Not an expert and basement projects. Any drawback to using a vapor barrier and green sheet against a mostly below ground level basement?
Bad idea to use a non-breathing VB in a below ground basement. Reason being that no such basement wall will remain totally moisture free. Adding a solid vapor barrier such as poly sheeting creates a surface for water vapor to condense and then collect. Any wood or other building material trapped behind the VB will rot and decay. You are far better off to have a breathable barrier (such as the paper baking on fiberglass insulation). This way the temperature and humidity control of the finished basements heating and cooling system can help dry any minor amounts of moisture behind the walls.
There is no harm in using 'green board' instead of regular drywall other than the additional material cost. However, if you have a basement moisture problem that would require the use of green board over conventional drywall, you have moisture issues that really need to be addressed prior to drywall installation. Basically, green board is not a cure, just a method of putting off damage for a longer time. If you have a moisture leak in a basement, eventually even the green board will be destroyed.
Here is a great site that can give you detailed advice on building practices based on the type of construction and location.
Also look at the section on vapor barrier guidance linked on the left side of the page.
You might want to consider paperless drywall instead of regular or greenboard drywall. It uses fiberglass instead of paper for the facing.
Any advice given here is general in nature and is not necessarily valid for your given area. If in doubt check with your local codes enforcement department for what is required when doing electrical, plumbing or structural work on your house. Permits may or may not be required in your area and home owners may not be able to DIY some tasks. I have no way of knowing if you have the skills needed to complete the tasks you are asking about, when in doubt seek professional assistance.
My advice may be worth exactly what you pay me for it. :-) For the record I did not stay in a Holiday Inn Express last night.
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