause degradation and ultimately failure.

Quick and easy to use, the results are immediate. Expanding foam can also be used for temporary work, then cut away and clean off when ready to proceed with a more permanent solution.


Materials and equipment

Unlike disposable canisters, a foam applicator gun provides full control. The Expanding Foam can be applied in moderation, then the canister can be closed off and used again on another occasion, avoiding waste.

If not closed off correctly or left empty any remnant foam left behind inside the applicator gun will set hard and render the gun unusable; always have a spare canister ready to replace an expired can.

It is also recommended to have a canister of gun cleaner to hand. It won’t dissolve cured foam inside a gun (or elsewhere) but it will dissolve sticky fresh foam from an accidental spill.

Before procuring and using a foam applicator gun it is of advantage to understand the avoidable pitfuls.

Here are 10 top tips…



Foam applicator gun – Screwfix £19.99

Expanding foam gun grade – £5.99

Foam gun cleaner – £4.99


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Extensive volumes of air ingress/egress can be slow and imperceptible. By starting with the larger holes a reduction in air change may also be imperceptible as air will consequently move through smaller holes more quickly. By starting with the large we expose the small and progress can be measured when the wind begins whistling through the keyhole.


Start with the large… and expose the small

Chimneys voids, top and bottom
Closing off the chimney inside at its base in the fireplace is relatively easy, by ‘tightly’ plugging the hole, this could be quickly achieved with a foam applicator gun. However, this can lead to unintended consequences. If air can enter the chimney at the top, cold air will become trapped as a frost pocket and trapped in place will result in cold spots on the internal room surface which will attract warm moist air which will begin to manifest the symptoms of damp. A disused chimney should also be capped to prevent the accumulation of water ingress which is no longer evaporated by the use of the fire through draught.

A disused chimney would therefore best be closed off both top and bottom.

Close off with tightly packed insulating fleece, both bottom and top then cap off the pot with a purpose-made or bespoke cowl.


Chimney capping cowl – Travis Perkins £25.66

Hemp insulation – Celtic Sustainables £186.00


Caulk applicator gun


Decorators caulk is an affordable and easy way to prevent air-ingress up from between the floorboards. Using the trigger gun the gaps are filled, being water-soluble, excess decorators caulk can be wiped away with a sponge and any residue remaining on the boards can be lifted with WD40, an oily rag, once the caulk has cured.

The small gaps between floorboards can add up to a large hole, allowing slow, imperceptible air-ingress.


Screwfix Sealant adhesive dispenser gun – £19.99

Screwfix – White caulk – £1.39

Decorators Centre – Brown caulk – £1.87
A box of twelve tubes is sufficient for a couple of rooms for a little over a pound per tube.




Practitioner stories

76-year-old non-scientific woman gathered the following

76-year-old non-scientific woman gathered the following – Whis Collis

Capping two chimneys

Capping two chimneys – Thomas Richards

Don’t beware the temporary measure

Don’t beware the temporary measure – Sarah Jones-Morris

A beautiful 1850’s Semi – a history of chimney damp spots

A beautiful 1850’s Semi – a history of chimney damp spots – Simon James Lewis

Foam applicator gun

Foam applicator gun – top ten tips and tricks

Blog category – voids