History of Current Building
Today's St Paul's Cathedral, which sits on a religious site that saw its first building constructed in AD 604, came into being after circumstances caused a requirement for a new design and building to be considered.
The Great fire of London dating to 1666, created an opportunity for a new church on the site, to replace the existing Gothic building, that had been constructed by the Normans in 1087 which had been damaged beyond financial and practical repair from the fire that had ravaged the city. A decision had already been made to replace the Norman Building, and the fire accelerated the decision making and planning for the present building that stands today.
Sir Christoper Wren was commissioned to design the replacement, he had already started work on the plans in 1661, 5 years before the fire.
Wren wanted to unite the religious communities and design the building using Neoclassical, Gothic and Baroque styles within its construction. He built a "Great Model" to illustrate his plans, that can still be seen in the crypt of the church. This model showed his plan for a great dome to top the building.
The Construction of the Dome
The dome itself is made up of 3 domes,
The first inner dome of brick is designed as a cone with an open top to allow light to pass into and down to the centre of the church below. It doesn't support any weight of the main outer dome and only reaches about half way up to the height of the external dome, a difference of around 50 feet.
The second dome is again a brick construction cone, this part of the dome supports the 700 ton lantern at the top and converges with the outer visible dome. It constitutes the main weight bearing part of the construction.
The third dome is made predominantly of a wooden frame and an outer wooden dome encased in a lead shell.
The Great Model
Completed in 1647, it was one of Wrens first designs, It was made into a 1:25th Model by William Clere, and was made so that the building could be imagined in size by the viewer at eye level. The model itself sits in the crypt of St Paul's, however it was eventually rejected. Its resemblance to today building is notable, however there are some significant differences, being a second spire that doesn't exist.
The Warrant Design
Sir Christopher Wren drafted a few plans for the new Cathedral, one of whom was given Royal Warrant by King Charles II and became known as the Warrant Design, most likely drafted in 1674/5. The final structure we see today is a considerable difference to what was planned originally shown above, there are no minutes taken in building meetings indicating such changed were approved, however there are records that exist in the Wrens family memoirs that state the King was please to allow Wren ‘the Liberty, in the Prosecution of his Work, to make some Variations, rather ornamental, than essential, as from Time to Time he should see proper; and to leave the Whole to his own Management’.
The construction of the building took 40 years in total to complete, after 22 years of building, government pressure and impatience caused a decision to be made to half Wrens wage. In 1710 construction was completed and Wren petitioned the government to pay the rest of his owed wages, which they did.