Can insulation cause damp?

5 October 2020 Kingspan Insulation UK

Having insulation fitted is one of the simplest and most effective ways to make your home more comfortable and cheaper to run. However, due to issues arising from poor quality installations in the past, concerns have been raised that these measures may create problems with damp. In this blog, we discuss what can cause this and how, with proper planning and care during design and installation, these issues can be avoided. Using a TrustMark registered installer is an important part of making sure that the work is done professionally.

Addressing existing issues
There are a number of things which can lead to existing problems with condensation and damp. These include:
•    rising damp - where moisture is drawn up from the ground into porous materials in the wall and floor;
•    rainwater and penetrating damp – moisture entering through defects like broken tiles or bricks, missing pointing or damaged gutters;
•    flooding damage – flood waters are absorbed by walls and floor constructions, causing damage and increasing condensation risk.
•    spills and pipe leaks;
•    moisture contained in construction materials like mortar and plaster, which is released as they dry;
•    moisture generated by your activities in the home; and
•    airborne moisture and flueless heating appliances. 

Before any insulation is installed in a home, the TrustMark registered installer should first carry out a thorough inspection to look for signs of existing damp (such as damp walls, flaking paintwork and rotten timbers) or issues with the condition of the property which may cause problems in the future.

They should then take steps to identify the causes and address these, such as resealing around windows and doors, repointing and replacing tiles, clearing airbricks, fitting fan vents in humid areas such as bathrooms and kitchens, and repairing the damp proof course. It may also be necessary to replace damaged timbers and plaster internally.  

If your property is situated in a severe or very severe wind driven rain exposure zone then they may also introduce some additional measures to prevent or reduce the level of penetrating damp, such as rendering the outer wall of the building or applying a barrier cream.

Once the causes of any damp are addressed, the construction should be given time to fully dry before any insulation is installed.

Assessing ventilation and planning limitations
When measures such as insulation, double glazing or draught proofing are properly installed in a home, they will make the property more airtight. Whilst this will help to reduce draughts, it can also allow humid air to become trapped in your home, reducing the air quality and potentially leading to condensation issues (see below for more information). For this reason, it is important that ventilation is carefully considered and addressed as part of any improvement work.
What causes condensation in homes?
All air is capable of holding a quantity of water as vapour. In a typical building, this water vapour can come from a variety of everyday activities including occupants breathing, running hot taps or boiling a kettle. 

When air reaches its maximum capacity of water vapour it is described as being saturated. It will then begin to shed any excess water. The warmer the air is, the more water it can hold before becoming saturated. The term relative humidity describes the amount of water vapour in the air compared with the amount needed for it to reach saturation at its current temperature.

Crucially, as air cools it is able to store less and less water. Eventually it reaches a level where it becomes saturated – this is known as its dew point. Condensation is the result of warm air meeting a cold surface, dropping in temperature to its dew point and depositing excess water vapour as liquid on the surface. This can either occur on the face of a construction (surface condensation) or inside when the vapour meets a cold material inside the construction (interstitial condensation). You can read more about the different types of condensation here.
Your chosen TrustMark registered installers should first ensure that any existing ventilation measures which are unaffected by the planned work, such as air bricks and ventilation gaps at eaves, are clear of obstructions. They should then consider how the insulation measures you are having installed may impact existing ventilation throughout your property, the likely relative humidity in the different spaces within your home and what new ventilation measures may be needed to bring this to an acceptable level. This work may include carrying out pressure tests on your home and should be performed by a suitably trained individual. 

They should also consider potential restrictions on your property which may prevent a successful retrofit. For example, for some listed properties it may not be possible to fit solid wall insulation due to limitations on external alterations. This might prevent the use of external render and insulation, whilst the presence of particularly porous materials in the walls may make them unsuitable for internal wall insulation. The advice and guidance of an appropriately qualified retrofit professional should be sought in such circumstances, particularly for much older properties.

Assessing Condensation Risk
To help installers, when calculating a U-value for the area being insulated (a measurement of how effective the entire construction will be at preventing heat loss) our technical services department also provides a Condensation Risk Analysis (CRA). The CRA is calculated under the British Standard BS 5250: 2011 +A1: 2016. It allows the risk of interstitial or surface condensation to be estimated based on a number of factors including:
•    the individual components within a construction (e.g. brick, size of cavity, block, insulation, plasterboard); 
•    the order in which they appear;
•    climate data for the building’s location; and
•    an estimated relative humidity based on factors such as how many people live in your home and its size.

The CRA analysis can allow alterations to be made which minimise the risk of condensation. This can include adjusting the thickness of the insulation layer and where it appears in a construction. Vapour control layers may also be introduced to prevent water vapour from moving from the warm to the cold side of a construction and condensing. 

Care with detailing and installation of insulation
Once they are satisfied with above, the installers should then carefully plan how the insulation is going to be fitted, including creating detailed drawings for areas such as junctions. This planning is important to limit so called ‘thermal bridges’. These are created when materials which penetrate through a construction are less resistant to heat transfer than the surrounding construction – as a result, they act as a route for heat to transfer out of a space. Common examples of potential thermal bridges include roof rafters and junctions around windows and at room corners. If these areas are not addressed, they can create cold spots which allow condensation to form. 

Leaving any area uninsulated whilst insulating others can also act in a similar way as a thermal bridge increasing the heat losses through any uninsulated area and therefore reducing surface temperatures and increasing the risk of surface condensation and mould growth.

To prevent this, the installers should look to insulate these areas whilst also ensuring effective ventilation is incorporated where required. For example, if they are planning to install insulation internally in a room-in-the-roof, insulation will typically be fitted between the rafters with an air gap of at least 50 mm between this layer of insulation and the sarking boards. This allows air to ventilate out through the eaves rather than condensing on the cold sarking boards. A further layer of insulated plasterboard will then typically be fitted below the joists to prevent them acting as thermal bridges.

Finally, the installation itself must be completed with care and attention. Insulation boards and vapour barriers should be cut and fitted accurately with no gaps or variations in the materials used compared with those in the plans. 

These steps may seem like a lot to consider, but TrustMark installers must all undertake dedicated training around insulation retrofits to gain their certification, and so should be both familiar with these requirements and skilled at dealing with them. By adopting this thorough process, your installer will be able to ensure that the proposed insulation measures are appropriate for your home and are properly designed and installed - preventing issues with damp and saving you money for years to come.

Kingspan Insulation Ltd

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