Understanding the Vital Role of Airflow and Ventilation in Buildings
Living in an older building should be an enriching experience, yet it can become a costly ordeal for some property owners. Discovering issues like dampness, dry and wet rot, or the presence of death watch beetles can be unsettling. Thankfully, effective solutions do not necessarily require substantial financial investment or the removal of significant original building materials.
Surprisingly, remedial work has led to greater damage and loss of fabric in many properties compared to the initial problem.
There are two fundamental concepts that require careful consideration.
Proper management of the historic building is necessary to mitigate or eliminate damp-related problems.
Should your home encounter issue with damp and decay, it is imperative to address the root causes and allow sufficient time for the affected areas to dry thoroughly. This approach is critical for preserving the integrity of the building’s original fabric.
The enduring quality of older buildings, many of which have withstood the test of time for up to five hundred years, is a testament to their construction. Maintaining these structures with suitable materials and methods ensures they remain cherished homes and profitable investments for the foreseeable future.
Getting to Know Your Building
Exploring the reasons behind dampness in older buildings and the increased prevalence of damp and decay issues in the last few decades.
A comprehensive understanding of older building construction is vital for proper repair, especially since buildings predating the mid-19th century have different properties and behaviours than modern constructions.
Unlike modern buildings that use cavity wall construction to inhibit moisture penetration, older buildings typically allow absorbed moisture to evaporate from the surface. This process is facilitated using “breathable” lime-based mortars, renders, and internal plasters, which promote moisture evaporation instead of trapping it within the walls.
In timber frame and clay lump buildings, walls were traditionally covered with porous lime plaster on both the interior and exterior surfaces. Similarly, solid brick and flint walls were built using lime mortar and internally plastered with lime. These porous wall systems can absorb moisture in damp conditions and release it through evaporation during dry spells, allowing the building to “breathe” and maintain a healthy environment.
Older buildings often had floors constructed with ventilated suspended timber or brick and clay pammets placed on sand, facilitating the evaporation of ground moisture. This process, involving only small amounts of water vapor, remains invisible and does not result in wet walls or floors.
Alterations such as replacing a lime render with a cement render or transforming a timber floor into a concrete floor can compromise the inherent breathability of older buildings, which may contribute to issues like dampness and decay.
Over the years since the 1950s, many owners of older buildings have opted to weatherproof their properties by applying cement renders, waterproof coatings, oil-based masonry paints, and waterproof sealants. Additionally, traditional porous floors have been replaced with concrete floors incorporating damp-proof membranes.
While standard practice in modern homes involves connecting a damp-proof membrane to a damp-proof course in the walls, this approach hinders evaporation through the floor in historic buildings. As a result, any moisture is forced to travel under the non-porous floor until reaching the walls. If the walls are unable to release moisture due to cement render or waterproof coatings, it will accumulate and contribute to deterioration.
However, sealing walls and floors to resist water penetration does not consider the moisture produced internally within a property from common daily activities such as cooking, washing, and drying clothes.
Consequently, these alterations, made with good intentions, inadvertently promote moisture buildup within the walls by obstructing the building’s ability to “breathe.” Once the building fabric becomes damp, it provides ideal conditions for the proliferation of wet rot, dry rot, and the death watch beetle.
Older buildings naturally retain moisture within their breathable fabric. Using a ‘damp meter’ to assess moisture levels in lime plaster, brickwork, clay lump, or wattle and daub will typically register as damp, even though these meters are more accurate when used for measuring timber moisture content.
However, when used on bricks, plaster, and wallpaper, these meters often display readings that are too high, incorrectly implying that a wall is damp when it is in a completely normal equilibrium state with its environment.
The Root of the Issue: Common Causes Behind Damp Problems
Damp problems can arise due to neglect or poor maintenance, while others may be indicative of more significant structural issues. Investigating all potential causes of dampness thoroughly is essential, as there could be multiple factors contributing to the problem. Keep in mind that the damp area might not be near the source or could be associated with work conducted several months or years ago.
Diving Into Dampness: A Breakdown of Its Primary Causes
Cement render, plaster, waterproof coatings, and sealants prevent the structure from breathing and lead to a build-up of moisture within the walls when applied to the walls of older buildings. This then causes the walls to deteriorate.
Applying cement render, plaster, waterproof coatings, and sealants to the walls of older buildings restricts their ability to breathe, resulting in moisture retention within the walls and progressive deterioration.
When a concrete floor is installed inside a building to replace an older breathable floor, it redirects ground moisture towards the walls, leading to heightened dampness within the walls.
Elevated ground levels can result in damp penetration when external ground levels are permitted to rise to the same level as or higher than the internal floor, enabling direct water penetration into the walls.
The installation of concrete paths surrounding a building can hinder moisture evaporation and channel ground water towards the walls. If the interior wall is covered with breathable lime plaster, trapped moisture may escape into the room, resulting in damp patches and peeling wall finishes, particularly if the wall is heavily saturated. In contrast, if the wall is coated with impermeable cement render both inside and out, the moisture will be trapped within the wall’s structure, leading to progressive decay.
