Hi all; I ran into something I have not encountered before. Inspection a lake front cabin (35 feet from the water). The home is built into the hillside so there is 5 feet of clearance at the front and about 2.5 feet at the rear. There is glass fiber insulation between the floor joists, but they have used landscape fabric as a vapor barrier. To my thinking the landscape fabric will allow moist air from the lake to permeate the glass fiber.
Any one else seen this type of issue?
My first thought is they used that to hold the fiberglass insulation in place as well as a way to restrict ‘pests’ from damaging the insulation. 
Agree, and seeing as BC is a Cold Climate area, any vapor barrier should be on the warm side/floor side of the insulation material.
IMO, the external moisture levels in cold climate areas are insignificant to the application. Even in Summertime heat, you have maybe a few weeks of any significant humidity to contend with.
(Note: I lived in Vancouver, Washington for twenty years. We only averaged about 2-3 weeks of annoying humidity every July).
That landscape fabric is not a vapor barrier. It is not even a vapor retarder. As such it does not have any affect on moisture.
That spun polyester fabric allows air and water to freely pass through.
As others have already said, it is used to hold the insulation in place and keep pests out.
I suggest you look at this link link,
and then read up on vapor barriers and vapor retarders and how they may be applied in warm and cold climates differently.
It’s to prevent weeds from growing in between the floor joists, jk… 
I used to have a Kitchen that was on piers. The floor was insulated and initially someone used those metal rods to hold the insulation up. This is over dirt in NW NJ and we had weeks that would struggle to get over 25 degrees.
Needless to say, some years on, the insulation was completely useless.
When I tore that kitchen off the house and rebuilt it from a 10’x12’ galley with 2"x4" walls to a 16’x24’ with 2"x6" walls, I insulated the floor with 10" pink batts, vapor barrier in, and added 1.5" Zip System insulated panels(i.e. zip plywood with foam glued on it).
I wish I had thought about using landscape fabric like this on the old setup. I used a bunch of plastic sheeting that was always falling down and not particularly effective.
It looks like mobile home bottom board underbelly wrap from here.
Agree with these fellas.
Geofabric, landscaping fabric, is not a WRB, Weather Restrictive Barrier. "Weather barriers stop moisture, rain and wind from passing through the building envelope. However, they also allow water infiltrating the wall system to dry out quickly. Properly installed vapor barriers can also act as air and water barriers. They would then be considered a non-permeable air barrier.
Vapour barrier would be under floor planks or under subfloor sheathing.
I concur, the geofabric is to keep the glass fiber bats in place between floor joists.
Hope that helps.
Robert
I can’t see close enough…but it looks like an air barrier, Much like what is put under trailers to hold the insulation up or what they use to wrap houses with. Air barrier would be ok as it’ll hold the insulation up, help prevent condensation from forming on framing and keeps critters out. It’s not a bad idea. On mobile homes the air barrier is part of the thermal barrier. Don’t want to use plastic though. In some jurisdictions the underside of exposed crawlspaces elevated on piers for example are required to be sheathed in.
