The orangery and boot room roof is a contiguous flat roof with a glazed central roof-light lantern to each room. It is my view that flat roofs are notorious for leaking and should therefore be avoided at all costs. However during the design phase I was concerned that if the orangery roof were to be sloping, constructed entirely from glass as a conventional modern conservatory the solar gain in summer would drive the internal temperature uncomfortably high rendering the room unusable as a sitting or dining room. I did want the orangery to be well lit though so the compromise was a single storey addition to the house with a flat roof and roof-light or lantern structure. Having conceded that the orangery roof would be flat the next decision was how it would be constructed. The most cost effective construction would be to use a modern polymeric waterproofing membrane solution such  as Rhenofol or Fatra. Both essentially use PVC membrane sheets that are fitted to the roof and water tightness is assured by welding seams at sheet joints or at formed areas with a heat gun.  Whilst this form of construction is effective it does not look as attractive as a traditional lead roof. As the bedroom windows from the main bedroom suite look out over the orangery roof we decided to opt for a traditional lead roof.

The orangery roof was built into the RSJ structure described in “Bulletin 18” as a timber frame covered in marine plywood sheets. This steel and wooden structure was then covered with a lead sheet cladding to make it water-tight. There are various grades of lead that can be used. These are designated as “Code 4″ or Code 9” for example. The number refers to the weight of a square foot of the lead sheet. Accordingly at nine pounds weight per square foot Code 9 lead sheet is quite thick and would normally be used on the most prestigious buildings. Code 4 lead sheet is quite normal for general domestic use. However in view of the quality of the build we wish to achieve we opted for Code 6 lead sheet for the orangery. The following photographs show the process of fabricating the lead cladding:-

The plywood-finished wooden structure of the orangery roof ready for lead cladding

Lead sheeting and tools made ready. Note that these are placed on the temporary cover on the up-stand to which the roof-light lantern over the boot-room will be fixed.

Drainage gullies are formed and the cladding begins to take shape.

Some joints in the lead are welded.

The joints in the lead sheets are formed by beating the lead into shape over wooden formers called “mop-sticks”.

Orangery lead gutter box.

Completed orangery lead roof showing mop stick joints.

Aerial view of the completed lead roof Note the two rectangular formers to which the orangery and boot room roof lights will be fixed. These are covered with a temporary PVC sheeting.

The structure of the staircase of the main stair hall that is accessed from the front door of the ground floor and provides access to the first floor is best explained by reference to the screen shots from three dimensional computer aided design (3D CAD) model shown below. The first illustrates the overall form of the so called imperial staircase. This is a staircase with divided flights with the first flight rising to a half landing from where it divides into two symmetrical flights, both rising with an equal number of steps and turns to the next floor.

Imperial Staircase computer model showing the divided flights of stairs rising from a half landing.

When constructed from stone each step is separately crafted and assembled into the structure and relies on each step being supported by the step below rather like the individual elements of a masonry arch support each other. Indeed the CAD screen shot below showing the side view of the staircase illustrates how the steps to the half landing effectively form one side of an arch.

Computer model side view of the staircase showing how the first flight of stairs to the half landing forms one side of an arch form.

By reference to the floor plans in the Architectural Style and Floor Plans page of this blog it can be seen that the dinning room fireplace structure forms a buttress to help support this half arch on the other side of the supporting wall which also divides the stair hall from the dinning room. Initially it was intended by the architect that the staircase and associated first floor gallery should be constructed entirely out of stone. The problem with this form of construction is that there is a limited number of sources of stone that are certified to be able to achieve the torsional strength necessary for the stairs and gallery sections that are cantilevered from the surrounding supporting walls. When presented with samples of such stone we felt that none was a particularly decorative stone in that the samples didn’t look much better than concrete in our opinion! Moreover fabricating the stair and gallery structure in this way would be very expensive requiring the precision forming of a large number of substantial, heavy blocks of stone. The staircase is an integral part of the house central core structure and so obviously needs to be constructed along with the ground and first floor walls. Once built therefore a highly expensive finished item would have to be protected or even put out of bounds for the balance of the build programme so that it would not be damaged during the process of the remaining work.  After much deliberation and after consulting JGB, the ground-work and concrete form-work contractors that we had engaged, we decided that the core of the stairs and gallery floor would be manufactured as an in-situ cast reinforced concrete structure that would then have a decorative stone cladding. Apart from being a much more economical approach it has the advantage that the unclad concrete stairs can be used during the rest of the build since the cladding can be added as a final finishing operation. Additionally there are a large number of decorative stone finishes to choose from. In the CAD models the reinforced concrete core is shown in blue with the decorative cladding shown in the creamy yellow colour. The undersides of the gallery and stairs shown blue in the CAD picture below will eventually given a plaster finish.

