A beautiful 1850’s Semi – a history of chimney damp spots

Saturday 17th February 2018

Since purchase in 2016, various damp problems have manifested in numerous locations, several of which focus upon the centrally located chimney stack. Despite multiple attempts to resolve the problem; chimney and roof repairs, clearing and repairs to gutters, the symptoms have persisted.

Following a recommendation and introduction from London based https://www.eco-renovation.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 afternoon of Saturday 17th February 2018. 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:

  1. The observations, symptoms and probable causes.
  2. Overview of moisture management.
  3. The potential solutions to mitigate the symptoms.


1. The observations, symptoms and probable causes

This Beautiful 1850’s Victorian Semi has stood well against the test of time. However, doors and windows have become dysfunctional, the building design has been altered to the detriment of the internal weather and the stylish modernisation of both the kitchen and bathroom has failed to include appropriate moisture extraction. Meanwhile hidden under the surface is a Smörgåsbord of ‘damp remediation’; a history of gas fires as well as unsuccessful repeated attempts to prevent water ingress. There are also indications that some of the historic plasters may have been inappropriate, to begin with.

Simple care and repair, a knowledge-led approach to redecorating and appropriate moisture management can sensitively and incrementally tip the balance from cold and damp to warm and dry.



Entered from the hallway above the basement is divided into two sections. The main area underneath the kitchen has been tanked and fitted out as a dwelling room and has access out into a sunken courtyard via glazed french doors. Behind this room, underneath the entrance lobby is what would appear to be a cold storage larder. It is now used as a store and has been punctured by the installation of utilities.


a. A draughty door to the basement

The door to the basement, under the stairs in the lobby, is draughty. This door should be draught-proofed, with a vinyl seal and a brush fitted to the bottom.


b. Draughty basement service voids

The gradual progressive installation of services has created uncontrolled air-ingress/egress into what has now become part of the thermal envelope. These holes should be closed off, there are a variety of options but a recommended simple, low-cost solution is an expanding foam applicator gun.


Saturday 17th February 2018

Saturday 17th February 2018

Saturday 17th February 2018

Saturday 17th February 2018

Saturday 17th February 2018

Voids created by the installation of services.


c. Tanking – a history of damp remediation

To create an additional dwelling room the walls within the main section have had a tanking membrane installed. If air-tightness is improved and moisture levels reduced, this may be considered of no harm, however in the long term to avoid moisture building up behind the membrane, this ideally would be removed and replaced with a breathable layer. A further benefit could be had if this was hygroscopic and insulating such as bio-aggregate: hemp and lime 1:1.


Saturday 17th February 2018

A tanking membrane in the main basement room is visible from the rear section under the lobby.


d. Symptom – moisture condensing on cold surfaces

Cold air sweeping through the draughty door frame (between the two rooms) is vortexing to concentrate a cold spot on the adjacent wall, leading to moisture dropping out and peeling paint. This is exacerbated by the lack of architrave; an architectural detail designed to break-up the air current and prevent such degradation. This door should be draught-proofed, an architrave and skirting board fitted, the Smörgåsbord of vinyl paint, gypsum, cement and tanking removed and an appropriate plaster applied.

High moisture levels are also indicated by the rusting of the nearby cold metal socket.


Saturday 17th February 2018

Cold spot caused by cold air-ingress through the draughty door leading to moisture dropping out and peeling paint.


Saturday 17th February 2018

Symptom – high moisture levels indicated by condensing on and rusting cold metal socket.


e. French doors – moisture condensing on cold surfaces

Adjacent to the French doors, the cold air-ingress in this top corner creates a cold spot, attracting moisture and causing water vapour to condense or drop-out on the surface. With the doors opening onto the cold frost pocket of the sunken courtyard, it would benefit from being replaced with high-performance integral doors and frame. In the meantime reducing the source of moisture and adding a vinyl draught seal should suffice. A window lining could also be considered.

Saturday 17th February 2018

Saturday 17th February 2018

Symptoms on the wall adjacent to cold draught. ‘Blimey… what a draught!’


f. Laundry drying

As a convenient heated utility space, the basement room is at times used for drying clothes. With large air-ingress/egress creating cold surfaces and a radiator creating warm convection currents it is not advisable to use this as a drying space. With improvements made first to air ingress/egress preventing cold spots, an SR-MVHR (Single room, mechanical ventilation heat recovery) may mitigate occasional indoor laundry drying.


