The best thing would be to locate an old photo, as close to 1920 as possible. Next best would be to let us see a picture of your house and we can make long-distance diagnoses and suggest column styles.
Occasionally the pilasters or half-columns attached to the house aren't replaced at the same time, so some original fabric survives that way, and the column pattern can be inferred.
The top diameter of a column should be equal to the breadth of the beam that sits on top of it, and vice-versa. Then, depending on the order of the column (Ionic, Doric, Corinthian, Tuscan, Composite, etc), the main diameter is ascertained, which just leaves the height, which is knowable.
Casey

You could try looking at the Chatsworth site which has lovely (and expensive) columns, and IIRc also has some info on sizing and styles.

One thing to keeep in mind is that the columns should be fatter than you may think. Our modern eyes are daily assaulted by skinny little twigs that pass for columns in "classically"-styled houses in subdivisions that don't look able to bear the weight of what's above them. (Never mind that modern building techniques make it possible.) For a column to be successful it must look as if it could carry the load visually.

The other thing is that columns, especially taller ones, really need to have some entasis to them, or an optical illusion makes then seem too skinny. Entasis is a subtle fattening of the colum at the middle height which counteracts the optical illustion and makes the column look well-proportioned.

Another thing is that it's important to have pilasters set against the elevation of the house at the back of the porch, matching up (but not necessarily matching in style, for instance you could have rectangular pilasters with round columns) at least the corner columns on the front. Otherwise the whole thing looks slapped on and not integrated with the building.

If you want to read about the classical dimensions of columns (at least as interpreted by neo classical styles in the 19th c here in the US), I recommend Asher Benjamin's book. (Practical House Carpenter????) I can get the exact title if you'd like to look it up. It's a Dover reprint these days; your public libray may have a copy.

Also, before you abandon your present ones (even if they are in bad shape) you might consider repairing them. I think there may be publication for sale at John Leeke's webpage (www.historichomes.com) that deals with column repairs. Columns are frequently in need of restoration as they are exposed to a good deal of weather stress. There are some installation techniques that can help you mitigate it going forward.

HTH,

Molly~

Thanks! Molly - I've been walking around the neighborhood and realized exactly what you have said - that most columns look too thin. I found 1 house that looks like mine (fieldstone and shingles facade) and it has much fatter columns than my house. My current columns do not look original which is why I am planning on replacing them along with other repairs we need to make on the front of the house. Thanks for the info!

I also want to mention that there are no half columns or pilasters, not on my house or its twin. But I'm sure the portico and columns were part of the original design because of the way the stonework is laid on the front of the house. I should really find my digital camera and post a photo!

Check out my album for some ideas,

The PorchGuy

Here is a link that might be useful: My Album

Turncraft makes quite a number of classically proportioned fiberglass columns that are weight bearing and don't rot. They do not have entasis, but are wider at the bottom than at the top. I find this looks right on most jobs where the columns are between 8' and 10'. They are quite easy to install and not too expensive.I have used them on a number of jobs inside and out. The wholesaler in upstate NY, Brockway-Smith is in Albany which might be close enough to be easy for you.

Do look at the pictures of how the columns fit under the architrave ( the lintel), and how the roof set on the system. Modern builders tend to hide the header (architrave, lintel) within the frame. It should be visibly spanning the columns and supporting the roof.
Columns against the house tend to be square because they end the rectangular wood frame, easier, neater construction. Free standing columns tend to be round because you brush past them, no pointy edges to jab you.

I am glad you are walking the neighborhood and seeing how porches were done in your town. Each part of the country has its own charming vernacular idiosyncrasies - some because of a particular builder and his skills, some because of available materials or weather conditions. Even in the 1920's when railroads could deliver goods people saw in magazines or places like the Sears catalog, there are lots of regional variations which I find wonderful.

Hi,
This is a project I worked on several years ago; the pilaster was all we had to go on, the rest of the design was inferred from it.
{{!gwi}}
The column capitals were recreated from a cast taken from the pilaster and duplicated in a circle.
{{!gwi}}

The whole portico; I duplicated the railings based on an original photo.
{{!gwi}}
Casey

ahh, beautiful, Casey! - made my morning! thanks

There's a book at my local library that might be of interest to you. I believe the title is "A Field Guide to American House Styles". It has info on recognizing architectural styles, and if I recall correctly, it has very detailed info as to what type of column is found on each period and style of house. Good luck!