We are looking to improve the heating in our house, and understand that this will be achieved either through external insulation or internal dry-lining. In order to make a decision what are the pros and cons of each?
This question arises time and time again and there is no clear answer, otherwise one system would flourish and the other would filter out. Clearly, an insulated wall is better than an uninsulated wall and there are a number of factors that need to be considered when deciding which is the most appropriate in a particular set of circumstances.
Theoretically, it is possible to get a good result with both options. The first issue to consider is the principal of how the insulation performs. If the wall is insulated on the internal surface, then the property will tend to heat up very quickly, however, it does not hold on to the heat and the house will cool down very quickly.
On the other hand, if a wall is insulated on the external face, then the wall has to heat up before the insulation will be effective. Accordingly, it will take longer for the property to heat up but on the corollary it would also take longer for the property to cool down, as the wall effectively acts as a thermal storage mass. So internally insulated systems would suit houses with short-term occupation such as working couples etc, whereas an external insulation would be better suited to a house which is largely occupied most of the time and particularly if there are young children or elderly residents.
Consequential costs
The next issue to consider is the cost but not only the cost of the insulation but all the consequential costs of fitting the insulation in place. It will prove extremely disruptive to dry-line the internal face of the walls in any property as this will discommode the occupants and they may even have to vacate the property to facilitate the work.
Furthermore, there will be an inevitable impact on various features including skirting boards and window boards which will have to be removed to facilitate the application of the new insulation lining. With older properties there will also be an impact on features such as cornices which would have to be taken down and renewed. There is also considerable impact on services such as electrical sockets, light switches and radiators etc which have to be temporarily disconnected and refitted on the room side of the insulation.
Clearly, this gives rise to a lot of additional costs and disruption and one would most likely end up having to carry out a complete redecoration of the property on completion of the work.
On the corollary, insulation can be applied to the external face of the walls with little or no impact on the occupants of the property. There would also be minimal impact on the physical characteristics of the building and while windowsills or decorative features such as quoin stones etc would have to be adjusted there would be minimal impact on the property.
Difficulties
Applying insulation to the interior face of the walls will also have the added disadvantage of reducing the size of the room by the actual thickness of the insulation, which could be up to 100mm (4 inches), which could have a significant impact on a relatively small room. This often gives rise to particular difficulties in the vicinity of staircases on gable walls. We would also advise that sometimes it can be difficult to avoid issues such as cold bridging when dry-lining the internal face of walls, as it may not be possible to get a continuous layer of insulation where say an internal wall meets an external wall.
As stated at the outset, there is no single right answer to this question and it really is a case of weighing up all the factors and coming up with the right answer for the particular situation. Your local chartered building surveyor will also be more than happy to assist and help you decide on the most appropriate solution for your situation.
Val O’Brien is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie
