Case Studies

Refurbishment and Extension of 1970’s Office Building

87 – 89 Pembroke Road, Dublin 4

Construction Value - €6.5M

Existing Building

The existing office building housed a professional institute with a bank branch on part ground and first floor. The building was T-shaped - three storey to the front and four storey to the rear, however the ground level comprised mainly of a reception area and small library/shop recessed. The impression of the building facing Pembroke Road, therefore was that of a two storey building sitting on top of a bank branch and void area.

The façade was constructed from concrete where the walls effectively provided the structure in a series of ring beams linked vertically with concrete piers. Yellow brick covered the façade and the windows were of a horizontal proportion formed in a hit and miss pattern.

 Facade before brickwork was taken down

Uncovering the Structure

As with many refurbishment projects, the nature and quality of the existing structure cannot be determined until it’s exposed. The process of design, however, by it’s very nature, must make some assumptions as to the quality and formation of the structure below the building fabric. When dealing with buildings which continue to function with sitting tenants, it is not always possible to carry out a detailed study of the structure at design and planning stages. The design, therefore, must take cognisance of the structure and principals in relation to proposed new facades need to be flexible as the exact nature of the structure cannot be determined until it is fully exposed. In this project, we made assumptions regarding the location of the vertical piers and height of the ring beams which were upstand; this means the depth of the beams rose from the floor level up to window cill level. Although, the brick façade seemed to be in good vertical alignment, we could not rely on the structure underneath to be plumb.

Exposed structure

Unlike a new build, a refurbishment project provides more technical issues to overcome. As with this project, the true nature and condition of the structure at design stage could not be determined. In many respects the design of new facades and glazing need to be carefully considered and design flexibility should be built-in when considering proposed finish and building systems.

The planning department will not be forgiving should the thickness of walls need to increase due to a secondary support structure being required to deal with out-of-plumb structures. Similarly, the client will not be happy with additional costs, programme overrun, liquidated damages etc. Of course, where there is not the opportunity to uncover the structure and have it surveyed prior to design, the client must be informed that there may be some further detailing required and the quantity surveyor should also make enough provision in preliminaries.

When we finally uncovered the structure, we found the upstand ring beams to be in sound condition but the edges were poorly finished leaving uneven surfaces and an uneven horizontal line. The gable wall, constructed of formed concrete, was also found to be out-of-plumb. The proposed facade was a granite cladding system suspended from a pinned steel hanging frame fixed back to a sub-frame providing a certain level of flexibility and tolerance. As each fixing needed a minimum level of cover (distance from the bolt to the edge of the beam/wall) each fixing location needed to be checked and supplementary measures were taken where there was insufficient cover provided, in the form of localised concrete pours or the addition of steel angles.

The Brief

As with most commercial briefs, our brief was to maximise the site and maximise the value.

This was to be achieved by increasing lettable floor area, modernising the office interior and providing up to date services and IT capability. The building layout also needed to be flexible enough to facilitate multiple lets.

Although the main building was going to be temporarily vacated, the bank premises were going to remain trading throughout the construction programme. In this respect, the bank were very accommodating and worked with the design team and contractors through the whole process. For example, our proposals included the removal of their existing external wall and construction of a new façade at ground floor level. The process of constructing the new façade included the insertion of thick steel plates before the front wall was removed in order to maintain security. Other areas such as common staircases and escape doors also needed careful attention. In a refurbishment project, where tenants are left in-situ, both the design team and contractor must work together as certain decisions need to be made and acted on quickly. Once the structure was uncovered, we found existing infill wall panels were not sufficient to maintain security therefore gaps needed to be filled and temporary steel plates secured overnight while concrete cured or mortar set.

Existing sites in built-up areas must also provide sufficient contractor compound areas and address boundary conditions. Access to gable walls may need the cooperation of your neighbour and if adjacent buildings are in close proximity, an offer to carry out a condition survey (or photographic) survey prior to construction should be made – this may include the insertion of tell-tails over existing cracks. In this respect, we contacted the neighbouring properties and agreed protection measures, access and treatment of common boundary walls.

The brief was further complicated as office tenants were considering the possibility of moving back into the building when completed. They required a small lecture hall and wanted to develop accessible multi-functional areas ground floor level.

