City of Cotati Public Works
Police Department Roof
Assessment and Recommendations
201 West Sierra Ave, Cotati, CA 94931
Cotati Police Department
IR Project No. 2025-007-01
Report Date:
July 18, 2025
Prepared for:
Craig A. Scott
Public Works Director/City Engineer
City of Cotati
Prepared by:
Edward J. Anisman, AIA
Interactive Resources Inc.
117 Park Place
Richmond, California
94801
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 2
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Observations by: E. Anisman
and C. Young
Date: 07/10/2025
General Overview
Roof Condition Summary:
Existing condition and possible
life expectancy based on visual
observations and limited test
cuts. Summary at right in noted
in bold font.
In Failure 0 to 2 years – N/A at specific areas requiring immediate repair Poor 2 to 4 years – Low Slope (BUR) Built Up Roof
Fair 4 to 7 years – N/A
Good 7 to 10 years – N/A
More than 10-years 10+ years– N/A at typical roof
1. Scope of Work
This assessment is limited to an assessment of the steep asphalt shingle roof system at the Police Facility Roof with specific attention to determining the cause of the water penetration into the building as well as preparing bid document for the repair of the deficiencies.
The assessment was provided by Interactive Resources with technical support from Enterprise Roofing. In addition to visual observations, critical flashings at the Hallway skylight the roof slope transition where water tested .
2. Observations
Cotati Police Department Roof: General observations include the following:
• Overall Condition: The roof is in generally good condition for its age and – with the exceptions noted below – would be expected to perform well for another 10 years or more.
• Deficiencies: The following deficiencies were observed:
o Hallway Skylights: Deficiencies were observed at the curb flashings at the large skylight above the Hallway.
o Unit Skylight: Flashing deficiencies were observed at the small skylight at the east end of the Hallway, resulting in water entry to the rooms below, including the Interview and Records Rooms.
o Roof Slope Transition: The roof slope transition that occurs over several rooms, including the Exercise Room, was not properly installed. Deficiencies include exposed remedial nailing at the transition and damaged shingles due to wind uplift at this same area. Water testing this area resulted in an active leaks in the Exercise room in the location of a stained ceiling tile.
3. Water Penetration History
and Field Observations
Water penetration was reported by the client at the following locations:
• Exercise Room
• Above the juncture of the Hallway, Service Aid, Personnel Records and Interview Rooms (just below the easternmost unit skylight)
Note: Stains were observed on the suspended acoustical ceiling panels at both locations.
4. Roof Area (Approximate) ±15,000 sf
5. Roof Membrane
The building’s roof is consists of an asphalt shingle roof system, approximately 20 years old.
The overall general condition appears good; mineral surfacing is intact and fully covering the underlying asphalt impregnated glass fiber base. Additional service life for the system is estimated at ten years, consistent with what appear to be a 30-year warranted system.
6. Insulation Glass fiber batts under roof deck
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 3
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
7. Roof Slope The typical roof slope is 4:12, with a reduced stope of 2.5:12 to accommodate the architectural features on the West Sierra Avenue Elevation.
8. Drains and Overflows: Perimeter gutters and downspouts are provided.
9. Structural Deck Type Plywood sheathing over 16” TJI trusses at 24” on center
10. Parapet Walls Not Applicable
11. Copings Not Applicable
12. Wall Flashings Not Applicable
13. Penetrations Plumbing vent, exhaust fans, etc.
14. Skylights
Skylights have been provided for daylighting the Hallway and include the following types:
• Hallway Skylight: A long 6’x72’ is located at the roof ridge and centered over hallway • Unit Skylights: Three (3) total, each 4’0” square are provided at the ends of the main hallway and at the branch leading to the Break Room.
15. MEP systems Not Applicable
16. HazMat Report A HazMat report is not in the Scope of Work for this assessment.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 4
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Executive Summary
General: The roof is in generally good condition for its age and – with the exceptions noted below – would be expected to perform well for another 10 years or more.
Deficiencies: The following deficiencies were observed:
• Hallway Skylight: Deficiencies were observed at the curb flashings at the large skylight above the Hallway. • Unit Skylight: Flashing deficiencies were observed at the small skylight at the east end of the Hallway, resulting in water entry to the rooms below, including the Interview and Records Rooms. • Roof Slope Transition: The roof slope transition that occurs over several rooms, including the Exercise Room, was not properly installed. Deficiencies include exposed remedial nailing at the transition and damaged shingles due to wind uplift at this same area. Water testing this area resulted in an active leaks in the Exercise room in the location of a stained ceiling tile
Repair Scope: Based upon our observations, a repair scope is recommended to address the specific deficiencies noted above; the balance of the roof should be retained for the remainder of its expected service life of approximately 30 years.
