Paxton Court self-build houses by Sheffield Solar Building Cooperative, 1983 -1986
EXTRACTS FROM REPORT WRITTEN BY CEDRIC GREEN AND JANE LINFOOT
This housing is included in the Pevsner Guide to the Buildings of Sheffield
This is a project involving the construction of thirteen low cost, low energy, passive solar houses and a demonstration building in Sheffield UK . Sheffield City Council have supported the project since its inception in 1982 and the Coop acquired the site in Gleadless in 1983. Having obtained planning permission for the site the Coop purchased it from the Council, paying the market price, but negotiating an arrangement by which the payment was in instalments. The majority of the construction work has been carried out on a self build basis by the Coop members, each of whom will purchase a house as they are completed. This form of labour was decided on to keep building costs low and in the hope of greater satisfaction of the occupiers with their own houses.
Work on site began in June 1983. Initially it was expected to take 18 months to complete the project, but in the end it took 3 years. I was a founder member of the group and built one of the houses. The hours spent on architectural work, technical drawings, work in obtaining permissions, supervison etc. was given in return for an allowance against hours of labour on the buildings. The original house design was developed for "Moya" , a house on a small site in Suffolk, and the way in which this house type could be used at a higher density was developed and entered for the 1st European Passive Solar Housing Competition in 1980 "A House for All Seasons" where it won joint 2nd Prize. This layout was adapted for the site in Gleadless, and new house types were developed for the steeply sloping parts of the site.
Three basic house types were developed, namely, a three bedroomed semi detached (T2), a semi detached starter home (T3) and a single storey court house (T1), all offering scope for variation and extension. All materials and labour skills are traditional to the building industry. The houses have a timber frame internal construction, with brick and blockwork insulated cavity outer walls, tiled roofs and timber and glass conservatory. Construction was designed carefully to make things straightforward for self builders.
This project has a number of unusual and interesting aspects; its solar and low energy designs, its self build approach, the cooperative organisation and the low-cost building implications. The following report aims to describe the project generally and give information on each of these aspects in more detail and in relation to the project.
SITE & HOUSING LAYOUT
The site, at an altitude of 600 metres, is located in the suburb of Gleadless and is approximately 3 miles from the centre of Sheffield.The area is easily accessible by road and is well served by public transport. The site slopes towards the south west, and presents a pleasing aspect overlooking Meersbrook and across the valley. It is well drained; and water, gas, sewer, mains drainage and electricity services are in close proximity. The site arrangement is effectively a cul-de-sac, with no future possibility of through traffic. Access to the site has been made by constructing a short spur road off Spring Close Mount. The site, and land adjoining, is owned by the Sheffield Corporation. In layout the houses are arranged around a short combined pedestrian and vehicle access which is classed as a 'mews court'. Every house has a garage space and car parking space, and the intention is to try to create a feeling of community in the grouping and landscaping treatment of the space by avoiding the appearance of an estate road. Future development planned by the Corporation is for the wooded land adjoining the east side to become a recreational park. Pasture land adjoining the southern side is scheduled for further private housing development. The north side is bounded by Gleadless Road and the western side by a Corporation housing estate. But between Gleadless Road and the highest houses, there was to be a communal open area, to be developed as allotments or orchard by the Residents' association. At the end of the scheme, the residents voted to add this space to the gardens of the top houses, and a small extra price was paid by the owners.
THE HOUSE DESIGNS
The Coop houses are low energy houses, and the designs incorporate features for passive solar energy collection and thermal storage. The thermal system is described in detail in its own chapter. Here we will discuss the background to the Coop designs before considering each in detail.
The aim was to provide a house which would respond to the seasons
and to its users. The winter living space was designed to be small,
snug and warm. In spring the walls were designed to fold outwards,
allowing the house to expand and to become spacious and open plan.
The project was designed to be low cost, providing the minimum of
accommodation in traditional, more expensive, construction, for
winter use. The conservatory provided a large area of extra space
which could be used as living space constantly throughout the summer
and on most spring and autumn days, yet at a cost which was relatively
low. The open plan arrangement of the winter accommodation aimed
to maximise use of a small space. The conservatory acted as a solar
collector, and the passive solar gains from this linked to an appropriate
storage system and a well insulated house structure were aimed at
making a house which was nearly self-sufficient in heating, except
in the coldest part of the year.
