Monday, April 21, 2008
On a rainy day in Spring, a young man's thoughts turn to ...GUTTERS! I had occasion to be at the John Marshall House this afternoon in the midst of a downpour. I was meeting with the contractor who is preparing to begin the roof replacement there, hopefully within a week or ten days. As part of the job, they will be adding half round copper gutters to the roof edges in an effort to control the disposition of rain water.
Some twenty years ago, we added the brick ground guttering shown in the photograph above. This was best practice at the time, as gutters were considered not historically accurate. The gutters that had been on the building for some time were removed and not replaced during the 1974-76 major restoration of the house. You can still trace the staining left from the many years they had been in place against the bricks on the edges of the house. In the 80's moisture infiltration into the basement walls was very evident and growing worse. The gravel that was meant to absorb the rain falling off the roof and disperse it to the storm drain was dug out down to foundation level and a French drain system installed. The shallow V-shaped brick ground guttering was meant to channel the majority of the rain water into drains piped directly into the storm sewer. The water that escaped this first system would then be captured by the French drain.
This greatly improved the moisture problem in the basement, but resulted in another unintended consequence. Raindrops falling two full stories onto a brick surface tended to explode upwards and create a constant moisture on the bricks above the ground gutter. These got moist, and because of the showing caused by the surrounding buildings, never were directly exposed to drying sunlight. As a result, moss grew and held the moisture there even longer. So back to the simplest system of controlling rainwater - roof edge gutters. When these are in place, the brick ground gutter will be removed and the grading corrected to slope away from the building. We likely will go back along the surface perimeter with some pea gravel for both decorative and moisture issues. The French drain system will be left in place, as there is no evidence that it is failing.
Rain is a good thing and we certainly need it in good season, but it can be a threat to an insufficiently protected historic house!