Importance of High Quality Cameras

The Importance of a High Quality Camera and Interchangeable Lenses to The Survey Process

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Windmill during demolition phase of conversion in 1981

I was recently commissioned to carry out a full structural survey on a converted windmill in Nottinghamshire. I’ve surveyed a water mill before but this is my first windmill. Having said that the building was reduced in height as part of the residential conversion that took place in 1981 and no working parts were retained. Once the height was reduced a cut timber conical roof was installed that was fully covered with butt jointed timber planks prior to being covered with a bitumen and felt roof coating. This would not have been my choice of roof covering and perhaps it was a commercial decision taken by the developer or perhaps it was a more reasoned decision based on the buildings height and local  exposure to high winds? After all, windmills are generally sited in windy locations and we have to consider the potential for roof chatter or even tiles being ripped from the roof in high winds. Roof chatter derives its name from wind uplifting the tiles so they make a chattering sound in high winds; usually caused by insufficient nail fixings.

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Conical roof nearing completion in 1981

It is difficult to inspect a roof at this height from the ground and this is where the zoom lens and a decent camera really pays dividends. By walking a good way from the property I was able to zoom in and take shots of the roof from all angles and the resultant images when blown up on a computer screen provide valuable information with regards to final advice that is included in the full survey report. In fact the roof looks to be in reasonably serviceable condition but it has already overstretched its expected life cycle by quite some years. Without the images obtained I’d have been extremely uncomfortable in providing accurate advice relating to the roof condition and as a general principle I find the high quality zoom lens and camera to be an essential part of my surveying kit. For an unusual building of this height, it was absolutely critical.


Zoom Lens Reveals Enough Detail to make Informed Decisions about Condition. Note lightning protection system to left of RWDP.

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Should We Demonise All Cavity Wall Insulation?

Contextualising the argument against Cavity Wall Insulation

Whilst we completely acknowledge that wet cavity wall insulation causes a number of problems relating to moisture transference between the outer and inner leaf, potential penetrating damp and even a secondary condensation damp problem due to the reduced thermal value of a wet wall, we reject entirely the idea that even dry CWI causes problems and yet we are now seeing CWI blamed almost entirely for every damp problem encountered. Scare mongering has always been a great marketing tool but this claim makes no sense whatsoever.

Checking for condensation damp

We have encountered hundreds of condensation damp problems and statistically the problems of cold surface condensation are always worse in solid walled (poorly insulated) properties, the process for identifying primary cold surface condensation is quite simple.

Failed cavity wall insulation

Testing for moisture at depth rules out penetrating damp

We test for moisture at depth in the masonry to rule out penetrating damp and a secondary condensation damp problem caused by reduced thermal value in the building fabric. We record dew point temperature and also record wall surface temperatures to see if wall temperatures are at or below dew point temperature, if it is then this proves that you have an active condensation damp problem.

Proving that CWI is a problem

The same diagnostic process applies to cavity walls and if testing for moisture at depth in the inner leaf of masonry rules out penetrating damp and if CWI is installed then it is not causing a problem. I have recently read claims that even voids in dry CWI ’cause’ condensation but this is a marketing claim rather than being an actual fact. The argument is that internal surface temperatures are cooler (Possibly below dew point temperature) where the void in insulation is to be found. This is absolutely true but the whole wall would be at the same temperature (Possibly below dew point temperature) if no CWI was installed. All this really proves is that the CWI is having a positive effect on the wall surface temperatures where there are no voids.

Some home owners even had CWI installed to help mitigate for cold surface condensation issues as well as to reduce heat loss and indeed it helped and is continuing to help in many many cases. We are we not suddenly  going to reject the idea that improving wall surface temperatures is a significant factor in reducing issues of cold surface condensation.

Nonsense  statements made about cavity wall insulation

A mathematical relationship exists between ambient temperature (Ta), dew point temperature (Td) and relative humidity (RH), if:   Ta is = to Td then RH equals 100%, directly impacting on one value will affect other values. I recently read that CWI causes an increase in internal temperature and a subsequent rise in RH; this point was given in explanation as to why even dry CWI can cause condensation. Again, this is wrong and in fact the reverse is true, an increase in ambient temperature results in a decrease in relative humidity because warm air can hold more moisture than cool air. Generally speaking we wouldn’t even agree that CWI results in an increase in ambient temperatures because most occupiers do not suddenly take to turning up the thermostat on having CWI installed. What actually happens is that they generally have heating set to the same comfort levels but use less energy in maintaining those levels. It is rather simplistic to say that all recipients of CWI now run with higher internal temperatures in their properties so technically there would be zero effect on internal RH levels.

The single biggest direct impact of having dry CWI properly installed is that it raises internal wall temperatures above dew point temperature and therefore reduces the risk of cold surface condensation damp. If it is not inherently waterproof and if the potential exists to transfer moisture across the cavity then problems can occur but the issue needs to be contextualised and it has to be recognised that marketers are now latching on to the anti CWI campaign and these are quite often the same people that installed the product. It would in our opinion be foolhardy and unnecessary to embark on a National campaign to remove all CWI without first gathering evidence that it is actually causing a problem. Visual evidence of damp and decorative spoiling caused by damp does not prove that CWI is the cause of that damp.