Outside basement

g. Timber decay

The addition of a store, constructed from timber in the vaulted undercroft in contact with the cold thermal mass of the ground and walls in this frost pocket, has inevitably caused degradation. Keeping the area clean of leaf litter and other detritus will help, as well as adding ventilation holes top and bottom will allow air to circulate. If rebuilding, the design could consider thermally isolating the timber from the surrounding mass and raising the timber wall up off of the ground onto a plinth. In the short-term, this small area of decay should have a fungicide applied such as chlorine bleach or borax and then monitored to ensure it dies back and does not spread further.


Saturday 17th February 2018

Saturday 17th February 2018

Timber decay in outside store in the sunken courtyard


Dining room

h. Inappropriately installed air-vent

Despite only having one external wall, this room is cold. Uncontrolled air-ingress is falling down the chimney and into the room via this inappropriate vent. This vent should be closed-off as it serves no purpose, it should ideally be removed and replastered with the appropriate materials. Whilst redecorating consider the complete removal of what is likely to be a build up of multiple inappropriate materials. A feature fireplace could be installed and the chimney flue closed with sheep’s wool. For now, tissue paper/foam filler and perhaps papered over will suffice. There may also be air ingress coming up through the floorboards and under the skirting-boards, this should be reduced using something a simple as decorators caulk and a dispensing gun.

Saturday 17th February 2018

Chimney – inappropriate air-vent


i. Cement render

This house has a history of damp remediation. The outside wall has been cement rendered internally, with the possibility that the return to the alcove has been rendered as well. This indicated a vernacular approach to tackling symptom without addressing the root cause. The causes that lead to this remediation may have been the introduction of gas-lamps then gas-fires into the room and cookers and twin-tub indoor laundry. A combination of post-war building materials attempting to address the post-war change of lifestyle within a heritage property.

It would be appropriate to remove the cement render and apply a vapour permeable and hygroscopic lime plaster, preferably a moderately insulating hemp plaster. Ideally and depth permitting a Bio-aggregate: hemp lime wall insulation could be cast to the existing masonry and finished with Baumit RK38 – base coat and Kalkin Glätt – topcoat lime plaster – 1400 grade lining paper and clay paint.

Saturday 17th February 2018

Cement rendered – a history of failed damp remediation

Saturday 17th February 2018

Black mould – moisture condensing on cold vapour impermeable surface, the cement may also be applied to the return

j. Large inoperable window

The beautiful feature window is large, cold and painted shut. Servicing the window will make it operable once again to facilitate a ventilation strategy; sash locks should be fitted so it can be securely left open. The window would also benefit from polycarbonate secondary glazing, both cost-effectively draught-proofing as well as improving thermal insulation. This may be best applied in two sections as storage of such a large panel can be challenging, being able to remove and replace a smaller top section during spring and autumn may also be an advantage. This applies to many other windows in the property and could be looked at in more detail as part of further considerations.

Saturday 17th February 2018

Inoperable windows – painted shut


k. Historic smörgåsbord

On the dividing wall between the dining room and the lounge (in the dining room, behind the lounge fireplace) is a moisture related symptom. Peeling back the layers of remediation, the plaster that corresponds to the outline of the symptom is historic but may or may not be part of the original construction. It may be part of a historic repair using an inappropriate mix that worked fine until other influences were introduced.  Digging into the plaster it felt very hard, perhaps inappropriate aggregate or maybe gauged with excessive alabaster or gypsum. Similar symptoms are noted in other rooms adjoining this chimney. Perhaps the inappropriate plaster only became a problem once the fireplaces became disused, this chimney void has then become cold leaving essentially just a single skin brick wall (or possibly less) between the cold outside air and the inside. These symptoms account for the repeated unsuccessful attempts to address water ingress.

While redecorating, stripping off the paper will reveal these inappropriate repairs. The plaster patches can be removed and replace with a calcitic lime plaster (Baumit RK38 – base coat and Kalkin Glätt – topcoat lime plaster – 1400 grade lining paper and clay paint).

Saturday 17th February 2018

Back of sitting room fireplace – patches of moisture closed original plaster


Sitting room

l. Inoperable windows

Both windows in the sitting room have become inoperable, as with the dining room, restoring functionality, as well as the air-tightness and insulation with demountable polycarbonate secondary glazing will reduce the internal convection current currently pulling warm moisture-laden air into the room from other areas of the house.