 New site layout

Feasibility

When considering the feasibility of the site and environs, factors such as, working with existing floor plates, where to extend (rear/above) and working with existing structure all needed to be considered along with specific nuances such as; the location of the existing lift well, sitting tenants, how to maintain car parking to the front and rear and where to locate plant and services.

Site conditions included a fixed alignment of all properties fronting Pembroke Road, a general 3 to 4 storey height limit on adjacent buildings and a drop in size and scale to the rear where two storey mews houses were located off Pembroke Lane. The building’s restrictions included, a low floor to floor level, an internal lift well, a raised ground floor level preventing easy disabled access, sitting tenants and a need to carefully locate new structural columns in order to maintain car parking levels. Before the architectural design could be considered, firstly, the various site and building parameters were to be sensibly considered.

There main problems to overcome were;

1. Restriction on building height to the rear meaning extending to the boundary line would be an issue.
2. Restriction on building height to Pembroke Road due to the adjacent 3 to 4 storey height. The internationally renowned USA embassy is also only 3 commercial storeys tall.
3. Structure of ring beams and vertical piers.
4. Floor to floor heights only 3.07m.
5. Raised ground floor entrance.
6. Lift located internally restricting flexible building lets.
7. Visitor car parking required for the retail element of the bank.

Design

All good design takes advantage of site conditions but when considering a refurbishment project, challenges must also be turned into opportunities.

 We set out to maximise floor area. Our proposal increased the floor area from 2,293 sq.m (24,680 sq.ft.) to 3,837 sq.m (41,200 sq.ft.). This was achieved by extending to the rear but keeping the building line back from rear boundary walls. We also offered to incorporate sand blasted glass to the windows which overlooked the mews houses on the laneway. We also added a floor on top – as the floor to floor levels were only 3.07m high, an additional floor could be added without the building looking like it was out of scale and proportion in relation to the neighbouring buildings. In part this was also achieved by recessing the façade overlooking Pembroke Road. Due to restrictions on site coverage and plot ratio, the location of the plant room was proposed on top of the new floor. This area was positioned toward the centre of the building to ensure it could not be seen from street level.

The way in which the existing structure was formed meant that the series of ring beams and piers in the hit and miss pattern had to be maintained. The existing window cill level at only 680mm above floor level created problems in locating office desks beside the windows when the new raised access floor was inserted. The structure therefore informed how the façade was going to be designed. Unlike other buildings designed in the 1970’s, this property did not lend itself to being stripped back to a skeleton of columns and floors. A modern glazed façade therefore was not a practical solution. We therefore set to work within the confines of the hit and miss window pattern. We decided to regularise the façade design by reducing the window sizes, forming square openings. This was achieved by filling-in alternate right and left hand sections so that the new windows lined through vertically. As noted earlier, this was often difficult to achieve as the existing structure was often eroded at the edges or the piers were not necessarily aligned vertically.

 The completed 4 story height lobby

Once we achieved the square opening, the location of the window cill was a concern. In addition, we were raising the floor level by adding a raised access floor. We therefore decided to break up the window design by lifting the internal window cill level but maintaining the existing window cill level on the exterior. This was achieved by introducing sand blasted glazing to the lower section of the window and building up the wall behind.

The depth of the office floors and requirement to provide a flexible open plan with meeting rooms and cellular offices meant that natural ventilation was not practical. Therefore an air conditioning and heating system was considered as the only practical way of heating and cooling the internal layout. The floor to floor levels further restricted the type of system which could be considered. A close working design team is important in any project but is particularly important in a refurbishment project as each individual will bring unique skills to the table. Our M&E engineers proposed a new and innovated HVAC system which used the floor plenum to circulate the air rather than the ceiling void. This meant that the ducting could be kept to a minimum and vents were located next to desks where they could be further controlled locally – staff could control the heat/cooling by 5 degrees. One other and crucial consideration when adding a raised access floor into existing buildings is the height of the riser to the existing staircases. The floor is normally restricted to the riser height as the junction of the floor to the staircase is critical. Stairs generally cannot have differing riser heights and there are also restrictions if you intend to increase fight lengths or reduce lengths. Increasing floor height may also require the handrail and guarding heights to be increased to maintain regulatory standards. When creating a floor plenum, you are also creating a cavity and restrictions on maximum cavity dimensions will be relevant. In this project, we added fire cavity barriers into the plenum which also required fire dampers where the ducting passed through the barrier.