L-shaped conservatory was a response to the site orientation, and
the plan which evolved placed the bathroom and utility space as
a services core in the angle of the house not benefiting directly
from solar gain, and provided a courtyard outside on to which the
the Coop project was envisaged as consisting of a cluster of these
L-shaped or courtyard houses. Various factors led to the development
of additional designs.
accommodation in the courtyard house was large enough for a family,
and this was reflected in its cost. It seemed appropriate to develop
a cheaper starter-home alternative, with possibilities for later
expansion. This idea was increasingly attractive, as it offered
scope for a higher density of site development and therefore lower
individual costs for shared services. In addition to these factors,
the site considered by the Coop was fairly steeply sloping in places
and not suitable in
these places for the L-shaped design.
Coop members were anxious to have semi-detached houses rather than
terraced houses, and so the design developed was for pairs of semis
with a continuous roof. Taking account of the slope of the site,
each pair would consist of a three bedroomed, two storey house,
with the possibility of future extension into the roof space and
staggered in relation to this, a single storey house further up
the slope, which was a true 'starter home' but could be extended
upwards to provide bedrooms in the roof space later.
eventual site arrangement includes five L-shaped houses and four
pairs of semis. In fact, only the first pair of semis was built,
with one side as a starter home, as thereafter the Coop members
who were having starter homes found they could afford the extra
money and opted for
the extra space in the larger side of the semi, and so the final
three pairs of houses have staggered roofs and handed plans.
L-shaped house plan is set out on a 640mm grid, which is determined
by the 610mm square horticultural glass panes used in the vertical
glazing of the conservatory. The structural centres are at 2560
mm with four grid units to each structural bay.
roof trusses are supported at 2560mm centres on posts at the division
between house and conservatory and on the external walls of the
The L-shaped House Design
The L-shaped house plan is set out on a 640mm grid, which is determined by the 610mm square horticultural glass panes used in the vertical glazing of the conservatory. The structural centres are at 2560 mm with four grid units to each structural bay.
The roof trusses are supported at 2560mm centres on posts at the division between house and conservatory and on the external walls of the house.
The double row of posts between the house and conservatory support deep double beams which provide lateral stability and a services duct. The four posts at the centre of the house provide the corners of the central air duct through which air is drawn from the high level ducts along the top of the conservatory down into the hypocaust.
The post and beam construction between the living area is closed with glazed doors on winter days with the addition of insulated shutters on winter nights. This 'wall' between the heated space of the house and the conservatory can be opened up completely to provide a continuous living space in the summer - the glazed doors are hinged and fold back against the posts and the shutters can be re-positioned to form a ceiling in the conservatory which gives summer shading to prevent overheating. In certain cases patio doors have been put in instead of folding glazed doors, but these do not allow full opening of the space between living area and conservatory.
In order that the habitable rooms open on to the conservatory, it is preferable to locate the kitchen and bathroom in the services 'core' in the square of the house not opening on to the conservatory. The entrance of the house is also integrated on to this side of the house, leaving the conservatory aspect of the house with privacy.
The basic house type plan consisted of three structural bays in each direction. The internal layout is very flexible, and the differing requirements and preferences of the five Coop members having these houses have given rise to five very different houses within the same basic structure. In some cases, full or half bays have been added or omitted from one wing of the house, to increase or reduce the size.
The rooms which open on to the conservatory have high sloping ceilings, as can be seen from the section, whilst the ceilings in the services core are horizontal at 2.3m high. In some bedrooms galleries have been extended into the room, with their floors supported on the truss ties, to take advantage of the high ceiling space. Usually use has been made of the area above a flat ceiling for storage areas.
The accompanying plans show the variations which have developed. The last of these houses to be built was varied in that the central rows of posts were placed slightly further apart, in order to accommodate a door between them. This is typical of the continual modifications and evolution of design in response of individual needs which has been part of the project. In certain cases this has produced results which are a long way from the original intentions, but the low-energy aspects of the design have remained intact.
The Semi-detached Houses
The semi-detached houses have certain principles and design features in common with the L-shaped houses. The ratio of conservatory area to house floor area is much smaller however. The associated reduction of potential solar collection is counteracted by the compact nature of the accommodation which leads to lower heat losses.
In the three-bedroomed houses the kitchen, bathroom and staircase are located on the northerly side of the house, which cuts into the hillside. The living room can be opened to the conservatory to provide a continuous space in summer, using the same system of folding doors and shutters as is found in the L-shaped houses.