Analysis
Based upon our visual observations and testing, the overall condition of the roof was reviewed and found to be in good condition for its age – approximately 20 years old, dating from original construction – and expected to have an additional service life of ten additional years. Slope provided is consistent with that recommend for a steep asphalt shingle roof; condition of the mineral surfaced finish appeared in good condition, with no significant loss of minerals observed. The locations of observations and testing are shown in Exhibit A – Figures 1-3. Observed conditions are shown in Exhibit B – Photographs.
Deficiencies: Visual observations and water testing revealed the following deficiencies:
• Hallway Skylight: Deficiencies observed include the following; o Flashing and Perimeter Fastening: Deficiencies were observed at the curb flashings, specifically at the lengthy flashing at the long horizontal surface parallel to the ridge of the roof. installation did not provide a means of securing this flashing to properly resist wind uplift; as a result a series of roofing nails were used to secure the flashing. Not only are roofing nails inappropriate to resist wind uplift, but the wind uplift and expansion/contraction cycles of the metal have worked to loosen the nails (“popped nails”).
Mastic that has been applied over the nail heads is essentially a temporary fix and ineffective in the long run.
o Glazing System: There were no reported leaks due to water entry directly through the glazing system, i.e., the glass and the sealant systems surrounding the glass. The concealed sealant joints below aluminum trim (e.g., the “beauty caps” between pieces of glass) are protected from UV degradation and appear to be functioning adequately. The sealant ed at the lower horizontal edge of the glass appears somewhat weathered but performing adequately.
• East Skylights: Of the three unit skylights, only the unit at the east end of the Hallway, adjoining the small offices and interview room, appears to be a source of water penetration into the building. The glazing system appears to be weathertight. However, both the perimeter flashing and the inappropriate installation of the Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 5
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
unit immediately adjoining both a roof ridge and valley appears to have resulted in a non-performing installation. Remedial efforts to repair the flashing, particularly evident at the top of the valley, appear ineffective.
• Roof Slope Transition: The roof slope transition that occurs over the several rooms, including the Exercise Room, was not properly installed. Deficiencies include a lack of a sheet metal transition flashing, damaged shingles due to wind uplift and exposed remedial nailing at the transition. Water testing in this area resulted in water entry into the Exercise Room within approximately 10 minutes, occurring at the location of one of the stained ceiling panels. Exhibit A - Figure 3 shows a diagram of water entry.
Recommendations
Recommendations include the following:
• Hallway Skylight: Deficiencies observed include the following; o Flashing and Perimeter Fastening: Remove the perimeter metal flashings and adjoining ros of asphalt shingles. In weatherboard fashion, install a new self-adhering flashing membrane around the perimeter, approximately new rows of new asphalt shingles, and new metal perimeter flashing. Comply with skylight manufacturer’s installation instructions (if available ) and National Roofing Contractors Association (NRCA) recommendations. Select color of asphalt shingles that best match typical field of roof.
Note: Manufacture may be O’Keeffe since an O’Keeffe label was found on one of the unit skylights. o Glazing System: Although this system appears to be performing adequately, consider retaining a glazing contractor inspect the system and reseal where necessary. • East Skylights: Recommend removing the east unit skylight and reinstalling in compliance with skylight manufacturer’s installation instructions (if available ) and National Roofing Contractors Association (NRCA) recommendations. Scope of work will include new sheet metal flashings and asphalt shingles around the base of the unit.
Note: The remaining two skylights are most likely watertight as there were no reports of water entry in those areas and they were installed in the field of the roof, away for roof transitions such as valleys. However, it would be good to confirm.
• Roof Slope Transition: Recommend reconstruction of this transition to provide a functioning sheet metal flashed transition. To accomplish this:
o Demolition: Remove several rows of shingles as required to install a new continuous sheet metal transition.
o Self-Adhering Flashing: provide self-adhering flashing at the top of the 2.5:12 sloped roof. o Metal Flashing: Install metal flashing.
o Shingles: install new shoeing above the metal flashing, color to match field of roof. • Interior: Replace stained acoustical ceiling panels and repaint stained wall areas as required to match typical finishes.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 6
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Bid Documents:
Unless otherwise directed by the City, we will prepare a base specification section for to repair the deficiencies observed at the skylights and roof slope transition – including supporting details – suitable for bidding purposes.
Alternate Approach: Given the limited scope of the repairs and the importance of retaining a roofing contractor skilled in correcting the deficiencies observed, the City may want to consider the following:
• Repair Bid Proposal from Enterprise Roofing:
• Cost Estimate: Request a cost estimate from enterprise Roofing:
Cost Estimate
A cost estimate was not included in the Scope of Work.
Limitations and Preparation
Limitations
The services of Interactive Resources are provided in a manner we believe to be consistent with the prevailing standard of care. This report is neither comprehensive nor exhaustive and is based on limited observations of the project, limited exploratory demolition, review of documents cited and discussions with individuals listed. The information is for the exclusive use of the client to whom this is addressed.
