Key Personnel

The Allen & Shariff Team

Allen & Shariff’s people are the key to the firm’s ability to serve our clients well. Our highly skilled professionals are dedicated experts—people of integrity committed to helping our clients realize their vision, from start to finish. Learn more about the people that lead our talented team.

Zack Shariff, Chief Executive Officer, P.E., LEED® BD+C

Accreditations: B.S., Mechanical Engineering, University of Texas – 1981; Professional Engineer (P.E.) MD #21766 – 2006; LEED® Accredited Professional (LEED® AP) – 2006

Zack Shariff co-founded Allen & Shariff Corporation with William Allen. He holds a B/SC in Mechanical Engineering from the University of Texas and is a registered Professional Engineer as well as a LEED Accredited Professional. As the visionary entrepreneur of Allen & Shariff, his ingenuity, hard work, and perseverance created and sustained a successful, growing business for over twenty five years.

David C. Van der Vossen, Senior Regional VP of Engineering, P.E., LEED® AP, CGD

Accreditations: B.S., Business Management, University of Maryland – 1998; Professional Engineer (P.E.) MD #30756 – 2004; LEED® Accredited Professional (LEED® AP) – 2006; Certified GeoExchange Designer (CGD) – 2002; NCEES #25682 – 2004

As Senior Vice President, David Van der Vossen applies over 20 years of design experience to his projects. He is responsible for the overall technical design of his projects, as well as for the coordination of the work of the engineers, designers, and CADD operators on his team. He also consults with local regulatory agencies for design conformance of to regulatory standards and for conducting system analysis and comparisons with regard to economical and functional considerations. He is a member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) and International Ground Source Heat Pump Association (IGSHPA).

Hamza Tlemsani, VP of Engineering, Columbia, MD, P.E.

Accreditations: B.S., Mechanical Engineering, Georgia Institute of Technology – 1980; Professional Engineer (P.E.) MD, DC, FL, AL, GA, MS, NC, OH

Drawing on 38 years of MEP engineering experience, Hamza leads the operation of Allen & Shariff’s Columbia, MD office. With his extensive technical experience in HVAC, plumbing, and fire protection design and project management, he has served projects of all size: from tenant fit-out to central plant design. Informed by his expertise in DoD projects, healthcare, institutional, data center projects, and a large array of other project types, Hamza knows that the success of a project begins at inception of design.  Throughout the design process, he uses a hands-on approach, both with Allen & Shariff’s clients, and the personnel he manages.  This approach lends itself to his continuous quality control approach to the technical designs the Columbia office puts forth, and ensures that clients receive quality service and cost-effective, efficient, smart and reliable MEP designs.

Karin Farrell, General Manager of Operations, Construction Services

Karen handles the day-to-day activities addressing staffing, project management, financial analysis, and business development for the construction division.





David C. Price, Senior VP of Engineering, Pittsburgh, PA, P.E.

Accreditations: B.S., Mechanical Engineering, West Virginia University – 1996; Professional Engineer (P.E.) MD #12345, PA #12345

David Price has over 16 years of experience in mechanical engineering. David joined Allen & Shariff Corporation at their corporate headquarters in Maryland in 1997 and led the initiative to open an office in Pittsburgh. He is now a co-manager of the Pittsburgh office, and he manages the Pittsburgh mechanical group. David is responsible for project management and design of mechanical systems. He has completed new buildings and renovations including corporate office, higher education, multi-family, data centers, healthcare, industrial, retail, restaurants, hotel, transit, and non-profit spaces. As a Senior Vice President, David ensures that high quality and practical professional services are provided and that corporate goals, objectives, and plans are effectively executed.

Diane E. Bookwalter, VP of Engineering, Pittsburgh, PA, P.E.

Accreditations: B.S., Architectural Engineering, The Pennsylvania State University – 2005; M.A.E., Architectural Engineering, The Pennsylvania State University – 2005, Professional Engineer (P.E.) PA # PE077079

Diane Bookwalter brings extensive experience in electrical engineering to Allen & Shariff. As Vice President, she serves as co-manager of the Pittsburgh office and electrical department head. Diane is a hands-on leader who is actively involved in project design while providing design leadership, quality assurance, and staff mentorship. She has worked on a diverse range of projects including higher education facilities, offices, hospitality, hotels/multi-residential, industrial, and government facilities, among others. Diane has extensive experience in laboratory design and leads ASE’s science & technical projects. With dual degrees in Architectural Engineering, Diane understands the coordination required between engineering disciplines and the building architecture. She is an advocate for team communication between all members of the project because she believes great engineering and great communication go hand-in-hand. Diane’s teamwork strategy has been a proven method of creating lasting relationships, landmark projects, and client satisfaction.

Richard Bowser, VP of Engineering, Evans City

Accreditations: Associate in Specialized Technology in Architectural Design, Pittsburgh Technical Institute – 1980; Registered Professional Engineer (P.E.) PA#12345; Certified Energy Manager; LEED AP; Certified Sustainable Development Professional

Richard Bowser brings over 30 years of mechanical engineering experience to Allen & Shariff. His areas of expertise include managing projects from concept to completion, facilitating coordination between disciplines, conducting site surveys, making calculations for systems designs and equipment selection, technical writing, conceptual estimating, public presentations, and proposal preparation. Facility experience includes hospitals, assisted living, senior living, hi-tech, higher education, research, commercial, and industrial spaces.

Russ Sullivan, VP of Engineering, Evans City, PA, P.E., CEM, LEED® AP

Bachelor of Architectural Engineering, Pennsylvania State University – 1980; Registered Professional Engineer (P.E.) PA#12345; Certified Energy Manager & LEED® AP

Russ Sullivan brings over 30 years of experience in mechanical engineering to Allen & Shariff. Areas of expertise include managing projects from concept to completion, coordination between disciplines, complex problem solving, site surveys, master planning, calculations for systems designs and equipment selection, technical writing, conceptual estimating, public presentations, and proposal preparation. Facility experience includes hospitals, assisted living, senior living, hi-tech, higher education, research, commercial, and industrial.

William Pettitt, VP of Engineering, Salisbury, MD

Accreditations: B.S. Engineering (Mechanical), Messiah College – 1997; M.S. Systems Engineering, The Johns Hopkins University – 2004

Bill Pettitt overseas the office in Salisbury, MD and supports our clients from Annapolis, MD through the Delmarva Peninsula. Bill brings over 20 years of diverse mechanical engineering, project management, and leadership experience to Allen & Shariff. Bill’s experience developing and executing projects both domestically and internationally has helped finetune his skillsets in project definition, scope development, real-world engineering calculations, and system integration. In his role, Bill has a singular focus on creating a positive client experience, where effective solutions are developed in partnership with clients to meet their expectations and support their project vision.

William “Bill” Jackson, Operations Manager Middle East

Accreditations: M.S., Environmental Science and Engineering – Virginia Tech; M.A., Urban Affairs

Bill Jackson is responsible for overseeing the operations of the Middle East office as well as ensuring that projects are delivered successfully by the ASC project teams. Bill has over 35 years of healthcare experience ranging from strategic inception to project turnover to the client. His experience includes work with architectural, project management, and consulting firms, as well as running his own project management company. He has served in key positions in healthcare planning and construction at two major academic medical centers and has consulted at over 50 hospitals, planning and putting in place over 4 million square feet of space.

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