Previous surveys were undertaken by preservation and treatment companies, (April 2013 and June 2016), have diagnosed rising damp and have recommended a chemical damp proof course and cement render, and yet the Royal Institute of Chartered Surveyors describe ‘rising damp’ as a myth. Following an introduction from Building Managment Company, Simon James Lewis, Neighbourhood Construction CIC has been invited to ascertain the probable causes of a number of moisture-related symptoms being experienced at the property.
A site visit was undertaken on the afternoon of Tuesday 11th July. The following report documents observation and symptoms noted, speculates on the probable causes and makes recommendations for potential solutions. A number of short, medium and long-term interventions should be considered.
This report provides the following:
- The observations, symptoms and probable causes.
- Overview of moisture management.
- The potential solutions to mitigate the symptoms.
The observations, symptoms and probable causes
The use of a moisture meter is not a reliable method for determining the presence of moisture or the source of that moisture. Protimeter moisture meters measure the electrical resistance between two pins. When used for a property survey; interpretation of the readings can be misleading due to electrical conduction caused by other influences. Lead paint on timbers, iron content from furnace waist added to mortars and plasters, as well as the presence of water vapour at the surface, simply caused by condensation. Protimeter moisture meters are very good at determining the moisture content of timber when seasoning either for construction lumber or firewood.
The front courtyard acts as a cold sink, collecting and trapping the cold air. Cold air trapped during the night will be drawn into the property throughout the day.
Front entrance door
The draught-proofing around the front door is deteriorating and liable to be ineffective at preventing air ingress. Because the cold sink is outside the door, it has more than just the usual challenge of cross-ventilation to deal with, cold air is being pushed into the property.
Adjacent to the door is a service void, boxed in but connected to the exterior to allow pipes and cables to enter from the outside utility cupboard. This service void is draughty and cold and most likely to also bring cold air into the subfloor of the entrance hallway above. Within the basement apartment, the cold surface of the boxed service void will attract warm moisture-ladened air and has previously caused paint to peel away.
Living room, window
The sash windows would appear not to be being operated. For mid-summer this window should be wide open and in conjunction with an aperture at the rear of the property, good cross ventilation could be achieved. The side sashes are no longer operable and probably not required if the central sash is operable and maintained. The top and bottom sashes of the central window are screwed together using a sash window lock and the key for which was not evident. The central sash window has also previously been fitted with a sash stops. This device enables the windows to be left open without compromising security, however, the sash stops are missing and originally fitted in the wrong position. It is not possible to leave these windows securely open. The absent key, missing stops and inappropriate installation may indicate a long history of not being operable. Replacement keys for security locks are available from good hardware stores.
Although otherwise in good working order the window is also draughty and would benefit from polycarbonate secondary glazing. By covering the entire window polycarbonate brings down heating bills, improving thermal comfort and prevents unwanted air ingress/egress, that creates cold surfaces and moisture drop-out. Secured with a magnetic tape panels are demountable and can be removed and stored outside of the heating season. Polycarbonate could also be fitted to the single glazed window in the back room.
Adjacent to front window
To the right-hand side of the lounge window aperture, behind the shutter, the emulsion paint is lifting from the plaster. The plaster is a modern gypsum plaster, unable to buffer peaks in moisture, it is also thick and when penetrated to a depth of 12mm no cement was detected. Plaster in this location would have been applied thickly due to the uneven rubble stone wall. This location is cold, caused not only by the proximity of the window and the passing of cold air but also the high thermal mass of this thick exterior wall and the abutting wall in the courtyard. Isolated within the frame of the window shutter the plaster could be replaced with a moisture buffering insulating plaster, efforts should also be made to reduce the passing of air and reduce the sources of moisture.
Living room, base of chimney
At the base of the chimney breast, to the left of the fire, symptoms of moisture dropping out are present and white salts have been drawn to the surface as moisture has evaporated away. The register plate above the hearth is not airtight, detritus can be seen coming through from the void above. The chimney breast has large thermal mass and will be coldest at its base where the flanks meet with the high thermal mass of the ground. This flank of the chimney is being cooled by the slow steady passage of cold air ingress falling down the chimney. This cooling effect is constant and when confronted with a peak of warm moist air generated from sporadic periods of household activities; cooking, showering, etc, the cold surface attract the moisture laden warm air. Due to the high thermal mass, the chimney flank is never warmed and therefore continues to attach warm moist air.This phenomenon is common with chimney flanks.
