If you are looking at the adaptation of a specific house then really what is relevant is not the width of an average powerchair but the width of the wheelchair likely to be used by the person living in that home. Depending on size and type, a wheelchair's width could range from 21” (for narrowest motorised transport chair) to +40” wide (for heavy weight powerchairs, those used by plus sized people etc).
Doorways many need to be wider if the wheelchair user is turning into it from a narrow corridor etc, therefore the layout of the home is also relevant.
It may also be relevant how accurately the wheelchair user is able to control their powerchair through tight turns and spaces.
Here is a link to a pamphlet about wheelchair home design that you might find of interest:
Hope this helps
Jean Merrilees BSc MRCOT
You can read more of my posts at: https://community.scope.org.uk/categories/ask-an-occupational-therapist