Quick Answer: Do You Need Vapour Barrier With Foam Insulation?

What is the R value of 4 inches of spray foam?

Closed-cell spray foam has a far better R-value per inch than other, less effective insulations like cellulose, fiberglass, or even open-cell foam.

All these have R-values ranging from R-3.2 to R-3.8 per inch.

The R-value of closed-cell foam is R-6.5-7 per inch..

Can you spray foam the underside of your roof?

Most unvented attics incorporate Spray Polyurethane Foam (SPF) on the underside of the roof deck and attic walls. … Using spray foam facilitates the easy and efficient creation of a layer of insulation and a continuous air barrier at all interior surfaces of the attic that are adjacent to the outdoors.

Where should you not use spray foam insulation?

When NOT to Use Spray Foam InsulationFor areas that are too close to electrical boxes:For areas too close to ceiling light boxes:Open-cell spray foam on your roof:For closed-cavity spaces:If you have a history of skin, respiratory, or asthma problems:

Should I put plastic over insulation before drywall?

Without poly beneath the drywall, water vapor hits the drywall and diffuses through to the drier (in summer) indoor air. By installing a sheet of poly there, you cut off that drying mechanism and water that finds its way into walls can stay there longer and do more damage.

Do I need Vapour barrier with spray foam?

You do not have to put any vapour barrier as spray foam acts as a vapour barrier and an insulator, unlike blown in insulation where with blown in insulation you must put a vapour barrier since blown in insulation is not solid like spray foam, just make sure it is the right type of spay foam insulation.

Does insulation come with a vapor barrier?

In mixed climate areas, the vapor barrier is optional depending on the total design of a building. In cold climates, a vapor barrier is almost always needed. The facing on faced insulation acts as a vapor retarder. If you need a vapor barrier and your insulation is unfaced, you must cover it with a polyethylene film.

Should I insulate the underside of my roof?

But the best solution is actually to insulate both the attic floor and the underside of the roof. In this way you prevent the heat from the rooms below escaping to the attic rooms above. At the same time, the areas below the roof benefit from increased comfort both during the winter and the summer.

Do vapor barriers cause mold?

The Problem With Vapor Barriers 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.

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.

Do I need a vapor barrier over my insulation?

After the insulation is in place you will want to add a vapor retarder, sometimes called a vapor barrier, if you need one. Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter.

What are the pros and cons of spray foam insulation?

List of the Cons of Spray Foam InsulationSpray foam insulation does not always fill every possible cavity. … Spray foam insulation might encourage water damage for some homeowners. … Spray foam insulation can sometimes shrink. … Spray foam insulation requires a lot of experience to get it right.More items…•