Computer model view illustrating the underside of the staircase and first floor gallery as it will be seen from the ground floor of the stair hall.

Computer model of the staircase and first floor gallery viewed from above. The parts of the diagram shown in blue in this view of the model are the parts of the stairs and gallery that are embedded into the supporting walls. the diagram shows how the stairs and gallery are cantilevered from the supporting walls.

The photographs below show the concrete formwork under construction and the completed staircase with the concrete cured and formwork removed. The pictures show how slender the stairs and gallery floor are so that they appear to “float” in mid-air.

Timber formwork for the left hand flight of stairs and gallery floor under construction.

Right hand stair flight form work.

Stair formwork viewed from the dining room via the partially completed stair hall/dining room wall.

Lower stair flight formwork.

Completed stair formwork showing the steel reinforcement in place.

Completed concrete core of the Imperial style main staircase with the formwork removed.

A view of the concrete core of the left hand side of the main staircase.

Staircase with formwork removed from the soffit of the galleried landing.

A view from the library door of the staircase and gallery soffit.

A view from the kitchen door to the stair hall of the staircase.

The above ground building (i.e. the ground floor and first floor) is of a conventional double skin, cavity, block-wall construction with a substantial amount of thermal insulation built into the cavity. During the design phase we considered using ground source heating for the house from an ecological point of view. However the structural engineer advised that the Ridge End sub-soil being mainly sand does not provide a good medium for heat to transfer from the ground to the extensive underground heat exchanger pipework that would need to be installed as part of such a system. I was also concerned about the technical risk associated with such systems since ground source heating is a relatively new technology compared to conventional gas boilers. I came to the conclusion that there was an element of “eco-tokenism” associated with such systems and considered that I was probably better off spending money on as much thermal insulation as could practicably installed into the structure. For this reason, as in the basement, we opted for thick concrete block inner walls to give a high thermal mass and 100mm thick thermal insulation in the wall cavity. Therefore the inner skin was built with the blocks mainly laid flat to give a wall thickness of 200mm (8inches). Additionally the fenestration will be double glazed incorporating Celsius glass. Celsius glass is a state-of -the-art window glass which has the property of reflecting heat back to source, reflecting solar radiation out in summer and internally generated heat back in during the winter. Incorporating these simple but effective energy conservation measures from the outset of the build we decided that the heating system that will ultimately be installed is based on a pair of conventional gas boilers, in a dual redundant configuration for reliability. The heating system and fenestration will be the subject of a future posts to the blog.

The photographs below illustrate the cavity wall construction.

The rear elevation of the house showing the inner skin of the cavity wall with blocks laid flat and the partial installation of the Kingspan “Kooltherm” insulation blocks in the cavity.

The front elevation of the house around the front door showing the inner skin of blocks laid flat with the “Kooltherm” insulation blocks installed in the cavity and the partially completed outer skin with concrete blocks laid on end. Note the construction of the occulus windows either side of the front door opening.

The structure of the orangery is quite slender so to ensure its structural integrity it has been constructed around a frame of rolled steel joists (RSJ’s) The photographs below show the erection of the steel frame and the subsequent concrete block wall in-fill.

Erecting the orangery steel frame with the aid of a mobile crane.

The completed orangery steel frame. Nick the site foreman and Bill check out he boot -room dimensions.

The inner skin block work with insulation for the Orangery columns around the vertical RSJ’s of the framework. Note the Cotswold Guiting-limestone stone plinth.

A close-up of the stone plinth with its protective polythene sheet removed. The stone is sourced from a quarry in the Cotswolds and is known as Guitng Limestone. The concrete and brick block work above the plinth will be rendered with a lime-mortar like cream-coloured render to give the classical regency stucco against contrasting ashlar stone finish.

