Crawl space problem

Hello everyone…
One of my client wants cover the whole earth of his basement a plastic sheet (some kind of vapor barier).

I know that it will stop the humidity to rise however I think it also block the humidity to scape. I have seen many crawl spaces that actual water stays on the plastic and has no place to go…

Which method would be the best?

Thank you

Is it a basement or a crawlspace and what area of the world are you in?

It’s a crawl space, walkable, not habitable…
We are in Montreal, Quebec, Canada


The plastic in the crawl space is a great idea. Over lap the seams and tape them well. Bring the plastic up the wall some and use acoustic sealant to glue it to the concrete. Then have them use rigid insulation on the concrete. You now turn it into a semi conditioned space. It will now only need 1 sqft of venting for every 1500 sqft. If you were to close all vents I would have a humidistat with an alarm. If there is water on the plastic it’s unusually caused by bigger issues.

Please forgives to be incontinent for interior decoration.

the smoker you drink the player you get

That’s Chinglish Barry. Translated it means, if you don’t understand the purpose for a vapor barrier, you probably shouldn’t be doing home inspections.

Thank you

glad my mentors showed a bit more patience otherwise i’d still be on the nipple and in diapers
although the prior is still enjoyable
the latter may be in my future

back to the OPs ?
this may help guide and explain further](

You can tune a piano but you can’t tuna fish.

In the southern part of the US a full 100% vapor barrier in the crawlspace would be the correct answer…however as someone who has also lived in the somewhat frozen north
Foundations may be damaged by excessive moisture from frost so I would check further before covering 100% of the ground in a crawlspace in your area. Leaving a small amount of grade uncovered may act a sort of relief valve to prevent damage to brick/block in the event the foundation become to wet and cannot dry.
Ask more experts in your area who are familiar with crawlspace construction in cold climates.

Love both …thanks … Roy

Thank you Jeff,

It’s one of those things that everyone has different oppinions…

Don’t let the bullies stop you from asking questions. You will always get the arrogant know-it-all’s. There are alot of good people here, and its better to ask then guess.
Barry, I agree, my mentor showed a bit more patience and I still work with him and learn from him. There are those that are Great Teachers and those that can only wish.

Good post.

Hi Massoud,

In Canada crawlspaces are required to have ground cover. If it is an unheated crawlspace it must be 10 mil poly (other materials are permitted though), joints lapped at least 4 inches and weighted down. If it is a heated the crawlspace the poly requires 12 in of lap.

I am fairly certain these requirements have been in place since 1975 so anything built after that should be installed in this manner. If the crawlspace is older than this requirement these are a definate recommendation of good building practice.

Great links Barry…:cool:


He’s in Canada. A plastic cover in the crawlspace is very common and is good. It helps reduce the amount of moisture entering the crawlspace from the soil. If it is sealed at the laps and edges it may reduce radon, if that is a problem at that home.
If you see water on top of the plastic there’s a good chance that water is getting in from outside or there’s a plumbing leak. You should look to find out where the water is coming from.
Keep asking questions on the message boards Massoud, that’s how you learn. There are many people here who are happy to help those who want to learn.
If you post in the Canadian forum you may get help more specific for Canada, like post #16 from Gerald.