So how common are cavity wall insulation failures?

As an interesting aside to this piece and perhaps to underpin our point… I recently received a telephone call from the founder  member of CIVALLI, the cavity wall insulation victims alliance. It was explained to me that BBC Wales had done a piece on cavity wall insulation failures, which had been picked up by BBC East Midlands, who also wanted to do a piece on the alleged high levels of cavity wall insulation failure. Unfortunately, the fly in the ointment was that CIVALLI didn’t know of any failures in the East Midlands and thought that I might be aware of a ‘victim’ to help validate the piece. I explained that I knew of no ‘victims’ and also that I thought the BBC Wales X-Ray piece was in my view, an irresponsible piece of journalism that made no sense of the facts presented. I’m not interested in sensationalist news stories, I’m interested in facts and evidence and my personal experience is that cavity wall insulation failures are not as common as CIVALLI would have us believe; perhaps the fact is illustrated by virtue of the fact that they were not aware of a single case of failure in the East Midlands that could be used to support another sensationalist news story.

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Alternative Support – Timber Decay Case Study

An Unusual Approach to Providing Support for Replacement Floor Timbers


New tannelised timbers at risk of further decay.

I thought this item worth posting purely because of the unusual approach adopted to dealing with the problem… The problem found is fairly typical; a cellar that would have originally been incredibly well ventilated due to an open coal chute had at some point seen the chute bricked up. This drastic reduction in air flow resulted in high relative humidity levels in the cellar, which is subsequently absorbed by the timbers, thereby placing them at risk of timber decay.

In this case the floor joists had all been recently renewed and ordinarily, the method adopted to replace the floor joists would be to build them back into the wall, ensuring that a ‘boot’ is formed around the end of the joist using a DPC material to ensure that the timber is not in direct with wet brickwork, or you could install joist hangers and sit the floor joist ends  on those.

What was clear is that the the high humidity levels that caused the original timbers to rot were still present because on testing the timber moisture content we found  moisture content to be above the 20% danger limit for ongoing risk of timber rot.


Bespoke steel supporting framework

What is unusual about this particular case is that once the new floor joists were installed someone saw fit to specify a bespoke steel frame around the perimeter walls to support the joist ends. This must have been a very costly and to my mind completely unnecessary installation.  The joist ends appeared to be built into the masonry though I can’t say if they had the required bearing surface and perhaps the specifier was concerned about further rot to the joist ends and adopted this belt and braces approach.  They would have been far better to deal with the root cause of original timber rot by reinstating the volume of air flow that previously existed with the open coal chute.





Bricked up coal chute significantly reduces air flow to cellar.

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What happens when you apply waterproof render to old buildings

Managing damp problems in old buildings

Damp building made worse by specialist contractors.

A while back we were commissioned to investigate a damp problem on an old public library. The library had previously been used as as a Town Hall and when the decision was taken to convert the building, damp proof contractors were called in to deal with a damp problem that we do not believe was particularly serious. Stripping external masonry paint from the wall base plinth, lowering perimeter ground levels, improving sub-floor ventilation and dealing with defective and blocked rainwater goods was all that was required to cure the problem.

However, the specifier got in a ‘specialist’ to deal with the damp and this resulted in the internal walls being rendered with cementitious tanking to dam in the damp. A treatment that is completely inappropriate for this very old and historic building. Interestingly the internal render was applied to a height of around 4 to 5 meters and work was obviously very poorly scheduled because electricians followed the damp ‘specialists’ into the building and chased out their cement render in several locations to install electrical cables. These areas were then patched with a standard plaster system. Can you guess what happened in these areas?

It took less than two years for the system to fail and you can see how and why it failed in the next two video clips.

Induced rising damp: Part 1.

Induced rising damp: Part 2

You absolutely must recognise the difference between a management solution and a cure. Management solutions, as offered by many specialist damp contractors/salesmen  are by their very nature, destined to fail. The vast majority of damp problems can be cured with nothing more than minor building works and specialist contractors are not required.  Your aim should always be to cure rather than manage the problem and on that basis, specialist treatments will rarely, if ever, be required.





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Wall Base Plinths – Are they a Good Idea?

Are Wall Base Plinths A Good Idea? 

Wall base plinths are generally poorly understood and I attribute this to the confusion caused by a damp proofing industry fad for installing cementitious wall base plinths in the 50’s, 60’s and 70’s. It was a perceived treatment for wall base damp long before retrofit chemical injection became heavily marketed. The basic idea for installing brick wall base plinths, as seen in many thousands of old properties, was a good one, but a whole damp remediation industry ran with a sound principle and because they didn’t understand it, they ruined it. Original brick plinths generally preceded the widespread installation of a physical damp proof course, though you will occasionally find both an original brick wall base plinth and a physical damp proof course, usually of slate. Generally speaking, our experience has been that if you see an original brick wall base plinth then there won’t be a physical DPC installed.


