Crescent Valley High School Roof Investigation

Transcription

1 Crescent Valley High School Roof Investigation Project: Corvallis School District Crescent Valley High School Roof Date: July 26, 2011 Report By: Rowell Brokaw Architects: Mark Young, AIA, Chris Andrejko GENERAL INFORMATION The Corvallis School District (CSD) has asked Rowell Brokaw Architects (RBA) to assess the condition of the roofs at Crescent Valley High School (CVHS), which have developed increasing amounts of leaks over the last few years. CDS would like to know if it is possible to extend the life of the existing roof until the next bond cycle, which is several years away, or if funds will be needed earlier to replace the roofs. Mark Young and Chris Andrejko of RBA made an initial site visit on February 4 to meet with Greg Lecuyer and Kim Patten to understand the overall problem, and then followed up with another meeting on March 9 with Kim Patten, Tim Phillips and Doug Tiller to review existing building documents and discuss ongoing maintenance and repairs that have occurred. EXISTING CONDITIONS CVHS was built in 1969 and consists of 4 main buildings typically constructed of concrete and masonry walls, with a roof structure of solid wood decking over glulam beams and purlins. Building A has a metal roof structure and deck. The exterior walls form low parapets around low slope roofs with a shallow sawtooth profile. Slopes are approximately 1/2 per foot and drain to level valleys containing roof drains. One or two mechanical penthouses occur on each of the roofs (See Figure 1). Because mechanical equipment is in the penthouses, there is minimal rooftop equipment or penetrations at the main roof. The buildings range in size from 31,500 sf to 108,400 sf, for a total of about 250,000 sf of roof, including penthouses. The original roofs were built-up bituminous roofs with gravel topping applied over ½ rigid insulation. All of the buildings were re-roofed in 1985 with a Hypalon single ply roof membrane. The single ply roof and additional 1 1/2 fiberglass board insulation was mechanically fastened over the existing roofing. It appears that there were early failures at the valleys after the re-roofing, with records showing multiple replacements of roof membrane and wet insulation from 1983 to The hypalon roof is still the current roofing on the CVHS buildings. LEAKS AND MAINTENANCE Over the last few years, an increasing amount of leaks have occurred at most of the roofs, and various fixes have been applied. Most leaks have occurred at valleys and low points, as the roofs were designed without drainage crickets, causing water to pond (See Figure 2). In addition, pinholes have increased as the roof ages, causing additional leaks in other locations. For the past few years, CSD maintenance staff have spent

2 many hours during the school year looking for leaks and applying spot patches of sealant. Over the summers, they have cleaned and covered the valleys and large parts of roof with roof coatings in an effort to prolong the lives of the roofs. Roof A was entirely coated with Tremco SRC in 2006, and has not experienced leaks since then (See Figure 3). Roofs B and C/D/E were coated with Neogard Elasta-Gard in the valleys and other areas, and have experienced failure of the coating in submerged areas (See Figure 4). 2 of 14

3 ISSUES FOR ROOF REPAIR In RBA s assessment, the issues with the roof are as follows: Cost and Funding: With the next bond cycle in 2018, funds for re-roofing will not be available for another 7-8 years. Given the time required to assemble bidding packages and the possibility of phasing work over multiple years, it is possible that any interim solution will need to last up to 10 years. Future funding should be weighed against the ongoing and probable rising costs for finding and fixing leaks. Age of Current Roofing: The service life of the Hypalon roof system is approximately 20 years, and this roof is well past that age. The surface is chalked, and badly worn or brittle in some areas. As the roof deteriorates further, the amount of pinholes and leaks will increase. In addition, much of the roof has become brittle, making it a less desirable substrate for a coating. Design of Roof Drainage: Without drainage crickets, it is not possible to avoid standing water in the valleys. With the aging roof and uneven substrate of insulation, the problem becomes worse, as the drains no longer are the low points. Although membrane roofs and coatings can withstand periodic ponding, they are not designed or warranted for prolonged submersion. This is likely one factor in the delamination of the Neogard Elasta-Gard coating. Wet Substrate: Based on observations from CDS staff, the insulation has become wet in many locations due to leaks. It is likely that the insulation has not had the opportunity to completely dry out, and receives additional moisture as more leaks occur. Moisture trapped under a roof membrane will try to escape through the membrane as the temperature rises, creating pressure beneath the membrane. This results in bubbling of the membrane and ultimately, tears or delamination. This is also likely a factor in the Neogard Elasta-Gard failures, but any roofing or coating will have difficulties performing well over a wet substrate. Potential for Asbestos: The possibility of asbestos in one of the existing roofing layers was brought up. RBA contacted PBS Engineering + Environmental to discuss an asbestos survey performed sometime between 2002 and Sample cores were taken from the Building D and F roofs, and no asbestos was found. Since all of the roofs are similar, it is probable that there is no asbestos in any of the roofs. However, PBS and RBA recommend that CSD also take additional samples as a precaution. Roofing at Mechanical Penthouses: Based on reports from CSD facilities staff, there have been less problems with leaks at the penthouse roofs. Due to the fact that there is less risk for water damage in these enclosures, they can likely be addressed by spot patching over the next 10 years. However, they should be fully re-roofed at the same time the main roofs are fully re-roofed. Walkway Roofs: Open exterior walkways provide covered connections between the 3 of 14

