Should I remove the plastic sheet in my cellar?

Justin D'Arcy
Updated: Dec. 7, 2020

Hi Mike, I've been reading a lot of the posts on your site with interest and have a question about our existing cellar, in the house we just bought.  It was built 20 years ago and the construction is as follows.  Outside walls, gap to a metal stud wall, which is filled with insulation plates (soft foam type), then there is plastic sheeting which runs from the ceiling down under the floor.  Lastly there is a plasterboard wall.  When we bought the house there was a lot of mould on the inside of the cellar, so visible on the plasterboard walls.  Mostly that was visible behind furniture, but we had an inspection done and there was a lot of moisture detected in the walls.  We've opened the lower 1m of the walls to reveal that all of the mould is on the plastic sheeting, so between the sheet and the plasterboard wall.  There is nothing behind the sheet. 

We have still perfomed some wall injection repairs, as the company that inspected did say there was a problem in the joint between the wall and floor.  Putting that issue aside, all the insulation was dry and between the insulation and the plastic sheet was dry.  Based on the information on your site regarding not needing a vapour layer in front of the insulation, I'm wondering whether we need to replace / repair the plastic sheet, which we also cut at 1m in order to get behind it.   Thanks in advance, Justin

Responses (2)

Justin D'Arcy
Justin D'Arcy 3 years ago

Great, thanks for the quick response.  One clarification.  If I make more holes to let the moisture escape, does this not mean that the moisture will not cause mould on the iside of the outer wall instead of on the plastic sheeting, or are you saying that because the moisture will be cold air on a cold wall, there will be no condensation forming and therefore no mould.  We are indeed planning to get one, or maybe two dehumidifiers, as the cellar is being split into separate areas.