Our MD Jon Battle investigates Timber and Damp Surveys and asks if they are really worth undertaking.

Mortgage Valuation surveyors visit a property on behalf of the bank, not the buyer. They regularly recommend that the buyer pays for a ‘Timber and Damp Survey’ as a condition of obtaining the mortgage.

Why are they doing this? Is it because they

• Are alerted when their moisture meter starts beeping
• Are unable to investigate further as they have other surveys to do that day
• Don’t have the right expertise in this area?

I have been a Chartered Surveyor for 22 years and I’m still not exactly sure what a Specialist Timber and Damp Survey entails*. However, I have had feedback on this from clients and vendors. They tell me the specialist appointed to carry out the survey, often a Timber Preservation/Damp Proof Course (DPC) contractor, attended the property with a moisture meter (most of which are designed to be used on timber), pressed it against the wall and skirting boards, but didn’t appear to do anything else.

You need to see timbers to survey them

Mortgage Valuation surveyors should know that you cannot survey the ‘timbers’, which are basically the joists hidden beneath floorboards and carpet/laminate, if you cannot see them. I do not know any vendor who will allow you to destroy their floor covering and often floorboards to get access to the sub-floor void.

But you need to access the void to physically inspect the joists and take moisture content readings from them. This is especially true where they bear off the brickwork as moisture can track from ground to brickwork to joists.

Measuring moisture

You need to take relative humidity (RH) readings in the sub-floor void. These are measurements of the moisture in the air at a given time. Depending on whether it is January or July, you will get completely different results because RH% is relative to climatic conditions. Lack of ventilation affects RH% so you also have to check the air-brick vents are clear and sufficiently numbered. RH% is also a big factor in the growth of dry-rot fungus which will destroy timber.

Testing for ground salts

A proper rising-damp inspection should include drilling out samples of plaster and masonry and testing for the presence of ground salts (potassium, nitrates, chlorides, sulphates, magnesium, sodium etc). The salts are transported within ground-moisture when rising-damp occurs. The moisture rises due to ground-soil pressure and capillary reaction, up through pores in the masonry. When the pressure fades at around 1m above the floor it stops rising.

When this moisture evaporates as vapour into the room, the salts are left behind and contaminate the plaster and masonry. They can appear as tiny white crystals known as efflorescence. Sometimes they are visible but often they are not. You cannot physically remove them without hacking off the plaster.

These salts are hygroscopic which means they attract moisture from the air, just like salt on chips absorbs the grease. We create moisture by breathing, cooking, and washing and drying wet clothes inside the house without proper ventilation.

When the salts become damp, a chemical reaction creates an electrical charge and the salts become electrolytes. This is a further problem because most moisture meters work on an electrical capacitance basis, and this chemical reaction sends the moisture meter reading off the scale.

So what is causing these meter readings?

This begs the question, are the off the scale moisture meter readings affected by rising-damp moisture, salt contamination or man-made condensation?

Often a previous rising-damp or lateral penetration damp (horizontally through the wall) problem may have been resolved/blocked but the salt contaminated plaster was never hacked off and replaced.

But will the specialist tell you this?

In fact, will the specialist even know this, and will they …

• Know the difference between a lateral damp problem and a rising-damp problem
• Note the orientation of the wall (north-west walls are most exposed in this area of the country)
• Confirm the wall construction (solid or cavity-wall)
• Establish the condition of mortar and render and any other breaches that will allow moisture in
• Know that original lime plaster and modern gypsum plaster are not compatible on damp walls because one is vapour-permeable and the other is not, which makes the wall sweat, or
• Understand that one is naturally alkaline and will neutralise the acidic salts whilst the other will perform badly
• Realise that black ash mortar was sourced from furnaces post-war and has a high sulphur content which when exposed to moisture, oxygen and carbon dioxide creates sulphuric acid which is highly hygroscopic?

So in conclusion I wonder how many people, on the advice of a Timber and Damp Survey, have invested £4,500 in a new damp proof course that wasn’t actually needed?

I recommend this article for further reading:

Also, please feel free to contact me directly for advice in this area, or to discuss your survey needs.

*As it happens, most mortgage companies would not allow me to carry out one of these surveys because I am not a member of the Property Care Association (PCA). If I complete the application form and pay the subscription I would be a member in a few weeks. In contrast, it took me seven years to become a Chartered Surveyor.