And make sure doorways are wide enough to accommodate a wheelchair if it comes to that, “comfort height” toilets, grip bars for showers and toilets.
My parents built a house with most of this stuff and the walk-in shower to ensure they can stay in their house as long as possible. They recently added the higher toilets and grip bars not so much for themselves but for their aging friends who come to visit for dinners, etc. It’s allowed them to stay sociable while accommodating their guests’ and their own needs.
Also don’t forget adequate lighting. Night lights located close to the floor can decrease fall risk when elders are going to the bathroom. Pocket doors are also helpful to make things more accessible . You may want to choose a cooktop vs a stand alone stove because it can be left open underneath to accommodate a WC in the future. Wall ovens are easier to access. Drawer dishwashers are easier to access. Controls for the cooktop should be in the front so there is no reason to reach over hot elements. No scald features on faucets. Keep flooring changes to a minimum with no distracting patterns.Front loading washer and dryer on pedestals are also helpful.
For more suggestions , research " aging in place " or “universal design”
Yes to the wall ovens and drawer dishwashers. My parents have those as well. Bending over to load/unload some of the traditional dishwashers (Bosch is very low) can become more difficult.
Also be cognizant of flooring materials that are less slippery/less likely to cause tripping.
Mentioned up thread, this may be the This Old House season. https://www.thisoldhouse.com/watch/concord-cottage
The difference is that they took an existing small barn and made it into a cottage. Might be worth viewing for all their ideas about making a space friendly for aging.
Our state is officially calling them ADUs too. The authorities are urging folks to build them to help ease the housing crunch, but so far don’t believe folks are doing so for many reasons (especially many folks just have very small lots to begin with–building an extra dwelling on a small lot is “squishy,” or worse.
Granny houses or flats are slightly different than guest houses in that they have exterior and interior features that are geared to the elderly and allow aging in place without the need for future renovations . http://www.eldercottages.com/
I follow a blog by an interior design couple and they are in the process of building a “bungalow barn” for a parent (soon to be grandparent by their adopted child!).
It’s been fun watching the process. Though the barn does have a loft I believe all the living space for the grandparents will be on the first floor and the loft is either for storage or for other out of town guests. Not sure if I can post the link (will I get in trouble for trying?) but google “The Lettered Cottage Bungalow Barn”. It’s adorable!
Yes, ADU is the common term. We’ve avoided using the term “granny flat” or “mother in law apartment” because they imply an addition to the main house, and that’s not what we want. Many towns are reconsidering their ban on such dwellings because they realize that many homeowners just want to house their parents, rather than build rental units for extra income.
My H’s aunt and uncle built one in their backyard for his grandfather. It was essentially a stand alone studio apartment. It worked out beautifully. He walked to the big house every night for dinner, but otherwise was totally independent. One night he didn’t show up for dinner and they found him in bed with all evidence of having passed peacefully. He was 96, still safely driving himself and his friends around and saw all his scattered kids, grandkids, and great grandkids in the months before his sudden death. I often think of his end of life as the model for what I would want.
Look online at Tauton Press’ books, publisher of Fine Homebuilding magazine, plus FH’s website. They’ve done lots of articles on small homes and accessory cottages, sometimes compiled in their several books on same topic. Dwell magazine also has done many feature articles on small and accessory homes, but you’d need an archive to search for articles - again, check website. Our suburb has loophole in its zoning code which allows accessory apartment on 2nd floor of freestanding garage, which translates into a 400 SF (2-car) or even 600 SF home. We’ve now at least two dozen of these backyard homes thus far.
I have designed a detached garage/ADU unit at 900 square feet that is presently being professionally done by someone with CAD experience. It was difficult to find someone who wasn’t design&build ~ I have a builder to do the job and have been quoted $100 sf. so all in I"m estimating $100K.
But called mother-in-law apartments where they are.