Heritage Retrofit

BCD SPECIAL REPORT ON

HERITAGE RETROFIT

FIRST ANNUAL EDITION

THE EASY WINS

A strategic approach to improving

energy efficiency in traditional homes

RACHEL COXCOON

HE PAST three years have seen

an explosion in retrofit activity,

not least because of the heavily

promoted (but now defunct) Green Deal

programme. External wall insulation in

particular has been promoted heavily by

government as the number of unfilled

cavities and lofts has diminished and

policymakers’ attention has turned to

the ‘hard to treat’ sector, which includes

almost all buildings of traditional

construction.

However, the list of

approved measures under the Green

Deal did not include some of the simplest

available interventions. An unfortunate

side-effect of this omission has been

to focus public awareness on the more

expensive, disruptive and (for traditional

buildings) potentially damaging

measures

at the expense of easier, cheaper and less

disruptive ones.

Growth in demand for these more

expensive measures has also created

opportunities for less skilled operatives

to move into this area of work. This

has increased the risk of poorly applied

external wall insulation systems being

carried out by general building firms

without the specialist knowledge needed

to specify each system to the bespoke

needs of the house in question. This is

especially true of traditional buildings,

which function differently to modern

ones, particularly with regard to how

air and moisture move around them.

Modern buildings rely on a high level

of air and moisture tightness, and the

design aim is to create a sealed envelope

that keeps most moisture out through

the use of moisture-resistant materials

and finishes. Excess moisture such as that

generated in bathrooms and kitchens

is typically expelled mechanically via

extraction fans or, at the very least,

trickle ventilation in windows.

Applying an external render that

adds to the already impermeable design

can significantly improve some more

modern buildings in terms of thermal

performance. By contrast, traditional

homes (partly because they pre-date

the technical ability to achieve moisture

tightness) have tended to work with flows

of moisture. Damp from the ground,

driving rain and occupant use would have

travelled through the walls and occupants

principally relied on sunshine, wind,

heating and ventilation through windows,

chimneys and draughts in order to keep

the building at an acceptable equilibrium.

Since many traditional homes were

not originally constructed with an internal

bathroom, plumbing or central heating,

and because the idea of taking a daily

bath or shower would have seemed like

madness to many of our predecessors,

the amount of moisture generated

daily by a household would have been

much lower. Most traditional homes

now have these features, so the fabric

of those buildings must deal with far

higher levels of moisture than in the past.

When coupled with the application of

impermeable insulation materials and

insufficient ventilation, this can have

disastrous consequences. Moisture that

would previously have travelled through

the walls is now trapped inside. Mould

and mildew can build up and eventually

cause damage to the fabric. It is therefore

vital that those living in traditionally

constructed homes are asking potential

contractors the right questions about the

system that will be used and the way that

excess moisture will be dealt with.

Less well documented, but perhaps

of equal concern, is the effect that new

external finishes can have on the historic

significance of many traditional buildings.

The Centre for Sustainable Energy (CSE)

Tightly packed Georgian housing in Bath: intrinsically sustainable design with a low ratio of external envelope

to interior