Should a roof have a vapor barrier?

Unless you have a building with high humidity, the roof will perform just fine without a vapor barrier." The second representative said, "A Vapor Barrier or Retarder is NOT required for our "PVC" or other manufacturer warranties.

Does a roof need a vapor barrier?

If the interior use of the building requires conditioned air and has relative-humidity percentages great enough to condense if the exterior temperatures get cold enough, a vapor retarder is needed to prevent the movement of this conditioned air into the roof system where it can condense and become problematic.

Where does vapor barrier go on roof?

For conventional buildings, a vapor retarder is typically installed under the roof insulation, i.e., on the warm (interior) side of a roof assembly. For a vapor retarder to be effective, the temperature at the bottom side of a vapor retarder must be warmer than the dew-point temperature.

Do I need a vapor barrier in my attic?

In hot-dry climates a vapor retarder should also not be installed, but attics can be vented. All attics — vented or unvented — should have an air barrier (a properly detailed airtight drywall ceiling, for example) regardless of climate.

Do you need a vapour barrier on a cold roof?

Wrong! sadly, it's often the way – out of sight, out of mind, but the humble VCL is actually a very important part of the roof build-up. Be it a cold or warm roof construction, the primary function of a VCL is to keep warm moist air from inside the building – inside the building.

Vapour barriers for roofs and walls explained

Does a warm flat roof need a vapour barrier?

To use EPDM for a warm deck flat roof construction, solid (closed cell) roof insulation such as Kingspan or Celotex should be placed on top of the roof deck, rather than in between the rafters. A vapour barrier will then need to be installed to reduce condensation in the roof structure.

Should I insulate my roof rafters?

Insulating between rafters will do no good, because the attic should be ventilated, and the rafter insulation would be between two unheated spaces. You can add insulation to the floor; the more the merrier. Just don't put it in the eaves. Also, make sure the attic is well ventilated.

Should you put plastic over insulation?

Without a vapor barrier in place, condensation inside the walls could ruin the insulation and promote the growth of harmful mold and bacteria. Plastic, specifically 6-mil polyethylene plastic, is the most commonly used vapor barrier.

What is a roof 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.

Do vapor barriers cause mold?

The Problem With Vapor Barriers

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?

Reinforced polyethylene plastic sheeting (poly) comes in a variety of thicknesses and strengths. A 6 mil thick poly is commonly used as a vapor barrier and offers short-term savings to the homeowner.

Is Tyvek a vapor barrier?

Is DuPont^™ Tyvek^® a vapor barrier? No, DuPont^™ Tyvek^® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.

What is the difference between a vapor barrier and a moisture barrier?

Moisture barriers function to help in preventing water from entering inside of the wall cavity. On the other hand, vapor barriers basically prevent water vapor from the interior of the house to filter through the wall and condense on the warm side of the insulation.

Does insulation need a vapor barrier?

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 thickness of plastic do you need for a vapor barrier?

Vapor barriers should be at least 6 mil in thickness to effectively cover the area and create a moisture barrier. Triangle Crawl Space Solutions uses both a 6 mil material for simple vapor barrier installation and a thicker more durable 12 mil vapor barrier material depending on the budget and needs of the home.

When would you use a vapor barrier?

A vapour barrier is an important component in building construction. Its purpose is to help prevent water vapour from reaching building walls, ceilings, attics, crawlspaces or roofs, where it can condense and cause building materials to rot or grow mould.

Can you use 4 mil plastic for vapor barrier?

OVERVIEW. Our 4-mil plastic sheeting is a multipurpose film perfect for a wide variety of construction or DIY projects. This medium-duty plastic sheeting is commonly used as a vapor barrier in between insulation and drywall, used as a drop cloth or a temporary cover for equipment and supplies.

Can I insulate the underside of my roof?

Open-cell spray polyurethane foam or closed-cell spray polyurethane foam (ccSPF) insulation can be sprayed along the underside of the roof sheathing to provide a conditioned and insulated attic space that can be durable and efficient in all climate zones (see Figure 1).

Is it better to insulate ceiling or roof?

If you are deciding between insulating the roof deck or the ceiling, Insulating your ceiling should be the priority. Not only is it easier but ceiling insulation is beneficial in a number of ways: Keeps the temperature in the building regulated. Saves on energy costs.

How do I insulate my roof rafters?

Warm loft. An alternative way to insulate your loft is to fit the insulation between and over the rafters – these are the sloping timbers that make up the roof itself. You can use rigid insulation boards, carefully cut to size, or you can have foam insulation sprayed between the rafters.

How do I stop my flat roof from sweating?

Installing a good vapour barrier underneath the rafters in a roof will prevent warm air from entering the roof void from below. Multifoil insulation has shiny, reflective layers to keep heat inside the building, ensuring no risk of condensation.

How thick should insulation be on a cold flat roof?

An uninsulated flat roof has a U-Value of around 1.5 W/m2K. When insulating one, you're aiming for a value of 0.25 W/m2K or less. To achieve this, you should insulate your flat roof with insulation boards totalling around 150mm thickness.

Does cold roof need ventilation?

Cold Roofs

A cold roof is where all of the insulation is placed either between and under or completely under the joists or deck. No insulation is on top. In this way the roof itself is kept cold. You only need ventilation in a cold roof.