The History

Constructed in 1897, the Pierhead Building was originally required as a replacement for the Bute Dock Company's headquarters which were destroyed by fire in 1892. The building served this purpose for the Bute Dock Company, G.W.R. Ports, South Wales Ports and Associated British Ports until it was leased by the Welsh Office in 1998.

The building incorporates a French-Gothic Renaissance theme with carved friezes, hexagonal chimneys, gargoyles, an ornate clock tower and a natural Welsh slate roof. Such details and its prominence in the developing Cardiff Bay area have earned it a grade one listed building status. The building provides a historic centre-piece to the newly developed Cardiff Bay area and is now home to the Visitor & Education Centre for the National Assembly for Wales.


The Project

The entire scheme included remedial works to the glass clock face, replacement of sash windows and paneling as well as the removal and replacement of the existing natural Welsh slate roof. The building remained occupied and in use throughout the entire contract period.

M. Camilleri & Sons Roofing Ltd was appointed as a specialist contractor, with a commencement date of 26 April 2005. At the time of construction, Cardiff Docks was obviously heavily used by the coal mines of the South Wales Valleys. Therefore, due to the high concentration and flammability of coal dust in close proximity, the roof structure of the Pierhead Building consists of a steel frame network incorporating horizontal steel members at close centres in lieu of a traditional timber rafter construction.


This led to problems as the underlay / counterbatten / batten / slate build up which was specified could not easily be fixed to a steel substrate. Furthermore, Cadw (the historic environment agency within the Welsh Assembly Government) were insisting that any alteration in finished roof level be kept to an absolute minimum.

The Solution

After many meetings with Dalkia Plc (appointed to provide Facilities Services for The National Assembly for Wales), we were instructed to omit the underlay and counterbattens to most of the roof, with new slates being fixed to the existing timber battens. However, due to the age of the roof, these battens were found to have hardened to such a degree that standard slate nails could not penetrate them. This factor, together with the absence of an underlay, led to a new suggestion:

1. Strip existing roof coverings back to the battens, which were fixed to the steel frame.

2. Fix counterbattens to the existing battens, to allow a drape in the underlay.

3. Install a high performance breather membrane across these counterbattens.

4. Fix slating battens over the breather membrane, fixed through the counterbattens and into the existing timber battens.

Whilst not fully compliant with BS5534: 2003, this solution offered a higher level of protection than the original proposal as well as causing a minimal 25mm height differential, which would be barely noticeable from ground level. However, this slight variation brought a requirement for greater attention to lead detailing at abutments as well as the existing lead shrouds and finials which were to be re-used.




Furthermore, as the slate gauge was dictated by the centres of the steel purlins, further protection was afforded as the 70mm headlap (as recommended by Welsh//Slate in accordance with BS5534) actually increased to 80, 100, 120 and 140mm across the entire roof. However, this was not the biggest problem which presented itself to our slaters.

The specification stated that not only were all hips and valleys to be close-mitred, but all courses were required to line through on each elevation. The fact that most adjacent roof pitches were unequal, coupled with the varying slate gauges dictated by the steel frame, meant that significant attention to detail was required, as was a very high level of skill and workmanship. However, despite these obstacles, the requirements of the specification were achieved with excellent results.

Summary

Over 18,000 Capital grade Ffestiniog natural Welsh slates, sized 500 x 250, were used in a roof area exceeding 950m2.
In addition to this, some 200m2 of sheet leadwork was added by parapet gutters, vertical lead cladding and lead flat roofing.

This project secured 1st place in the Slating Category of the NFRC's 2006 National Roofing Awards.