General
This section provides a detailed review of 4 over-cladding options to the external walls, which includes:
- Option 1 – Full Architectural Over-Cladding (Kingspan)
- Option 2 – Full Rendered Structural Cladding (Structherm)
- Option 3 – Brickwork to Ground Floor Level with Architectural Over-Cladding above.
- Option 4 – Brickwork to Ground Floor Level with Structural Rendered Cladding above.
For all four options, the existing windows would require replacement with either new PVC or aluminium double glazed units that are compliant with the current Building Regulation approved document, part L2b.
In all options we have assumed that the building will remain in occupation throughout the works and that the existing cladding panels will be retained. Any existing services on the face of the building including external lighting, rainwater goods, signage etc would need to be refixed to the new cladding.
The aluminium capping detail applied to the parapet of the refurbished ophthalmic unit could be replicated on the parapet of the single and multi-storey sections of the ‘New wing’.
Additional energy saving features can be introduced in option 3 and 4 by way of the integration of partial fill cavity wall insulation. Option 2 could have integral insulation within the structural cladding. Insulation of this nature would potentially give 0.35 W/m2/K, which would satisfy any future changes to the current building regulations.
To comply with BRE recommendations, horizontal fire barriers should be placed at every floor level above 2 storeys. These barriers comprise of 900 x 200mm rock fibre panels, density 140kg/m3, applied in a continuous strip around the building. However, the only area where this would apply is on the plant room towers, which are not included within this study.
Option 1 - Kingspan – Optimo Architectural Cladding
This option proposes that the existing single and multi-story buildings be over-clad by means of an architectural cladding panel as highlighted in the appendices. The architectural cladding panels considered for the purpose of this report is the Kingspan KS Optimo wall panel.
The Kingspan Optimo range comprise of an insulated steel cladding panel, which comes in a range of finishes including ribbed and smooth options. These panels are 70mm thick with a Polyisocyanurate insulation core, compliant with part L2 of the Building regulations.
The panels have a hidden jointing system and come in 600, 900 or 1000mm widths and range between 1.8m and 12m in lengths.
To minimise disruption to the hospital the existing cladding would be retained, and the Kingspan cladding would be fixed to a new secondary steelwork frame, which in turn would be fixed directly back to the existing stanchions.
There is a possibility of interstitial condensations occurring between the retained and new cladding panels and a vapour barrier fixed within the cavity between the existing panels and the Kingspan panels would prevent this from occurring.
Our proposal allows for the removal of the existing window units from the Oxford Method Research cladding panels and for new PVC or aluminium casements to be incorporated in to the Kingspan cladding system. To enable the windows to be fixed between the existing panels and the Kingspan panels a new galvanised steel frame would be required around the window openings. This would be integrated into the secondary frame work.
Window fabricators approved by Kingspan include Hyatol Windows Limited and S Dudley & Sons Limited. Both of these companies have extensive experience of working with the Kingspan range of products.
Kingspan offer a 10 year standard warranty on their Optimo Range. In addition, the suppliers can provide a 15 year warranty on the standard PVDF coated Optimo range. This is extended to 20 years if the Corus Colorcoat Celestia finish is specified.
Advantages and Disadvantages
- Modern architectural appearance
- Improved thermal efficiency
- Retains original wall units, minimising disruption
- Requires secondary steel frame work
Option 2 - Structherm - Structural Render
Over-clad the existing single and multi-storey OM buildings by means of a rendered structural cladding system. Please Refer to Drawings L051424 01 – 04.
The structural cladding system proposed is manufactured by Structherm Building system. Structherm have been previously specified to clad Oxford Method type construction, for which we enclose the Dfee case study for William Parker school project in Daventry (Appendix C).
The Structherm structural insulated Render System comprises of a structural steel wire spaceframe module in the form of a series of warren trusses interconnected by vertical and longitudinal wires. The panels have a 55mm thick core of expanded polystyrene encapsulated within the space frame. The external face of the panel is finished with a primary layer of reinforced base coat render and finally with a Structherm Flesscoat Cortina marble aggregate. This gives the panel good impact resistance, flexural capacity and ability to provide racking shear to the existing structure.