Kitchen aperture to lounge
The wall separating the kitchen from the lounge has been partially removed to create a large aperture. This provides the landlocked kitchen at the centre of the property without a window, emancipating the kitchen and providing a vista. Moisture vapour generated in the kitchen can enter directly into the lounge without passing through the corridor. Fortunately, this aperture is at a low level, the ceilings are not interconnected, therefore moderate amounts of moisture vapour will ‘pond’ at the kitchen ceiling before hopefully being extracted. Inevitably excessive moisture will enter the lounge from the kitchen.
Kitchen extractor, hob, and oven.
The oven is fortunately electric and therefore not as large a source of moisture as natural gas. The hob is gas, which in addition to the moisture produced from the cooking process itself also creates large amounts of airborne moisture during combustion. The kitchen extractor, located in the canopy over the hob, is connected to a flexible hose which disappears into the ceiling void. It is impossible to determine if it is appropriately connected to the outside of the property. The flexible pipe would not be an appropriate material to take it the long distance to the rear of the property, a rigid pipe should be in place. It is not uncommon to find them terminating within a floor void due to the unforeseen complexity of navigating around floor joist to get to the outside. There are some unusual pipes exiting the property at the rear but they are un-louvred and therefore, if they are connected, the extractor could be a source of unwanted air ingress when not in use leading to cold spots.
Whether the extractor is connected to the outside should be addressed as a priority. Further investigation is required to ascertain the exit route of the ventilation pipe. In the authors opinion this pipe may well be connected to the rear chimney, from its location it would be easy to run it sideways and into the rear chimney, where it would be unable to push air up the chimney and instead it would instead enter bedroom 1 through the fireplace and could be an explanation for the moisture problems there.
There is no door on the kitchen, moisture generated here will migrate unimpeded throughout the apartment and be quickly pulled towards any one of the many cold surfaces throughout this basement apartment. The door to the kitchen should be reinstated however it is appreciated this may not be desirable, if not then every effort should be made to improve the functionality of the other doors and ensure they are used when cooking.
Corridor, cold spots
In the corridor between the kitchen and the bathroom, there are symptoms of moisture on the thermal mass of the bathroom wall. At this juncture in the apartment, the slow passage of cold air will be continually be drawn through, either coming from the rear to the front vice versa. This cold air always passes around this corner at a low level making this surface a corner cold. When a peak of moisture occurs in either the kitchen or the bathroom this cold corner will attract moisture vapour and cause it to ‘drop-out’ as condensation. This symptom is also noted on the outside of the wall to bedroom 1 where the ill-fitting door to the back room is directing a cold draught towards it.
The functionality of internal doors could be improved, they may not have been fitted to the door jambs as good as they could have been. Door latches need to function well to hold the doors closed, improved functionality is likely to improve the likelihood of being operated. Closing internal door dramatically slows the passage of cold air through the building, therefore reducing the risk of cold spots. Latches should be renewed and the door jambs refitted for a good seal where necessary. Whilst door jambs are removed, a vinyl draught strip can be added for greater effect. This will improve thermal comfort, reduce energy bills and aid with moisture management. Operating operable doors will control cross ventilation and prevent the internal convection of moisture from source to the symptom.
The bathroom has no window; there is a low powered extractor which operates in conjunction with the bathroom light and can be isolated from the light using a switch outside of the room. The strategy for isolating the extractor vent is unknown. Extractors operating in conjunction with the lights are often isolated when noise is unwanted, perhaps while taking a relaxing bath, and then not switched back on. Manually operating the extractor, in conjunction with mindful occupant behaviour, is preferable to having them connected to the light, timer or humidity control.
As with the kitchen, further investigation is required to ascertain the exit route of the ventilation pipe, which again would be complicated via the ceiling void; why was it not simply boxed in through the corridor? Also, the length of this pipe run would increase friction reducing the effectiveness of the low-powered extractor pushing from the bathroom. A more appropriate installation would have the extractor fitted where it exits the property pulling air from the bathroom. A newly installed rigid pipe installed through the corridor would also reduce friction. A louvred baffle should be fitted to the outside to prevent unwanted uncontrolled air ingress/egress. Various modern and intelligent extractor solutions could be considered once issues with the exit pipe are concluded.
As with many ground floor converted apartments, the bedroom has been fitted with French windows – a pair of glassed doors. This allows access to the rear courtyard via both back rooms so they may both be used as bedrooms. The functionality of a door, rather than a window, inevitable compromises the ventilation strategy. The doors are double glazed and of good quality, however, the fitting could be improved to prevent unwanted air ingress especially as they connect to the cold sink of the courtyard.
