Progress Gallery

Lawtech Ltd was appointed as Principal Contractor to carry out major refurbishment works to three high rise tower blocks for Chester & District Housing Trust.

In July 2010 we were approached by its Framework Client British Gas to develop a design and cost model for the upgrade of three large tower blocks in the Blacon area of Chester. These were to be upgraded to current building regulations in respect of the thermal performance of the properties. The scheme was to be part-funded under the Community Energy Saving Programme (CESP) by British Gas.

The CESP targets households across Great Britain in areas of low income to improve energy efficiency standards and reduce fuel bills. There are 4,500 areas eligible for CESP. CESP is funded by an obligation on energy suppliers and electricity generators. It is expected to deliver up to £350m of efficiency measures (Source DECC).

We developed the initial design further with the client’s architects, structural engineers and surveyors to include a large element of other works to take advantage of the scaffolding being in place for the funded works. We tendered for and secured these other works as an addition to the contract.

The Building Structure

Wimpey No-Fines

The Blacon towers were constructed using the Wimpey No-Fines method. No-fines concrete is a non-propriety material used for the construction of walls in dwellings and was very popular in the post war era. George Wimpey & Co Ltd developed a system of housing using this material and traditional building methods from the mid 1940’s onwards. Since the system of construction involves cast in-situ walls the method is very adaptable and can accommodate several configurations.

In order to use load-bearing no-fines concrete walls for structures over 5-storeys in height, it is necessary to use large wall thicknesses which is uneconomical in terms of speed of construction and useful floor area. High-rise buildings are therefore constructed normally using a reinforced dense concrete frame with cast-in-situ no-fines concrete infill walls. The no-fines walls, which are usually 12 inches thick, are rendered externally in a variety of coloured finishes using natural stone chips as dry dashing. The dense concrete frame is mostly encased by the cast-in-situ no-fines concrete walls. The use of no-fines concrete makes it possible to cast up to 25 feet of wall height in one lift due to the low hydrostatic pressure generated by the dry uncompacted mix. Internally the no-fines concrete may be hand plastered although generally dry-linings have been used. Floors are mostly cast-in-situ dense concrete slabs although precast concrete floors have occasionally been used. The concrete roof slab is usually 5½ inches thick and is finished with an asphalt waterproofing membrane. The surface dressing generally comprises white limestone chippings on bituminous solution to reduce the affects of solar radiation.

The Plan

Work commenced on site in December 2010 with the agreed scope of works as follows:

• Prelims & Scaffolding
• New Insulated Flat Roof
• External Wall Insulation
• Renewal of Balcony Railings
• Internal alterations to Ground Floor Communal Areas
• Landscaping
• Concrete Repairs
• Asphalt Renewal

Suggested Elevation

• Ground Floor and 1st Floor - 2-storey brick plinth
• 2nd to 12th floor - New white render - better insulation
• Roof screen - New top for the building to hide the lift shaft/telcom works
• Balconies - New coloured glazing and railings
• Entrance bay / canopy - New entrance and canopy
• GROUNDS

New Landscaping

The Works

External Wall Insulation

Enabling works & Ducting

Before any external wall insulation can be installed there needed to be extensive enabling works to the buildings, not least to the large amount of gas pipes and flues. Current regulations require all external gas pipes to be encased in a conduit that can be easily accessed in case of emergency. As can be seen in the photographs above external gas pipes covered a large part of the building and this was encased in an aluminum powder coated conduit bespoke to this contract.

TECHNICAL SPECIFICATION

PROJECT:

Chester District Housing Trust

ECOROCK SPECIFICATION
Topcoat: EcoRock Top Coat
Base Coat: EcoRock Reinforcing Mortar
Grain size: 1.5mm
Topcoat Colour: TBA

1. REINFORCING MORTAR SYSTEM ON SLAB
The system is built up from an EcoRock aluminium base profile fixed at dpc level using a spirit level where necessary. The base profile is fixed true to line and level in full lengths wherever possible, using the profile connectors at joints, fixing at approximately 300mm centres using 6/60 hammer plugs.

