REVIEW OF EXISTING ROOF CONDITIONS

REVIEW OF EXISTING ROOF CONDITIONS

Lawrence Public Library

707 Vermont Street

Lawrence, Kansas 66044-2371

June 23, 2008

INTRODUCTION

At the request of the Library Director, Bruce Flanders, a review of the existing roof condition of the Lawrence Library was completed. Two site visits were made, one April 3, 2008, and the second on June 13, 2008.

The library building was constructed in 1972 utilizing cast in place columns and roof structure. The original building drawings indicated a built-up roof system over 1.4” of urethane insulation on the main roof. The center portion of the building consists of a clearstory structure over the central part of the Library. On either side (east/west) of the clearstory are screen walls separating those roof areas reserved for air-conditioning equipment. At the building perimeter the roof structure terminates at the edge of the concrete structure, there is no parapet. Roofing is terminated by use of a bent piece of continuous flashing.

Record information such as shop drawing submittals or repair records were not available at the time of the site visit. Copies of correspondence dated June of 1974, were later found and reviewed. This correspondence was generated due to the appearance of blisters and leaks in the roof system approximately two years after the building was completed. Reference is made in a letter dated August 10, 1978, from the Celotex Corporation, to removal and replacement of approximately 6,500 square feet of roof membrane, felts, asphalt, and gravel plus 16 vents.

OBSERVATIONS MADE

The existing roofing is a built-up system with a modified bitumen cap sheet. This system does not compare with the use of gravel mentioned in the previous correspondence. The roof in place is most likely a replacement system and not the original system. Based on the height of the perimeter flashing the insulation is probably about 4” to 6” in depth.

The modified bitumen cap was missing approximately 75% of its’ surface granules. These granules help protect the cap from ultra-violet degradation by reflecting light away from the system. This in turn helps cool the roofing.

Blisters were noted in many areas of the roof. Blisters are generally caused by air being trapped in the system during installation. As long as the blister remains intact water will not penetrate, however as the blister ages, expands and contracts, or is damaged, the membrane will split allowing water entry.

The roof surface is flat with many low areas that pond water. Roof drains serving the main roof are located on the east and west edges of the building, or those areas where drop ceilings in the finished spaces below, conceal the drain lines. Drains serving the high roof are connected to exposed downspouts which deposit water directly onto the main roof.

It was raining during the first site visit; there was little if any water flow to the drains. Photos taken during this time show some of the areas of standing water. Standing water as also noted around air-conditioning equipment, where drainage is restricted to paths around that equipment. An additional site visit on June 13, 2008 occurred approximately 12 hours after a rainfall. Standing water was present on at least 50% of the roof surface. The only possible way for this water to leave the roof in most locations is through evaporation. Moss and layers of scum were noted at the clearstory wall and several spots in the center of the roof indicating that these areas rarely if ever dry out.

Pressure was applied to several seams of the cap sheet which produced air bubbles indicating a gap in seam through which water will penetrate.

Flashing and counter-flashing appeared to be intact. The majority of roof leaks can be accounted to failure in the flashing and counter-flashing.

There are twenty four roof vents on the main roof. Vents generally have a limited area of coverage of about 100 square feet as lateral movement of vapor through a roof system is restricted. Base on that area the vents can handle about 2400 square feet of the low roof which is about 20,000 square feet in total area. The practical use of vents has been debated as to their effectiveness, and many roofs are not vented.

MAINTENANCE REVIEW

Maintenance staff noted three previous leaks. Two leaks occurred near the exterior wall of the clerestory, and the other near air-conditioning equipment. Leaks are more likely to occur in those two areas rather than the main roof as most leaks are associated with failure of the counter flashing systems serving penetrations such as the clerestory wall or roof mounted equipment. No leaks were reported in the vicinity of the blistered area in the southeast corner of the main roof.

SUMMARY AND RECOMMENDATIONS

The roof is showing signs of aging and is nearing the end of its’ service life. It probably still has five or so years of service assuming the Library is willing to accept the probability of additional leaks during that time period. It’s difficult to determine when any leaks will develop. This is a cast in place concrete roof structure which does not have the number of gaps or seams that a metal roof structure would have. It’s possible that there is water present in the roof insulation which if allowed to accumulate further, could start to find gaps or seams through the concrete deck.

If the Library is to remain in this facility for the next fifteen to twenty years, then a new roof should be installed. Ideally replacement should be completed as soon as possible. If immediate replacement is not possible then the Library should plan and budget for a new roof within the next five year period.

To help in this planning, the Library could also consider obtaining the services of a company to collect core samples of the roof in those areas where blistering has occurred to determine if moisture is present and determine the condition of the underlying roof components. Or, obtain the services of a company to provide infrared analysis of the roof. This provides more accurate information of the roofs’ condition which a visual inspection alone cannot provide. If the quantity and dispersion of water is limited, it’s more likely the roof will perform within reason with limited potential for leakage over the next five years. If results indicate substantial saturation, then immediate replacement needs to be considered to avoid any potential water damage and to increase the thermal efficiency of the roof structure.

Estimated cost for a new roof today -- $301.000.

The estimated projected cost for a new roof five years -- $392,500

The projected cost is based on a 5.4% increase per year, which may vary due to recent sharp increases in many constructions materials.

The estimates do not include fees for professional services. When replaced, consideration should be given to improve the roof slope by use of tapered insulation or sloped lightweight insulated concrete. Estimates presented are based on the use of tapered insulation. The estimate also assumes a roof system similar to that installed.

Michael W. Rode

Registered Architect, Kansas 2587