Internal Wall Insulation

For the direct fix systems, high thermal performance foam insulating materials, such as Polyisocyanurate (PIR), Polyurethane rigid foam (PUR), Extruded Polystyrene (XPS) or Phenolic are usually used. The batten system can also use Glass and Mineral Wool insulation.

IWI does mean that there will be a reduction in the internal size of the room. This could be anywhere from 40-100mm per wall, and where you might have two or three external walls on a single room the reduction will be obviously be slightly greater.

Although you do lose some of the room size, the walls will be warmer and therefore furniture can be placed closer to the wall, as in many colder properties the furniture is set away from the cold surface.

The science behind the forming of condensation and mould growth would normally say that insulating the internal skin brings the dew point and therefore the condensation issue into the building. However, it is important to understand that the use of a Vapour Control Layer is essential in preventing the condensation building up internally.

When choosing IWI as a solution, ensure that you get the right advice first; installing an insulation layer to an internal wall with no consideration of preventing condensation would be a mistake.

WI is an ideal solution when other methods of insulating the walls are not possible. If you have a solid wall construction, cavity wall insulation is not possible and external wall insulation may not be suitable, due to conservation areas, historic / listed buildings or practicality. IWI is also a cheaper alternative to external wall insulation.

There is always going to be a certain amount of disruption when internal works are undertaken on an inhabited dwelling. Ideally, the installation of IWI should be undertaken on a room-by-room basis to make the process easier and less disruptive.

Most solid wall construction of 225mm brickwork would have a current U Value of around 2.07W/m²K, which is highly inefficient. Using a high-performance foam insulation with a 12.5mm plasterboard, around 40mm would achieve 0.80W/m²K and 90mm would achieve circa 0.30-0.25W/m²K. For glass or mineral wool then 65mm overall would achieve just below 0.5W/m²K and 95mm would be circa 0.34W/m²K.

This is dependent upon which method or system is chosen. Typically starting at around £35 per square metre, IWI would be more expensive for the system fix solutions; however, these systems are typically available with a guarantee.

IWI retains more the heat from the room, with less heat loss through the fabric of the building.

IWI can be installed any time of the year and is not weather dependent unlike EWI, which can be problematic if installed in the winter months.

IWI will ensure that the external character of the building remains.

IWI is generally less expensive than EWI.

Loss of room space is an obvious disadvantage, with general disruption due to the replacement of radiators, sockets etc.

Hybrid solid wall insulation is when there is a requirement to use both IWI and EWI on the same property.

An example of this could be where the gable end of the building can be insulated with external wall insulation; however, due to retained features the front and the back of the property can only be treated with internal wall insulation.

The main problem when using both internal and external wall insulation on the same building is thermal bypass. Thermal bypass is the escape of heat from the property and is mainly at junctions or where both internal and external wall insulation overlaps.

To prevent thermal bridging, it is recommended that there is a 400mm overlap between the systems, (this is usually best provided by the IWI system by returning the system for a short run).

When installing any fabric measure which will improve the air tightness of the building, the current ventilation methods of the property should be considered.

If the property does not have a ventilation system, it might be worth considering getting one installed or be aware of improved building fabric and make sure that you open the windows to allow for natural ventilation.