A problem understood is a problem solved

JCA Team:
Rory Duncan
Nigel Hammett RIBA SCA
Project Design Team:
Johnston Cave Associates (Architects)
Project type:
Quinquennial Inspection
Project year: 2008

Our quinquennial inspection revealed a bit of an unholy mess.

The Crypt kept flooding and the damp crept up the walls damaging the very fabric of the ancient building we were tasked to report on.

The culprit was obvious. The surface water ran down the external steps and was joined by a leaking roof downpipe before running under the door and into the lower Crypt. Unfortunately there was then nowhere for it to go.

The problem seemed strange to us. The gullies for the downpipe and the new water tap were correctly set at their relative ground levels but as this was higher than the Crypt floor, the water simply flowed to the lowest level. 

To prevent flooding, the floor level of the Crypt should have been higher than the external ground – and must, we thought, have been the way the Crypt was built.

A careful inspection of the external steps showed that most risers were approximately 180mm high but the riser by the Crypt doorway was only 100mm. This gave us our clue to what the real problem was.

It appeared that the ground level had built up over the centuries by about 80mm and was now above the floor level of the Crypt.

Further close inspection of the Crypt doorway showed us that there was a threshold stone that was flush with the external face of the building and extended into the ground. A stone threshold would normally be designed to prevent any water entering the room, but this was mostly buried. It neatly served to confirm our thesis. 

A proper solution was now obvious; lower the ground by at least 75mm to the original ground level and the water would flow away from the church rather than in to it. Just as it had done when built.

From our previous work on churches over the years, we also suggested that this excavation would reveal an area of paving or stone aprons by the base of the Crypt steps designed to stop water ingress.

To absolutely resolve the problem - at least until the earthworms caught up again - we recommended the installation of a drainage channel to the base of the steps and the external ground area of the doorway. The rainwater gully and the water supply gully should then be lowered to the new ground level and connected to the channel drains.

Finally we recommended paving or otherwise covering, to seal the area of ground formed by the corner of the steps, lower Crypt and boiler room wall to improve surface water disposal.

With the problem fully understood, we were given the go-ahead to get the problem solved.