The issue of providing a level entrance for disabled access was another consideration. The existing floor level was raised by around 850mm in order to [in part] facilitate a small basement plant room. The relocation of services was crucial in being able to reduce the ground floor to external ground level meaning that the basement plant room could be demolished. As the bank were sitting tenants throughout the construction programme, this also meant that their floor levels were to be maintained.  The dropping of the ground floor left a void between the new floor level and that of the bank. Again, for security reasons, the temporary measures such as propping and securing had to be considered in advance. Once the decision was made to drop the floor level, this allowed a greater internal floor to ceiling height to be achieved and this leant itself to locating a small conference room directly off the reception area – in accordance with the brief.

Car parking was an issue for the bank as it aimed to maintain a retail function at this location therefore customer access and convenient parking was paramount. The existing car parking layout was not perfect with car space lengths of around 4 metres and a driving aisle of 3.5 metres. We initially intended to introduce a curved façade to the bank at ground floor level but this would have reduced the car park area further. Reluctantly therefore, we maintained a flat façade. Any attempt to redesign the parking layout to current standards inevitably resulted in a loss of spaces. Perhaps one of the few advantages of a refurbishment project is that you are dealing with existing site conditions. Rather than loose valuable parking spaces therefore, we decided to leave the existing layout as it was and instead concentrate on controlling accessibility by creating a one way system.

The brief’s requirement for ultimate flexibility meant that the internal lift was not suitably located for a multi-let property. We decided to turn this problem into an opportunity by forming a new structure to house the new lift outside of the front façade. We understood that this proposal would require a leap of faith by the planning department and this could only be achieved by designing a piece that was a statement rather than a small add-on. We decided to use a contrasting stone with a natural colour which was far removed from the grey granite. There were no structural restrictions with this element therefore we decided to maximise the glazed area with the use of structural glass in turn opening up each floor plate with natural light and views across the city. The contemporary style of this entrance façade was further extenuated by the rotating of the front plane to form a wedge. Both ends were glazed so that the red slab could be considered a stand-alone piece and the wedge shape allowed the insertion of a revolving door without impacting on the parking driving aisle. The entrance area leading into the communal reception was flooded with light through the three storey high void.

 

Proposed design

 

Finish and Completion

Through the design process many elements are considered for their ability to meet building regulation standards, durability, finish, colour and texture. In choosing a stone finish, the type of stone is crucial as, for instance, granite is hard wearing whereas sandstone and limestone can be soft and porous depending on where they are quarried. The texture or finish is also important and there are many ways in which a stone can be finished such as bush-hammered, sand blasted, honed and polished. For this project we chose a hard wearing granite for the main building façade but wanted to introduce different textures to form another pattern on the façade. To contrast and to create a sharp line around the window openings, we chose a dark navy blue. The stone was bush hammered and the square pattern picked out through sand blasting.

The sand blasting of glass to the lower sections of the windows creates a cloudy appearance similar to the finish on granite. The large geometric entrance slab was picked out in a red quartz sandstone which was polished to darken the appearance and provide an extra protective element.

We kept the material pallet simple and aimed for subtlety when choosing textures and creating contrasts by using the natural colour of stone. Stainless steel was used sparingly. We decided to provide a parapet upstand to the recessed penthouse floor in order to maintain proportions on the stone façade and this reduced the need for a full height handrail. The use of plate glass was also carefully considered. Apart from the entrance lobby, plate glass was only used as a canopy over the penthouse doors.

Good quality lighting was also a factor in detailing the façade. This element is often overlooked but the quality, type, style and finish of all elements which make up the building façade are key to maintaining a high level of finish and building design. The appearance of a building at night is important and consideration should always be given to this point if the building is to be lit in any way. The position of the façade lighting was chosen in two key locations. Firstly, large ground lights flood the façade from the ground upward, diminishing up through the building height. Secondly, we used an up-light to light the glazed canopies at penthouse level creating a distinctive strip of light reflected back into the space facing the road.

Following completion, the previous office tenants decided not to take up the option of moving back into the property, however, the contractor took the building and located his head office there.

 Completed front elevation