Interactive Resources does not warrant or guarantee the performance of any in-place or future construction on this project, whether or not it incorporates any of the recommendations contained herein.
Preparation
This report was prepared by:
Edward J. Anisman, AIA
Exhibits
Exhibit A - Figures
Exhibit B – Photographs
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 7
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Exhibit A – Figures
ROOF PLAN KEY
1. Water Damage: Shaded area shows approximate location of stained suspended acoustical ceiling panels and reported water penetration.
2. Slope Transition: Slope transitions from typical 4:12 to 2.5:12 at this line.
3. Water Testing: Water penetration occurred when hose spray was directed at this location.
4. Hallway Skylight Deficiencies: Flashing irregularities – including popped nails – were observed at the base of this skylight.
5. Hallway Skylight Repair: Proposed area of repair shown hatched.
6. Unit Skylight: Improperly installed skylight to valley is questionable Figure 1 – Roof Key Plan
Note: The roof plan shows the location of field observations and water testing relative to areas of water entry into the building at the east end of the Hallway and the Exercise Room below.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 8
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Figure 2 – Floor Plan
Note: The floor plan shows where water damage was observed within the building as well as the relative location of the skylights to the areas of water entry
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 9
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Figure 3 – Building Section at Exercise Room
Note: This building section shows the roof slope transition relative to the area where water entry was observed in the Exercise Room as a result of water testing.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 10
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
Exhibit B – Photographs
Photo Description
1. Police Department Roof – Overall View
2. Hallway Skylight – Overall View: The Hallway
skylight extends over most of the Hallway below.
Deficiencies observed primarily concern flashing
into the roof system.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 11
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
3. Hallway Skylight - Ridge: Flashing detail at ridge
shows remedial work.
4. Hallway Skylight – Roof Head Flashing: Head
flashing was poorly installed and does not conform
with recommended roofing practices. Deficiencies
include:
1) Remedial Work: Remedial repair at edge.
2) Inappropriate Fasteners: Use of roofing
nails to secure the flashing instead of
threaded fasteners. Roofing nails were
observed to be backing out at various
locations since a roofing nail cannot
counteract the force of sheet metal
expansion and contraction cycles.
5. Hallway Skylight – Glazing Detail: A “beauty cap”
was removed to show what appears to be a
watertight glazing joint. The arrow indicates the
sealant at the drip edge of the system, that appears
moderately weathered, but overall serviceable.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 12
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
6. Hallway Skylight – Interior View: No indication of
water damage to the interior walls of the Hallway
was reported by the client or observed at the site
visit.
7. Unit Skylight – Overall View: Location of this
skylight – at the east end of the Hallway – in the
immediate proximity of the convergence of both a
ridge and valley has created challenging flashing
conditions. Original installation did not properly
address these conditions, leading to water
penetration to the rooms directly below this
skylight. Arrow denotes condition at the top of the
valley.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 13
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
8. Unit Skylight – Valley Detail: Photo shows
conditions at the top of the valley, including
remedial work.
9. Unit Skylight - Manufacturer: Label incinerates that the unit was manufactured by O’Keeffe, a reputable
Bay Area manufacturer.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 14
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
10. Roof Slope Transition – Overall View: The
transition from the standard 4:12 roof slope to the
2.6:12 roof slope (encircled in yellow) for the accent
feature for the West Sierra Avenue Elevation
(outlined in blue) was poorly executed. Instead of
providing a sheet metal flashing for the transition,
the shingles run continuously from the less steep
slope of the roof at the right to the standard 4:12
slope at the left. Observed deficiencies are shown in
the photos below.
NOTE: Water penetration occurred in the Exercise
Room below when water was sprayed against this
transition
11. Roof Slope Transition – Wind Damage: Wind uplift
damage was observed along the transition.
Police Department Roof – Assessment and Recommendations 201 West Sierra Ave, Cotati, CA 94931
P a g e | 15
117 Park Place
Richmond, California 94801
510.236.7435 | www.intres.com
City of Cotati – Police Department Roof Assessment and Recommendations Interactive Resources Project No. 2024-010-03
12. Roof Slope Transition – Remedial Repairs:
Numerous roofing nails have been installed along
the transition to secure thee shingles from wind
uplift. Use of exposed nails does not comply with
roofing industry standards.
13. Roof Slope Transition – Underlying Damage:
Fasteners at the recommended installation nail line
have failed due to wind uplift. Arrow denotes a hole
in the shingle where the nail was installed due to
uplift damage.
14. Roof Slope Transition – Exercise Room: Ceiling
stains observed in the Exercise Room. Water testing
the Transition above resulted in active water entry
in the area of the stain at right.