To minimise disruption to the hospital the existing cladding would be retained, and the Structherm structural cladding would be fixed directly to the main steel stanchions. Based on survey findings, the position of the external stanchion relative to the external face of the cladding would require an infill timber packer the height of the column to be mechanically fixed to the face of either the UC or the RHS. This would provide a continuous support to the structural cladding.
The BBA certificate (No 03/4022) for the structural cladding system (enclosed in Appendix B) demonstrates the panel can be designed to span 3.0 metres without secondary support, and thus not laterally loading the existing cladding panel. In addition, the panels could be designed to provide a degree of racking capacity to the overall frame.
The panel type specified by Structherm is a T100 GE50 (expanded polystyrene) which would suffice to achieve a benchmark U-value of 0.35 W/m2K when fixed back to the envelope.
A preliminary interstitial condensation risk analysis indicated no potential problems with this method of over-cladding. However, in order to ensure absolutely no risk from interstitial condensations a vapour barrier would be fixed within the cavity between the existing panels and the structural cladding.
We understand the window sizes are to be maintained hence new PVC or aluminium casements could be inserted into the existing units. Where window/door reductions are proposed, Structherm have recommended a double panel arrangement to accommodate the reduction.
BBA certificate for the structural cladding suggests the Strutherm system should remain effective for at least 30 years with a low level of maintenance.
The storey high panels are lightweight and can be manhandled on site by one person.
The additional weight of the structural cladding is in the order of quarter of the weight of brickwork, hence by inspection no further enhancement would be necessary to the foundation for a two-storey building with structural cladding.
The proposed installation could be covered by an insurance warranty against retrospective defects of materials and workmanship.
Advantages and Disadvantages
- Improved thermal efficiency
- Retains original wall units, minimising disruption
- Wet trades could cause unnecessary mess
- Will require periodic repainting or cleaning
- All materials can be carried on to site
Option 3 – Brickwork to Ground Floor Level with Kingspan Optimo above.
Brickwork over-cladding to the ground floor levels with architectural cladding panels to the 1st floor levels of the OM buildings. Option 3 should be considered with and without partial fill insulation. Please Refer to Drawings L051424 – 07.
Where window/door reductions are proposed, this will require the introduction of a steel angle at the new window sill height.
The brickwork panels should be fixed back to the stanchions by means of stainless steel masonry ties. Propriety galvanised lintels and cavity trays are to be considered over both the doors and new windows.
In accordance to the perimeter detail at ground floor, rolled steel angle may require fixing to the face of the ground floor slab to provide sufficient support and bearing to the external leaf of brickwork.
Vertical expansion or control joints will be determined by three factors; the construction sequence, existing construction joints, or at minimum of 12 metre centres. As detailed on the ophthalmic unit, a brick pier could possibly conceal the movement joint.
Where cavity wall insulation is deemed necessary, a 40mm thick phenolic insulation board would satisfy the U-value requirement. It can be fixed back to the existing cladding panel by either a propriety adhesive or mechanically by two part plastic dowel and plug assembles.
For all areas of the building above 1st floor height an architectural panel range such as Kingspan KS Optimo would be fixed back to the existing frame work as described in Option 1. The architectural cladding panel could be detailed either flush with the masonry wall or stepped in.
Advantages and Disadvantages
- Brickwork appearance ‘links’ the building visually with the Ophthalmic Unit
- Improved thermal efficiency
- Retains original wall units, minimising disruption
- Requires additional trades on site
Option 4 – Brickwork & Strutherm Structural Render
Brickwork over-cladding to the ground floor levels with a rendered structural cladding system to the 1st floor levels of the OM buildings. Option 4 should be considered with and without partial fill insulation. Please Refer to Drawings L051424 – 05.
This option would combine the brickwork over-cladding described in Option 3 with render structural cladding system described in Option 2. The structural cladding could be detailed either flush with the masonry wall or stepped in.
Advantages and Disadvantages
- Brickwork appearance ‘links’ the building visually with the Ophthalmic Unit
- Improved thermal efficiency
- Retains original wall units, minimising disruption
- Requires additional trades on site
- Wet trades could cause unnecessary mess
- Will require periodic repainting or cleaning
©2004 Oxford Method Royalties Management Group