2. FIXING OF ECOROCK SLAB
The EcoRock stone wool Slabs are fixed to the substrate using EcoRock Adhesive Mortar and applied with a 10mm serrated trowel to maintain a flat level surface. The slabs can be cut on site (with a sharp knife or fine- toothed saw), maintaining close butt joints. The slabs are set out in a staggered brick pattern, and alternatively lapped at external corners. Application rate varies between 4 – 5 kg per sq. metre.

Mechanical fixing of the slabs is done by drilling an 8mm hole through the slab into the substrate. The EcoRock TI anchor is pushed through the insulation into the substrate and the centre pin is then hammered home until the head of the anchor indents the surface of the insulation. The fixing anchors shall be positioned 100 – 150mm from each corner to give a rate of 8 fixings per sq. metre. On the 1000mm x 500mm slab it equates to 4 fixings. The anchor length should be insulation thickness plus 45 mm minimum.

3. FIXING OF CORNER PROFILE
The meshed plastic corner profiles shall be fixed, true to line and level at external corners, and true to window/door lines at window/door openings, before application of the reinforcing coat. EcoRock adhesive mortar shall be applied to both sides of the corner at maximum 300mm centres into which the bead shall be firmly pressed and then troweled flat. The EcoRock adhesive mortar shall be allowed to dry before applying the reinforcing coat.

4. APPLICATION OF REINFORCING COAT
The EcoRock adhesive mortar is applied with a trowel to a depth of usually 5 – 6 mm using a 10 mm serrated trowel and then levelled using a large steel rule. This gives an application rate of 4.0 – 4.5 kg/m² for a 25 kg bag. The universal reinforcing mesh is floated into the surface of the render and surface troweled level. The universal reinforcing mesh must be taken up to the corner profiles. The reinforcing coat is allowed to dry for a minimum period of 2 days before brush or roller application of EcoRock Masonry Sealer.

5. APPLICATION OF THE TOP COAT
The EcoRock Silcoplast topcoat is troweled on to a thickness determined by the grain size of the topcoat 1.5 – 3.5mm and then randomly structured using a plastic float. The finished coat has a roughcast character and is weather resistant, water repellent, and permeable to vapour.

6. APPLICATION OF SEALANT
EcoRock sealing tape should be incorporated at all windows, door reveals and other edges of the system where there is no metal profile.

7. STORAGE OF MATERIALS
Dry bagged materials must be kept dry and ideally stored on pallets. Bucketed products must be stored and protected from frost and direct sunlight.

New Insulated Flat roof

A complete strip off and replacement with a new insulated flat roof was carried out. During the design process Lawtech proposed a different specification to the one that was initially envisaged. Lawtech suggested the LPL liquid membrane roof due to its robust guarantee but mainly due to its ease of maintenance into the future. Lawtech agreed with the Client’s QS that full life cycle costs were important and it was essential that, on such a high structure, maintenance costs were considered. Access to the roof and getting materials to the areas was easy and did not require scaffolding to be erected. The LPL roof system allowed all this and was chosen by Client as an excellent alternative option.

Renewal of Balcony Railings

Initially the railings were to be removed and replaced with new. However, Lawtech’s design team, after site inspection, put forward a proposal to keep the existing frame, and replace the glass panels with something different. The Client worked on a design and as a result a saving was made against the contract sum but with no detriment to the long-term maintenance of the structure.

Internal fit out & Landscaping – Currently in progress

Lawtech is one of the largest installers of external wall insulation systems across the UK with offices in Rochester and Glasgow. Lawtech is UKAS accredited to ISO 9001 & ISO 14001 and is an active member of both the NIA & INCA.

Lawtech is able to act as a Principal Contractor on multi million pound “green” retrofit schemes installing and managing multiple energy saving measures, and in addition as a specialist façade contractor working with other contractor partners. We are able to offer advice and assistance in respect to grants and funds schemes available under CERT, CESP and from 2013 Green Deal.