Saturday 17th February 2018

Window latch – indications of not being operated.


Saturday 17th February 2018

Inoperable window painted shut.


m. Sitting room fireplace

The fireplace is not original and has likely been through many iterations to reach the current version. This early Victorian property is more similar to Georgian than the later Victorian, mass production period. The original fireplace may have had an open grate, used for burning wood and was probably soon modernised with a Victorian fireplace, for the more efficient combustion of coal and with closable flue access to prevent the draught when not in use. Of this, we can not be sure but it could be an explanation for an early change in materials and subsequently symptoms; stripping back the layers may reveal this history.

Adjacent to the fireplace is a gas supply pipe, at some point in the 50’s and 60’s ‘the gas man cometh’ (again) and the draughty installation by the heating engineer still remains. Perhaps the replacement of the ‘dirty coal’ fire was due to early adoption of the newly nationalised gas industry in 1948, perhaps encouraged by the advent of the clean air act of 1957 or the rising price of coal in the 1960s and the discovery of North Sea gas in 1965. For a heritage property, this is all part of its story and has just as much value as the original features.

It is possible that the fireplace had a back boiler, either as part of an earlier solid fuel stove or as incorporated into the gas fire that heated water in a hot water cylinder upstairs and this could further explain the symptoms. Further investigation would reveal no doubt that this chimney has seen many fires.

The current fireplace is a modern replica and may have been installed with a coal-effect gas fire in the ’80s, ’90s. It has now had the gas burner removed and is again in use as a ‘real fire’. This should be approached with caution as although designed to contain a gas flame, the ‘real fire’ has slowly made a comeback. Is the existing hearth suitable for solid fuel and is an appropriate flue liner in place? This fire should not be used, combustion should take place in a modern stove fitted with the appropriate liner and fitted by a registered HETAS installer. Stove recommended.

Who knows what histories will be uncovered by re-decorating this fireplace. Inappropriate materials can be removed and replaced. However, meanwhile the hole to the subfloor would benefit from closing off, either pragmatically with a little expanding foam filler and decorators caulk or in a traditional context perhaps flax/hemp fibres, linseed oil and window putty would make a great ‘stopper’.


Saturday 17th February 2018

Saturday 17th February 2018

History of gas fires that can lead to excessive moisture.

History of British Gas



n. Sitting room front wall

This section of the external wall, adjoining the alcove has been ‘lined’ with plasterboard, a further attempt at ‘damp-proofing’. This remediation most likely occurred in response to the decorative damage caused by the moisture generated by the gas-fire. This now hollow section is probably connected to the sub-floor allowing air-ingress, subsequently making this section of wall cold.

When redecorating it would be appropriate to remove the lining and apply a breathable and hygroscopic lime plaster, preferably a moderately insulating hemp plaster. Ideally, and depth permitting, a Bio-aggregate: hemp lime wall insulation could be cast to the existing masonry and finished with Baumit RK38 – base coat and Kalkin Glätt – topcoat lime plaster – 1400 grade lining paper and clay paint.

It would also be advisable to remove the inappropriate, vapour-closed paint from the mouldings.


Saturday 17th February 2018

Dry lined with plasterboard, history of ‘damp-proofing’ condensation may be building up behind.


o. Air-bricks

Outside to the front and side of the property, air-bricks have been installed to the subfloor. A property of this age would have originally been constructed without air-bricks. They are of modern age and no doubt installed as part of the ‘damp-remediation’ works.

Saturday 17th February 2018

Modern airbricks installed to the subfloor in the front of the house.


Saturday 17th February 2018

Airbrick outside the dining room, cement rendered internally.


Saturday 17th February 2018

New airbricks installed in the front of the lounge.


Saturday 17th February 2018

New airbricks installed on the side of the lounge.


Saturday 17th February 2018

New airbricks installed on the side of the lounge.



p. Cooker hood

The cooker hood does not connect and extract to the outside, this recirculating unit serves only to filter airborne grease from cooking but does not remove moisture vapour from the room. Units such as this normally have the option to switch from recirculation to extraction. An extraction pipe should connect the unit to the outside and a backdraft shutter should also be added where it meets the outside to prevent unwanted air ingress. Units of this age are notoriously underpowered and only capable of overcoming the friction of a short exit pipe passing directly through.

