Thanks so much for those images! My front porch is similar to yours and I was thinking of replacing my 4 columns with redwood as well. That looks so much better than I had envisioned!
For the back porch, I was hoping to be able to remove the middle column and the column closest to the hose. I would not dare remove them without an engineer approving the work for liability purposes.
My concern with wooden columns is the longevity and maintenance required. Especially in the back porch that leads to the driveway, where I have to use salt to keep snow slush from icing over - the back porch/driveway are on the north side of the house and are in shade all day long.
Do you plan to do the work yourself? Personally, I think an engineer is way overboard for something like this. Unless you really want to remove as many as possible and might be on the edge of what's safe. There are all sorts of beam span tables you can find online for this stuff and those often have info about the uprights for them too. I found a lot of that online when I was looking at pergola design specs and requirements. I can't imagine 4x4's handling any lower load than those aluminum posts. In my case they only hold up the roof over the patio and aren't holding any load from the structure of the house so I know mine are fine.
I too am a bit worried about how the wood will weather. This is the 3rd redwood piece I have at my house - first was rough cut 2x12's I used to build a raised vegetable garden, second was 4S 2x6's I used to build a planter for herbs as well as some edging for the grass. I'm using Penofin on all of these pieces.
- The rough cut raised planters are now 2yrs old look just as they did when I first stained them except for the color becoming a little less bright.
- The 4S herb planter is a couple months shy of 2hrs old and the portion which is most exposed to the sun needs touching up. This wood soaked up a lot less Penofin than the rough cut lumber so I think that's why it already needs touch up.
- The front posts are only about a year old now and look perfect still. They don't get much sun so I think they'll last quite a long time.
One of the reasons I chose Penofin is that it's a stain/oil which means I should be able to re-apply just about anytime and the only prep is cleaning and maybe a very, very light sanding. If I'd used a poly or something like that it would be likely the old, weathered finish would need to be sanded off completely before refinishing. That's a lot of work I wasn't interested in. And of course there's always paint as an option too - means you could use doug fir as well which would be a big cost savings over redwood.
You'll have to check your local codes but around here you're required to have any wood posts like this sitting 1" above the surface to keep water off the bottom of the post. Most any post base on the market will already have this 1" standoff. Below is a link to the ones I used. There were cheaper options out there but IMO they look like ****. So I spent more and got these which are really simple and sleek looking.
https://www.homedepot.com/p/Simpson...lvanized-Concealed-Post-Base-CPT44Z/204842292
These were used to connect the posts to the beam on top, then I painted them matte black to match the post bases.
https://www.fastenersplus.com/Simps...igY1Du0ugBfiwcsPlGYLTHlp5lJoZurBoCf9MQAvD_BwE
As nolimits76 mentioned you definitely need braces in place before removing the old posts. We just used a bunch of 2x4's to support the beam while we removed the old posts and installed the new ones.
