Renovating an old property can be one of the most rewarding ways to create an individual home packed with character – but before you start, you need to be sure the building can withstand the kind of scheme you want to undertake. Here are some key elements to consider prior to putting your cash into a project.
If your house was built before 1919, it’s likely to have been made using very different methods and materials to those that are available today. Pre-1919, popular construction products were stone, timber, lime, earth and clay, all of which are generally soft and permeable.
Unlike modern materials, which are designed to keep moisture out of the building envelope, these traditional components readily soak moisture up from their surroundings and facilitate its evaporation.
A good balance between absorption and evaporation prevents the building fabric from becoming damp. This is referred to as breathability.
This system works extremely well; hence many traditionally constructed buildings have survived for hundreds of years.
Unfortunately, it is very common for alterations and repairs to historic structures to incorporate modern materials, such as cement mortar and render or impermeable plaster and paint. These products will interfere with the equilibrium of water absorption and evaporation and the mixture of both can cause serious damp issues.
So, the first priority when you assess a heritage property should be to identify where inappropriate non-breathable materials have been used and consider what damage they might be causing.
Because most modern construction products are less flexible than the original materials underneath, they will tend to crack and let in water that is then trapped – a potential cause of damp.
Even in cases where the breathable performance of the building has not been compromised, its balance depends on it not being exposed to excessive levels of moisture. Issues are usually caused by rainwater.
You will need to check that the roof is in good repair and properly detailed, so that rain can’t get trapped or concentrated in vulnerable parts of the building.
Ensure gutters are adequately sized and in good repair, with sufficient downpipes leading to surface drainage that carries rainwater well away from the building. Problems with gutters tend to be the main cause of damp in old buildings.
Other external factors to look out for are raised ground levels or hard landscaping up against the base of walls, which will tend to concentrate water in this part of the fabric.
In addition, dense planting or vegetation against walls may inhibit evaporation of water that has been absorbed by the permeable fabric.
These issues can cause dampness in the base of external walls, which can be confused for rising damp. Misdiagnosis can lead to expensive, intrusive and unnecessary remedial work.
Internally, look out for leaks from pipes, joints and defective seals around sinks and showers. Modern day household chores – such as cooking, cleaning, drying clothes and bathing – generate significant amounts of water vapour.
This will be absorbed by breathable surfaces and will tend to condense on cold impermeable services. If the amount of water vapour within the building is not well controlled, there is a risk of damp and mould growth, which can be harmful to the health of both the building and its occupants.
You should check that there is adequate ventilation throughout the house to do this; but particularly mechanical extraction in kitchens and bathrooms.
Assessing the fabric of an old property can be difficult without experience. To the novice renovator, many normal characteristics of historic buildings can look quite alarming.
Because they were constructed with soft materials and shallow foundations, significant deflections often occurred early in a building’s life. Heritage properties are very robust and flexible, so even quite considerable historic structural movement is rarely a cause for concern.
However, you do need to look out for any recent structural movement, which will generally be indicated by significant cracks, failure of masonry units, fractured timbers or the opening up of joints.
Small cracks, particularly to internal plasterwork, are usually just a result of normal movement within the fabric. If the building is or has been damp, there is a significant risk of timber decay – particularly to floor joists, where they are embedded into masonry.
You should check the solidity of any timber floors; if there is excessive movement or deflection as you walk on the floor you must examine the joists for signs of decay.
Wood boring insects – woodworm and deathwatch beetle larvae – can attack timber in damp buildings and can cause serious structural issues.
However, most beetle damage found in old buildings is less serious than it first looks. The larvae cannot usually strike structural timber, except in the presence of serious long-term damp.
Almost all old buildings show signs of attack by wood boring insects, but this is usually historic and superficial. If during your assessment you think you find an active infestation, consult an expert with a proper understanding of historic buildings.
An infestation will only be sustained in the presence of significant damp and the solution will lie in resolving the causes of that damp. Chemical spraying is almost always ineffective and not advisable in a home environment.
For occupant comfort, managing heating bills and minimising CO2 emissions, it’s important to consider the thermal performance of your heritage property.
The standard assessment methods used to prepare Energy Performance Certificates (EPC) do not work well for old buildings and tend to understate their energy efficiency. This means that your house is very unlikely to be as cold and draughty as you are originally led to expect.
Having said that, you should look out for areas where thermal performance can be improved. The biggest factor in determining the energy efficiency of an older building is whether it is damp. This is because damp walls conduct about 30% more heat than dry ones.
Draught-proofing is a good way of reducing heat loss. Check windows and doors to ensure they fit well and are effectively draught-stripped – even keyholes and letterboxes can be the source of significant air currents.
In principle, old windows should be retained and refurbished, possibly with the addition of secondary glazing. Poor quality modern windows should be replaced; in most cases with appropriate double-glazed units.
Check the level of insulation in the loft. A good thickness of a natural material such as sheeps wool, hemp or wood fibre is necessary in order to achieve a combination of strong thermal performance and appropriate moisture management. In addition, evaluate the potential to insulate below suspended timber floors.
Your assessment of a heritage property should not be limited to the functional issues above. A major benefit of owning an old house, both in terms of its value and the pleasure of living in it, derives from its character and surviving historic features.
You should aim to develop a good understanding of the kind of building you’re dealing with so you can identify the important features that contribute to its history, character and value.
Very often, period features such as timber windows, fires and old plasterwork have been removed or covered up by past owners. Consider the potential for opening up and reinstating them.