CABRILLO Historic Structures Report

REPAIR PROCEDURES (continued)

Bituminous Roofing

Description

The flat roof at the Army Radio Station is covered with composition roll roofing. Roll roofing is a type of built-up roofing that consists of paper or felt saturated with tar, asphalt, or other waterproofing compounds. The material is rolled out parallel to the eaves and lapped one or two inches over the course next to it. Roll roofing is not long lasting and tends to buckle, but it is a quick, inexpensive method of covering structures.

Condition

The composition roll roofing material on the Radio Station was recently replaced. In February of 1999, the old roll roofing was removed, the wood decking beneath was surveyed, new bituminous roll roof was applied, and the seams were sealed.

Recommendations

Survey the roof annually for buckling and leaks, especially at seams, penetrations, and at the edges. Properly applied, this material should have a life expectance of five to ten years.

Grade and Vegetation Issues

Description

Many of the Cabrillo structures are constructed underground, partially underground, or were historically topped with a camouflage of earth and vegetation. As a result, three conditions occur: hydrostatic pressure, erosion and subsidence, and excessive or out-of-control vegetation.

• Hydrostatic pressure build-up. Examples: Army Radio Station and all underground or partially underground structures.

• Subsidence. Examples: Battery Bluff North and South Gun Placements.

• Excessive Vegetation: Examples: All structures with camouflage roofs.

Conditions

Hydrostatic Pressure

Hydrostatic pressure is lateral pressure exerted by water-saturated soils on an underground or partially underground structure. This condition may cause structural deformation as well as water infiltration.

Water Infiltration

Water infiltration from either standing water or hydrostatic pressure can create moisture-related problems within walls (such as reinforcing rod corrosion), as well as moisture problems at the interiors of the structures.

Subsidence and Erosion

Subsidence refers to the settling or collapse of unstable terrain. Battery Bluff is subsiding and falling into the water below. If this condition is allowed to continue, the Battery Bluff Gun Placements will be lost. Erosion refers to the gradual washing away of loose soils.

Excessive Vegetation

Excessive or out of control vegetation can cause damage from invasive roots and by holding moisture against building materials.

Recommendations

1. Hydrostatic pressure and moisture penetration can only be completely alleviated by digging around foundations and applying watertight membranes at the exterior of the structures. This is a costly and invasive solution and is recommended only as a last resort. Observing hillside drainage above and around the structures may provide mitigation. Create swales as required to divert water away from structures.

2. Subsidence: Consult a soils engineer to determine the extent and rate of subsidence. The soils engineer may establish a monitoring program, and recommend mitigation procedures. These procedures should be reviewed by a park ecologist. Structures in danger of loss from subsidence should be thoroughly documented.

3. Erosion: Clear away all loose soil and restore pathways around the structures.

4. Monitor the vegetation surrounding the structures. If the vegetation becomes invasive and destructive to the concrete roofs or other adjacent material, survey the plant types, remove the vegetation, repair the roof system, and determine if, and to what degree the vegetation should be replanted. As part of the repairs, provide a watertight membrane at the concrete surface before replacing the earth and vegetation.

Recommended Tests

1. Hire a soils engineer to study subsidence conditions.

Grade and Vegetation References:

Scott, Gary. Historic Concrete Preservation Problems at Fort Washington, Maryland. APT Vol. X No. 2, 1978.

Weaver, Martin and Frank Matero. Conserving Buildings: Guide to Techniques and Materials. Chapter 12, Foundations and Footings. John Wiley & Sons, Inc., New York, 1993.