The building will be primarily comprised of a veneer brick with concrete masonry unit backup wall.  Aluminum windows are placed in every classroom and are utilized often to achieve LEED guidelines for natural light.  There will also be an aluminum curtain wall system used at various places to compliment certain design elements.  One of the primary features is a three story curtain wall which will provide great outside views from the media center.  The entrance to the building also features the aluminum curtainwall.  In each of these applications of windows or curtain walls, special attention was needed to ensure proper STC ratings of the systems.  The minimum rating is STC 35.  This is important to reduce sound transmission since Interstate 495 is approximately 90 feet from the building at its closest point.

This building will feature different types of glass depending on the application and design intent.  The windows of the classrooms will be insulated glass with an airspace.  Low emission coatings will be applied.  The aluminum curtainwall will feature a similar system applied at a different scale.  The curtainwall also has different shapes of panels for design purposes.  Certain sections of the curtainwall will have spandrel glass to hide ceiling spaces from outside view.  Another enclosure being used exclusively in the gymnasium is a translucent wall panel.  This will assist in providing natural lighting effects.

The roof will be enclosed with a Built-Up Asphalt system.  On top of this, a top sheet is specified to be a glass fibered cap sheet with white coarse mineral granule top surfacing and mine mineral on the bottom surface.  The roofing materials must meet or exceed a Solar Reflectance Index of 78.

Geothermal Wells being Drilled

The structural system for Carderock Springs Elementary school is structural steel.  The average bay size is approximately 25’x25’ in most locations, however there are some various angled walls and irregular architectural design in some places where the bays and typical structural system will vary greatly.  The individual steel specifications vary immensely to call out a typical size.  The building also has varying grades which also makes the system differ from typical design of the foundations and the overall steel design.  The slabs on grade are 4” thick with reinforcing provided by WWF6x6xW1.4xW1.4.  This rests over 4” of gravel and below that is undisturbed earth or approved compacted fill.  The slabs on deck are 5 ½” thick on 1 ½” x 22 GA. Composite steel deck. 

The typical foundation system are a series of spread footings connected by strip footings on the exterior wall of the building.  The interior columns are supported by spread footings.  The typical spread footing can range from 2’-0”x2’-0”x1’-0” to 15’-0”x12’-0”x1’-8”.

The roof is supported by a typical 20K4 joists spaced at 5’ O.C. spanning approximately 32 feet.  The Gymnasium roof is supported by masonry bearing walls and has 28K12 joists at 5’ O.C. spanning a distance of approximately 72 feet.  The roof of the Multipurpose Room bears on masonry walls and has 36LH10 joists at 5’ O.C. spanning a distance of approximately 78 feet.

The overall building service will be rated at 265/460V, 3 phase, 4 wire, rated at 1600A.  The secondary service will be 120/208V.  The building has 21 panelboards and 7 transformers which distribute the overall service throughout the building.  There is also a 100kW backup generator which will service emergency lighting and life support systems throughout the building.

The lighting in the classrooms consists typically of 8’ long pendant mounted lights for general lighting purposes in 2 rows along with 2’x4’ recessed lighting near the chalkboards.  The staff offices consist primarily of 2’x4’ recessed fixtures.  All of these lights are specified to be 32W T8 fluorescent lamps for easy of serviceability by the maintenance staff.  In the gym, the lighting is provided by 250W metal halides pendant mounted to the roof.  The multipurpose room consists of primarily 2’x4’ recessed fixtures.

The primary heating and cooling system utilized at Carderock Elementary is a closed loop water Geothermal system.  There system consists 120 wells which are drilled to 540’ into the earth which in then are connected to the building’s 49 water source heat pumps.  These heat pumps are located in small mechanical closets throughout the building which provide individual controls for the various rooms inside the building and on average can handle a heating and cooling load of approximately 22 MBH.  Outside air is provided by 6 rooftop mounted Energy Recovery Units and are connected to the ducts.  The ERUs also provide some heating and cooling capacity to assist with the building’s heating/cooling needs.  The Gymnasium, Multipurpose Room, and Media Center receive its conditioning exclusively from these ERUs while the classroom and educational spaces are primarily heated and cooled by the Geothermal heat pump system. 

This building has one elevator and 3 stair towers which provide vertical egress throughout the building.  Each of these towers are independent of the structural steel system and are constructed with masonry bearing walls.

Metal Stairs being set into Tower

Carderock Elementary has an automatic fire extinguishing system.  The building primarily has wet pipe systems with sprinkler heads located in the classrooms, offices, corridors, and storage closets.  There are also visual and audio alarms located in the building to complement the sprinklers.  There are very few fire rated walls located in the building.  The stair towers consist of 1 HR rated walls and the mechanical closets and certain storage areas receive 1 HR smoke rated partitions.

This project is being delivered using design-bid-build method with a Guaranteed Maximum Price contract.  HESS is acting as the construction manager and is at risk but is not self-performing any contracts.  The major contracts were all publicly bid.  These contracts include, site work, concrete, steel, roofing, drywall, fire protection, geothermal system, mechanical/plumbing, and Electrical.  An additional requirement for this project was to have Minority Business Enterprises receive a percentage of the contract sum.  Each of the public bids were required to have the MBE paperwork signed in order to have an eligible bid.  In addition to standard requirements to bid, these contractors also had to be pre-qualified with Montgomery County Public Schools.

The remaining contracts were private and reviewed by HESS.  Some of these contracts include interior signage, building equipment, doors and frames, and finishes.  Once the private bids were received and reviewed they were presented to the school district for approval to establish the final contract value.