4 buildings. These still have the original built-up roofing, which have been patched over the years. Because they are exterior space and easy to patch, there are currently no major concerns about the roofs, except for their overall age. It is possible to maintain these roofs with asphalt patching for the next 10 years, but they should be re-roofed as part of any full re-roofing project. 4 of 14

5 OPTIONS The scope of work, cost and schedule presented below are broadly defined, and meant to give a general idea of timing and budget to assist BSD to decide on a direction to take. Once an option (or variation of option) is selected, more detailed design, cost analysis and scheduling will need to be examined. OPTION 1: APPLY COATING OVER THE EXISTING ROOF: This option is an attempt to extend the life of the existing roof by applying the Tremco SRC coating over all main roofs except Bldg A, which has the coating. It has the least first cost, can be implemented quickly, and is the least invasive. However, since it does not address the inherent roof design and moisture problems, it poses the most risk of failure, and beyond a warranty for defects in sealant material, no warranty is offered. Tremco has told us this product only has a life of a few years, so it would likely need to be re-applied for it to last 10 years. RBA has little confidence that this coating option will be worry-free, given the history of roof failures with this roof design. Scope of Work: Prepare specifications and diagrams for bidding (if work to be executed by Contractor). Building A and Penthouse roofs could be optional depending on year of reroofing and upkeep of maintenance cycle. Walkway roofs not included. Clean roof surface and prepare surface according to coating manufacturers surface preparation instructions (Pressure wash by CSD). Replace any damaged or deteriorated roof drains. Apply Tremco Vulkem SRC coating over Bldgs B, C/D/E and F initially. Re-coat all Buildings in five years, unless coating fails earlier. During the life of the coating, inspect roofs on a regular basis (bi-weekly, at minimum). Clean out drains and accumulated debris, and direct ponding water to drains. If all roofs cannot be completed in one season, an option is to coat the valleys of all roofs, along with known problem areas, during the first season, leaving the remainder of the roofs for the following season. Approximate Installation Cost (B,C/D/E,F Year 1; A,B,C/D/E,F Year 5): By Contractor (Pressure wash by CSD): $4/SF x 356,100 SF = $1,424,400 Add 16,700SF for Small Penthouses Year 5: $66,800 Add 9,300 SF for Walkways Year 5: $37,200 By CSD: $1.70/SF material cost x 356,100 SF = $605,370 + $192,000 (CSD Labor Cost) = $797,370 Total Maintenance Cost: Inspect and clean debris: 3 full FTE days/month = $11,520/year. Attend to possible leaks and failures: (50% current time spent on leaks) 5 of 14

6 $15,000/year. Summer patching: (possible in spots, particularly later years) $15,000/year. Possible Schedule of Work: Install by CSD: Documents, procurement: 1 month (?). Install by Contractor: Bid documents, bidding, permit, contract: 2 months min. Install by CSD: 3-4 summers, beginning 2011 (1 building per summer) Install by Contractor: 1 summer and fall, or 2 summers, possible beginning 2011 Pros: Possible for CSD to self-perform work with manufacturer s approval. Slight possibility of bidding work for this summer with minimal documents. Least initial cost. Roofs are not exposed, so possible to continue work during the school year. Wait to re-coat Bldg. A, Penthouses, Walkways. Cons: Extreme uncertainty whether the installation will remain trouble free. At least two cycles of coating will be required to extend roof life 10 years. No warranty possible for 10 years. Moisture in insulation substrate will still be present and may cause future problems. Valleys will still create ponding, which may shorten the life of the coating, and could cause other unforeseen problems. Interim solution will require re-roof in 10 or less years. 6 of 14

7 OPTION 2: NEW DRAINAGE CRICKETS AT VALLEYS / APPLY COATING This option cuts out the existing level valleys and adds drainage crickets to mitigate the main design problem with the roof. With proper drainage, a less expensive roof coating could be used over the remaining existing roof. The recommended coating would be the Tremco SRC coating that was used on Building A, since it has generally worked on that roof. The less expensive Neogard Elasta-Gard coating is not recommended because of previous failures. While wet insulation will be removed from the valleys, there will probably be moisture under the remaining roof, which may cause problems in the future. Although this approach decreases the risk of failure, existing problems with the rest of the substrate may still cause leaks, so the prospect of the roof remaining trouble-free is uncertain. Like Option 1, the coating will need to be re-applied every few years. It is still an interim solution, and all buildings will need to be re-roofed within 10 years or less. Scope of Work: Prepare specifications and drawings for bidding. For roofs not completed the first season, the Tremco SRC coating should be applied over known trouble spots, and roofs should be inspected and cleaned more thoroughly on a regular basis until patched. Building A and Penthouse roofs could be optional depending on year of reroofing and upkeep of maintenance cycle. Walkway roofs not included Clean roof surface and prepare surface according to coating manufacturer s surface preparation instructions. Remove approximately 20 ft wide strip of top membrane, wet/damaged insulation, and deteriorated roof drains. Install tapered insulation crickets with cover board that blend to the existing roof and direct drainage towards roof drains. Install hypalon-compatible membrane (hypalon is no longer manufactured) and weld to existing roofing and roof drains. Apply roof coating over the remainder of roof, overlapping new membrane. During the life of the repair and coating, inspect roofs on a regular basis (biweekly, at minimum). Clean out drains and accumulated debris. Re-coat all roofs in five years, unless coating fails earlier. Approximate Installation Cost (not including mechanical penthouses): It is difficult to get an accurate cost for this hybrid approach of patching and coating, but removal of valleys alone will result in 20%-40% new roofing. Add coating over the remainder of main roofs and recoating at 5 years, and the cost over 10 years is well over the cost of Option 1. It possibly approaches or exceeds the cost of a full re-roof. Maintenance Cost: Inspect and clean debris: 2 full FTE days/month $7,680/year. Attend to possible leaks and failures: (25% of current time spent of leaks) $7,500/year. 7 of 14

