A survey report undertaken on behalf of the prospective purchaser has highlighted symptoms of moisture. Following an introduction from the vendor’s surveyor, https://www.desbruslais.co.uk, 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 morning of Thursday 2nd February. The following report documents the observation and symptoms noted speculate 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.
1. The observations, symptoms and probable causes
This property presents itself very honestly, unlike so many others it has not been freshly painted prior to being offered for sale and therefore allowed for gaining a good insight into the causes of moisture readings previously taken.
It is not surprising for moisture to be present solely due to the time of year. 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 waste 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.
a. Kitchen extractor, hob, and oven.
The oven and hob are fortunately electric and therefore not as large a source of moisture as natural gas, which in addition to the moisture produced from the cooking process itself also creates large amounts of airborne moisture during combustion. However, the kitchen extractor, located in the canopy over the hob, is not connected to the outside of the property and is instead only recirculating air from the kitchen rather than extracting it. Connecting the extractor to the outside should be addressed as a priority, it’s exit location in relation to the boiler flue outlet should be considered and a louvred baffle should be used to reduce air ingress when not in use.
b. Kitchen door
There is no door on the kitchen, moisture generated here will migrate unimpeded throughout the apartment and be quickly pulled towards any cold surfaces. This is most likely to be towards bedroom one, to the cold north aspect at the rear of the property, which also has greater external wall area, thinner walls and a flat roof that is most likely uninsulated. 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.
c. Kitchen aperture to lounge
The wall between the kitchen and lounge has been partially removed and a large access hatch created to facilitate dining. 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 exiting via the high-level wall vent. Inevitably some moisture will enter the lounge from the kitchen. The lounge is located to the warm south aspect at the front of the property.
e. Kitchen wall vent
This un-louvred vent will allow warm moisture ladened air to exit the kitchen, however, it will not do so at an appropriate rate when peaks of moisture are produced whilst cooking. When not required the vent cannot be closed, it is, therefore, a problematic, unwanted and an uncontrolled source of cold air ingress/egress. The fitting of this type of uncontrolled air vent was very common during the early conversions of these Victorian properties into bedsits and flats. The vents may also indicate that gas fires were originally fitted throughout the property prior to central heating being installed. Now, however, they supply inappropriate uncontrolled ventilation, making the property inefficient to heat. There are many more of these vents in the property, they should be either closed off or removed altogether.
Note: the vents used throughout the property are of a style and period that may contain asbestos. They currently presently no hazard in-situ but if removed appropriate precautions should be taken.
f. Living room, gas fire, and flue
There is a coal effect gas-powered fire, it is unknown how often it is currently or previously been used. The combustion of natural gas creates large amounts of airborne moisture which will then seek out cold surfaces on which to condense. The chimney flue is also likely to be contributing to uncontrolled air ingress/egress; the use of this appliance should be kept to a minimum or avoided altogether. The gas supply should be disconnected and the flue closed off.
g. Living room, the base of the chimney
At the base of the chimney breast, to the right of the fire, symptoms of moisture are present. The chimney has large thermal mass and will be at it’s coldest at the base where it meets with the mass of the ground. This flank of the chimney may also be cooled by cold air ingress coming down the chimney.
The fire surround is constructed from vapour ‘closed’ materials and the fitted shelving to the alcoves each side also prevent vapour from being distributed along the base of the wall. The flank of the chimney presents itself to the room as a cold spot of high thermal mass. Slow to be warmed it continues attracting warm moist air towards it, moisture vapour will begin to saturate the modern gypsum plaster and it is unable to defuse moisture to the substrate behind. The walls have most probably been cement rendered along with the concrete floors, a hidden history of unsuccessful damp remediation.
h. Living room, windows
The sash windows to the sides of the bay appear inoperable and are becoming painted shut. The sash window at the centre of the bay is operable but currently difficult to access due to furniture. Its use is probably less desired at this time of year, however, the window is not fitted with sash locks, these would allow the window to be left slightly open without compromising security and if used in combination with a window at the rear of the property create cross-ventilation during clement weather. These sash windows would benefit from polycarbonate secondary glazing, by covering the entire window they prevent unwanted air ingress/egress, bringing down heating bills and improving thermal comfort. Secured with a magnetic tape the panel is demountable and can be removed and stored outside of the heating season. Polycarbonate could also be fitted to the sash windows in bedroom one and two.
i. Corridor, cold corner
In the corridor adjacent to bedroom two, the exterior corner shows symptoms of moisture ‘dropping out’. Alternating between wet and dry, the metal corner bead embedded within the modern gypsum plaster is beginning to rust. At this juncture in the apartment, the slow passage of cold air will be continually drawn through no matter what the prevailing wind direction, either coming from bedroom one to the lounge or from the back door to the lobby door or vice versa. The slow steady passage of 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.
j. Internal doors
Some of the doors have either warped a little overtime or were never fitted to the door jambs as good as they could have been. Door latches are beginning to fail with age and no longer hold the doors closed, other locks and latches are likely to follow.