In the starter home, the initial accommodation is provided on the ground floor, with the kitchen and bathroom on the north side at the 'back' of the house. The utility room or study is also located on this side of the house; this latter being the space into which the stair will be fitted at a later date. The living room and bedroom areas open on to the conservatory. The accommodation provided here is minimal, but ideal for a single person or couple, who wish to take advantage of lower rates whilst having the option of expanding their accommodation later without the expense and inconvenience of moving house.
The starter home can be 'expanded' by making use of the roof space to provide up to three bedrooms, and inserting the dogleg stair in the downstairs utility or study area.
The section of the starter home differs from that of the three bedroom semi. The starter home is essentially a single storey house with room for expansion in the roof space whereas the three bedroom semi is a two storey house with room for expansion in the attic. The attic space in the starter home, however, has much more headroom. The structural section and trusses used for each of these house types are different, although they are designed to have a common roof ridge. The two house types interlock beneath the common ridge, the starter home being staggered backwards and having a higher ground floor level, making this pair of houses ideally fitted to the slope of the site.
In fact, only the first pair of semis was built with one of each type of house in the pair. The remaining three pairs were built with both halves as three bedroomed houses. The roof trusses, which are situated in the centre of each house are designed to give maximum free space across the centre of the attic where the headroom is highest, and this gives potential for future expansion. The only starter home to have been built took advantage of this potential immediately and was built with three bedrooms in the attic space. As yet none of the two storey semis have been extended into the attic space, although gable windows to the attic have been included. In these houses the dogleg stair can be continued in above the existing staircase to give access to the attic.
Again these houses are built relating to a one directional grid of 640mm which relates to the glass size of the horticultural panes used. The roof lights in the sloping ceilings of the bedrooms relate to this grid; the roof truss and double posts are also positioned on this grid.
The scope for individual plan variation is less in these houses than in the L-shaped houses, but again individual requirements have resulted in differences and innovation. The most marked of these is the planned extension forward of one conservatory which will result in a double height and double depth conservatory. "MOYA" - House for Mr and Mrs C Oldham - Charsfield, Suffolk
"Moya", the house for which the original design concept was developed, was in fact built by a local Suffolk builder in the summer of 1984, whilst the Coop project was on site and provided further opportunity for design variation and development. Because of the close links with the Coop project it seemed appropriate to include details of "Moya".
construction of the Coop houses is a hybrid of load bearing brickwork
and timber framing. The main variation in construction is between
the semi detached, two storey houses and the L-shaped single storey
houses. Further variations arise from the different gradients encountered
on various parts of the site, and from the desire of the Coop members
to experiment with different techniques and solutions to problems
as work progressed.
reason for the hybrid construction was to take advantage of the
speed of construction associated with the erection of a timber frame
which had been pre-fabricated on site. The masonry walls provide
much of the thermal mass which provides a large amount of the heat
storage in the building and these also provide support for the timber
frame once they are constructed.
following paragraphs will outline the construction of the various
building elements and highlight variations in these. The general
annotated cross-section of the type 2 building will illustrate their
relationship and the specification clauses will give further detail.
footings are concrete strip foundations below walls, stepped where
necessary. The posts of the timber frame have pad foundations. Where
there is a concrete sub-slab to the floor this has been thickened
for blockwork partitions.
slope of the site, which is very steep in places, meant that many
of the external walls of the houses are retaining walls. The construction
of retaining walls is obviously less straight-forward and more expensive
than simple external walls and they did provide the self builders
with problems, especially at first.
methods of construction of retaining walls were tried, in order
to try to overcome the practical difficulties of continuity of the
damp proof membrane. What looks fairly simple on section often becomes
very complex when it becomes three-dimensional.
height of earth retained was limited to a metre wherever possible
and the variation of construction were:-
the exception of the 6 houses at the top of the site the ground
floor construction of the houses is a hypocaust construction, through
which warm air from the conservatory is blown by a fan, and the
hypocaust acts as a heat store. The mechanics and theory of this
is explained more fully in the section on the thermal system.
hypocaust has a 100mm concrete sub-slab on hardcore, sand blinding
and damp proof membrane. This sub slab was laid before the external
walls were built above ground level and edge insulation of styrofoam
was included below it.
