THE DEHUMIDIFICATION PROJECT

There are four main causes of humidity in the cloister and these interact closely with each other.

a) Alterations to the original buildings

Up until the thirteenth century, the cloister corridors were on one floor only and the perimeter buildings to the east and south were not so high as they are nowadays. So the proportions of the cloister’s open area were in keeping with the size of these buildings. When the height of these buildings was later increased, the open area in the cloister became a sort of "well", with the result that there is poor air circulation within the cloister and the amount of direct sunlight is much reduced to the extent that some walls, especially those on the southern part, are in almost permanent shadow.

b) Changes in floor levels

Surveys have shown that floor levels and the level of the land on the southern side of the complex have been significantly raised, but not in equal proportion, with respect to the levels of the original construction.

The following differences in level are especially noticeable: the surrounding land (now the monastery garden) is higher than the floor level inside the building; the floor level in the southern building is a meter above the level of the cloister corridors; the open area of the cloister is above the level of the corridors (see section A-A). The two main results are:

1) the corridors are at the lowest level of the whole area and are thus most exposed to humidity from the subsoil;

2) the lower parts of most of the cloister walls are in direct contact, on one or other of their lateral surfaces, with soil filling.

Probes have shown that these soil fillings are mostly made up of soil mixed with various types of detritus (see archeological excavation cards), which means they have a high absorption capacity and a high rate of water seepage which directly affects the wall surfaces in contact with them causing substantial rising damp in the overlying walls. Therefore it is not surprising that the most pronounced deterioration has taken place on the cloister’s southern perimeter wall where the soil filling behind the wall is higher.

Probes have also shown that the floors are separated from the soil beneath them only by a thin pozzolana based layer. This means that rising damp spreads unhindered, which explains most of the damage that can be seen on the floor surfaces.

c) Marked presence of salts

Analysis has shown that there is widespread presence of salts and nitrates on many of the cloister surfaces. This can be explained by some of the typical activities that have taken place in the monastery over the years: the cloister area was also a burial ground while the surrounding premises were used as storerooms for food, much of which was preserved in salt. These areas were also used as stalls for animals whose dung is rich in nitrates, and this use continued right up until the twentieth century in the southern part of the cloister. In addition, the surveys have also shown that it was common practice, not only here but also in other parts of the monastery, to use garden soil for filling purposes. These gardens were also the site of the monastery’s main rubbish tips that were periodically burnt and covered with soil. So the soil used for filling purposes has a high content of partially burnt food remains mixed with bone fragments.

All these factors mean that there are large quantities of mineral salts dissolved in the soil. As water passes through the soil, it carries the salts into the walls where they are deposited internally or on the surface. Given the fact that these salts are strongly hygroscopic, they absorb more humidity from the air (which is saturated due to poor ventilation), thus giving rise to damp surfaces. The situation is made worse, though not to the same extent, by condensation.

d) High level of humidity in the subsoil

The siting of the complex on a hill which is partly artificial means that there is no danger of infiltration from a water-bearing stratum in the vicinity. Notwithstanding this, the subsoil beneath the cloister and the surrounding buildings contains significant quantities of water which rise through capillary action to the higher levels. So the presence of this water is due to other reasons.

One of the main factors is that the cloister is situated at the center of a complex water disposal system, with large quantities of water draining into it from various sources, for instance:

1) rain water falling directly on the exposed parts;

2) rain water on the roofing that converges on the cloister through a system of gutters and drain pipes;

3) waste water from the fountain in the middle of the cloister garden and from the twelve washbasins located on the upper floor of the surrounding buildings.

The exposed area of the cloister is 140 sq. m. and the roof area that drains into it is 685 sq. m. Therefore, the total area that drains into the cloister is 825 sq. m. Since the average rainfall in Rome is 800 mm., the total flow of rain water into the cloister can be estimated at 660 c. m. per year, to which must be added about 40 c. m. of waste water from the wash basins and the fountain, making a grand total of about 700 c. m. / year. Furthermore, the maximum rainfall in Rome over brief periods is about 40 mm. in twenty minutes, so flash flooding of water flowing into the cloister can reach the very high figure of 30 liters/sec.
The drainage system for this enormous quantity of water was never carefully planned or conceived as a single system. It is the result of alterations and various additions carried out without proper design criteria and often with bad workmanship. Therefore, not only does it function inefficiently but also the various components of the system are falling to pieces.

In order to understand the present situation, it is useful to look back over the various alterations that have been made to the system.
As was often the case in the past, the rain water that fell onto the roofs of the monastery buildings was probably collected and used as a reserve water supply. Instead of the conventional cistern located in the middle of the cloister, in this case there is a sort of well, ten meters deep, located nearer the south side and offset diagonally with respect to the overlying structures. It was discovered by Muñoz but was then forgotten about, until brought to light again recently after excavating (see archeological excavation cards, survey I). The base of the well had originally been paved with pieces of marble, as can be seen from existing traces and from comments made by Muñoz who mentioned that the base of the well included the Damasus inscription fragment which is now on the east wall of the cloister (R.A. 261).

