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. It's the first line of defence against high vapour pressure air entering the roof structure and causing interstitial condensation..
Moreover, 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.
Also Know, what is a warm roof construction? A warm roof is a type of roof construction which has an insulation layer above the rafters, and immediately below its weatherproof membrane. A warm roof construction allows heat to be conserved within a property – without the need for a ventilation system.
Also asked, does Celotex need a Vapour barrier?
I use Celotex or Kingspan insulation boards which are foil faced, and then I cover them with separate plasterboard. The cheapest insulated plasterboard which uses expanded polystyrene does NOT have a vapour barrier, so don't use it!
What is the purpose of a Vapour 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.
Related Question Answers
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 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.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. Where should vapor barrier be installed?
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.Is it OK to put plastic over insulation?
The special paper lining one side of the insulation is sufficient to block moisture and air. Some builders choose to attach a separate vapor barrier even with faced insulation, however. It doesn't hurt anything. The result, when finished, is a super-insulated wall with a foam vapor barrier instead of sheet plastic.Is 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.Do you put Vapour barrier on interior walls?
Normally interior walls do not require a vapor barrier, but there are some situations where it is highly recommended. The paint acts as a vapor barrier as well. A continuous plastic vapor barrier behind the drywall will protect the interior walls of these areas from water damage.What is the difference between a Vapour barrier and a breather membrane?
Vapour control layers are positioned to the inside of the insulation in order to minimise the amount of warm moist air entering the construction. Breather membranes are positioned to the outside of the insulation acting as a weather barrier while still allowing moisture particles to escape from the inside.Can you walk on Celotex?
you will be able to walk on the single layer over the celotex I just meant the celotex wouldn't take your weight whilst the installation was going on.Can I use DPM as a Vapour barrier?
Can you use a DPM as Vapour barrier? You can use a DPM sheet as a VCL and it will do the same job as long as it is sealed correctly and placed in the correct position – on the warm side of the insulation.Is Celotex better than rockwool?
Quilt is not "poorer" than Celotex, it is just less efficient heat insulator at the same thickness. Rockwool is fire resistant too, whereas Celotex it's not. Rockwool has better sound resistance at a given thickness too.Does Rockwool need vapor barrier?
Note that rock-wool insulation only comes un-faced, meaning there's no kraft-paper or foil barrier. Depending on the situation, you may need to install an independent permeable membrane to serve as a vapor barrier.Can Celotex be used for loft insulation?
Some people may prefer to use rigid insulation board to insulate the loft space – for example Celotex or Kingspan – the process is pretty similar to above, although you will need less depth to achieve the same insulation levels (than mineral wool). You will also need a hacksaw to cut the insulation to size.Is foil backed plasterboard a Vapour barrier?
Foil backed plasterboard have the same properties as standard wallboards but come with a metallised polyester foil which creates an effective vapour barrier to limit moisture diffusion.Is Celotex bad for your health?
Celotex products are NOT classified as dangerous for supply. Health and Safety at Work, etc.Do I need a Vapour barrier in my garage?
No, you don't need a vapor barrier. The wall needs to dry to the inside. The poly would prevent that.Does a warm roof need venting?
The enclosed void of a warm pitched roof does not require to be ventilated. Rather than actively ventilating to the outside, entrapped water vapour diffuses through the vapour permeable underlay; negating the need for forming cavities or voids below the underlay.What is the difference between a warm roof and a cold roof?
You create a warm roof, or a cold roof, simply by applying the layers of the roof in a different order. In a cold roof, the insulation is applied between the rafters, but in a warm roof, the insulation is applied on top of the existing roof surface.How do you build a warm pitched roof?
In a warm pitched roof construction the thermal Insulation is placed in the rafter line. The position of the Insulation can be wholly above or partially between and above the rafter; alternatively it can be positioned between the rafters or partially between and below the rafter. 