hypocaust construction was usually completed once the shell of the
house was completed. In the first two houses this was constructed
of bricks on edge which were arranged in spaced rows to support
sheets of corrugated tin or plastic on to which concrete was poured
to give a 100mm thick slab. A screed finish was put on top of the
As the Coop members did not like this method in practice later hypocausts were constructed of bricks on edge supporting 50mm concrete paving slabs with a 50mm screed laid on top of the slabs. A further refinement was to lay two bricks flat instead of one brick on edge, as these provided a more stable base for the paving slabs than the bricks on edge.
certain L-shaped houses the slope of the site meant that the fill
below the sub slab in the floor bays at the extreme south western
end of the house was going to be excessive, so in such cases end
bays had precast concrete beam suspended floors, with insulation
As these parts of the floor were a long way from the central air duct where air was to be pumped into the hypocaust it was felt that sacrificing the hypocaust in these bays was not going to detract from the thermal system of the houses concerned.
the floors in the conservatories are simply tiled concrete slabs,
but in one house the hypocaust construction has been taken right
through into the conservatory, with under slab insulation.
important element in the hypocaust construction for the functioning
of the thermal system is the provision of gaps and grills to return
the air from the hypocaust extremities to the onservatory.
important is the arrangement of the bricks in order to direct the
air moving through the hypocaust so that air will go to all parts
of the hypocaust and will not short circuit and return to the conservatory
before it has given up its heat to the hypocaust structure.
in the houses on the lower part of the site the bays with suspended
concrete floors are isolated from the main hypocaust construction,
in the six houses at the top of the site the whole upper hypocaust
floor is actually formed from precast concrete beams.
slope of the site in this area meant that the original hypocaust
construction was not feasible. Here the cavity between the site
concrete placed on the ground and the suspended concrete floor form
the hypocaust cavity into which warm air from the conservatory is
can be seen from the sections, the timber frame is much more extensive
in the one storey house design than in the semi detached houses,
although in both cases the timber elements are all cut and drilled
according to detailed timber schedules, and lists of elements leads
to great speed in frame construction.
the single storey house first, the timber frame is prefabricated
initially. Once frame construction begins the frame can usually
be erected in a weekend on top of the sub slab of the floor. The
frame is supported by a series of temporary posts which support
the frame until the external walls are built. The frame is squared,
levelled and anchored and then provides the setting out for the
external walls which are built up to the frame. In later houses
the backs of the trusses were supported on a wall plate and the
temporary posts removed and used on the next house.
advantage of this method is that the roofing felt can be put on
immediately the frame is secured, the external walls can be built
up and the temporary supporting posts can be removed once the walls
have been built to support the frame. The roof can be tiled immediately,
the conservatory glazed and the whole building envelope can be completed
in a smooth, fast operation.
the semi detached houses, the timber elements are pre-fabricated
and integrated and fixed as the external walls are built.
there are variations on the number of trusses used. This particular
self-build group is short of people confident in carpentry skills,
and so in some cases, instead of having a truss and boarding on
the gable walls, brickwork load bearing gable walls have been taken
to roof level.
views show the timber frame construction.
all the internal partitions were designed to be stud partitions,
for ease of construction and later flexibility. Coop members, again
due to a lack of carpenters, found blockwork construction preferable,
although this entailed thickening of the floor slab below partitions
and obstruction of the hypocaust in places. Blockwork partitions
were also preferred due to their increased sound insulating properties.
Where precast concrete beam floors were used, blockwork partitions were limited to one storey in height, so upper floor partitions were constructed in studding.
external walls were constructed of an outer skin of brickwork, a
75mm cavity, 100mm inner skin of insulating 'Thermalite' blockwork
with foam cavity fill insulation injected after construction.
floor was insulated with 1m wide 50mm thick styrofoam edge insulation.
semis the first floor ceiling joists were 125mm deep and insulation
was put in here in addition to between the 125mm roof rafters. Where
the attic space was not going to be used immediately, extra insulation
was included above the first floor ceilings. Generally 200mm of
fibreglass insulation was used, in between the joists.
the single storey houses, where the ceilings sloped, separate ceiling
joists were positioned below the roof joists to allow for at least
200mm of insulation and to give space for ventilation, over the
the ceilings are flat 200mm insulation is included between the ceiling
shutters provide winter insulation between the houses and their
shutters are constructed from plywood glued to a simple timber framing
with a 25mm polystyrene insulating core. They were made on site
initially, but later were subcontracted.
