Timber research questioned by the concrete industry
The latest research findings and assumptions
from the UK Timber Frame Association (UKTFA) are questioned by the
concrete industry.
In a new report, ‘Comfort and Cost’, the
timber industry attempts to demonstrate the expected costs of
achieving the higher levels of the Code for Sustainable Homes
against a background of rising temperatures to 2080. A number of
design assumptions and misconceptions undermine the research
findings.
These include the statement that “the
difference in thermal mass between new build masonry and new build
timber frame construction is not a significant factor affecting
either thermal comfort or energy consumption, now or within the
lifetime of the building.” “In fact, the thermal mass provided by
masonry construction is becoming an increasingly important aspect
of housing design, as it helps ensure summertime comfort in our
warming climate”, explains Tom de Saulles, building physicist at
The Concrete Centre. “Even a moderate amount of thermal mass can
improve comfort in hot conditions, a fact supported by CIBSE Guide
TM36 which deals with climate change adaptation. Thermal mass can
also improve energy efficiency during the heating season, and if
used effectively in housing design will achieve a worthwhile amount
of energy savings over a building’s lifetime”, said de Saulles.
“This is can be seen by modelling standard house types using the
draft SAP 2009 tool, which takes fuller account of thermal mass
than the current version of SAP which will be replaced next
year”.
We would agree that thermal mass is one
of several elements affecting comfort, but In extreme summer
conditions the main adaptation measures available to timber frame,
i.e. ventilation and shading, are unlikely to be enough to keep a
home comfortably cool. The research suggests doubling the
plasterboard in timber frame homes, but this will have a limited
effect since it only increases the thermal mass of an external wall
from 9 kJ/m2K to 18 kJ/m2K compared to the 60
to 190 kJ/m2k available in masonry walls. “Even if you
double the plasterboard, it will still have three times less
thermal mass than that of an aircrete wall with dryling”, explained
de Saulles. ”Also with a timber frame dwelling there is no option
of having a concrete first floor which can contribute significantly
to the overall thermal mass.
The research also highlights the benefits of
air tightness in delivering energy efficient housing and claims
that it is easier to make a dwelling airtight using timber frame
than masonry. This is not the case, and it is important to note
that there are many tested examples of extremely airtight masonry
housing, both demonstration and non-demonstration, which use a
robust air barrier to ensure long-term air tightness with no
concerns regarding movement, twisting or dimensional stability.
Furthermore, it is unfortunate that the research does not give due
attention to whole live costs. Other areas conveniently overlooked
include maintenance issues, durability, fire risk, flooding, rot
and infestation.
“Thermal mass is one of the elements affecting
comfort”. It is good that this is recognised by the timber industry
but their argument of needing very little does not stand up to
scrutiny”, concluded de Saulles.
Ref: TCC622