Expert Witness Service



‘In theory, theory and practice are the same. In practice, they are not.’

Santa Fe Institute.


Building Problems


EAA can provide an expert witness service to clients or design teams who experience problems with modern ‘energy-efficient’ buildings, or on older buildings where insulation has been added. These issues can range from ‘just’ thermal discomfort and excessive energy bills to condensation and mould growth.

The words ‘expert witness’ do not mean that a matter has to ‘become legal’ and involve lawyers and the courts. This is very much a last resort. Sometimes those involved want an independent expert to help them understand and agree what went wrong, amicably establish the best way forward and avoid repeating similar mistake(s).


Theory versus Practice


If your building was constructed in the last ten to 20 years and was described as ‘energy-efficient’, how much energy does it really use, especially for heating, compared to what it was predicted to use? The usual answer is from ‘slightly more’ to ‘very much more’.

The heat loss of newly-constructed buildings often exceeds the level predicted when they are designed. The efficiency of the heating system can also be below-par. With these discrepancies combined, the resulting energy performance is often much worse than predicted.

The chart below is not unusual. After moving into a modern, ‘energy-efficient’ detached house and living there for three years, the occupants are paying a gas bill which is 2.6 times higher than the Building Control calculations said that it would be. The gas bill is supposed to be £360 per year but it is actually £940/year. Note, this set of figures exclude fuel price rises over the three years.

Expert Witness Picture 1


The predicted space and water heating bill in an ‘energy-efficient’ detached house vs. the actual gas bill.


NOTE: The actual gas bill three years after moving in, averaged over years two and three.


Source: EAA.



Below is a similar picture for offices. Two years after completion, an award-winning ‘green’ non-domestic building uses over twice as much energy and emits over twice as much CO2 as it was predicted to do at design stage [1].


Gap between actual and predicted energy performance for an award-winning green building.Expert Witness Page, Image 2




Second line – how much CO2 it should have emitted.


Fourth line – how much CO2 it actually emitted.



Source: reference [1].



Some people only become aware of the discrepancy when the first bill arrives. It is an unwelcome ‘reality check’. The energy underperformance can lead to higher than expected energy consumption and bills, lower thermal comfort and higher CO2 emissions. If good thermal envelope design is particularly lacking, there may also be an enhanced risk of condensation and mould growth.


Five Case Studies


Here are five cases in which EAA was asked to report on why a building project was underperforming and/or why a particular feature had failed. Fortunately, only one of these cases ‘became legal’.

The descriptions are anonymised, because the identities of those involved are not important; also, they value their privacy. But the reasons for the failures are important. Others should seek to learn from them and ‘do it right, first time’.


Condensation and Mould Growth


In the 1990s, the owners of a detached bungalow in northern England replaced their wooden bay windows by PVC-framed double-glazed windows. They believed that this would improve their level of thermal comfort and that their winter condensation problems would be eliminated.

However, their comfort improved very little. There was as much if not more internal condensation and mould growth than with the previous single-glazed wooden windows. Why?

Working with Fenestration Associates [2], EAA calculated the heat loss through the centre and edge of the new double-glazed PVC windows. The results showed that the seller of the windows had misrepresented the U-value of the PVC frames and had overstated the benefits from their use.

With the owners represented in court by a specialist construction lawyer, a financial settlement was reached. This enabled the owners to install some genuinely energy-efficient, high-performance double-glazed replacement windows. These provided the comfort and freedom from condensation which they had expected from the original replacement windows.


Excessive Solar Gains


In the 2000s, a charitable trust in southern England requested an urgent survey and report on its new offices. The building had won several architectural awards. But as soon as the first occupants moved in, they experienced significant overheating and thermal discomfort.

The air temperatures in the offices reached 30 degC in sunny March and April weather. The peak summer temperatures were even higher.

A survey established that the building was badly orientated on its site. A highly-glazed facade faced due west and there was little shading by trees, other buildings, etc. The peak incoming solar radiation in summer on a west wall coincides with the warmest time of day; i.e., mid to late afternoon.

The window area was also too high for a naturally-ventilated office. The client went ahead with the recommended remedial work.

This building’s overheating problems had nothing to do with poor construction. They were attributable to limited knowledge. The risks could have been sidestepped by wiser decisions at an early design stage, costing the client little or nothing.


Excessive Heating Bills


In late 2009, the owners of a detached house in the Midlands asked for help. They were spending over £3,000 per year to heat their new home, which had been built in 2006-07 on a direct labour basis and had underfloor heating. But they were still cold and draughty.

In this dwelling, the so-called ‘performance gap’ was over four-fold. The predicted heating bill of this house had been under £700 per year.

During a site visit, it was concluded that the walls and roof were not designed or built in a manner which could effectively keep the heat in. The dwelling was tested and was found to be twice as draughty as the maximum cited in the 2002 Building Regulations. Recommendations were made on how to reduce draughts and address the inadequate cavity wall insulation.

The off-peak E10 electric underfloor heating system was unfit for purpose. With no natural gas, the choice of fuels was limited, so the owners decided to fit an oil condensing boiler with modern controls, supplying the same underfloor pipes. This would emit 50% less CO2 per unit of heat than the E10 heating and cost 30% less to run.


Failed Roof Glazing


In 2013, advice was sought on remedial work to a new ‘Passivhaus-certified’ building. Within months of completion, the triple-glazed sealed units in its rooflights had failed; i.e., the edge sealant had degraded and water vapour had migrated into the interpane space, causing visible condensation.

On inspecting the drawings, the rooflights were designed in a manner which made early failure of the sealed units all but inevitable. They had also been wrongly installed within the thermal envelope.

The rooflights may have insulated very well. But they did not meet other essential criteria, including drainage and ventilation of the sealed unit.

Moreover, the rooflight that had been suggested as a potential replacement was itself unsatisfactory in design. Had it been fitted, it could have failed within a few years and needed a second expensive replacement.

A rooflight from a different country was sourced. The new supplier appeared to understand the need for both high energy efficiency and correct design and installation.

Expert Witness Picture 3


Sealed Unit Failure.


Seen in a triple-glazed window in the early stages, when the condensation is only visible in cold weather. Sealed unit failure is unsightly. It also means that the argon or krypton originally used between the pane(s) has been lost and replaced by air. Not the building cited in the text.


Picture © EAA.


Unsuccessful Retrofit


In late 2014, advice was sought on a Grade II Listed oak-frame building on the English/Welsh border. The owner had retrofitted the gable end wall with thermal insulation and an air barrier on the inside nearly ten years earlier. Unfortunately, the work had not reduced heat loss in those rooms as much as expected and the wall’s acoustic properties remained very poor, largely due to the extent of air movement.

A brief survey of the weatherboarded wall from the outside showed that, although the plastic foam insulation used was acceptable for the purpose, excessive gaps had been left between the foam slabs and the hardwood frame. These air gaps partly negated the value of the added insulation.

No material was present in the weatherboarded wall which could act as a wind barrier and keep air out of the insulation layer. The ‘breather membrane’ which the owner planned to use would have been unsuitable and would not have resolved the problem; it was too air-permeable. The owner now plans to seal the gaps between the frame and foam slabs, and fit a suitable wind barrier on the outside of the wall, in summer 2015.





[1] Curwell, S, et al, “The Green Building Challenge in the UK”, Building Research and Information, 27 (4/5), 286-293 (1999).

[2] Formerly, now best contacted via