barkingdonkey - (I like the name!) I assume you're talking about the LP Smartside Product when you say smart trim; I have never personally used that particular product, but we have used and really like the MiraTec trim boards for trimming out around windows, corner boards, frieze and rakes, etc. The MiraTec is much cheaper than the HardieTrim boards and to me is easier to work with. You can get it pre-painted which I highly suggest if you are going to go with white trim. Our painters griped and complained the whole time they cut those trim boards in against each lap of the HardiePlank siding. We used the 5/4 (1") thick boards in 6" for the skirt/belly board and 4" for everything else. Just be sure you have your installers flash really well behind all joints in your siding and between your Hardie & trim boards no matter what product you choose. I would make them go overboard on flashing if it were me, especially on top of the windows so that no water has even the slightest chance of getting trapped behind your trim &/or siding. I think this is the most under valued part of the whole installation process. Here are a few pictures of the most recent house we've trimmed out with MiraTec 5/4 trim boards as I mentioned before, HardiePlank siding and stone: From Hunters Glen - Lot 38a Signature Plan From Hunters Glen - Lot 38a Signature Plan From Hunters Glen - Lot 38a Signature Plan Good luck with your siding. I'm sure you're getting excited!

I'm a retired finish carpenter, US Northwest coast. I put primed 8" Smartside on my own two-story house three summers ago. I chose to vent the wall behind the siding. That took a bit of time. I then pre-painted each piece with one coat of SW Superpaint, rolled and back-brushed, and then did a second coat once the siding was on the wall, also rolled and back-brushing. I primed all nail heads before the final coat. I flashed behind every joint and caulked every seam with OSI. I faced nailed every board by hand to eliminate overdriving the nails; no air nailer was used on the siding. It took 400 hours by myself, working evenings and weekends, but that also included tearing off layers of old siding, fixing the sheathing, replacing the soffits, replacing all the windows, and building a new front porch, so it wasn't a normal siding job. This summer, for the first time, I checked all caulked seams for shrinkage and cut out and re-caulked and painted small sections around four windows and three joints on the west and south walls. The siding and joints everywhere else looked as pristine as the day it was installed. I have absolutely no complaints or concerns with my decision to go with this brand of siding. One final thing, I left a unpainted 1-inch triangle-shaped piece out on the patio exposed to the weather the summer I did the job. It's still sitting there. The edges have swelled only slightly and cracked slightly, but I still can't chip even a small piece from the edge with my fingernail. I'm beginning to think it's indestructible.

I'd go with Hardie. That being said, the install is absolutely critical that a couple grand shouldn't play a role in your decision; the Hardie installer does.

4" smooth will be difficult to find, I believe. You might review Boral siding. Very good quality, and available in smooth, but 6" (5.5" actual) is the smallest they make. It could be installed so the exposure is less. http://www.boralamerica.com/TruExterior http://www.boralamerica.com/Media/Default/Resources/Siding/TE-Siding-Trim-Product-Guide_FINAL.pdf