Upon the discovery of dampness, virtually anywhere in the property, most people automatically assume that it’s the result of a failure in some aspect of the external coverings; either that or a fault with the plumbing, which of course it sometimes is. 

They suspect the walls, the roofs, the gutters, the bath or the central heating system etc.  What they never consider is that sometimes – most times actually – the offending dampness results from moisture produced inside the house, which is struggling to get out.

This survey arose because the house was suffering from damp patches on the chimneybreast, and the client, who was a most helpful and experienced civil engineer, automatically assumed the problem was being caused by a fault with either the flashings, flaunching or pointing on the chimneystack.  This was the case even though he had had all of these items inspected and ‘repaired’ on previous occasions.

So, given that he’d had trusted builder/roofers attend to the problem beforehand, I’m not quite sure what he expected me to discover, especially as I had no intentions of going onto his frosty roof. However, what I did discover came as a complete surprise to him.  It was something he’d never even considered….

 Property                                   Cheshire

Instructions                             

To inspect the property and provide an opinion on the causes of dampness to the internal gable walls, particularly in those bedrooms to the left-hand side of the house.

Background                            

The client has lived in the property for the last five years, and he suspects dampness was probably evident at the time he moved in.  He now wishes to re-decorate the rear bedroom but does not wish to do this until the above problems are resolved.

The client has gone to considerable trouble to ascertain the extent of the dampness in the affected walls, and I am extremely grateful for his most helpful, preparatory work.

Disclosures                   

I am not aware of any affiliation, financial or otherwise, with the client or the property. 

Limitations                              

Limited to the instructions.

Restrictions                             

The survey was non-invasive.

Date of Survey                         

November 2008

Weather                                   

Fine, clear.  The summer and autumn of the recent year have been extremely wet, and relative humidities have been much higher than normal, for extended periods.  These latter conditions will have had a considerable effect on the problems associated with this house.

 Viewing Orientation

Unless otherwise stated, all observations are made as if looking towards the house from the front.

Type of Property

Detached house, c1930’s with accommodation over two floors.  There is gas central heating and partial double-glazing in PVCu frames.

External Observations

The property is orientated such that its front elevation faces in an easterly direction, and it has brick, cavity walls beneath a clay-tiled roof.  Given its age there will have been a damp proofing course (dpc) installed within its walls at the time of construction.  There are no indications that this has failed and there are no high ground levels that would compromise it.

Ascending externally against the left-hand, gable wall are two, brick-built chimneybreasts, and these terminate above the roofline in two, separate chimneystacks with an approximate, maximum height of 1200mm.  These stacks run parallel to the front/rear axis of the house and their right-hand elevations face towards the north.

Each stack contains two flues, and each flue is terminated in either a pot, with weather cowl, or in the case of the rear flue, simply by means of a weather cowl.  There are no indications that these cowls are faulty and thus vertical rainfall should not enter into the flues themselves.

Although I could only view the stacks from ground level, using binoculars, I did not see any obvious indications of faults in either the flaunchings, pointing or flashings.  However, it should be noted that I could not see the right-hand faces, which are obscured by the roof pitch.

The pointing on the external face of the chimneybreasts is in reasonable condition and I did not form the impression it is suspect.

There were traces of algal growth on both chimneybreasts; this affected their full height and extending on to the stacks themselves. 

Although these chimneybreasts face in a southerly direction, a large, deciduous plane tree, adjacent to the carriageway on ***** Road shades them.  This shade will be particularly noticeable when the tree is in leaf during the summer months, although even when its leaves are shed, the branches will still reduce any sunlight striking this wall.

External Observations

First Floor                                

Rear Bedroom: there is distinct staining on the gable wall of this room, in a position approximating to the rear, external chimneybreast. Although the stain is to the upper section of the wall, it also slightly affects the ceiling adjacent to it.

Though there was once an open fire in this room, this feature has been removed and the fire opening has been sealed.  Ventilation has not been provided for the associated flue.

Moisture meter readings confirmed that the stained areas were either damp and/or contained contaminant salts.

Front Bedroom: although there were no obvious signs of distress to the gable wall, moisture meter readings provided a pattern similar to that in the rear bedroom.

Once again, the fireplace has been sealed and ventilation has not been provided.

Bathroom: the extractor fan in this room is manually operated, and as such will probably not be used as often as it should be.  In addition, I think it has been sited in an unsafe position, over the bath, where it will be susceptible to water splash from the shower, immediately beneath.