Saturday 17th February 2018

Recirculating cooker hood not connected to the outside.


q. Under the kitchen sink

There is no isolation valve to the outside tap. Regardless of wether, this is insulated or not, without a shut-off valve that can be used in winter to isolate the outside tap, there is a risk of frost ‘bursting the pipe’. The cold metal passing through the wall may also be creating a ‘cold bridge’ resulting in moisture drop-out leading to degradation of the plaster. Plastic pipe sleeved with insulation (connected via an isolation valve) should be used if the installation is reconfigured.

Saturday 17th February 2018

Outside tap, no isolation valve internally.

Saturday 17th February 2018

Outside tap, no pipe lagging externally.


r. Obsolete or inappropriate kitchen vent

Visible from the outside, above the back door to the kitchen, this vent is a later addition, either added inappropriately or for a purpose now unknown. It does not appear to connect with anything internally and so no longer serves any purpose. It may, however, be related to the proximity of the current gas boiler which could have been required for the installation of an earlier version. Perhaps this installation of an older style water heater required an uninterrupted permanent opening for safe and efficient combustion. The current boiler draws air directly from the outside through the same aperture as the outlet flue heat exchanger. This vent is obsolete but further investigation is required to ascertain whether this vent is now closed or not.

Saturday 17th February 2018

Vent above back door to kitchen.


s. Combination Boiler

The boiler is a little old, an upgrade would improve efficiency, and future-proofing its replacement should be considered. However, a greater reduction in heating bill heating demand can be achieved by addressing the draughty envelope of the building.

Saturday 17th February 2018

Combination boiler.


t. TRV’s – thermostatic radiator valves

Thermostatic radiator valves control which rooms are heated and by how much, particularly useful during spring and autumn when the need may be to take the chill off an occupied room on an evening rather than heating the whole house. They also allow each radiator to call for heat individually, resulting in improved response time and heat where it is needed most, rather than some radiators ‘starving’ others – everyone gets a go.

TRV’s are inconsistent throughout the property. Some radiators have them others do not and where they are installed they are old. A systematic audit is required to ascertain if they are all working correctly, however as the circuit will require draining to install the missing valve it would be simple and advisable to replace them all. Furthermore, if an ABV (automatic bypass valve) is fitted across the flow and return pipes adjacent to the boiler then a ‘dump’ radiator would not be required and further efficiency and functionality can be achieved.

Modern TRV’s are bi-directional and can be fitted to either the ‘Flow’ or ‘Return’ side of the heating circuit. However, earlier thermostatic radiator valves needed to be fitted onto the ‘Flow’ side of the radiator to operate correctly. If fitted onto the ‘Return’ side they are pulled open by the direction of water travel preventing them from closing when they get up to temperature. This is not an uncommon fault, either because they were originally fitted incorrectly, or perhaps due to an alteration of the circuit.

It is also not uncommon to find old TRV’s stuck open due to the radiator never getting up to temperature and never turning themselves off (starved by others radiators on route) typically in the attic where demand is high and the distance to the boiler is greatest.

Do away with the ‘Dump’ radiator, fit new Honeywell Thermostatic Radiator Valves to all radiators/towel-rails and install an Automatic Bypass Valve between the Flow and Return under the boiler.

Saturday 17th February 2018

Saturday 17th February 2018



u. Internal doors

All of the internal doors need attention. The doors have been dipped and stripped of their vapour-control gloss layer and have subsequently warped, cracked and are in a generally poor state. Internal doors provide more than modesty to a room, before our modern approach to heating the whole house with central heating each room had its own fireplace. When heating the room, a well-fitting door slows the convection of warm air escaping from the room and the subsequent draw of cold air that is pulled in to replace it. Closing a well-fitting door is instinctive when heating a room with a coal fire but less so when using a radiator as the demand of a radiator can be fed constantly by a central heating boiler without consumption feedback to the user.

The functionality of the doors has deteriorated over time, along with our understanding of when to operate them. This has coincided with the increase in the moisture generating activities and appliances within the home; gas lamps and fires, cooking, laundry, bathing and showering.

Now, however, even with the internal doors closed, warm moisture ladened air is able to migrate from source to symptom. Typically from the kitchen and bathroom to a cold spot located in an unheated room. Improving functionality of internal doors would be of great benefit to the property.

Essentially, ensuring all latches are functioning, and adding a supplementary doorstop with an integral vinyl seal, corresponding with the shape of the doors, will be advantageous. Additionally, filling the cracks, repainting with an oil based primer, undercoat and gloss should prevent further distortion and warping of the doors.