Symptoms of moisture are also present, in the corner, adjacent to the fireplace and adjoining the wall to the kitchen. The fireplace and chimney are draughty, cold air entering the room via the fireplace will create cold spots encouraging condensation. Furthermore, if it is found that the kitchen extractor has also been connected to the chimney moisture-ladened air may be finding its way into the bedroom.
Bedroom 2 – back room
The back door to the courtyard is draughty and is likely to be the greatest cause of unwanted air ingress entering the apartment. The connecting door to the corridor is also ill-fitting and has clearly produced a cold spot which has attracted moisture to drop-out. The window in the back room, although single glazed is reasonable airtight there is little evidence it is being used.
There was no evidence of drying clothes on radiators however no external clothes line was evident. It is understood that a laundry drying facility is available in a communal part of the building.
The apartments radiators are not fitted with Thermostatic Radiator Valves. TRV’s would allow each radiator to be individually controlled for more efficient use and better temperature uniformity. With appropriate control, heating can be used to warm rooms prior to the activities that produce moisture.
As with the front courtyard, the rear courtyard is a cold sink, trapping cold air before it enters the apartment. It was noted that there are unusual, un-louvred, pipes at ceiling height exiting at the rear of the building. The purpose is unknown and should be investigated.
Overview of moisture management.
This basement flat is unable to mitigate the moisture being generated within and the symptoms noted can all be attributed to condensation caused by the normal everyday activities of the occupants, cooking, showering, laundry etc. It may be possible to reduce the amount of moisture being produced, how it moves around the property and lessen the effect that moisture vapour has when it occurs. Simple no-cost and low-cost intervention should be considered before more extensive alterations to the fabric.
Observation alone can inform how we approach cooking showering and laundry as well as knowing when and how to operate our heating, windows, and doors. A simple audit of these activities can often be enough to note how much moisture is produced, how it can be reduced and identify cues which require us to respond with appropriate actions to lessen the effects. We can then choose to put in place appropriate and intuitive strategies.
When using the kettle, observe how much excess water has been boiled and how much less moisture is produced when measuring and boiling just what we need. When cooking, observe how much moisture is being produced, the amount of water boiled off from each pan as well as from the combustion of gas. By using the hob less, the oven more or simply cooking a little slower we can kerb the rapid generation of moisture that then disperses around the home. The aroma of cooking migrating around the house should be a cue for door closing.
How often are showers taken and how long do they last, we often discover they are longer than we thought and as occupancy grows this can begin to add up. Shorter showers produce less moisture, being mindful of opening the window and closing the door after showering can make a significant difference, more so than being reliant on an extractor.
The heating can be programmed to warm the interior fabric before showering in the morning and again prior to cooking on an evening. When the weather is clement plan to get laundry outside, if dried inside it should be allowed to dry slowly on a clothes horse, equalising its moisture content with the room. Forcing moisture out using a radiator should be avoided, if this is difficult to schedule, a tumble dryer should be used.
Ventilation should be controllable and the occupants should be mindful of how and when to control it. During summer months, it is good practice to open windows and allow cross ventilation. During spring and autumn, diurnal temperature fluctuation requires good practice to open windows during warm days but ensure closed on cold nights. Operating windows and doors can facilitate a beneficial through-draught or prevent the convection of warm air.
Observing our homes and becoming familiar with how they work leads us to make informed choices as to how best operate them and with time becomes intuitive. With a strategy in place, a planned response, it becomes easier to implement our intentions.
As with so much of the UK housing stock this property is draughty, however, simple improvements can be made at low cost. The slow but steady passage of cold air through the property is reducing the surface temperature at specific parts of the interior. Meanwhile, when moisture vapour is produced it migrates unimpeded around the home, carried by internal convection currents.
The warm moist air is pulled toward cold surfaces to replace the air that falls away as it is cooled and becomes heavier. As the air is cooled its capacity to hold onto moisture vapour is reduced and vapour is deposited as condensation. Moisture is conveyed from source to symptom.
The apartment has many unnecessary and inappropriately installed vents, these should be closed off. This could be simply achieved by plugging with cotton wool or tissue paper, then the change can be observed before considering more long-term adaptations. Perhaps expanding foam filler, covering with paper, paste and emulsion paint, or removing the vents altogether.
By reducing uncontrolled air ingress/egress the apartment will be easier and more affordable to heat and reduce the risk of cold surfaces. By closing internal doors the convection of warm moist air to these cold surfaces is slowed and by improving the functionality of the window they can be better operated to control air movement.
