Frank Pattern Roof Drain and Overflow
The Frank Pattern roof drain and overflow includes the primary and secondary or overflow roof drain in a convenient one piece base. Both roof drains are bottom outlets and the model numbers are 850-2N, 850-3N and 850-N.
- Both roof drains have 8-1/2″ diameter bowls and they are available in 2″ through 4″ pipe outlets. They both have no-hub pipe connections.
- Each roof drain has a combination protective gravel stop/membrane clamp (flashing ring) which compresses to make a water tight seal and prevent leaks.
- The entire roof drain assembly has a resistant Duco coating.
- Each roof drain has a dome or leaf grate that prevents debris from entering the roof drain. It twist locks into the membrane clamp and creates a secure connection.
- Dome height is 6″ and will filter out debris.
- 100% cast iron construction
- Add a sump pan to make a watertight connection and to prevent standing rainwater. See below
When should you use Frank Pattern roof drain and overflow in a bottom outlet version?
You should use the Frank Pattern 850-N roof drain and overflow in the bottom outlet version when there is sufficient space between the roof and ceiling. .
This is a vital first step that should be taken in order to determine if this is the correct roof drain for your project. Also, please review the installation video below before purchasing.
What is a common application for this roof drain?
Frank Pattern 850-N roof drain in the bottom outlet version is ideal for residential and light commercial roof drain installations such condominiums, apartment buildings, restaurants etc.
This is due partly since the bowl size is smaller, about 8-1/2″ or so, compared to the medium and large commercial roof drain bowl sizes that are 12″, 15″ or 16″ in diameter.
The larger diameter drains are used on larger projects such as warehouses, manufacturing plants etc., whenever there is a large surface to be drained.
It can be used on any roof where you have at least about 14″ of clear horizontal space between the roof joists, and 15″ of vertical space.
1) Pipe Pitch, correctly sloping your roof drain pipe is VITAL
- Factor 1/4″ per foot of pitch or angle on the piping if possible. In some cases, 1/8″ per foot slope may be acceptable. Refer to your plumbing code.
- Make sure there will be enough slope on the piping and that it will not be back pitched.
- If you plan on using this roof drain in an area on the roof that is used as a walkway, be advised that the dome will extend above the roof or deck surface.
2) Keep the pipe runs separated
Make sure the pipe runs for both of the roof drains are separate. Aside from being a a plumbing code requirement, the overflow piping provides a secondary of removing rainwater should the primary roof drain become clogged. This safety feature can prevent a flat roof from collapsing under the stress created from excessive standing rainwater.
What Does The Membrane Clamp Do?
- The membrane clamp is the center piece in the roof drain sketch. It is intended to provide a watertight seal where the roof membrane contacts the roof drain. It clamps the roof membrane to the roof drain body in three places. When cutback sealant is applied to the membrane prior to the clamping step, it will provide the necessary seal. There are many You Tube videos that show this process. SEE AN EXAMPLE HERE
SCP roof drain sump pan – should you use one?
- A true roof drain sump pan should be used to make sure that your roof drain is lower than the surrounding flat roof surface.
- There are a number of factors that go into making that evaluation but the thickness of the roof plays a big part. A thin roof membrane will result in the membrane clamp being higher than the roof which will create standing rainwater. A thicker roof will be the opposite. If it’s uncertain, err on the side of caution and use the sump pan.
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