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Having created the main outer concrete cavity for the swimming pool as part of the main basement structure the next stage of the swimming pool construction was to line the cavity with insulation material. The insulation in the form of rigid poly-isocynanuranate foam boards similar to those used to insulate the basement walls was applied to floor and walls of the pool. These boards are about 100mm (4inches) thick and have a very low thermal conductivity to prevent heat loss from the pool water to the surrounding sub-floor of the basement.  Pipework for the pool water inlets and water filtration and sterilising system were installed into channels cut into the foam insulation.  Similarly conduits that will be used to house the electrical wiring for the lamps that will ultimately installed in the pool were also set into channels cut into the insulation.

Pool insulation with pipework.

When considering swimming pool construction, concrete is the optimum material of choice. The method of creating a single cast shell that is widely regarded as a leading method of construction for high quality, luxury swimming pools is “Gunite”, a dry spray method of spraying concrete. Gunite is a small aggregate and cement, mechanically mixed together and fed, in a dry state, into the hopper of a ‘gun’. The mixture is forced by air, supplied by a 600 cubic feet per minute compressor, to a nozzle, where water is added, and the resulting wet mixture is sprayed at high velocity on to the surface to be ‘gunited’. Other methods of concrete construction include Shotcrete, a ‘wet spray’ method of spraying a high cement content, small aggregate ready mix concrete, at velocity on to the shuttering and reinforcement. These two methods contrast with the poured concrete, or ‘Shutter and Pour’ method which involves pouring concrete into conventional wooden forms as used so far in the construction of the basement. Another option for swimming pool construction is to use masonry block where the walls are constructed with concrete blocks.

Before the gunite is applied however a matrix reinforcing steel mesh was constructed over the base and walls of the pool:

Swimming pool detail showing the thermal insulation, water filtration pipework and steel reinforcing mesh for the gunite concrete.

Applying the gunite concrete. This was really hard work and like holding on to the business end of a rocket!

Close up of the gunite being applied. It was a great demonstration of Newton’s third law of motion: action and equal and opposite reaction!

Another view of how the gunite was built up over the steel reinforcement, layer by layer.

Gunite applied little by little until the entire pool was covered.

Shaping and smoothing the gunite.

The Gunite or shotcrete method  has many benefits:

1. No Joints, No Cracks.

Owing to the way in which the concrete is applied, through a spraying method that typically builds up in layers, the Gunite pool shell is a complete, continuous shape  which is important to create a strong pool shell without joints that can give concern for leaks and potential cracking due to movement. Other materials used to construct pools include fibreglass, plastic and metal, but Gunite sprayed concrete creates a strong layered shell, which is extremely hard and dense, making it stronger than normal concrete. From this tough foundation, the pool can then be finished to create a highly durable, luxury swimming pool.

2. New Depths

A pool’s depth can often depend upon the selected method of construction. Some concrete pools are created using hollow blocks, which are filled with a concrete mix to form a solid wall. Pools built in this way however, have limitations on vertical wall depth, in order to withstand the stresses of containing several tons of water and the external soil pressure. Gunite pools can be made to be much deeper because of the high strengths achieved with the method and have no limitations on steel and concrete design.

3. Flexibility of Shape

The Gunite spraying method of construction is ideal for pools with an intricate shape, as the technique provides the flexibility to design and create a pool to any desired shape. Irregular curved shapes are much easier to construct with gunite. Although we haven’t exploited this aspect in the Ridge End pool since we have opted for a simple rectangular shape, the gunite method has made it easier to sculpt the steps and seating area into the pool.

4. Economical

For larger pools, where reinforced concrete would be used, a Gunite sprayed pool would almost certainly be a cheaper alternative. The Gunite method is faster to complete than the conventional shutter and pour method, which helps to speed up the entire construction process.

5. Personnel and Work Space

Gunite requires only a small team of operators, which includes the Nozzle-man, responsible for placing the concrete and controlling its hydration, the Gun-man, who regulates the supply of the mix and the air from the gun and the Mixer Operator who ensures the sand and cement are correctly proportioned and of good quality. The Gunite method is also useful for working on difficult access sites, as the operators require only a 50mm diameter hose to reach the working area, which can be up to 80 metres away from the plant and materials so less space is required during the construction process. This aspect of gunite was particularly advantageous in the confines of the Ridge End basement.