Saturday 17th February 2018

Kitchen door.


Saturday 17th February 2018

Warping has resulted in a poor seal between the doors and the rebated frames.



1850 The world’s first gas-powered bath was designed!

v. Bathroom window

The bathroom window has swelled due to condensation and doesn’t close. In cold weather, this makes the room difficult to heat as well as allowing a constant, but low, ingress of cold air creating a cold-spot in the bathroom and beyond. Adjusted to fit and the room will be easier to heat reducing the risk of moisture dropout. Following showering the window should be opened wide for a brief period to create turbulence and rapid air change, then closed to allow the fabric of the room to be warm. During clement weather, the window can remain open.

Saturday 17th February 2018

Draughty bathroom window


w. Bathroom fireplace

The disused fireplace is liable to be draughty, with cold air ingress creating cold spots within the room and beyond. As with the other fireplaces, a little sheep wool blanket can be added.

Saturday 17th February 2018


x. Shower

The modern bathroom has been fitted with push-fit plumbing. There are many advantages to using plastic pipe and fittings however it can be problematic when used to connect the shower control valve to the head. This section of pipe is concealed within the wall, when depressurised there is a risk of decoupling or intermittent leakage and a small amount of residual water. No symptoms were noted.


Saturday 17th February 2018



Saturday 17th February 2018

Push-fit plumbing


Saturday 17th February 2018

More push-fit plumbing and flexible soil out-let.


y. Bathroom towel rail

The bathroom towel-rail radiator has no thermostatic radiator valve. Good control of this room would be advantageous, taking the chill off prior to showering is very quick when it is the only radiator calling for heat. – see TRV’s

Saturday 17th February 2018


z. Bathroom extractor

Above the shower, there is what would appear to be a Zone 1 low voltage light with integral extractor. Successful extraction can be very problematic, extractors are often underpowered, unable to overcome friction in the ducting pipe beyond a very limited length (1.5 metres). When the duct passes through an unheated cold void such as a loft, condensation occurs and they can often be found filled with water. Furthermore, they are seldom fitted with a good backdraught shutter, consequently, cold air ingress can occur so that the extractor becomes the source of a damp problem rather than the solution.

It was not possible to identify where the extractor duct exits the building. It is not uncommon to find that the ducting is not connected, responsibility for its connection to the outside is often overlooked during an aesthetic refurbishment. For example, perhaps fitted by an electrician who has presumed that the exit duct through the roof was to be completed by a general contractor or roofing contractor. Further investigation is required, however even if an exit route is determined it is unlikely, due to the length of ducting required, that this extractor is sufficient. A new Envirovent ECO dMEV unit is recommended.

The Envirovent fans do come with ultra-low voltage models that can be installed within zone 1. However, Zone 1 extends to 2.25m above finished floor level, therefore, due to the hight of the ceiling, it is unlikely to be in Zone 1. Envirovent have this on their website.

Saturday 17th February 2018


Bedroom 1

aa. Chimney Vent

Following removal of the fireplace, a vent was installed. This vent is unnecessary and inappropriate, serving only to allow uncontrolled cold air ingress into the room and should be sealed. If removed care should be taken not to break it as it is of style and period that would suggest it is made from asbestos and should be treated as such. Double wrapped in plastic, it should be possible to dispose of at the local council waste facility – enquire for confirmation and conditions.

Saturday 17th February 2018


bb. Chimney damp spot

Higher up, approximately of picture hanging hight, there is a moisture spot in the centre of the chimney breast. Due to the combination of a suspected cold spot, impermeable layers applied in an attempt to solve the original symptoms, the wallpaper on top is holding onto the moisture that is concentrating in that specific location. Over the years many attempts have been made to prevent water ingress from the outside. Peeling back the paper revealed a Smögåsboard of layers, notably a patch of plaster that is non-original yet still old and historic. The patch of plaster was hard, potentially gypsum and unable to defuse the moisture settling on the surface. Perhaps a little of what was to hand used to repair damage from picture hanging over the years or maybe a symptom of a more complex underlying historical problem with the chimney.

Built in 1850, this early Victorian property is very late Georgian in its style and construction. As previously mentioned the fireplaces have been through many iterations and the chimney itself has endured the corrosive effects of the combustion of a variety of fuels, wood, coal and gas.

