We have been very busy in 2014

by grosvenor on November 11, 2014

I know it has been a long time since I last found the time to update the website with all the projects Grosvenor has been working on in 2014. Over the next few weeks it is my intention to put that right! The various project I will cover include a new welcome centre building, constructing paths and reinstating a river bank for the National Trust, a full refurbishment of a basement in a grade 2 listed building in Hove, a beautiful conservatory on a wonderful country cottage in West Sussex, bespoke trellis fencing and a reconstruction of the Japanese pergola at Nymans gardens.

But for my first report, I am going to focus on the construction of a stunning contempoOrangery - April 2014 (3)rary Orangery for a client in West Clandon.

This first image is of the site at the planning stage.

Grosvenor was engaged by the client to carry out all of the construction and landscaping works in order to build an Orangery to the rear of his home. Alitex (manufacturers of exceptional conservatories and greenhouses) had introduced us to the client as a contractor with whom they have successfully worked with in the past and who could trusted to deliver a product reflecting the quality of the roof lantern, patio doors and windows they were supplying and installing.

The site was to prove a difficult one in terms of the ground-works required to meet building control approval, being both on a slope, having a sub-soil of London clay and to cap it all being in close proximity to a mature willow tree. As a result the structural engineers design required the construction of a reinforced raft style foundation slab supported on 4 concrete piles to a depth of 9m. To achieve this our team of ground-workers initially reduced the levels of what is called the oversite (the footprint of the new building) to the required depth This is always calculated from the finished floor level required and in this case consisted of the following: 20mm floor cover (tile and adhesive),15mm electric under floor heating mat and latex seld levelling compound, 75mm floor screed,a damp-proof membrane, 100mm foil backed insulation, 250mm reinforced concrete slab thickened to the perimeter (outside 500mm) to 500mm in which a reinforced steel edge beam was constructed, a damp-proof membrane and finally 150mm of a polstyrene type expansion/ contraction board (Cellcore HX). A total oversite dig of 860mm!Wilcockson - Raft  (3)

Our piling contractors were then able to excavate the piles as per the structural requirements. essentially a pile is a load bearing column that transfers the load attached to it down to a point whereby that load can readily be supported. Concrete piles are the norm which consist of a drilling a hole in the ground (mini or needle piles are typically 150mm in diameter) and back filling with concrete complete with steel reinforcing bars.

Following this and after some works to alter the arrangements for storm water drainage, the ground surface of the oversite was laid over with the Cellcore boards – different specifications for under the edge beams and for under the floor slab. The function of the Cellcore boards (offcuts can be seen behind the reinforcing mesh in the image) is to isolate the entire raft foundation from the expansion (when wet) and the contraction (when dry) of the sub-soil. Sandy soils are relatively unaffected in volume from when they are waterlogged to when they are dry and therefore do impose varying conditions onto foundations, however clay soils do (note the cracks appearing during the summer months if your lawn is on a clay soil) and London clay is considered as one which is affected more than most! This problem is accentuated by trees which draw moisture out of the soils at a rapid rate and are therefore very much a part of the calculations when a foundation is designed.

Wilcockson - Raft  (1)

Once the Cellcore boards were in position, the shuttering was constructed to create the exact sizing of the orangery and the whole area was then lined with the first of the damp-proof membranes. The steel edge beams were then made and attached to the top of the piles and two layers of steel mesh were located at the correct depth with in the concrete slab and interconnecting into the edge beam reinforcing steel. The concrete was then poured, vibrated to remove any trapped air bubbles and tamped off to a smooth finish. This image shows the second layer of reinforcing mesh just about to be covered with concrete.

The masonry structure thereafter was relatively straight forward being a 100mm fully filled cavity with with both internal and external skins in blockwork to the top of the parapet where the cavity was closed with an insulated closer. Steels and lintels had been accurately set on appropriate padstones in order to support the roof lantern and carry the masonry and roof loads over the patio doors and window apertures. The roof structure was then installed in a format known as a ‘warm’ roof (the structural timbers are all to the inside of the insulation), firrings (under the insulation but over the roof joists) are used to create a fall on a flat roof to ensure the rainwater runs off in the direction required. The deck is then installed consisting of 12mm OSB and very long screws, the boards are extended up the inner side of the parapet wall above the roof line and across the wall cavity finishing just short of the outer edge of external block. A bonded rubber membrane was then installed to the entire roof and parapet not only weather-proofing the roof but also the parapet wall and the access to the cavity. Lead flashing were the made to wOrangery Complete - Nov 14 (2)eather the joint between the roof lantern and the rubber membrane. The parapet was finished with a stone capping.

Alitex were able at this point to install the roof lantern, the patio doors and the window. First fix electrical works were carried out and then the exterior was rendered, the floor insulation, second damp-proof membrane, the floor screed laid and the interior plasterboarded (ceilings) and plastered to a smooth finish. After a short drying out period, the decorations were then applied internally to match the extended kitchen and externally to match the house. Finally internally the second fix electrical works were carried out including the under-floor heating mat, the latex self-leveling compound to secure the mat and then the floor tiles laid. Outside, a close-board fence was constructed to the boundary line and a raised patio stepping down to lawn level was also constructed using black bricks to match those on show to the house and Indian sandstone. Other touches included the making of two planted borders.

Orangery Complete - Nov 14 (3)Reflecting on, and viewing the finished product my thoughts are inclined towards the fact that so much of this project cannot be seen and to remind all who intend to carry out building works that groundworks are so often the great unknown and should be tackled by a skilled and competent team.

If any of the above article  coincides with a similar project you maybe considering then please call Martin Blake for a discussion and a no obligation quotation.

 

 

Previous News