20
BCD Special Report on
Historic Churches
19
th annual edition
going to be unexpected features below
ground, from vaults and early foundations
to Victorian gas lighting and heating
systems and, of course, human remains.
Features that are to be retained, such as
fragile brick vaults with shallow structural
arches, are often far enough below the floor
system to allow them to be spanned dry with
pre-cast concrete lintels but sometimes they
are too high and localised concrete caps
may be required, all subject to agreement
with the county archaeologist and designed
by an experienced structural engineer.
The health hazards associated with
old burial vaults and ruptured lead
coffins must be taken very seriously.
Minimum disruption
The nature of the
system and the speed of construction means
that a re-ordering programme can be carried
out with the minimum of disruption to church
activities. With the replacement of the floors
to nave and aisles in a large parish church,
for example, once the church committee
volunteers have taken out the pews and loose
furniture, the stripping out can commence
immediately after the Christmas break and
the church can be ready for use by mid June.
Disadvantages of the dry system
Few disadvantages have been identified
with the dry system to date but the
primary ones are explored below.
Floor levels
To date, the system has
relied on being laid to total flatness where
large areas are being installed because of the
practical difficulties of laying the crushed slate
substrate to very shallow falls. Small areas of
ramp are perfectly feasible, however. While
locally formed ramps can readily be included,
a suitable finished floor level must therefore be
agreed which addresses adjacent floor levels in
the optimum manner. Existing church floors
are seldom level and in a large parish church
there may be a difference of up to 100mm
between one end of the nave and the other.
Future floor fixings
Allowance must
be made for any future holes in the floor
(
for doorstops, staff or handrail sockets for
example) by putting solid timber blocks in
the underfloor heating layers and recording
their positions accurately. Although there
are specialist tools which can cut the upper
layers without disturbing the pipes below,
this is not without risk and the consequences
of a hole in a pipe would be very serious.
‘
Tick-over’ temperature
The thermal
response time is very rapid compared to other
types of underfloor heating but as there is
little dense material to provide any kind of
thermal mass, the flow temperature of the
water should be higher than that required
for a conventional screed. During the cooler
months the heating system needs to be
kept ‘ticking over’ continuously at about 12
degrees so that the heating can quickly be
brought up to the desired temperature.
Housing the manifold(s)
A home will
need to be found for the manifold(s) – the
multiple pipe union(s) where single feed and
return pipes are divided into several circuits of
piped warm water. Manifolds must be located
in easily accessible and well-ventilated places.
On balance, dry systems offer perhaps
the safest and most practical method of
introducing underfloor heating into a church.
When combined with the introduction
of more comfortable and flexible seating,
underfloor heating has obvious attractions for
the congregation, and can help to ensure the
viability of an underused church. However, not
all older churches will be able to benefit from
this approach, particularly where their existing
flooring, fittings and finishes are deemed too
significant to change. The effects of fluctuations
in temperature on ancient and fragile fabric also
need to be taken into account. Although more
easily renewed than a screed, the introduction
of a dry system of underfloor heating is not
reversible and the loss of any historic fabric
always requires careful consideration. In
principle and in practice, each case is unique.
Further Information
British Standard BS EN 12058: 2004, Natural
stone products. Slabs for floors and stairs.
Requirements, BSI, 2005
British Standard BS EN 1264–5:2008, Water based
surface embedded heating and cooling systems.
Heating and cooling surfaces embedded in
floors, ceilings and walls. Determination of the
thermal output, BSI, 2009
Jupiter Heating Systems Ltd
see page 21
Stone Federation Great Britain
Underfloor Heating Manufacturers’ Association
John Minter
RIBA was co-director of Cyma
Architects from 2000 to 2007 and has been with
Lee-Evans Partnership since 2007. He has been
the project architect for four church re-ordering
projects involving underfloor heating.
The re-ordering programme at St Mary the Virgin,
Ashford, Kent, pictured, was carried out by the
following contractors and consultants: Jupiter Heating
Systems, Keystone Natural Stone Flooring and Paving,
Farnrise Construction, Clifford Rickards Associates,
Canterbury Archaeological Trust, English Heritage
and MLM Consulting Engineers.
Typical manifold installation
Typical new stone floor/existing wall junction detail incorporating perimeter duct for power/audiovisual cabling (Image: Lee-Evans Partnership)