The symptoms manifesting in both rooms served by this stack, as well as the two rooms that back onto it, are caused by the high airborne moisture generated by modern living. This warm, moisture-ladened air condenses onto the surface of the cold single skin brick wall of this disused chimney. The symptoms noted correspond with a Smögåsbord of inappropriate materials on the ‘room-side’ of the wall used to repair it at specific points. These materials are hard, moisture ‘closed’, preventing diffusion as well as potentially making the spot colder.

The origins of these repairs are unknown, maybe a cosmetic repair from hanging pictures, or more likely caused by the historic failers of the parging, chimney lining, which could have then lead to sections of the brickwork being further thinned. This may have been caused by inadequate knowledge of the parging mix when originally built, or perhaps constructed with due diligence it simply didn’t respond well to the change in fuel being combusted.

The fireplace downstairs should not be used until a new stove and flue liner has been installed. Further information on the historical chimneys linings.



[Photo of chimney damp spot – bedroom 1]


Bedroom 2

cc. Further chimney damp spot

To the rear of the chimney, moisture is again settling on the surface of the wall. As described before this is a cold spot and a Smörgåsbord of inappropriately applied materials, no doubt attempting to ‘treat’ the damp. As well as addressing the high moisture and cold spot, the plaster itself should be removed back to the brick when redecorating and an insulating plaster coat applied.

Saturday 17th February 2018

Cold spot and Smörgåsbord – gypsum, PVA and vinyl paint trap moisture in the lining paper.



dd. Original stair access

Behind its original door, the start of the original Victorian stair access to the top floor is still present. This staircase has now been blocked off part way up and the rest has been removed, where it passes through what is now the bathroom. Perhaps because of its narrow width, prohibiting access for modern furniture up into to the loft room.

Saturday 17th February 2018

Original stair access, now a cupboard.


ee. New stair access to top floor attic room

The modern addition of the new open stair access, probably installed to make the top floor more accessible, has unintended consequences. Putting to one side building regulations, falling, collision, fire/smoke protection etc, the open staircase permits the convection of warm air to travel unimpeded up to the attic room where it will cool in the uninsulated space and fall back down into the house. The constant convection of heat loss further exacerbated by the draughty internal doors as well as a large amount of air ingress/egress.

As much as it may be desirable, for authenticity and nostalgia, to reinstating the origin stair access and remove the new staircase. The simplest and most affordable course of action would be to box around and fit a door to the bottom of the new staircase.

Saturday 17th February 2018

New stairs cutting through the spindles and continuous curved Geometrical Handrail.


Saturday 17th February 2018

New stairs should be boxed in and have a door fitted at the bottom of the flight.

Saturday 17th February 2018

New stairs permit larger furniture but now the footprint of the attic room is much smaller.


ff. Attic room window

The unimpeded convection of heat up through the house to the cold uninsulated attic room above is further exacerbated by large amounts of warm air exiting out of the attic window. The unnoticed air egress from the attic is pulling cold air in downstairs, the stairwell is stratifying the air and becoming a chimney.

Unlike air ingress, egress can easily go unnoticed, we don’t directly feel the effects, other than in our heating bills. However, to prevent unwanted and unpleasant cold air ingress below in the rest of the house this faulty window needs closure. A modern roof light allows for ventilation during clement weather making it possible to seal shut the little window. Don’t put off the temporary measure, if it can’t get out, it can’t get in.


Saturday 17th February 2018


gg. Chimney

Looking up from the attic skylight, the cowl to the left could be associated with a modern metal flue liner for a wood stove. However, it was reportedly fitted by a contractor attempting to address suspected water ingress from entering the chimney. This would confirm that the chimney is indeed unlined and has been so since its construction in 1850. It is advisable not to use this chimney until a modern stove and chimney lining are installed. The redundant chimney, with the clay cowl, would benefit from a little sheep wool blanket rolled up and tucked into the top to prevent cold air ingress creating a frost pocket and condensation trap. The terracotta ‘hood top’ cowl is demountable.


Saturday 17th February 2018

Left – Sitting room chimney pot – metal rain cowl, (recently fitted)

Right – Bedroom 1 chimney pot – hood top, terracotta cowl


2. Overview of moisture management.

This beautiful Victorian semi is cold and draughty. As with many properties of age, the decline in maintaining operational functionality of the doors and windows has coincided with an increase in the moisture generated by modern living. Meanwhile, our modern approach to home improvement has put form before function, both kitchen and bathroom lack effective extraction and internal alterations to the design of the building further exacerbate the internal weather.

