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How to replace a bathroom vanity with a bathtub?

Getting Established

How to replace a bathroom vanity with a bathtub?

Hi all,

We are currently planning / thinking about remodeling our main bathroom and we are looking at moving the vanity and reusing the currently vanity floor drain and water pipes for the new freestanding tub, both drains are 40mm - is there any issue to do this ?


Also where the new location of the new Vanity is going is on an internal wall that doesn't have any waste or water pipes, am i allowed to run the 40mm waste pipe horizontally through a stud wall to the outside of the house where i will get the plumber to connect it into the external PVC drains (this is a 40 yr old house) 


Below is the proposed design for the bathroom 



Getting Established

Re: Replacing Vanity with a Tub

Hi Justin,


It sounds like you're planning a significant bathroom remodel, and I can help you with some advice regarding your project:


1. Reusing Vanity Floor Drain for Freestanding Tub:
- If both drains are 40mm, you should generally be able to use the existing vanity floor drain for the new freestanding tub. However, ensure that the drain location and plumbing can handle the water flow from the tub. Consulting with a plumber to confirm that the drainage system can accommodate the change is a good idea.

2. Running 40mm Waste Pipe Horizontally Through Stud Wall:
- Running a 40mm waste pipe horizontally through a stud wall to the outside is possible, but there are a few things to consider:
- Building Codes: Ensure that your renovation complies with local building codes and regulations. Some areas have specific rules about plumbing modifications.
- Structural Integrity: When cutting into stud walls, it's crucial not to compromise the structural integrity of the wall. Ensure that any modifications are done safely and correctly.
- Pipe Slope: Maintain a proper slope (typically 1/4 inch per foot) for the waste pipe to ensure effective drainage.
- Professional Help: Given that it's a 40-year-old house, getting a professional plumber to assist with or review the installation can help avoid potential issues.

3. Proposed Design:
- Your proposed design looks promising. Ensure that all new plumbing connections are accessible and maintain the required clearances for maintenance and functionality.


If you have any more specific questions or need further assistance, feel free to ask. Good luck with your bathroom remodel!


Best regards,

Bunnings Team Member
Bunnings Team Member

Re: How to replace a bathroom vanity with a bathtub?

Hello @justinc1981 


Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about your bathroom renovation.


It's great that you've received great advice from @PlumbMaster-Zee. Just to add to the suggestions made, I recommend speaking to your plumber first and show them the plans you had in mind. You can still save money by doing all the hard work such as concrete cutting and re-tiling. 


But it's important that the plumber approve where the waste pipe will travel and where the water source can be diverted to as they will be aware of the rules and regulations of the local council regarding plumbing work. 


For example, you've placed your shower at the far end wall near the window, the practical diversion to provide water for your new vanity location is to run the pipework in the ceiling cavity and run it down the other wall. It is a much better way rather than drilling into your stud wall and weakening its structure.  


I don't see any hindrance with your new bathroom layout, and I think it's an excellent use of space.


Let me call on our experienced members @Nailbag @Dave-1 and @homeinmelbourne for their recommendations.


If you have any other questions we can help with, please let us know.




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Home Improvement Guru

Re: How to replace a bathroom vanity with a bathtub?

Evening @justinc1981 

ID like to say howdy and welcome to the Bunnings Community :smile: Envious of your bathroom plans I must say!

Im just wondering if your mockup is to scale? The bathroom door looks like it wont be able to open all the way?


With the question about the size of the pipes I would suggest to hit up the plumber and ask them if it can be done (I havnt had experience in this side of the plumbing) so would err on the side of caution.


The only other concern is that horizonatl pipe through the studs in the wall. A plumber will be able to recommend if its possible or go straight down through the bottom floorplate in the wall if possible.



Becoming a Leader

Re: How to replace a bathroom vanity with a bathtub?

Hi @justinc1981 , @PlumbMaster-Zee has pretty much covered the key points of consideration. If you open up the wall cavities yourself, then my advice would be to then call on the plumber to run all of the pipework. As its been mentioned, there are building codes that need to be adhered to and no plumber would/should connect your work to the main system for legal reasons. 


The plumber is going to need to be involved once you have stripped out the bathroom for their rough-in. At this stage you will need all your plumbing fixtures (taps, bath shower mixer as these come with the dimensions and behind wall connections the plumber will need to install. Anyone unlicensed are not permitted to perform this work. at this stage of the rough-in is where you would get your sparky in for the newly located GPO's, vanity GPO, feature lighting, exhaust fan etc.

You will also need to know what type of waste the new shower will have. For example rectangle grate and length or round/square grill and their location. The shower floor will need to be prepared (lowered) if you intend to have a walk in shower. Your tiler/yourself will need to screed the shower floor then waterproofing can happen. If you're getting a professional to waterproof, then I highly recommend an accredited person that can provide certification on completion. This will be required for any warranty comeback. I'm personally going through the process now of chasing up the previous owner builder of my home as the waterproofing was not done correctly and now I'm dealing with water damage.


Hope this also provides further insights.


regards, Nailbag


Re: How to replace a bathroom vanity with a bathtub?

Hi Dave,


Thanks for your reply, the drawing it to scale and the hinged door will be removed and changed to a cavity slider as the hinged door would swing and hit the vanity unit.


I have since spoken with a plumber and i will frame out the wall that the vanity waste pipe is going to run along to avold cutting into the wall studs 





Re: How to replace a bathroom vanity with a bathtub?

Hi Nailbag,

Thanks for your reply, we were going to use a preformed shower tray but without know if the current shower (in the same location as the new one) has been recessed into the slab or just a screeded on top. So since the photo i uploaded we have changed the shower to a have a hob but will no glass door to allow us to do a traditional slopping shower tray as i didn't feel like cutting into the slab to give me extra room to have a walk in shower (like my partner really wanted) .. but once i get the pricing done and i gut the bathroom and see what i find 


I was considering doing the waterproofing myself but i'd rather have that lovely warranty paper work to fall back on 




Re: How to replace a bathroom vanity with a bathtub?

Sounds like you're on the right path. Shame about the walk in shower, but it does require about a 20-30mm grind out for the fall plus what ever drainage type. Slab floors make bathroom Reno's a lot more complicated. I once bought a house to Reno with a flat roof and slab floor. Promised I would never do that to myself again 😉



Re: How to replace a bathroom vanity with a bathtub?

Hi Nailbag,


Thanks for your feedback, yes the open shower that the other half really likes is going to be the death of me .. i was looking at using a preformed tile over shower tray with a grate drain and we will need to chisel out 32mm to allow for the correct drainage 


The fun things we get ourselves into lol



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