December 2023

U-values
BREAKING DOWN THE NUMBERS
As Sunny Lotay, National Commercial Manager at PermaRoof Commercial, explains,
U-values have recently undergone regulatory changes to enhance energy efficiency in
new builds and renovations – but he says there is still some concern about how these
are calculated and how best to ensure the right value is given.
Below, he discusses what contractors need to understand about U-values for both
commercial and domestic projects.
U-values determine whether a building
meets the required energy standards,
helping drive forward more efficiency and
bringing down carbon emissions.
Thermal transmittance - the U-value - is
measured in units of W/m²K, which stands for
Watts/meter square Kelvin. This illustrates
how effective a material is as a heat
insulator by indicating how quickly it
will lose heat. The lower the U-value,
the more efficient the construction is at
keeping heat flow through the structure to a
minimum, for instance, a U-value of 0.5 will lose
heat at double the rate of a 0.25 structure.
If the U-value is not calculated correctly, the
impact is a concerning loss of heat, which for
homeowners and building managers means
higher fuel bills. Not to mention the negative
effect this has on sustainable housing and
commercial properties.
As experts in the industry of flat roofing, we know
the difficulties contractors face in trying to meet
tight budgets and deadlines – but we are also
aware of the importance of building regulations
and ensuring these are upheld for our clients and
customers.
Contractor compliance
In 2022, the UK building regulations were
updated to include revised, lower U-values for
new builds and renovations – essentially
requiring thicker insulation. These updates are
designed to improve the energy efficiency of
buildings and reduce the carbon footprint.
Left: Sunny Lotay.
The new regulations now state the
walls, floor and the roof all need to meet
minimum U-value requirements depending
on the situation and materials used. Part L of the
building regulations covers the requirements for
roofing in particular, which specifies that all roofs
to rooms (except those in unheated buildings)
must be thermally insulated to a maximum
U-value of 0.15 W/m²K for new build and
0.18 W/m²K for refurbishment.
These changes to Part L for England and Wales
have been implemented to cut carbon as part of
the Government’s move towards its target of Zero
Carbon Ready Homes by 2025. The aim is to
ensure building practices reflect this shift by
helping to reduce carbon output for new homes by
30%, and for other buildings by 27%, when
compared to the standards in 2013.
This is because heating and powering buildings in
the UK accounts for 40% of our total energy
usage. As a result, increasing the thermal
performance of all properties is essential for
reducing the demand for energy, the need for heat
and power in homes, and for reducing energy bills
too.
Calculation and installation
When calculating the U-value of a flat roof,
contractors need to consider all areas that
contribute to thermal performance such as
screeds, timber, air spaces, and plasterboard.
Many insulation manufacturers have useful
U-value calculators for an approximate figure.
But in practice, this can only be backed up
through correct installation.
If insulation is fitted poorly, with gaps and cold
bridges, then the U-value can be considerably
higher than desired, no matter how good the
individual products are.
When installing a flat roof, suitable insulation is
required to minimise heat losses in the winter
and control excessive solar gains in the summer.
This will help to conserve energy and ensure
thermal comfort is maintained within the
building. Without appropriate flat roof insulation,
the project will not pass building regulations.
Furthermore, speaking to the right people and
utilising expertise when needed will ensure the
installation achieves the best results. Whether
you are a contractor, homeowner or commercial
property owner, it is crucial to get the right advice
from reputable suppliers to avoid being mis-sold
or misinformed. PermaRoof has a team of
registered installers nationwide to provide
guidance to contractors on projects.
Contact PermaRoof
www.permaroof.co.uk
PermaGroup
50 TC DECEMBER 2023