The building, through the application of inappropriate materials and changes in how the house has been heated over time, is now unable to mitigate the moisture being generated within. The symptoms noted can all be attributed to moisture condensing on cold areas and on materials that are unable to respond. The moisture, as usual, is created 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 interventions 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 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.

Internal weather

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.

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 external 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 in 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.

Thermal envelope

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 attic bedroom, installing insulation would be beneficial but also costly and invasive. If the room is not in primary use a more cost-effective and pragmatic approach would be to isolate the room from the rest of the house with a well-sealed door and heat only on brief occasions when used to accommodate a guest. This strategy could also apply to the basement, where wall insulation would very beneficial but also lower cost.

For other rooms, internal wall insulation could be considered, both to reduce heat loss and improve response times when heating. This could be applied extensively by removing all of the existing plaster and replacing it with hygroscopic and insulative materials. Or more pragmatically by simply removing localised areas (for example the Smögåsbord of inappropriate ‘damp-proofing’ or lining such as the cement render in the dining room and dry-lining in the sitting room) and applying something more appropriate to the area that has suffered decorative deterioration.

Any future alterations, maintenance or simply redecoration will provide opportunities to improve insulation and increase the moisture buffering capacity by using vapour permeable and hygroscopic materials. Care must be taken in the specification and installation of naturally hygroscopic materials to ensure they can sufficiently diffuse moisture vapour.

Simply repairing with Lime plaster ensure it is predominately air lime and contains calcitic aggregate (hygroscopic) – such as Baumit RK38 and Kalkin-Glätt.

Many natural materials can help this process including wood fibre insulation, insulating hemp plasters and cast hemp & lime Bio-aggregate. Care must be taken not to apply synthetic vapour closed paints to these materials, vapour permeable and hygroscopic paints should be used such as Earthborn and in conjunction with lining paper.


3. The potential solutions to mitigate the symptoms


  • Observing cooking, showering, routines, make a connection with operating windows and doors, to purge peaks of moisture and slow convection currents around the home. Laundry strategy.
  • Starting with the large holes to expose the small, reduce unwanted air ingress/egress using an expanding foam applicator gun and a little sheep’s wool. Don’t beware the temporary measure.
  • Install Kitchen extractor and replace bathroom extractors – further consideration of SR-MVHR single room, mechanical ventilation heat recovery.
  • Fit TRV’s (thermostatic radiator valves) and ABV (automatic bypass valve) to the heating system. Heating can be programmed to warm the interior fabric before showering in the morning and again prior to cooking on an evening.


  • Improving the 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. Installing doors to the attic and basement.
  • Restore functionality to windows.
  • Adding polycarbonate secondary glazing to sash windows in the lounge and single glazed window in the back room.


  • When redecorating avoid synthetic paints and gypsum plaster. Decorative repairs should be undertaken with lime plaster and breathable, hygroscopic finishes.
  • Where walls require extensive removal of the existing Smörgåsbord, add hygrothermal insulating plaster or preferably cast Bio-aggregate.
  • Basement ‘insulation’ to improve heating response time and buffer large thermal mass on the basement walls and the ground.
  • Insulate the roof – or isolate from the rest of the house.



This house is draughty and difficult to heat, temperature differentials are large and the opportunity for internal weather storms, causing moisture to drop out, is high.

A chimney stack is part of a complex combustion system, that if not properly understood can lead to, well-meaning but ill-informed solutions attempting to prevent moisture getting in. This combination of inappropriate inventions applied to a complex structure can cause a myriad of symptoms. Without an internal inspection of the chimney, several informed assumptions, based on previous experience, have been made to help develop the conclusion.

With the initial intervention of appropriate low-cost and no-cost solutions, informed by the Principles (people, internal weather, thermal envelope and damp) quick, high-impacting improvements can be made. Further to this renovation of the doors and windows in combination with the installation of TRV’s, can continue to improve the situation, allowing the occupier control of their indoor environment. Once these short and medium term options have been implemented, the larger scale interventions can be looked at in context.


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.

Historic Environment Scotland Technical Paper 15

Assessing risks in insulating retrofits using Hygrothermal software tools. Heat and moisture transport in internally insulated stone walls.

Joseph Little, Calina Ferraro & Beñat Arregi

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