An offset drain, also known as an offset toilet flange, is a special type of drain used for installing floor-mounted toilets. Unlike standard toilet flanges that sit directly on top of the drain pipe, an offset flange sits next to and connects to the drain via an elbow piece.
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What is the purpose of an offset drain?
The main purpose of an offset drain is to allow installation of a toilet when there are obstructions directly over the drain pipe location. Some common situations where an offset flange is required include:
- Concrete floor installation – Concrete floors are typically poured over piping, leaving the drain pipes encapsulated. An offset flange allows the toilet to be installed next to the drain location.
- Drain pipe replaced off center – If an old drain pipe needed to be replaced but the new one ended up slightly off center, an offset flange allows the toilet to be installed in the correct spot.
- Raised bathroom floors – For wheelchair accessibility, some bathrooms have a raised floor installed over the subfloor. An offset drain lets the toilet be mounted on top of the raised floor while connecting to the drain below.
- Floor framing obstruction – Obstructing floor joists, ductwork or other framing may cover the desired toilet location. Offset flanges allow the toilet to be moved next to framing obstructions.
By offsetting the toilet flange, drainage pipe obstructions or other situations no longer prevent proper toilet installation. The offset flange redirects the waste to the main drain pipe through a jog in the piping.
Offset vs Standard Toilet Flanges
There are a few key differences between a standard toilet flange and an offset flange:
| Standard Flange | Offset Flange |
|---|---|
| Sits directly over drain pipe | Sits next to drain pipe location |
| Direct vertical waste path | Elbow fitting provides offset waste path |
| For open drain pipe locations | For obstructed or unavailable drain locations |
The standard flange mounts directly on top of a drain pipe coming up from the floor. With an offset flange, an elbow below the flange offsets it horizontally to the side of the drain pipe location. This elbow fitting provides the “jog” in the waste path required when the vertical path is unavailable.
Offset Drain Installation
Installing an offset toilet flange takes a bit more work than a standard flange but follows a straightforward process:
- Locate existing drain pipe – The drain pipe coming up from the floor needs to be located and exposed. This is typically 3-4” diameter PVC pipe.
- Cut drain pipe – The drain is cut to install a new elbow piece. This is usually done a few inches above the floor.
- Glue elbow – A 45 degree or other angled elbow is glued onto the drain pipe to provide an offset.
- Attach flange – The offset flange is attached on top of the elbow to provide the toilet mounting surface.
- Extend as needed – Additional piping, a second elbow or spacers may be needed to position the flange properly.
- Anchor flange – The offset flange is anchored to the floor to provide a stable mounting surface.
Proper measurements are taken throughout the installation process to ensure the offset flange is positioned correctly beside the toilet location. The elbow angle and piping extension length provide the flexibility to route the waste as needed.
Offset flanges come in a few different designs:
| Offset Flange Type | Description |
|---|---|
| PVC | One-piece molded PVC flange with elbow |
| Stainless steel | Stainless ring with separate elbow fitting |
| Brass | Brass ring with separate elbow fitting |
The one-piece PVC version provides the simplest installation option. Stainless steel and brass flanges are higher quality but require joining to a separate elbow piece.
Installing the Toilet on an Offset Flange
With the offset flange securely in place, installing the toilet is essentially the same as a standard flange:
- Wax ring – A new wax sealing ring is placed over the waste flange pipe.
- Toilet – The toilet is lowered into position with the bolts inserted through the base holes.
- Nuts and washers – Nuts and washers are threaded onto the bolts below the toilet base.
- Securing – The nuts are tightened by hand, then fully tightened with a wrench to secure the toilet.
- Caulk base – Caulk is applied around the base of the toilet to seal against the floor.
- Connect water – The water line is connected to the toilet tank or bowl fill valve.
The only difference is that the toilet is positioned next to the offset flange rather than directly on top. Proper alignment is important to keep the toilet base perfectly centered over the offset flange.
Offset Drain Maintenance
Routine maintenance is critical on an offset drain to prevent blockages and keep it functioning properly:
– Periodically check elbow and piping for leaks, cracks or joint problems.
– Snaking the drain line to clear blockages is helpful to keep waste flowing freely.
– Flush the toilet multiple times if water drains slowly to clear out mass in the piping bend.
– Monitor the area around the base of the toilet for any leaks which indicate a poor seal.
– Make sure floor bolts remain tight to prevent shifting of the toilet base.
Issues are typically minor blockages that can be cleared with a drain snake. Major blockages may require removal of the toilet for access. Watch for deterioration of lower elbow joints over time.
Conclusion
Offset drains provide an indispensable solution for installing floor-mounted toilets where standard flanges just won’t work. While a bit more complex than direct flange installations, offset drains allow proper toilet function even with piping obstructions. Careful installation and maintenance keeps these unique drains working smoothly for the long run. With the right offset setup, a toilet can be plumbed in even the most problematic drain locations.