The almost completed pool showing the sculpted steps and seating area at the shallow end of the pool.

The subcontractor that we have engaged to construct the swimming pool is a company called Guncast Swimming Pools. Guncast takes its name from Gunite, having perfected the technique over thirty years of luxury pool design and construction. They will be responsible for the design, construction and installation of the swimming pool structure and all the associated water heating, filtration and sterilisation as well as the  air handling of the pool hall ventilation. They will also supply and install the sauna and steam room and associated plant.

Following the completion of the basement shell and the roof had been left for about four weeks to allow it it to cure to nearly full strength it was time to start constructing the ground floor features. The basement structure had consumed 347 cubic metres of water-proof pudlo concrete, 75 cubic metres of C35 specification concrete and 150 cubic metres of lean mix over-site “blinding” and back fill. It also incorporated some 120 tons of steel rebar reinforcement.

The photographs below speak for themselves and illustrate the emergence of the ground floor rooms.

From front to back of the photograph, in the foreground the west elevation is seen with the window openings for the drawing room. The bricklayer in the picture is constructing what eventually will become the open fire chimney of the drawing room. Beyond, the dining room begins to take shape and at the far side of the dining room is the kitchen. The window openings to the orangery can be identified by the dull red steel lintels.

This is a wider angle view of the west elevation showing the window openings for the drawing room to the right of the picture and the library windows to the left.

This is a view of the south elevation with the two kitchen windows under construction.

This photograph shows the foundations for the orangery and “boot room” adjacent to the kitchen. The openings with the dull red lintels are for the windows from the orangery to the kitchen. The large opening will eventually be the casement door from the kitchen to the orangery. The opening with the bright, galvanised lintel is the link from the boot room to the kitchen.

This is a view of the curved side of the stair hall under construction. Note the timber former used by the bricklayers to achieve the correct circular form. The opening shown is the doorway from the hall to the kitchen.

The interior of the walls of the basement are lined with Kingspan Kooltherm K8 Cavity Board which is a premium performance insulation, with a fibre-free rigid thermoset phenolic core, faced on both sides with a low emissivity composite foil facing.

The whole of  the interior concrete walls of the basement are lined with an inner wall constructed from concrete blocks measuring 150mm x 215 mm x 440mm. However to reduce heat loss from the basement to the surrounding earth this inner wall is constructed with a cavity that contains Kingspan Kooltherm K8 cavity insulation board. This is a premium performance thermal insulation with a fibre-free rigid thermoset phenolic core faced on both sides with a low emissivity composite foil surface film. We have opted for insulation board that is 100mm (4 inches) thick to provided better than normal thermal insulation performance. This construction design means that the inner walls will cause the basement to have high thermal capacity and superior insulation to the surrounding ground so  that it will maintain a steady temperature requiring minimal heat input from the house heating system. The photograph illustrates the inner wall design whilst under construction. Some 8500 concrete blocks will be used in the construction of the basement interior.

The complete perimeter of the basement walls includes a corbel structure to reinforce the join with the wall and the basement roof/ground floor. This has caused a small complication to  the basement inner lining wall where it meets the basement roof. The insulation and block work has had to be reduced in size to accommodate the corbel as can be seen in the photograph. Specifically this has involved using two bricks faced flat with another brick laid on end nearest the roof and much thinner insulation board. Inevitably the insulation at this point will not be as good but this is compensated for by the fact that all this structure will be above the suspended ceiling of the eventual basement.

Charlie Viner the senior brick-layer on site smiles for the camera whilst constructing the basement inner lining walls.

Ollie builds one of the walls that forms the swimming pool changing room.

Mortar for the bricklayers is delivered to the basement in tubs by the fork-lift truck. These are lowered down through the ground floor slab penetration that will be eventually occupied by the house lift and spiral staircase .

Empty mortar tubs are returned to the surface for refilling.

The internal structure of the basement begins to take shape. Here the entrances to the TV room (far left) the IT/multi-media equipment room (middle) and the basement toilet (right) can be seen. Note the cavity above the toilet door which eventually will accommodate a ventilation duct. The lower edge of this cavity indicates the eventual height of the basement ceiling. The internal structural walls are constructed from concrete blocks that are 100mm (4inches) thick, laid flat, rather than blocks that are 150 mm (6inches) thick that are used for the basement lining.