Sub floor ventilation, why spending a few pounds today could save you thousands tomorrow...

Often overlooked, sub floor ventilation is critical to the health of your home. If damp is at work, out of sight, under your floor boards, you could be accumulating a hefty bill that you could so easily avoid.

So let’s take a walk up to your front door and just see whether you’re harbouring a potential problem with your property.  First of all, what’s not original about your home? Has anyone added an extension, a new driveway or path? Are your borders raised with soil? Is there a car port, conservatory, porch or patio addition? Are there areas of decking or raised planters and flower boxes?  If so, the chances are that your air bricks which provide essential sub floor ventilation could be partially or completely blocked. 

Says Richard Walker, National Development Manager for Peter Cox Property Services, “It’s amazing how something so apparently small and insignificant as an air brick or two can impact on your home life so hugely.  I’ve even seen vents closed off deliberately with pieces of slate to ‘stop any draughts’ and others cemented over completely!

“But that’s precisely where all the problems start. Air bricks or air vents are normally fitted just above your property’s damp proof course and their job is to let air flow right through your property from front to back or side to side. This helps maintain the correct moisture level in your underfloor void.  Keep the moisture content to below 15% and you should be fine.  But once the level starts creeping up, then you can develop problems in the joists and floor timbers leading to, mould, damp, musty smells and eventually devastating Dry Rot.

“Modern properties usually have air-bricks spaced at around 1.5m apart but in older properties it can be very arbitrary, as can the size of the vents and what they’re made from.

“How are you to know if your sub floor ventilation is all it should be without a simple underfloor survey with a moisture meter?”

“These days”, says Richard, “as the water table is rising, and flooding more widespread, the problem really needs addressing early  - an ounce of prevention being better than thousands of pounds worth of cure. You can even help yourself by removing cobwebs, leaves and debris that can block vents. We’ll gladly show you how to keep them clear and clean with the minimum of effort.

So should you check your property’s sub floor ventilation?  The simple answer is yes. If you live in a home built before 1980, particularly in a pre-war, Victorian or even older home, it’s really worth a small investment now to have experts run a quick check for you. If your house is at pavement level, particularly in terraced properties, you really need to know what’s going on under the floor. If you notice your floors bounce, shift, creak or appear to be dropping away from the skirting boards – these are all tell-tale signs that the underfloor joists are already affected by moisture. Even if the problem is established, an early investigation can still help prevent it getting worse.

Says Richard, “Our inspections are hassle-free and don’t take long, although we do need to be thorough!  With the right meters, specialist know-how and equipment, the surveyors can be in and out in a very short time.  You will get a full report with any recommendations so you can breathe easy. I mean that quite literally. Diagnosing a damp or inadequately ventilated sub floor void early can actually help you avoid the mould and fungal decay spores which some people, particularly the young and old can be allergic to.

“If we do find sub floor ventilation problems, the reassuring news is that often we won’t even need to disturb your day to fix them. New air vents can be fitted from outside your property to achieve the necessary air flow and rectify your problem.  Where a property is at street level, we can’t lower the pavement but we can fit periscope vents to introduce air flow. Whatever solution we provide, it will be right for your property.”

Richard continues, “Recently, we worked on six houses near York racecourse, all of them affected by the raised water table and subsequently Dry Rot. Early detection in one house was key to the whole street agreeing to fix its mutual problem at source. The size and style of property isn’t the issue. The survey is similar wherever we go. It’s quick, easy and inexpensive so why wouldn’t you want to have your house checked out.

The fact is that you can protect your home and your family with just a little professional insight before problems have a chance to manifest.  You’re not only spending a little to save a lot, you’re also making one small investment to help protect your family’s long term health and well-being.

Depending on the circumstances, Peter Cox Property Services offer some surveys free of charge. The team will also consult for a quoted fee before you purchase a property, giving you extra confidence that you’re making the right move.

To discuss your property or to arrange a survey, please get in touch with your nearest office of Peter Cox Property Services at http://www.petercox.com/regions.php or you can also call 0800 789 500 to talk to the experts and we’ll send a surveyor with local knowledge of your area.

Transfusion and Diffusion Damp Proof Course Systems

Peter Cox have been successfully installing remedial damp proof courses in buildings of all types since 1951. At that time Mr Peter Cox ran a stone restoration company based in London. He had noted that stonework at the base of buildings was often eroded as a result of rising dampness and he devised a method of retrospectively introducing a damp proof course (dpc) without significantly disturbing the wall structure. The newly installed dpc prevented further damage to the existing stonework and protected any new replacement stone at the base of the building. His original method of installing a dpc was known as the Transfusion system; this was patented, gained Agrément certification and has been listed as a valid method in BS6576 since the publication of the standard.

In brief, a silicon based water repellent liquid is introduced into the base of the walls via drilled holes which are normally into the mortar joint. The siliconate absorbs or ‘transfuses’ into the capillaries of the masonry; this lines the capillaries with a hygrophobic layer which resists capillary attraction therefore controlling rising dampness. The silicone material does not block the capillaries; the masonry can still ‘breathe’ and the wall structure remains fundamentally unchanged. The silicon water repellent used in the transfusion system is water based and non toxic; it is completely inert once cured and has no deleterious effect on the masonry into which it has been introduced .

Due to the installation process generally being via drilled holes in the mortar joint there is minimal disturbance of the actual stone or brickwork and once installed the holes can be re-pointed with negligible aesthetic impact.

Images showing installation of transfusion system and diagrammatic illustration of principle.



The transfusion system has been employed in thousands of prestigious and historic listed buildings throughout the UK and in other parts of Europe including Venice and Gibralter. Well known examples in the UK include York Minster, Selby Abbey, The Royal Mint, The Bishops Palace of Lincoln, Burleigh House Estate and Normanton Church.

Transfusion being used in a thick stone column of a university building.





Normanton Church – this ancient church was within the flood area of the proposed Rutland Water Reservoir. Prior to filling the reservoir the ground level outside the church and the floor level inside was raised by approximately two metres. A damp proof course was installed by transfusion above the new level to protect the stone walls from rising dampness in what were to become fairly extreme conditions.

Normanton Church after completion of the reservoir – the church is now used for exhibitions etc.

In 2002 Peter Cox developed the Diffusion system which was a natural progression from Transfusion. It is installed in a similar manner, the essential difference being that the silicon based water repellent material is now in a thixotropic cream form rather than a liquid. This allows greater control of the installation. Installation is via 10 -12mm diameter holes, which again, when drilled into the mortar joints enables a dpc to be installed with minimal disturbance and visual impact on the building, making it ideally suited to historic buildings. The water repellent material has no deleterious effect on the masonry. Installation of a dpc in this way prevents rising dampness and once dried down, damage to internal decorations is prevented and further damage externally from freeze/thaw is controlled.

Diffusion dpc installation.



Elf cup fungus

Elf cup fungus is likely to be found in damp brickwork or plaster in buildings. The fungi require a damp environment and may feed off organic material in the walls or plaster.

It is important to locate and remove the sources of moisture, and to dry the structure and surfaces.

Elf cup and other species of Plaster fungi including Ink cap do not require any preservative treatment.

For more information about dry rot and wet control, and to arrange for a professional survey, contact Peter Cox.