8 Summer patching: (possible in spots, particularly in later years) $10,000/year. Interim Tremco SRC patching at problem areas while waiting to be re-coated or patched (1-2 years similar to current FTE spent of roof maintenance) $15,000. Possible Schedule of Work: Bid documents, bidding, permit, contract: 3 months. By Contractor: 1-2 summers, beginning 2012 Pros: Addresses major roof design flaw of level valleys and minimizes ponding. Without ponding, allows less expensive coating over the remainder of the roof. Probable less first cost than full re-roof. Wait to re-roof Bldg. A, Penthouses, Walkways. Cons: Leak detection, patching and maintenance will be required for existing roofs until they are patched and coated. Since hypalon is no longer manufactured, it may be difficult to find a compatible roof membrane. Difficult to patch new membrane onto deteriorated existing roofing with new membrane, and may not be possible to obtain warranty. Hybrid approach - uncertainty whether the installation will remain trouble free for 10 years. Although removes some of wet insulation, moisture probably will remain in other areas and may cause future problems. Will require ongoing inspection and possible future maintenance for leaks. Interim solution will require re-roof in 10 or less years. 8 of 14

9 OPTION 3: FULL ROOF REPLACEMENT This option replaces all of the roofs with a properly designed roof system that will last at least 30 years. All of the existing roofing will be removed so that moisture can be more predictably controlled with the new system. Tapered crickets will allow positive slopes to all drains, correcting the main roof design problem. In the roof system, insulation meeting or exceeding the current energy code will be installed, potentially saving energy costs for the future. In order to correctly install the roof at the edges and around penthouses, new flashing is also assumed. In addition, it makes sense to re-roof Bldg. A, Penthouses and Walkways at this time, since they will likely need to be re-roofed within 10 years. Scope of Work: Prepare specifications and drawings for bidding For roofs not completed the first season, the Tremco SRC coating should be applied over known trouble spots, and roofs should be inspected and cleaned more thoroughly on a regular basis until replaced. Remove existing and original roof to expose the roof deck. Remove sheet metal flashing and replace roof drains. Install 3 rigid insulation with tapered insulation crickets and cover board, directing drainage towards roof drains. Install roof membrane and new sheet metal flashing. Install walkpads from mechanical penthouses to roof drains and other maintenance areas. Approximate Installation Cost (includes mechanical penthouse roofs) Fully Adhered 80 Mil TPO or PVC (30 year roof): 251,300 SF - $2,235,000 Recommended 10% contingency for possible dry rot, etc. - $223,500 Deduct for mechanically attached ($150,000) Deduct for 60 mil (20 year) roof ($135,000) 20 year warranty (most common): $0.10/SF - $25, year warranty (available for 80 Mil): $0.15/SF - $38,0000 Maintenance Cost: Inspect and clean debris: 0.5 full FTE days/month $1,920/year. Interim Tremco SRC coating at problem areas while waiting for re-roof. ((1-2 years similar to current FTE spent of roof maintenance) $15,000. Possible Schedule of Work: Bid documents, bidding, permit, contract: 3 months. By Contractor: 1-2 summers, beginning 2012 Pros: Least risk of short and long term failure. 9 of 14

10 Long life of years, with warranties available to 30 years. Roof slope design issues will be fixed, allowing easier future re-roofing.. Substrate moisture problems will be fixed. Added insulation will increase the buildings energy efficiency Least cost over next 30 years - interim options will need similar re-roofing within 10 years. Ongoing inspection and maintenance minimized. Periodic cleaning of drains and debris. Leaks covered by warranty. Cons: Most expensive first cost. All roofs replaced, and requires replacement of metal flashing. Leak detection, patching and maintenance will be required on existing roofs until they are coated at least for another year. 10 of 14

11 FIGURE 1 Roof Diagram 11 of 14

12 FIGURE 2 Ponding in Valleys 12 of 14

13 FIGURE 3 Unit A Roof with Tremco SRC Coating 13 of 14

14 FIGURE 4 Failed Neogard Elasta-Gard Coating 14 of 14