are situated on the outside of the doors between the living and
the conservatory areas. They are designed to be closed on winter
evenings, and are intended to be moved to make a horizontal ceiling
in the conservatory to provide summer shading. Various methods of
fixing and shutter operation have been devised, depending on the
preferences of individual house owners. The original concept was
to have four shutters to each bay, hinged in pairs from the structural
posts for winter use, and hinged to swing upwards from the beams
for summer shading. This system utilises hinges with removable pins.
methods of shutter fixing adopted include simple sliding shutters,
which are more easy to operate with patio doors.
detailing of the conservatories is in keeping with the original
design philosophy of the houses; they are designed to be simple
to build, and to be glazed with horticultural glass to keep costs
low. In fact, regulation changes meant that the roofs of the conservatories
are glazed with 4mm float glass or toughened glass rather than with
horticultural glass. For safety, where toughened glass was not used,
an inner pane of polycarbonate or acrylic was specified, fixed with
beads under the sloping glazing.
grid of the whole house is a 640mm grid, with larger bays of four
grid units. This grid size originates from the horticultural glass
which comes in 610mm panes.
conservatory frame is built of simple planed timbers, and the glazing
is carried out as indicated in the details, with a putty-free method
which makes glass installation much quicker and easier.
of using rebated timbers, stops are planted on each vertical glazing
bar. The glass is bedded on a pvc covered foam strip and held in
place by parting beads pinned to the stops. On the roof glazing
beruing strips are screwed to the glazing bar, holding the glass
down on the pvc covered foam strip.
on these details have been used in practice, depending on personal
the base of each vertical glass window a kick panel of pvc is fixed
Louvred panels are included for ventilation.
Spandrell Panel Collector
spandrell panel solar collector is constructed with a black painted
ply panel, with insulation between the panel and the inside of the
house. The glazing of the panel is fixed with beads using horticultural
glass to the same detail as in the conservatory.
In certain cases where rooms have a high ceiling in the single storey houses, the spandrell collector begins higher up, the area below it being glazed to let light into the room above the shelf over the double beams.
SYSTEM (SOLAR TECHNOLOGY)
design of the single storey court houses is based on one that received
a second prize in the 1980 First European Passive Solar Housing
Competition and consists of an L-shaped plan with a continuous greenhouse/conservatory
inside the angle enclosing a small court. The concept which dominates
the design is of the greenhouse as a seasonal extension of the living
spaces, which are small, but with the addition of the conservatory
extension, are effectively quite spacious. The semi detached houses
are similar to the L-shaped houses in the principles of design,
conservatory, shutters and thermal storage.
wall which separates the rooms from the conservatory consists of
an inner plane of glazed doors and occasional opaque panels where
appropriate, and an outer plane of insulated hinged shutters. The
shutters hinge back in winter to open half the area over the glazed
doors, but in summer the whole of the shutter plane is raised to
form a complete ceiling in the conservatory and the doors and panels
fold right back, to open the room to the conservatory. Even when
the glazed doors between room and conservatory are closed the small
rooms retain a spacious feel due to the lack of visual barrier between
the rooms, the conservatory and the outside. This is obtained without
the disadvantages of draughts and heat loss which usually accompany
large glazed windows, due to the conservatory which acts as a buffer
zone. Summer overheating of the conservatory is prevented by the
shutter ceiling, which provides shading and isolates the solar gain
through the conservatory roof glazing, where it can be dissipated
through ventilators or, if required, drawn into the heat store.
the role of the conservatory in the house design can be seen to
be many fold. Not only does it provide extra living space for much
of the year, but it also acts as a buffer zone, reducing heat and
ventilation losses from the side of the house it covers, in addition
to its function as a passive solar collector of both direct and
diffuse solar radiation.
going on to discuss further the various parts of the house concerned
with collection and use of solar energy, it is worth considering
the other features and measures incorporated in the design, which
aim to minimise the energy consumption of the house. The lower the
energy consumption of the house the more significant the contribution
of solar energy becomes when considered as a proportion of energy
consumed. High levels of insulation are used in the roof and walls
of the house. 200mm minimum of insulation is incorporated above
ceiling level, using a structure of separate roof and ceiling joists
to give space for this in cases where ceilings are sloping. The
external walls have 75mm cavities, with insulated thermalite blockwork
inner skins, and cavity wall insulation. The houses are dug into
the hillside on the northern sides to reduce exposure and here are
insulated on the earth side of the retaining walls.