Ground Floor:                           

There were no visible or tactile indications of distress to the left-hand gable wall in either the front or rear reception rooms. Moisture meter readings did not indicate any particular problems on this floor. 

The front reception room has also had its fireplace sealed; ventilation has not been provided for the redundant flue.

The rear room is served by a gas fire, which will also restrict any ventilation via the flue.

Discussion/Conclusions

Although I cannot categorically rule out penetrating moisture affecting the flues, I doubt that this is actually the case, and I think the problems associated with the two bedrooms result from condensation, which is occurring both within the flues themselves and also on the internal surfaces of the gable walls. 

This has occurred because the open fires, which were once a feature of this house, have been removed, and ventilation was not provided for the redundant flues at that time. 

The installation of the gas fire in the rear reception room is also akin to sealing the flues; as for the majority of the time it will allow only restricted ventilation, and virtually none at all when the fire is burning. 

Thus, a situation has been created whereby the two chimneybreasts now form sealed, brick enclosures, running vertically on the external face of the wall; and these enclosures will almost certainly have a single, brick outer skin.  If I am wrong in this assumption, and they are in fact double, nine-inch skins, they will nevertheless be solid, without a cavity. Whatever their precise construction, their thermal qualities will be poor. 

Because of their southerly orientation, the outer faces of these chimneybreasts would normally benefit from the thermal gain provided by sunshine; however, the presence of the large plane tree will be reducing this benefit significantly, and thus the wall temperatures will be lower than could be expected.  This may well ensure that at certain times of the day, or more probably during the night time hours, they are below dew point, and condensation will occur on their internal faces. 

However, I think that this is more of a contributory factor than the main source of condensation, which in the main will be occurring either side of the roof-line, on the internal, right-hand faces of the stacks themselves. 

These areas face in a northerly direction, and thus will probably not receive sunshine at all.  They may benefit slightly in the early morning hours during the summer months, but this will be insufficient to warm them adequately.  In these areas, dew point will often be reached, especially during the hours of darkness. 

The main source of the moisture-bearing air, which is resulting in condensation, is almost certainly that generated in the bathroom, although bedrooms too are always susceptible to this phenomenon. 

As noted earlier, I suspect the extractor fan above the bath is not used as often as it should be, and if the doors to both the bedrooms and the bathroom are left open after bathing etc, moist air will enter the former.  The vapour pressure in these rooms will thus increase, and permeation via the gable walls will occur; thus moisture-laden air will enter the flues themselves.  The low temperatures and lack of ventilation in these sealed structures will then allow condensation to occur.

As this phenomenon will have been occurring for a significant period of time - certainly since the fire openings were sealed - it will have allowed moisture to soak into the internal brickwork of the flue, whence it will have travelled by capillary action onto the internal surfaces of the bedroom walls.  As this condensate will be contaminated by the salts and tars of fossil fuel burning, its presence will have discoloured the surface finishes.  In addition, the salts are hygroscopic and will readily absorb moisture from the atmosphere, thus they add to the overall problem. 

This latter feature, hygroscopic contamination, will affect the way the problem is dealt with; because although introducing ventilation into the flues should address the condensation, the contaminated plaster will remain, and will always absorb moisture from the atmosphere.  This is a well-known problem, and is often referred to as ‘salt damp’.                                          

There are two ways to deal with this: the contaminated plaster can be removed and replaced with a 3:1 mixture of sharp, well-graded sand to cement, which can then be skimmed with a multi-coat plaster; alternatively, a dry-lined, insulated wall can be erected against the damaged walls. This latter suggestion would also contain a vapour barrier to guard against interstitial condensation occurring within the structure itself. 

The former will cure the problem of salt contamination but will not improve the wall’s ability to deal with condensation; in fact it may make this problem worse. 

The second solution, the insulated stud wall, will deal with both problems, and I would recommend this course of action. 

Although the principle is simple, I have enclosed a small sketch, which may be helpful to you.

In addition to the above, I would recommend you move the extractor fan in the bathroom to a new location, away from the shower position.  At the same time, a more efficient model should be installed, and you may wish to incorporate an over-ride timer switch with it.  The Ventaxia LoWatt WCBT would be an appropriate option for this room.

I trust the above is satisfactory for your purposes but if you require further clarification please do not hesitate to contact me.

Surveyor                                   Patrick F Doyle CSRT M. Inst. R.T.S.

Qualifications                           Certificated Surveyor in Remedial Treatments issued by the BWPDA.

Date of Report                         December 2008