Asked by: Khadime Ases
home and garden indoor environmental quality

Is a vapor barrier necessary in a garage?

Last Updated: 21st March, 2020

31
No, you don't need a vapor barrier. The wall needs to dry to the inside. The poly would prevent that.

Click to see full answer.

Also question is, do I need vapor barrier in unheated garage?

If it is an attached garage and we are talking about the wall between the garage and the living space then no, you do not need a vapor barrier. The house side of the wall will be warmer than the garage and any vapor will stay in the garage.

Likewise, does a ceiling need a vapor barrier? All attics — vented or unvented — should have an air barrier (a properly detailed airtight drywall ceiling, for example) regardless of climate. Omitting a ceiling vapor barrier by arguing that "you have to let the moisture escape" or "because the house has to breathe out the top" is actually correct, in a way.

In this manner, are vapor barriers necessary?

In many colder North American climates, vapour barriers are a required part of building construction. You may find that vapour barriers are often not required in warmer climates. And, if installed in the wrong climate or on the wrong side of building materials, a vapour barrier can cause more harm than good.

Does open cell foam need a vapor barrier?

Open cell spray foam is not a moisture vapor barrier, and will allow moisture to pass. So, if you're considering spraying foam to the roof deck of your new or existing home, you want open cell. If there's a roof leak, water will pass through the foam, and you will quickly be able to find your problem.

Related Question Answers

Marlucia Solondoeta

Professional

Should I insulate an unheated garage?

Yes, insulation is always worth doing no matter if you heat the garage or not. My detatched garage is well insulated. In the summer, it stays 20 or more degrees below outside temperature just by keeping the doors closed. In the winter, the garage stays 30-40 degrees above outside temperature with no heat added.

Charisse Arigita

Professional

Does it make sense to insulate an unheated garage?

Unless your garage is heated, insulation will have little affect on the temperature inside your garage in cold climates. Insulating the garage won't make it warmer. The main purpose of insulation is to slow the conduction of heat from the walls and ceiling to the outside, and vice-verse.

Collado Piloto

Professional

Is it a good idea to insulate a garage?

If it isn't, you don't want to insulate; doing so can cause mildew. But if the garage is heated you should definitely insulate. Attached garages are one of the biggest sources of heat loss in a home, because of air leakage. Garage doors are big; a lot of air can get by them.

Godwin Wroblewski

Explainer

Should I put insulation over my garage?

If your home's HVAC system does extend into the garage, then the attic above it should be insulated as it would for any other room of the house. Homeowners also should insulate a garage completely, including in the attic above it, if they plan on turning the garage into another air-conditioned room.

Klara Oberlein

Explainer

Is it necessary to insulate a garage?

You do not need to insulate the entire garage, you could actually do fine insulating just the internal wall of the garage. By installing insulation in the walls between the actual living space and the garage, you will experience more comfort within your home.

Isauro Balaguer

Explainer

What type of insulation should I use in my garage?

The most common materials include expanded polystyrene (similar to Styrofoam), extruded polystyrene, and polyisocyanurate. Rigid foam offers a high R-value per inch of thickness and can be cut to fit almost any space. It's a good choice for thin walls and for insulating garage doors.

Helvia Sarralde

Pundit

What is the best drywall to use in a garage?

Drywall is the easiest and most economical covering for your garage ceiling. Use 5/8-in. -thick drywall if your trusses or rafters are spaced 24 in.

Xiaofang Ralfs

Pundit

What type of insulation is best for garage walls?

The best insulation options for your garage will depend on whether the space has existing drywall or if the walls and ceiling are exposed. The most common insulations used in garages include fiberglass, cellulose, spray foam, and injection foam.

Katiba Frezza

Pundit

What happens if you don't use vapor barrier?

If water vapor diffuses or infiltrates into the wall cavity and finds the cool surface, moisture problems can occur. Of course, you can have moisure problems here even without the exterior vapor barrier because of what Bill Rose calls the rule of material wetting.

Hilal Baganha

Pundit

Can I use plastic sheeting as a vapor barrier?

In simple terms, a vapor barrier is a material that won't allow moisture to pass through it, such as plastic sheeting. It's designed to stop the moisture before it can enter the wall cavities. There are two basic types of vapor barriers used with exterior wall insulation. The most common is paper-faced insulation.

Urs Quiceno

Pundit

Do vapor barriers cause mold?

The original reason for using vapor barriers was a good one: to prevent wall and ceiling assemblies from getting wet. This can lead to significant moisture problems and mold; problems occur when walls get wet during construction or more often throughout the home's life.

Yareli Llanso

Teacher

Should I put plastic over my insulation?

Back years ago, it was always said to NOT put a plastic vapor barrier over the insulation before hanging drywall or whatever material you decide to hang, as it would cause the room or building to act like a greenhouse.

Maurine Lichtenthaler

Teacher

What is the purpose of vapor barrier?

A vapor barrier (or vapour barrier) is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through the wall, floor, ceiling, or roof assemblies of buildings to prevent interstitial condensation and of packaging.

Lettie Trattles

Teacher

Where do you put vapor barrier?

Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions: the inner surface in colder climates and the outer surface in hot, humid climates. In existing spaces, oil-based paints or vapor-barrier latex paints offer an effective moisture barrier.

Yousif Duatis

Teacher

Where should vapor barrier be installed?

Direction. The placement of the vapor barrier depends largely on the climate where your house is. In warm climates, the barrier should point to the outside of the house, blocking the vapor from the humid outside air that may seep into the walls or ceilings.

Dariusz Niederlehner

Reviewer

Do interior walls need vapor barrier?

A vapor barrier is an essential part of a building, but it's often installed incorrectly or omitted entirely. Installing a vapor barrier on the (warm) interior wall of your cement brick house will prevent condensation and reduce air leakage through your walls and insulation.

Olav Thalhofer

Reviewer

Should you put plastic behind drywall?

The standard installation of a plastic vapor barrier is between the studs and the drywall, but there are some exceptions to this. In exterior walls that are below-grade, like basement walls, plastic should not be used at all.

Eulises Recchi

Reviewer

Should I put drywall in my garage?

You do not need 5/8" drywall for the garage walls. In the US, you need it between the garage and living space, but not on the exterior walls. I also recommend thinking about adding some outlets before you close the walls up - so much easier than doing it later.

Ignat Adelia

Supporter

Does cellulose need a vapor barrier?

With Modern's Cellulose insulation, a vapor barrier is not recommended except in very cold weather or high moisture areas such as spas or pool buildings. However, many building codes do require an Air barrier or Vapor retarder to be installed. Cellulose insulation has a high density compared to fiberglass.