This form of dampness poses significant threats to timber frame properties by potentially causing decay and structural compromise of the sole plate (the foundational timber member of the frame) and the wall studs. Similarly, saturation of clay lump walls can lead to their eventual slumping.
Poor ventilation restricts moisture evaporation within the building, contributing to condensation buildup on the walls.
Water ingress, or penetrating damp, occurs when water seeps through walls and roofs into a building. Common entry points for water infiltration include damaged or blocked guttering and downpipes, deteriorated pointing, cracked or missing render, decayed joinery around windows and doors, missing or damaged roof slates and tiles, and faulty chimney flashing. Additionally, staining on walls and ceilings could be caused by plumbing leaks.
Rising damp occurs when moisture from the ground is absorbed into walls. Although rising damp is frequently cited as the cause of dampness, most cases are due to other factors listed above. Genuine rising damp is rare.
Spotting the Signals: Identifying Indicators of Damp
Recognising a damp problem involves observing various signs, which can differ depending on the cause; typically, the presence of a musty smell accompanies many damp-related issues.
If you notice low-level staining or peeling paint on the inside of ground floor walls, it could be a sign of moisture accumulation within the walls, caused by a hard or waterproof render, high ground levels outside, or a non-porous floor. Moreover, structural cracking or movement at lower levels or in corners may indicate decay of the sole plate, which can cause movement in the timber frame structure above.
The presence of crumbling brickwork often points to damp bricks that are deteriorating over time. This deterioration is typically caused using unsuitable, hard, and impermeable mortar, which forces moisture to escape through the more vulnerable bricks. Furthermore, dampness in bricks can be intensified by leaky guttering or downpipes that fail to adequately divert water away from the wall surface.
Bricks that absorb moisture are prone to frost damage, where freezing and expansion of the trapped moisture cause the surface of the brick to be dislodged. This process leads to degradation and crumbling of the underlying softer material.
Condensation-related black spot mould often develops in corners and behind furniture within areas that lack adequate ventilation or heating. This mould is superficial in nature and does not impact the structural integrity of the building.
Staining on walls or ceilings is indicative of either penetrating damp or rising damp. Penetrating damp can present as localised patches of dampness that appear anywhere on a wall or ceiling, depending on the source of moisture. For example, a leaky gutter may cause a damp patch higher up, while issues with joinery can lead to dampness around window openings.
You can recognise rising damp on ground floor walls by a distinct ‘tide mark’ that ascends to about 900mm, or the height of a typical windowsill.
Discoloration on ceilings often points to problems like a leaking roof or defective chimney flashing. Additionally, it might result from a faulty water tank in the attic space.
The appearance of holes or fungi on timber often points to an infestation of wood-boring beetles or the development of wet or dry rot. Species such as the deathwatch beetle are especially prone to attacking moist wood.
Holes from the common furniture beetle, also known as woodworm, provide a significant source of income for timber treatment businesses. However, most holes in old buildings are inactive and do not indicate a current infestation. Check for fresh bore dust (sawdust) under the holes; its presence means you can dig around the holes in the wood to find new grubs.
Dry rot fungus spores are found universally. The fungus needs wood to have a moisture content of 20 to 40% to grow. It spreads by sending strands through dry areas to reach new moisture sources. Look for signs such as darkened timber, white or grey strands on the wood, fruiting bodies, and the distinctive large, square cracks known as ‘cuboidal cracking’ in the woodwork.
Affected timber, when suffering from wet rot, is light and crumbles to the touch. Wet rot arises from multiple fungi that grow in wood that stays perpetually moist.
The colour of the strands differs with each species. Wet rot fungi are restricted to the damp regions they infest. Affected timber will change in colour, with some areas becoming darker and others much lighter, often appearing bleached.
Problem-Solving Strategies: Resolving the Issue
Investing a bit of time to understand the real cause of the problem and thoughtfully responding could save you thousands of pounds.
To get expert advice, connect with a conservation expert or look for an independent specialist consultant or surveyor who can identify the cause and scope of the damp and decay.
Choose lime render and plaster over hard cement alternatives for superior performance. While it is best to replace them entirely, if budgetary constraints arise, concentrate on replacing the lower sections of the walls, particularly those near the ground, to address the issue. This approach is particularly beneficial for timber frame buildings, facilitating the drying process of the sole plate. For the finishing touch, apply lime wash externally and distemper internally to the lime render and plaster.
Older buildings are better served by avoiding cement-based renders and plasters, which can be detrimental to their longevity. Employing lime-based alternatives is preferable, but it necessitates an understanding of the material’s nuances and proper application methods.
Promoting Ventilation: Swapping Concrete for Breathable Floors.
Ensuring that the floor level is positioned beneath the sole plate is imperative in timber frame structures. While suspended timber floors, bricks, and pammets were historically favoured, Limecrete emerges as a contemporary substitute, especially if laid without a damp-proof membrane.