on the northerly sides of the house are kept to a minimum and where
they do occur they are small. All windows are double glazed and
all door and window openings are draught stripped to reduce infiltration
heat losses which can be significant. Lobbies and porches also reduce
ventilation heat losses from the houses, as do the conservatories.
shutters are incorporated on the large glazed areas facing on to
the conservatory. These south facing 'windows' get considerable
direct solar gain on sunny days and the use of night shutters ensures
that the overall effect of the large south facing glazed areas is
energy gain, not energy loss.
choice and sizing of the backup heating system is important. Gas
was the fuel chosen here, for a number of reasons. It is relatively
cheap per unit of energy when compared to electricity and oil; it
is clean and convenient and the cost of gas boilers and appliances
is low when compared to solid fuel appliances. Predictions of energy
usage for each house were made using SCRIBE and this enabled radiators
to be sized fairly accurately (rather than over sizing 'to make
sure' as often happens) and appliances were selected to ensure maximum
efficiency at the required output.
energy terms then the houses were 'well insulated, well sealed boxes'
but the internal planning of the houses can also have an effect
on their energy consumption. Bathrooms and kitchens were located
on the coolest side of the houses, whereas living rooms were placed
on the sunny, warmer side of houses.
the site, the houses were arranged so as not to overshadow each
other and each was orientated to maximise the solar gain.
summarise the design considerations and features which are important
for the low energy aspects of the house. Features of the design
specifications involved with the solar energy collection and storage
aspects come into three main categories, which are energy collection,
transfer and storage.
HYBRID AND PASSIVE SOLAR SYSTEM
main solar collector is the conservatory, which acting like a greenhouse,
collects energy from direct radiation and also diffuse radiation,
which results in a temperature rise of the air in the conservatory.
The warmest air is at the top of the conservatory, where the spandrell
panel collector acts to heat the air further. The spandrell panel
collector is an insulated matt black surface with glass panels in
front, and an air space between the two. The black panels behind
the glass absorb the solar radiation and air passing between the
glass of the panels is warmed. The spandrell panel collector is
situated above the glazed doors between the conservatory and the
living area and warm air from the conservatory is drawn through
the spandrell collector and warmed further before being transferred
to the heat store, via ducts and a fan.
air ducts are arranged slightly differently, depending on the house
type, the basic principle being that they are air tight and sealed
and allow air to be sucked from along the top of the spandrell collector,
down via a vertical duct and into the heat store which is under
the floor. Air transfer is by a single fan situated at the base
of the vertical duct. This fan is switched on automatically by remote
sensor when the air in the spandrell collector reaches a certain
temperature, and switches off again if the air falls below a certain
temperature. The fan prevents reverse siphoning of air out of the
heatstore into which the warm air is blown is an underfloor cavity,
with a heavy floor slab above, and often bricks for extra storage
spaced within the cavity. This is referred to as a hypocaust and
although each operates similarly, it can be constructed in various
of its method of construction, the principle of operation is similar,
in that warm air from the conservatory is blown into the underfloor
cavity, where it gives up 75% of its heat to the floor slab above
and remaining heat to obstacles it passes and the slab below. Having
travelled the length of the hypocaust (the air flow direction being
determined by the arrangement of 'obstacles' within the hypocaust)
the air is released back into the conservatory through ventilation
grilles, now cooled.
floor slab stores the heat and releases it slowly to the rooms above.
The release of heat does not appear to be impaired by carpet on
the floors of the rooms, but seems to be more affected by the floor
finish beneath the carpet.
actual hypocaust construction is done in one of two ways; the cavity
is formed between a 50mm concrete cover of the earth below the floor
and a floor formed of precast concrete beams with block infill and
covering screed, or a 100mm concrete sub slab is laid and bricks
are spaced out over this to support concrete paving slabs with a
screed on top. The choice of method used depends largely on the
cost of labour, as the first method is more expensive for materials,
and the second method, whilst being cheaper in terms of materials,
is more labour intensive.
construction of the house with thick, heavy bases of retaining walls,
and blockwork inner skins to external walls and in certain cases,
blockwork inner partitions, also provides a fairly heavy construction
envelope with associated heat storage properties.