Original brick plinths work well if correctly maintained. This one was built in 1880.

The thicker wall base gave extra protection against rainsplash and penetrating damp and generally acted as a larger buffer for damp. If you read my last blog then you may remember that I talked about buildings being built on the ‘overcoat’ principle. Well this is precisely how original wall base plinths work, they are generally constructed with lime mortar and so long as breathability is maintained then this thicker ‘buffer’ zone at wall base does a great job of protecting against wall base damp.  Unfortunately a remedial damp proofing industry latched onto this idea and started to install retrofit cementitious plinths in the mistaken belief that these too would help protect against wall base damp, which couldn’t be further from the truth. Anecdotally, retrofit cementitious plinths are said to help ‘shield’ the wall base from rainsplash but that function is outweighed by virtue of the fact that they shield against moisture evaporation from wall base.

When it comes to protecting against wall base damp, wall base ventilation  and subsequent moisture evaporation at wall base are absolutely critical. If a retrofit cementitious wall base plinth is installed then this critical ability is lost, moreover we often see retrofit plinths that have actually bridged an existing physical damp proof course so now you have double trouble, a bridged DPC and zero wall base ventilation.

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Retrofit cementitious plinth bridging original physical DPC









Occasionally we also see heavily spalled brickwork to original brick plinths, which results in a render coat being applied to form a new cementitious plinth over the top of the original brick plinth, an action that will most likely lead to severe wall base damp, as in the images below.

To round up, if you see a retrofit cementitious plinth installed then you should have it removed. If an original brick plinth is installed then you should respect the importance of this technical detail and maintain its breathability by keeping the brickwork bare and only repoint using breathable lime mortar.


Cement plinth formed over original spalled brick plinth





















Retrofit cementitious plinths are a bad idea.


Original brick plinth rendered ineffective by the application of external masonry paint.

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Seven Properties, One Problem

The Need to Maintain Moisture Equilibrium in Old Buildings

I have been lucky enough to survey some quite fabulous old buildings over the last two weeks; they all form part of the same estate and without exception they have all suffered damage from the use of incompatible materials in their historic maintenance regime.  Specifically, repointing has been done with Ordinary Portland Cement rather than the correct  lime mortar. All these buildings were constructed using lime mortar, with some of the buildings being thin joint construction built to incredible tolerances. What this means is that all these buildings are built on the ‘overcoat’ principle, which is to say that they are meant to absorb moisture and will go through seasonal wet/dry cycles. So long as we do not impede the buildings ability to breathe and therefore manage moisture, then these buildings will manage moisture perfectly well. As a general principle, the mortar joints should always be weaker than then the masonry units it holds together and this rule applies to ordinary portland cement as well as lime. However, once cement mortar cracks, it stays cracked, it has no ability to move with the building, whereas lime is much softer and has the ability to self heal. More importantly, it is sacrificial and its ability to breathe focusses moisture management or evaporation at the mortar joints. It will naturally erode and so long as the building is repointed with lime then the buildings ability to manage moisture will be maintained. As for these buildings, the qualities of lime mortar was forgotten for quite some time and I think that those responsible for maintaining the buildings genuinely thought that OP cement was a better option. It is certainly more favoured by modern bricklayers due to its ease of use and workability and I generally find that bricklayers just do not like using lime mortar.

Aside from moisture management we need to recognise the consequential damage caused by using ordinary portland cement on old buildings and the last slides below highlight that damage perfectly. Once buildings are repointed with OP mortar then moisture is diverted into the masonry unit where the higher moisture levels then leave the masonry susceptible to increased levels of spalling due to hydraulic freeze/thaw action. Bricks come out of the kiln with a dense outer ‘fireskin’ that has increased weather resistance, once the fireskin is lost then the underlying material is even softer and more susceptible to increased levels of spalling, the process is self perpetuating. Stonework is also affected by this problem and we’ve all encountered stone buildings where the cement mortar joints are standing proud of the stonework.

There are some general principles for working with lime that are not dissimilar to the principles encountered for OP cement and these are:

1. The slower the lime dries out, the better and more durable the end result. You should always wet down the surface being worked on to prevent moisture being drawn from the lime too quickly. You should also protect against direct sun and stiff breezes when drying out.

2. As for portland cement, frost can be very damaging to lime, and as lime takes longer to go off the threat from frost is even greater. This is really a timing issue and the use of anti-freeze additives should be avoided entirely.

3. The more you mix lime, the softer and more workable it becomes. Too much water increases natural shrinkage and as for Portland cement mortar, you should use as little water as possible. The water/cement ratio is as critical for lime as it for ordinary portland cement and the mix should be used as dry as possible and pressed firmly into place.

I am grateful to have made a positive impact on this estate now because the use of lime mortar is now fully understood and it is used as a rule rather than the exception. There will no doubt be some long term maintenance to replace spalled brickwork caused by the use of Portland cement but we have at least limited the potential for future consequential damage to these beautiful old buildings.

Seven Properties, One problem.

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