Adopting this solution results in a resilient floor finish that maintains breathability, promoting optimal indoor air quality. In cases where replacing the entire floor is not viable, installing a breathable channel around the room’s perimeter facilitates ventilation at the base of the walls, effectively combating moisture buildup and dampness.
Maximising Airflow: Channel Filling Choices for Better Ventilation
When addressing high external ground levels, it is essential to lower them below the floor level inside the building without jeopardizing shallow foundations. Installing a French drain along the perimeter of the exterior walls ensures proper drainage, safeguarding the base of the walls from moisture and dampness.
Preventing Water Damage: Slope External Paths Away from Building Walls
To combat dampness attributed to inadequate ventilation, it is advisable to ventilate rooms by opening windows and using heating appliances. Rectifying sealed or painted-shut windows to enable proper airflow is essential in preventing damp-related issues. In scenarios where ventilation remains insufficient, especially in challenging areas, installing extract fans or air vents may prove beneficial.
Investigate the roof, chimneys, guttering, render, brickwork, and joinery to determine the underlying cause of penetrating damp. Do not overlook the possibility of leaking plumbing. Utilise traditional materials consistent with the architectural style of listed buildings for repairs and ensure the fabric is thoroughly dried out before redecorating.
Effectively combating genuine rising damp demands a comprehensive plan of action. This includes strategies like lowering external ground levels, improving drainage using French drains, and choosing breathable materials for floors and walls. However, in unique cases where these approaches do not yield results, the installation of a damp-proof course may be the only viable option.
Injecting a chemical damp proof course into an older building seldom works and can make the problem worse. Water will be concentrated within the base of the wall below the level of the damp-proof course, causing its saturation and preventing it from drying out. This will then freeze, expand, and thaw over winter, damaging the stability of the wall.
Contractors encounter significant challenges in guaranteeing the effectiveness of a damp-proof course in older buildings due to the thickness and solid construction of their walls. To navigate this obstacle, many contractors choose to remove lime plaster and substitute it with modern waterproof plaster on injected walls. Regrettably, this tactic typically offers only a superficial solution to the persisting damp issue.
If a damp-proof course effectively resolves the problem, there’s little justification for resorting to waterproof plaster. As the wall undergoes drying post-treatment, salt deposits may appear on the lime plaster surface. These salts can be brushed away until the drying process concludes, serving as an informative indicator of the damp-proof course’s success. Additionally, they reveal any potential reoccurring issues that require attention.
With chemical damp-proof courses often proving ineffective in older buildings, the use of waterproof cement plaster serves as a pre-emptive measure to prevent damp from resurfacing. Regrettably, many contractors fail to adequately inform their clients about this approach and instead resort to cement render, which merely camouflages the issue, causing further damage to the structure. It is frequently observed that damp reappears above the height of the cement render after a few months.
Employing a physical damp-proof course is a viable choice for brickwork, including the plinth of timber frame buildings. This process entails cutting out a line of pointing and introducing an impermeable material, such as slate, to prevent moisture from rising the wall. While it may not be the perfect solution, it proves to be more effective than injecting chemicals into a solid wall and avoids the necessity of replacing lime plaster with waterproof plaster.
Inserting a damp-proof course into flint walls proves exceedingly challenging due to their irregular nature, which prevents the establishment of a seamless barrier. The presence of any gaps in the barrier would allow moisture infiltration, rendering the damp-proof course ineffective. Additionally, drilling into flint walls to administer a chemical damp-proof course carries the risk of wall damage and disruption to structural integrity.
The optimal solution for beetle and fungal damage in damp wood is to tackle the dampness that has created a hospitable environment for them.
To rid a building of death watch beetles, resolving the dampness issue is paramount. Though chemical methods can be effective in some cases, they are insufficient on their own. The primary strategy is to modify the specific conditions that death watch beetles need to survive.
Addressing an active woodworm infestation requires treating just the infested area. There is no need to spray the whole house if the problem is confined to one or two spots.
To combat wet and dry rot, you need to remove the dampness and allow the wood to dry. As the timber dries, the fungi will enter a dormant state and ultimately die off.
If a building society demands timber treatment and damp-proofing or an evaluation by a ‘specialist contractor’ as part of a mortgage agreement, you should consider consulting an independent expert to verify the necessity of such work.
Typically, this process is both time-consuming and costly, and it may fail to detect genuine problems. An assessment by a qualified, independent specialist surveyor or conservation officer that questions the need for these measures can usually persuade the building society to waive this mortgage condition.
Summary.
The subject of damp and decay in older buildings is quite complex, often resulting in well-intentioned but flawed efforts to resolve these issues. This complexity also makes it easier for unscrupulous or unskilled operators to mislead property owners. Timber treatments and damp-proof courses alone will not solve the underlying causes of damp. Their localised use may be beneficial but only as part of a larger plan to eliminate the sources of damp.
This guide is meant to offer a basic framework; however, each case of damp demands an individualized approach for proper resolution.