Draught-proofing internal doors, as well as the exterior envelope, will further reduce the unwanted steady supply of cold air as well as further limiting the convection of warm moist air. It will also make it more important for the occupants to implement controlled ventilation, functional windows and doors are required. Installing sash locks would make it possible to leave the windows locked open for ventilation and fitting polycarbonate secondary glazing would stop cold air ingress when the weather is cold. Replacing door latches, refitting door jambs and adding a vinyl draught strip will not only aid with managing moisture, they will also improve thermal comfort and reduce energy bills.
Choosing to undertake these simple maintenance and improvements restores functionality to the home, it is also ‘buying in’ and will inform how and when to operate them for the benefit of the property and the comfort of the occupants.
Improvements to the thermal envelope do not need to be extensive to make a difference. Once simple improvements have been made to windows and doors, vents and voids, we then might consider the fabric of the property. At some point in the future, a room by room refurbishment may facilitate more extensive works.
In colder areas such as the rear bedrooms, this could be applied extensively by removing all of the existing plaster and replacing or by simply removing and applying to the area that has suffered decorative deterioration. Care must be taken in the specification and installation of naturally hygroscopic materials to ensure they can sufficiently diffuse moisture vapour.
Any future alterations, maintenance or simply redecoration will provide opportunities to improve insulation and increase the moisture buffering capacity by using breathable and hygroscopic materials. Many natural materials can help this process including Pavadentro wood fibre insulation, insulating plasters such Diathonite cork plaster and Adaptavate Breathaplaster containing hemp. Care must be taken not to apply synthetic vapour closed paints to these materials, breathable and hygroscopic paints should be used such as Auro or Earthborn and in conjunction with lining paper.
The author has specified and overseen the successful delivery of many case studies and installations of hygrothermal interiors using a range of materials. Good results have been achieved; resolving both energy and moisture related issues. The hygrothermal model differs from the existing approach to damp remediation being applied by the vernacular renovation, maintenance, and improvement sector. With this in mind, care must be taken to ensure contractors understand the requirements when commissioning these works.
Neighbourhood Construction teaches the use of bio-aggregates such as hemp-lime in construction and retrofitting. We are currently participating in academic research to further the use of bio-aggregates for moisture buffering in renovation and refurbishment.
A detailed description of how to undertake these more extensive interventions is beyond the scope of this report. We would be happy to provide further advice if this option is considered in the future. We can also provide introductions to contractors from Bristol who have participated in our training workshops.
Assessing risks in insulating retrofits using Hygrothermal software tools. Heat and moisture transport in internally insulated stone walls.
Joseph Little, Calina Ferraro & Beñat Arregi
The potential solutions to mitigate the symptoms
- Investigate kitchen and bathroom extractors – connecting route to the outside.
- Observing cooking, showering, routines, make a connection with operating windows and doors, to purge peaks of moisture and slow convection currents around the home.
- Starting with the large holes, use an expanding foam applicator gun to reduce unwanted air ingress/egress.
- Heating can be programmed to warm the interior fabric before showering in the morning and again prior to cooking on an evening.
- The existing bathroom extractors could be replaced with a more powerful extractor. This should be fitted with a baffle, manually operated or an intelligent system.
- Improve functionality of internal doors, refitting door jambs and supplementing with a vinyl draught proofing strip. Draught proofing the front door, back door and french windows.
- Adding polycarbonate secondary glazing to sash windows in the lounge and single glazed window in the back room.
- Replace gas hob with electric induction.
- When redecorating avoid synthetic paints and gypsum plaster.
- Decorative repairs should be undertaken with lime plaster and breathable, hygroscopic finishes.
- If symptoms persist cut away and repair with a natural hygrothermal insulating layer.
- Add hygrothermal internal wall insulation to lounge, bedroom one and back room.
The damp proofing works proposed by others is costly, disruptive and unnecessary, and has most probably already been applied during the original conversion, without benefit to the property. The landlocked kitchen and bathroom, with no window and questionable extraction is a design compromise from initial conversion. A modern intelligent extraction system, such as MVHR may be prudent.
The property is draughty, this, in turn, creates cold spots that attract moisture vapour to condense. Simple low-cost, knowledge-led improvements could be made. The thermal envelope is closed; a history of damp remediation, renovation and refurbishment have introduced modern, synthetic, non-hygroscopic materials which have no capacity to buffer peaks of moisture.
With improvements in thermal efficiency the property would become easier and cost less to heat, this would then reduce the risk of moisture-related problems. When undertaking further refurbishment works, thought should be given to opportunities that can better manage both energy and moisture within the property, energy, and moisture are directly related.