Today, the floor is broken up and the base consists of a flattened layer of tufa (outcrop) which slopes to the west.
The position and rather special shape of this well-cum-cistern can be explained by the desire to make use of Roman walls in situ but at different angles to the rest of the site. Today, it doesn’t seem possible to explain how the rain water could drain away but, in the excavations carried out in the open area, large quantities of detritus resulting from the demolition of a brick paving surface came to light, suggesting that the whole open area of the cloister might have been paved with sufficient gradient to allow the rain water to flow into the well-cum-cistern.
During the same excavations, relatively modern ceramic material (18th-19th centuries) was found mixed in with the broken brickwork, suggesting that the changes to the cloister garden may have taken place in quite recent times.
Perhaps the garden that preceded the present one had a drainage system that has fallen into disuse. Indeed, part of such a system was discovered during the excavation carried out in the south-west corner of the cloister (survey VII). It consisted of a rectangular-shaped channel made of brickwork that ran through the open area along the west wall. With a slight curve towards east, it went through a forced aperture in the south wall of small arches to link up with a similar channel that ran parallel along the south side. The latter seemed to lead towards the west building. It is quite likely that it led out into Via dei Querceti where one can still see a drain hole with traces of water seepage. This drain, if it really carried all the water from the cloister area, must have been one of the sources of humidity that gave rise to the large triangular damp patch in Via dei Querceti, the tip of which is right above the drain hole.

After the works carried out by Muñoz, this drainage system was closed off, but it seems that the channels, even though filled with soil, continued to drain off part of the water into the subsoil.
However, this fact alone does not explain the persistence of dampness in the walls overlooking Via dei Querceti. But the lack of one cause produced another. Around 1970, a drain pipe was put in to carry away some of the rain water from the roof of the west building. The water from this new drain pipe fell directly onto the soil above the point where the old drain hole was.
Before Muñoz carried out his alterations, there had already existed a system of gutters and drain pipes that routed the rain water coming from the roofs of the nave and the transept towards the cloister onto the roof of the north corridor from where the water fell directly into the open area of the cloister.

Perhaps a similar system was arranged for the roofs of the perimeter buildings, as seems to be the case from a photograph dated 1914.
Muñoz placed the four drain pipes (which still exist) in the corners of the open area. He laid out the drainage system so that it would carry all the water from the previous system together with the water from the roofs of the galleries above the corridors.
The water from these drain pipes flows into four closed drains and from there through the brick channels into a first small storage space and then into the main well-cum-cistern. The water from the fountain follows the same route.
In the main cistern, the water accumulates for several hours, or even days in the case of heavy rain, to be dispersed probably by seepage into the subsoil, the characteristics of which are not known.
This system, to which the drains from the wash basins were subsequently linked, had a number of serious defects from the outset.
First and foremost, once the water reaches the subsoil, its dispersion path is an unknown factor. Secondly, the channels and the closed drains are too small and of very poor workmanship. As revealed by inspection and the excavations, the water pressure caused leaks with heavy loss of water into the subsoil.
In particular, the drain in the south-west corner, uncovered during excavations, was seriously damaged and water leaked into the old channel that to some extent regained its original function by transferring the water beneath the south corridor.
In spite of the fact that there are records of frequent replacements and repairs, the gutters and drain pipes are too small to cope with really heavy rainfall, especially the drain pipe in the north-west corner which also has to carry away the rain water from the basilica’s roofs. Unable to hold the massive flow of water, it overflows and floods the surrounding area with consequent damage even to the decorations beneath the arches.

Muñoz also kept the garden layout of the open area but did not provide it with a drainage system, so rain water goes directly into the subsoil and from there seeps into the corridors which are at a slightly lower level.
To make matters worse, the gravel paths laid out by Muñoz in 1970 were substituted by paths paved with small basalt blocks forming impermeable surfaces which slope to allow the water to run off. The water from the paths drains into four sinks that are linked by cement pipes to the cistern. In this way, the rain water together with the water used in the day-to-day garden tasks seeps into the subsoil where it joins the water lost through leaks in the system and spreads beneath the paved area. This paving has waterproof joints that do not allow transpiration so the damp moves out towards the external walls of the corridors and underneath them.

To examine ways of rationalizing the system, a survey of the sewage system was carried out. The monastery is connected to the public sewage system at six points: four on Via dei Ss. Quattro Coronati and two on Via dei Querceti. Of these latter two, the one carrying the waste water from the southern area of the complex dates from about 1970. The waste water from the bathrooms in the area of the cloister flows into a tank situated in the garden to the south of the library. The water flows through underground channels to a second tank at a much lower level situated at the foot of the south-west tower.