A lot of what I do for a living is evaluating old houses to see if they might be eligible for the National Register of Historic Places. That means I spend much of my time looking at what people do to their old house and talking to them about the changes they've made.
I'm always amazed and appalled at the folks who are so damn proud that they put in all new windows, doors and vinyl siding and replaced the old porch with a deck. Wha?! These are exactly the things that made your house interesting.
What I try not to say, but can't keep from thinking is: great, now everything that was old is new and the house is completely uninteresting. I just don't understand why people buy old houses if they really want a new one. There are cheap new houses. Many times cheaper than buying an old one and completely redoing it. So why make these changes that rob the house, and the neighborhood and community, of a building that might have been significant enough to be listed on a register kept by someone with the exceedingly cool job title of Keeper of the National Register?
If your old windows leak, plug the worst leaks, install storms, hang insulated drapes, or even cover them with window film in the winter. DON'T pull them out and stick in vinyl windows that don't even fit the original openings properly. A front porch is a thing of beauty that reminds us of the times when a family gathered in this cool spot on hot summer days to visit with the neighbors or look out at the cornfields. Even in some new housing developments, like West Clay in Carmel, Indiana, a "new urbanism" community (at least they call it that), porches are understood as important elements of community building, as well as design. Please, I'm begging you, keep your old porches. Use them.
Porches, windows, doors, siding. These are the fabric of your home. And these are key elements in your homes historic integrity. If you buy an old house, appreciate it for what it is, not what you can turn it into. Make changes if you need to on the interior but be sensitive about changing the exterior.
You may think your house isn't significant and it doesn't matter what you do to it. Maybe it's a common type, like a ranch. It's hard for us to appreciate what our parent's generation built. But, ranch houses of the 1950s are now old enough to be "historic." There are ranches on the National Register already, as well as entire districts of mid-century modern homes. Their aluminum windows and sliding glass doors are important elements of their original design. Keep them if you can.
And if you're looking at buying a home and just can't live with old windows, original doors and porches, on a house that's 50 years old or older. Please, consider just buying a new house, or a trailer. We need those old houses. They help define who we are and where we've been as a people.