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. 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 functioning doors will prevent the internal convection of moisture from the source to the symptom.
k. Bedroom 2
The grill on the window would allow it to be left open securely or could make the window inaccessible and unlikely to be operated. Sash locks should be fitted and used. There is a vent at the base of the chimney, this should be closed off to prevent unwanted air ingress/egress. Again polycarbonate secondary glazing would help to keep this room warm whilst bringing down heating bills and improving thermal comfort.
The bathroom has an operable window; there is a low powered extractor operated in conjunction with the light switch. The strategy for operating the bathroom window or extractor vent by the occupants is unknown, it was switched off at the isolator switch. Extractors operating in conjunction with the light switch often get isolated due to the unwanted noise from overrunning when the bathroom is used at night and then not switched back on. When taking a shower during daylight, moisture will not be extracted unless the light is switched on. Bathroom extractors are best operated manually from a separate pull cord. Manually operating the extractor is preferable to having them connected to the light, timer or humidity control. Daylight is also visible through the extractor, a louvred baffle should be fitted to the outside to prevent unwanted uncontrolled air ingress/egress. The extractor unit could be upgraded to a single room heat recovery unit.
m. Bedroom 1
At the colder north side of the property, the main bedroom extends out from the rear of the building. In parts, the room has three external walls and a small section of the ceiling is underneath a flat roof. As well as a large exterior wall area increasing heat loss it may be reasonable to assume that the level of insulation in the flat roof could be improved. At some point in the future, this flat roof may require attention and the opportunity to strip back and improve insulation should be taken. Insulation could also be improved from the underside.
Symptoms were noted in both far corners, each side of the french windows. To the left, an unnecessary air vent is making the corner cold and consequently below the paint is being lifted by the moisture that is condensing. To the right, the top corner has a swath of light staining illustrating the convection current in this cold corner. The vent should be closed off, efforts should be made to prevent moisture ladened air convecting to these cold corners. If decorative repairs are made there are a number of approaches that would make the surfaces less cold and more robust at buffering moisture. These could simply include replacing the plaster finish or greater benefit could be achieved by adding wall insulation. Also noted, security shutters may be inhibiting the appropriate use of the windows and exterior doors and a further unnecessary vent in the chimney breast is causing uncontrolled air ingress/egress and should be closed off. Again polycarbonate secondary glazing would help to keep this room warm whilst bringing down heating bills and improving thermal comfort. In combination with other draught-proofing strategies, installing polycarbonate to the sash windows in bedroom one and two should have priority over those in the lounge. Being in close proximity to the kitchen, access to operating the lounge windows is more likely to be required and with good airtightness achieved at the rear of the property the slow steady passage of cold air will be greatly reduced if air can’t get in it can’t get out.
There was no evidence of drying clothes on radiators however a folded airer was noted in the under stairs cupboard and no external clothesline was evident. Allowing laundry to equalise moisture content with the room is much preferred to forcing moisture out with the use of a radiator. A tumble dryer may be appropriate or a single room heat recovery extractor could allow the bathroom to serve as a drying room. Ideally, laundry should be hung outside on a clothesline however other strategies can be put in place that avoids force drying on a radiator.
2. Overview of moisture management.
This ground floor garden 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 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, 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 then a tumble dryer should be used.
Ventilation should be controllable and the occupants should be mindful of how and when to control it. During the 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 but 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, roofs, walls and floors. The small section of the roof to the rear of bedroom one is likely to be poorly insulated. At some point in the future, this flat roof may require attention and this would be an opportunity to make improvements to the insulation.
In colder areas such as the rear of bedroom one, 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 hemp plaster. Care must be taken not to apply synthetic vapour closed paints to these materials, breathable and hygroscopic paints should be used such as Auro 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 London 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
3. The potential solutions to mitigate the symptoms
- Connecting the kitchen extractor to the outside.
- Observing cooking, showering laundry routines, make a connection with operating windows and doors, to purge peaks of moisture and slow convection currents around the home.
- Heating can be programmed to warm the interior fabric before showering in the morning and again prior to cooking on an evening.
- Plugging the inappropriate vents to reduce unwanted air ingress/egress.
- The existing bathroom extractors could be replaced with a more powerful extractor. This should be manually operated and fitted with a baffle.
- Renewing internal door latches, refitting door jambs and supplementing with a vinyl draught-proofing strip. Draught proofing the lobby door and back door.
- Adding polycarbonate secondary glazing to sash windows firstly in bedroom one and bedroom two and if appropriate the lounge.
- Decorative repairs should be undertaken with lime plaster and breathable hygroscopic finishes and paints.
- When redecorating avoid synthetic paints and use lime plaster.
- If symptoms persist cut away and repair with a natural hygrothermal insulating layer.
- Improved roof insulation to bedroom one.
- Add hygrothermal internal wall insulation to bedroom one.
The damp proofing works proposed by others is costly, disruptive and unnecessary, and has in fact already been done without benefit to the property.
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.