These recommendations pertain to PVC duct installed below raised floors
and in or under a concrete slab. PVC duct conforming to the specifications
contained herein shall not be used in exposed applications. PVC duct
pipe and BlackMax® fittings shall be joined using the manufacturer's
recommended adhesive,* or an approved equal.
PVC duct shall be laid on level earthen surfaces. Large gaps under
the pipe shall be filled with selected backfill material, free of
sharp rocks or masonry material. Blocking under the pipe to achieve
a level laying condition shall also consist of select backfill material.
Do not use brick, rock or any other similar material to support or
level duct runs.
Using the duct plan supplied by the builder, place the register
boot boxes** at the locations designated
on the plan and secure them to the stem wall to prevent movement during
duct installation and backfill.
After the boxes are securely located, duct pipe and fittings can
be laid from the boxes to the air source or plenum. PVC duct pipe
and fittings shall be joined, utilizing a heavy bodied, slow setting
PVC cement. Cement shall be applied to both pipe and fitting surfaces
to insure a leak proof joint. Black to white connections shall be
joined using the manufacturer's recommended adhesive,*
or approved equal. Plastic fittings do not require concrete encasement.
A minimum of three (3) sheet metal or plastic screws shall be run
through the pipe and fitting walls to prevent movement of the joint
during the installation and backfill. Screws shall be located preferably
at the top circumference of the pipe to provide maximum joint integrity.
Screw heads shall be covered with PVC cement or one of the recommended
When duct runs and fittings installation is complete, and the duct
is connected to the plenum. It is recommended that a flanged PVC start
collar be used to effect this connection. The flanged start collar
shall be securely fastened to the wall of the plenum, utilizing PVC
cement. It is recommended that screws be used to hold the start collar
in place during installation. PVC duct pipe shall be inserted inside
the start collar, using PVC primer, cement, and screws to effect the
A visual inspection shall now be conducted to determine that all
joints and fittings are secure and properly located. Metal or wood
construction stakes shall be driven into firm ground adjacent to duct
runs, in locations that will prevent lateral movement and floating
of duct and fittings. This staking is essential and if properly located
will prevent lateral movement when backfill material is mechanically
Sand, gravel or other select backfill material shall be employed
to cover all duct and fittings. Normal site conditions allow duct
and fittings to be completely covered by backfill material, however,
in some cases the duct pipe will extend upward into the bottom of
the slab. No special precautions need be employed in this instance,
as PVC pipe and plastic fittings are sufficiently rigid to withstand
the loading of the concrete. Backfill shall be accomplished by hand
spreading or by light machinery (Bob Cat type). When machinery is
used, care shall be exercised to prevent such machinery from direct
contact with duct and fittings. Particular care shall be employed
to insure that the connections and duct at the plenum are fully supported
by backfill material. Tops on plastic boots**
shall be left intact until grilles are installed.
Raised floor installations for supports and insulation as per local
General Plastics BlackMax® and PVC products
may also be used for Exhaust, Ventilation, Combustion, Make-Up
air, and Products Transfer, as per local codes recommendations.
**May Also be used as extensions
Note: 18-24" PVC Pipe must be beveled on ends for fittings.
Plenum Boxes; cracks or holes in PVC plenums can be field repaired with
oversized pieces of PVC materials and IPS Primer, and 719 Adhesive,
or approved equals, with screws to hold in place.
PVC Pipe; same size pipe can be cut and used as overlays with IPS Primer
and 719 adhesive, or approved equals, with screws to hold in place.