This is an "American Foursquare" I believe, and a classic expression of residential architecture of its day.

IMO, any addition should not obscure or mar the classic architectural features or massing. Thus an addition to the left side will be challenging due to the need for access via the reception hall. I would keep the front of the addition as far from the plane of the front façade as possible, so that the front continues to read as a foursquare.

It's really challenging to start with a classic architectural style and add something that doesn't really mess up that which was originally attractive.

My recommendation is to find a skilled and experienced architect who knows about additions to historic residences.

Good luck on your project!

The bedrooms, closets and upstairs bathroom are also undersized and non-standard by today's criteria. It's not clear whether a bathroom of that size and configuration would be allowable in some locales. It's probably 5x7 which okay with some layouts, but not with that particular one.

I think, if you want to build a house from an old plan you might need to start with something that is 1) already bigger and 2) less rigid than a foursquare.

Check out "Classic Houses of the Twenties" by Loizeaux. I found it at the library and it has 134 old house plans! Lots of great ideas...and even a few first floor bathrooms and guest rooms :)

Here's a link....

Here is a link that might be useful: Link to book

The only period-appropriate side addition to a house like that would be a side porch on the DR side, or a solarium (same side). The addition you propose should go on the back. The DR becomes the bedroom, the kitchen becomes the DR, and the new kitchen and bath is added to the rear, with the MBR and MB above it. A side porch/side balcony (2d fl) completes the plan.
Casey

My grandparents had a foursquare farmhouse with almost this exact layout (as had thousands if not millions others during this period) -- their solution when expanding was to do what Casey mentioned: build out where the current back porch is.

My grandparents added a one-story kitchen and bathroom and expanded this into a back hallway area as well - vital to have a big back entry/mudroom area when on a farm! This also benefited the contemporary philosophy of keeping family areas more private at the rear of the house and 'public' spaces more immaculate at the front.

They then used the dining room as their master bedroom; helpful as they got older. You could turn yours into a family room, tv room, etc.

Keep checking out foursquares; although I live in an old house and don't at all mind smaller bedrooms, some folks don't like them, so it's not beyond conceivability to simply expand one of these plans by 10' or so all along the perimeter, to give yourself more space to play.

Here is a link that might be useful: http://antiquehomestyle.com/plans/

I really like Fourquares and we have our eyes set on one. I was thinking of adding a small extension in the front and a larger in the back and someone on this site mentioned that it would be unfortunate to alter the charm of these old houses and came to agree with that opinion.
I did a lot of research on these old houses and found a document that was really helpful. I have since made changes to keep the original look of the house intact, at least from the street view.

Here is a link that might be useful: American Foursquare (1900-1930)

Thanks everyone - very helpful!

I had come across this photo below, with a side addition to a foursquare, and I didn't think it looked too bad. But I do understand what everyone has said about being period-appropriate and true to the historic style of a foursquare.

As for small rooms - I have no problem with them. I know lots of people build homes thinking they'll be in them forever, so they build with only their own tastes in mind (and in fact, looking at the market for property, I've come across a few such houses), but that these very specific tastes hamper selling the home later on. I truly believe if I am able to build, I'd never move out and sell.

I am absolutely in love with Connor Homes, The New Old House, and Russell Versaci's Pennywise Home series - if I could find a historic home to purchase and fix up, I absolutely would. However, the area I want to be in (near my family) has very few of these types of houses, and even fewer with any acreage. Most houses here are either double-wides or lodge-style cabins. So I'm hoping to someday build by own new old house, accommodating for some of the shortcomings I see in older floor plans (like the lack of a first floor bathroom). I'd also like a guest bedroom downstairs so that as my husband and I age, we have the option of moving downstairs.

Thanks again for all the advice and the links!

Here is a link that might be useful: [American Four Square with Addition[(https://www.houzz.com/photos/exterior-classic-american-four-square-traditional-exterior-minneapolis-phvw-vp~382682)

I've seen modern adaptations of American Four-Square at various house plan sites.

They had better kitchen and bath options, but the same look and feel.

A four-square was a building type that had a major space in each of its four corners. This house type is most often associated with the Prairie Style and Colonial Revival Style but here it has been used for a predominantly Shingle Style house.

It's unfortunate that the downspouts would not have much chance of working without large expensive built-in collectors.