We built our house in 1990 with larsen trusses on the exterior for 12" of insulation (24" on center) - covered with Tyvek and western red cedar siding - no sheathing. The siding is warped and pulling out in a few places (on a few ends), and is too weathered to stain or paint. We're thinking about replacing it this summer and have been looking at vinyl or James Hardy cement-fiber board siding. I'm concerned about the weight, as well as the possibility of having to sheath it with 1/2 plywood once we remove the cedar. Anyone with experience or advice would be appreciated. We are in Eastern Maine. Thanks, Marie.

Marie,
Western Red Cedar over Tyvek tends to be problematic as the wood leaches things that are bad for the tyvek. There is a very good chance the tyvek is compromised by now. I am surprised you only got 24 years from WRC siding.

It is hard to speculate about the ability to hold weight without detailed knowledge of the construction of the Larsen Truss. In general, fibercement is heavier, vinyl is lighter. I would probably look at a vinyl shake as these are more ridged then straight vinyl
What was the insulation used, and was it densepacked or other?
Does the house have good overhangs or does the siding get rain on it ? This would make a decision about a rain screen detail under the siding more meaningful .

Cheers,
Eric

Why not reinstall wood? It will last longer than either the vinyl or the cement and is lightweight. Does have to be at least oiled, stained or painted occasionally as you found out, but fiber cement does too. If you want maintanence-free, you'll need to install metal siding. (but even that will eventually need paint)