houses also have 'bread box water heaters', which effectively act
as solar pre heaters for the conventional hot water tank. Water,
on its way to the hot water cylinder, passes first through a black
painted cylinder behind glass placed in a position where it will
receive a lot of direct solar gain. On a sunny day the water reaches
the main water tank at a warm temperature and so cools the existing
hot water in the tank much less than would a normal cold water feed
and also requires much less energy to bring it up to an acceptable
hot water temperature. The bread box water heater can be drained
and by-passed in winter to prevent freezing, although in a normal
winter this should not be required as the thermal mass of the water
in the tank and the double glazing will prevent freezing.
are the more practical descriptions of the solar features of the
designs, which are also summarised in diagrammatic form.
LOW ENERGY & SOLAR FEATURES
The buildings are orientated to maximise solar gain and arranged
to avoid overshadowing each other.
High insulation levels in roof and walls to conserve energy.
Small windows on the 'dark' northern side of the house; windows
are double glazed.
Economical planning of the heated area of the house.
Large amount of thermal mass in the building structure.
Control of ventilation and condensation using conservatory and lobby
as buffer zones.
Weather stripping to all door and window openings.
Conservatory as passive solar collector of direct and diffuse radiation.
Spandrell panel solar collector inside conservatory.
South facing double glazed doors opening on to conservatory to maximise
direct solar gain in 'heated area' of house.
Fan assisted transfer of solar heated air from collector to heat
Hypocaust floor heat store.
Bread box water heater.
Insulating night shutters.
Use of planting and hinged shutters to give summer shading to conservatory.
North side of house dug into slope, with additional earth berming
for shelter and insulation.
PROJECT INCEPTION & CO-OP FORMATION
way in which Sheffield Solar Building Coop was to be run was determined
at a very early stage in the project, by the small group of people
initially involved. Monthly Cooperative meetings were held from
a very early stage.
Whereas in some self build projects each group member builds their own house and the only work done jointly is on the shared parts, such as the road and service provision, this solution to group organisation was rejected here. One reason for rejecting this method was the difficulty of financing the building of all the houses at one time. In addition to this, the lack of building experience of most members of the group meant that no-one felt confident about, or indeed wanted to be involved in, such solo efforts. There was also a fairly strong ideological desire on the part of many group members to run the project on cooperative principles. The outcome of this was that the Cooperative was formed under the umbrella of ICOM - the Industrial Co-ownership Movement. The Coop was registered as a Friendly Society, non-profit making limited liability company, with its 'employees' the self-builders, as it 'owners'. The capital was #250 from each member.
Initially, the group involved numbered about seven; however the site finally chosen and its relatively high price meant that to make the price of each building plot economically viable, it would be necessary to fit thirteen houses on the site. The group size was correspondingly increased.
The original members had come together following an article in the local newspaper on Cedric Green's solar house designs. Other people had joined in after hearing about the project and inevitably some people had withdrawn at various stages. An advertisement was put in the local paper to find people to join in the project to increase the numbers to thirteen.
Of the thirteen people who eventually became the building members of the Coop, fewer had building skills than had originally been intended. The only person with carpentry skills dropped out at a very late stage and it was not possible to replace him with a person with similar knowledge. This lack of previous building experience led to very slow progress of the project initially and extended the expected duration of the project. The later profile of Coop members will outline the skills of the group. WORK ORGANISATION
organisation of the project was based on the Coop members working
together, initially on two houses. As each house was completed it
was to be sold to its owner, and work on the next house could begin.
In this way the Coop could limit the amount of money it needed to
borrow at any one time. In practice, work was often in progress
on more than two houses at a time, because it was more practical
and economical to excavate and put in foundations of a number of
houses together in the dry weather. The main object was project
planning to ensure that it was always possible to complete and sell
the next house in progression, whilst remaining within the loan
limit. At the same time, it was important to ensure that there was
always indoor work to be done during the bad weather. How this worked
can be seen in the chapter outlining the site diary.
building member of the Coop was required to work on the project
for a certain number of hours each week. The required number of
hours varied from 20 to 30 hours, depending on the size of house
that person was having. The working of hours was operated in a flexible
way, and any person having done less hours than they should have
done over a six month period was required to pay the Coop for the
hours they had not worked. This amount was paid in cash, worked
out on an hourly rate.
a person's house was completed to a 'habitable shell' standard it
was sold to them. The house price included the site cost, an amount
for shared road and service installations and the cost of materials.
