Where Does the Moisture Barrier Go in a Basement?

by Charlie
Where Does the Moisture Barrier Go in a Basement

You may already be aware of just how important moisture barriers are in a basement, but if not – they are critical. Basements are often thought of as damp, cold, moldy places, and yours will be if you don’t install a moisture barrier to keep the dampness surrounding the structure at bay. Because basements are partially or fully underground, they can get very damp.

Putting a moisture barrier in your basement is key to making it a functional space and preventing dampness from getting transferred to the rest of your home, but you might not be sure how to go about this properly. Where does the moisture barrier go? How do you fit it?

Where does the moisture barrier go in a basement? A moisture barrier is installed on the inside of the basement’s walls, before you put in insulation or finish the wall. The moisture barrier stops water from being transferred into your insulating layer, where it will cause mold and ruin your insulation. Without one, you will run into big problems quickly.

Do You Have to Put a Moisture Barrier on Your Basement Walls?

You must put a moisture barrier on the walls of your basement. The ground that surrounds your basement will often be very damp, and this dampness will leach into your basement if you do not prevent it with a barrier. It could compromise the structural integrity of the basement, and will cause other problems like mildew and coldness.

If your walls are concrete, you might be wondering whether water can really leach through them – but the answer is a quick “yes.” Concrete is not watertight and it’s very easy for moisture to leach through the concrete and into the room.

If it does this behind a wall that has been insulated, moisture will get into the insulation. Different kinds of insulation will respond differently to dampness, but it has a negative impact on most kinds. It may start to form mold, and will gradually start to destroy the insulation and the wall.

The mold might spread into other parts of your home, threatening your health and the building’s structural integrity. Breathing mold spores can lead to permanent health issues and may trigger conditions like asthma, so take this very seriously.

Damp will also ruin your decor and walls, leading to potentially expensive repair jobs in the near future. If you don’t address the source of the dampness, these issues will recur constantly, because more moisture will always be finding its way into your basement.

A moisture barrier is therefore critical, no matter what kind of insulation you plan to use, and even if the basement will only be for storage. Do not underestimate the value of this barrier in keeping your home and your family safe.

Is a Moisture Barrier the Same as a Vapor Barrier?

No, a vapor barrier is different from a moisture barrier. A vapor barrier is installed after the insulation has been put in place, and it goes on the warm side of the wall, just behind the drywall. A moisture barrier goes on the other side of the insulation, protecting it from the transfer of dampness.

Don’t confuse the two; one does not stand in for the other, and mixing them up could have serious consequences for your basement. You need a moisture barrier before the insulation can be fitted, while the vapor barrier should be added later.

Many people do use these terms interchangeably, so be aware of the differences and make sure you are installing a material that is suitable for each respective task.

Does It Matter If Your Moisture Barrier Has Gaps?

You might be wondering if you have to cover the whole surface behind your insulation with your moisture barrier. The answer is yes, you do. The fewer gaps and breaks there are in the moisture barrier, the better water will be kept out of the room. You should therefore try to run a continuous sheet, or the closest possible option, around the whole room.

What Materials are Used as Moisture Barriers in Basements?

You have a few different options, but common materials include things like foam board, builder’s foil, and polyethylene plastic sheets. These are all watertight and will prevent water from leaching from the surrounding ground into your basement. They will protect your insulation provided they are installed correctly.

Most of these materials are easy to obtain, but you should be aware that installation can be challenging if you don’t have much experience working with them. It is generally best to pay an expert to install this barrier, because if it is done badly, it won’t protect your basement.

It is also difficult to repair work that has been done badly and make it good without redoing the whole project – so on the whole, it’s better to get it right first try. Since the moisture barrier will be behind your walls, you don’t want to be ripping everything out to redo it after a few months or years.

Do Moisture Barriers Remove the Need for Groundwater Control?

You will still need to deal with groundwater control if you install a moisture barrier in your basement – even a particularly good moisture barrier. Water sitting around the basement will cause problems no matter how good the barrier is. Again, this is something that your contracting firm should be able to help with.

Building a basement is a tricky process, and often best left to the professionals. If you are good at DIY, you will be able to do parts of the finishing yourself, but the actual construction of the basement requires skilled laborers. Don’t try to dig and drain your basement by yourself; you may cause serious issues in your home.

Final Thoughts

The moisture barrier should be applied before the insulation is applied, and its job is to prevent moisture from passing between the concrete wall and your inner wall. Because basements are at least partially subterranean and it’s very damp underground, moisture barriers are a key part of preventing mold and mildew issues, and keeping your basement warm and dry.

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