I believe the building standard in Australia requires a separate sink and trough. I thinks it’s a silly requirement but if you’re using registered trades people they will probably stick to the rules. Do you have a picture of the floor plan you’re working towards? There are some great plan people here that can you with the layout.

Maybe a bit too off the wall , but I wonder if it is possible ( and legal ) to get some kind of basin that clips across the top of a laundry tub ?

Your idea of a 2 - in - 1 halves the plumbing and space , but you then struggle to wash your hands if you are soaking something ; likewise with grandkids it may be too deep to wash hands , so you have to use 5 or 10 times the water ?

Another possibility would be to get a narrow handbasin ( designed to hug the wall in a power room ) with a tap 'hole' on one end , BUT mount it 'sideways' by the tub , so it protrudes approx the same as your laundry tub ? As the 2 lots of water , and drains , would be side by side , maybe not much extra plumbing needed . It would be narrow , but maybe you could stand to the side if needed ?

Or obviously , just go conventional , and have the 2 seperate -- probably not a huge expense in the overall scheme of things .

60 SQM is plenty of space to make a comfortable granny flat...this plan that we designed and built as a holiday cottage includes a laundry and bathroom with a separate powder room and plenty of storage and we use a six plus seater table for kitchen work space to make more seating for guests and the alfresco has a barbq and giant table for crowds.. we built the cottage using a house rated steel shed that has raked ceilings, fully lined and insulated with double glazed windows and air conditioning

oklouise , I thought the mud room was the one with the handbasin hahaha . . . . . . . .

@oklouise, Thank you so much for sharing your design I greatly appreciate it . Is it possible to post more photos for the living kitchen area and the Alfresco??

@User, @oklouise, @frances strutt, Thank you all for your prompt replies and input I greatly appreciate it, it brought tears to my eyes because it shows a caring community within Houzz. Here are the initial sketches I received from the Architect Designer. Currently he put the Laundry in the hallway, but I would like to use the entire hallway as Wardrobes & Cupboards to maximise my storage. The cupboards will end at the study nook. Hence, I like to move the laundry next to the basin in the bathroom where it is currently “Linen”. I will not have a bathtub only shower. The bathroom designed for a wheelchair, because I have chronic back problem and one day, I may need a wheelchair. Also, my son and his wife don't like and want the side deck because it is eating in the grass area and will be very close to their main home. The granny flat will not be built on a concrete slab because the land is higher in the back (slope) and we don't want to excavate a lot of soil. instead it will be raised from the front by 1 meter and half. My son and his wife also don't like to see the pillars from their alfresco. My dilemma is between having the house I like and keeping my son and his wife happy by maximising the grass area, not closing the light on one of their living rooms and having good view to the backyard.

please describe your climate, where is north on your plan and do you have a site plan showing the original house with the new new granny flat on the block?

We did this in a small apartment bathroom. Sink is from IKEA. You can see washing machine space bottom left. Sink is large enough to fill a bucket or do some hand washing (of clothes) as well as bodily ablutions.

@Tom O, Thank you so much but if you add the washing machine how the water will be drained. usually the laundry sink has a hole to attach the washing machine hose to drain the water. This is my delima as most of the bathroom basins/sinks has one hole for the water tap.

the drain for the washing machine would be be underneath the sink into the same pipe that drains below the sink and is not a visible hole in the sink.. the washing machine taps and the power point would also be under the sink and hidden from view inside the cabinet.. if you inspect a modern exhibition house you can see many of these new ideas that make the plumbing much neater than previously

No, I thought this too but the trap under the sink has 2 connections for outlet water from appliances, like your kitchen dishwasher attaches to. This pic is in my kitchen but the apartment one is the same

I would worry less about catering to all your son’s demands assuming that he benefits greatly from you no longer living in the main house. Both sides will need to compromise.

You can use plumbing designed for a dishwasher - the washing machine hose plugs into the nozzle above the s-trap of the basic sink. The main thing to remember is that the washing machine waste water needs to be higher than the inlet hose (otherwise water will not fill the machine). But Im combing a laundry/bathroom in my current small renovation, and have no issue with having a large laundry tub as my bathroom basin also....

Dear @oklouise, I am in Sydney Australia, the weather is so pleasant, even in winter during the day the lowest could be between 50f-60f for only few days. We never has snow most of the year sunny.

Here are the photos, if you look to the last one my granny flat will be on this area the side of the main house and the side door will be removed to be replaced by nice paved/grass area to give me view of the street in front of the house , it is very nice

If the house is 1.5m at the front you will need to allow for a ramp for possible future wheel chair access at the moment you only have stairs. The Ikea sink sounds ideal but you could also use a simple drop in kitchen sink, stainless or coloured, I have used a stainless one in our laundry and works beautifully Tell your son that the piers can be covered with small shrubs. What aspect is the existing house at the front North, or other

@siriuskey, thank you so much yes , Agree that i may buy Ikea Sink , most probably my kitchen will be from Ikea as i liked their kitchens and their prices are also reasonable.

In regards to covering the piers, yes definitely will do some plants and small trees as you can see from the Architect sketches he also put some trees. Thanks

@Tom O, @oklouise, @bigreader Thank you so much all for your input, yes i searched Houzz as well and it is possible. to do all the connections underneath the sink like the dishwasher in the kitchen.

@bigreader, I paid for the land and will be paying for the build of my granny and will leave it to them after I pass away which will add value to their home. I was always independent woman especially after my husband passed away. Now i am living with my son and his wife since few month until i finish my granny.

It's not up to us to judge other peoples financial details and arrangements , so treat this just as an observation , but wouldn't it have been fairer to sell the house and all the land ( I gather it was 'your' house originally ) to your son at whatever price you agree , and you ( or they , depending on your arrangements ) pay for the granny flat , but I wouldn't have thought you'd pay more for the land .

Like I said , not up to us to judge on an anonymous forum , and I don't want to stir too much , just a comment .

We used this as hybrid laundry hand basin .. the mirror has since been hung

@wuff, this is beautiful

Get around the building reg by getting a toilet with built in basin.

I don't know how to use the CAD system to draw maps but I used the excel sheet to re-draw/re-design the granny flat and it looks like this

@idawoud13 thank you, we have only just completed renovating 1961 combined laundry bathroon area , it was a tiny space and no room for a hand basin. i love it, it has worked really well, best of all our 8 years of staged renovation is mow complete and retire at end of the year. good luck with your plans .. nice finishes and light filled space will make your new home feel luxurious . doesn’t have to be big just well designed and well finished .. best of all you have your loved ones close by

@wuff, Thank you so much, and congratulation for your renovation, I wish you will enjoy it for so many years to come.

Yes, I agree living into a granny flat next to my son was my husband wish before he passed away. It is good to be close to family. Also I love the suburb which I have been lived in for 22 years. My Daughter and her family is living close by too. Most of my close friends are living around and we always gather for a brunch, or lunch or watch movies. The good thing is most of my friends pick me up and don't let me drive most of the time when we go out. Thank you again