A refundable premium of £2,000 was also added to make sure
that they did not stop working until all the houses were completed!
The costs involved are outlined in the chapter on finance.
Only hours worked by the man of each house were counted - these are the people referred to as 'builder members' of the Coop. Wives & partners were members of the Coop and whilst many did spend many hours working on site, not just making tea but often doing heavy work - these hours were not counted. This was decided at the beginning of the project. The suggested site rule, from the Self Build model rules, banning women and children from the site altogether was not adopted.
Within this basic framework there were variations, with the Coop occasionally employing skilled labour from outside the Coop for certain jobs and individual Coop members employing skilled labour from outside for certain jobs on their own houses.
Plastering and electrical work were the main tasks for which outside labour was used. Any decision over questions of cost or hour allocation were made at the monthly Cooperative meetings of all members.
Before the start of the project on site the Coop had agreed to employ a full-time site foreman, but this was not done, and site coordination was taken on by the most experienced builder in the Coop. The lack of an official coordinator did cause problems, especially in the early stages, due to the inexperience of many members. Towards the end of the project things ran more smoothly, as various people became more accustomed to roles and took responsibility for the various 'departments' with more confidence and with the benefit of experience.
In the early stages, there were many cases of 'learning by mistakes' but occurrence of crises, which at first, it must be admitted were regular events, diminished with experience. The severity of most such crises was in fact exaggerated by initial panic and evidence only remains of one or two!
Luckily many of the Coop members had jobs involving shift work, which meant that they times when they worked on the site were staggered. This meant that there were rarely times when there were too many people for the jobs or space available.
Architectural students from the University also came to work on the site as part of their course work, supervised by Cedric Green. As well as doing general labouring jobs, small groups took responsibility for building the porches on some of the houses.
The fact that the project was going to run a lot longer than the initially anticipated 18 months became obvious at a fairly early stage. Mostly people began to view the hours they worked at the Coop as a way of life or a hobby rather than a chore, and also as an investment. People also found that it was much easier to work their hours once they had moved into their houses on the site and did not have to spend time travelling each time they worked on the site.
House and plot allocation
In theory, it is difficult to imagine how thirteen building plots on a site could be allocated to thirteen families, in a way that maximised satisfaction and minimised argument. In practice, the allocation was very logical and did not present a problem.
There were three house types, and generally people's requirements and budgets matched them to a particular house type.
The site layout suggested a sensible sequence of plots on which building should take place and the position of house types on the site layout was also fixed.
Thereafter, it was simply a matter of sorting out at which stage in the project people were going to be in a position to buy their Coop houses. Some people had distinct preferences to move in as soon as possible and others had reasons for wanting to put this off for as long as possible! These timescale variations acted as a deciding factor in determining who had which of the houses of each house type. LOW COST FEATURES OF DESIGNS
The low cost of the house is achieved by a combination of:
1. The compact planning of the heated and finished area of the houses (excluding greenhouse & conservatory)
2. The inexepensive additional area of the conservatory extension to living space
3. A design based on a structural grid of 40mm with minimum waste of materials and use of standardised doors, windows and components
4. Construction to a habitable minimum standard to be finished by owner/occupier
5. Reduced building time by rapid erection of timber frame and completion of weathertight envelope
6. Simple design and use of off-the-peg standardised elements allow greater use of unskilled labour in the construction process
7. Involvement of house owners in the Cooperative, contributing labour on construction of own houses and communal facilities (drainage, road, landscaping, communal rooms)
The houses were conceived as being low cost, providing compact and minimal heated living areas, in traditional construction. The conservatories aimed to provide extra space to expand into, giving extra living space for summer and sunny autumn, spring and even winter days. This expandable living space was provided at much lower cost, whilst also doubling as a solar collector.
The running costs of the houses was to be minimised, by providing a very well insulated building envelope to the heated area, and by using solar energy contributions for space and water heating. This was confirmed by the monitoring of no. 11 in 1987-88.
In practice the Coop members have found that the money they had available allowed for much more than the 'basic' finishes initially intended. In the cases of the single storey court houses some have been built in an extended form, so that the resulting heated living area is very large. In many cases the basic fittings intended have been rejected in favour of luxury fittings. The self build aspect of the houses has contributed considerably to the minimising of the cost.