Retrofitting Older versus Modern Buildings
The age of your house and materials used in its construction significantly affects the type of insulation materials you need and the approach you take to retrofit. Keep reading to find out how air flow and moisture function differently in old and modern buildings, as we dive into their construction styles and the recommended approaches.
Old buildings (before approx. 1930) were built with porous breathable materials, known as vapour open.
Modern buildings are built with waterproof and impervious materials and are vapour closed.
A Look at How Modern and Old Buildings Handle Moisture Differently
Breathable vs Vapour Tight
Old buildings
Old buildings were designed to be breathable, allowing natural air circulation even if somewhat draughty. Their walls absorb moisture when wet but dry out quickly due to good ventilation. Lacking damp-proof courses, they rely on underground air bricks that promote airflow and prevent rising damp, with some air also entering through leaky floors. Warm, moist air rises via chimneys and leaky windows, aided by vapor-permeable mortar and render. Overall, these structures are intentionally ventilated and breathable.
Modern buildings
Modern houses are vapour-closed, with damp-proof courses that prevent rising damp. Waterproof exteriors and cavity walls direct rainwater away, stopping moisture from penetrating beyond the outer bricks. Unlike older buildings, they lack chimneys that cause drafts. Windows open for controlled ventilation and seal tightly when closed, reducing draughts. These features make modern homes easier to insulate and retrofit.
Key things to consider prior to undertaking retrofit:
-
In 2019, the Government issued PAS 2035 (Publicly Available Specification 2035: Retrofitting Dwellings for Improved Energy Efficiency, Specification and Guidance).
This document outlines standards and methodologies for insulating existing buildings and installing low-carbon heating systems, such as heat pumps. Although insulation is a key focus, it is not reflected in the title, which simply refers to "retrofitting."
To make it more accessible, "Retrofitting Dwellings for Improved Energy Efficiency" has been shortened to "retrofit."
This guidance is crucial, as 90% of homes in Britain in 2050 will have been built before modern standards. Consequently, retrofitting existing homes is more important than setting standards for new construction. PAS 2035 has a sister document, PAS 2030, which covers certification schemes for installers.
-
There are two approaches to insulating old houses: one is to use breathable materials, such as sheep’s wool, and the other is to create a vapour barrier while paying attention to managing moisture.
Breathable materials can be much more expensive and may also require more space; that is, they need a thicker layer to achieve the same insulation properties. For both these reasons, but mainly due to cost, the Quaker Community has chosen the second approach of creating a vapour barrier and managing moisture issues.
Breathable materials can be much more expensive and may also require more space; that is, they need a thicker layer to achieve the same insulation properties. For both these reasons, but mainly due to cost, the Quaker Community have chosen the second approach of creating a vapour barrier and managing moisture issues.
-
Older homes can be retrofit and insulated to a high degree of comfort, but more care is needed. Failure to understand and take into account how older buildings perform is the cause of many unintended consequences - which can be extremely costly to rectify later.
Potential consequences, include:
condensation on the inside of external walls, or within the wall structure
mould, dust mites and bed bugs
frost damage
rot of floor and roof timbers, dry rot, wet rot
insect attack (e.g. wood worm)
increased indoor humidity and reduced indoor air quality (e.g. a persistent distinctive smell)
re-pointing falling off.
Therefore, care is needed but these issues can be designed out with careful planning.