Diffusion Membranes: Types, Characteristics, Application

2023 Author: Douglas Hoggarth | [email protected]. Last modified: 2023-11-26 20:16

• How the membrane works
• Vapor permeability is the main property of the membrane
• Membrane assembly
• Special membranes

Waterproofing roll material used for outdoor work must have one property - one-sided moisture conductivity. This is necessary in order to remove vapors from the insulation as a result of temperature changes and increased humidity. The only material that can do this job is the membrane.

How the membrane works

Possible variants of the name - conductive, semi-conductive, diffusion, superdiffusion and vapor barrier membrane (not a film!) Reflect the essence of the work of this layer. The membrane conducts moisture to one side - from the insulation - and concentrates it on the reverse side for subsequent drainage or weathering. Therefore, the sides of the membrane web are clearly marked - a pattern, a logo, a different color. Placing this material with the back side (by mistake) will lead to the fact that the insulation will get wet in a matter of weeks.

The web itself is a capillary pump formed by two layers of material:

1. Fleecy layer. It collects moisture and transfers it to the perforation. Moisture seeps through microscopic holes onto the back of the web.
2. Smooth perforated polyethylene layer. It collects moisture removed from the insulation.

The perforation density (the number of holes per unit area) directly affects the "throughput" of the web. The more of them, the higher the membrane's ability to remove water.

Vapor permeability is the main property of the membrane

On this basis, all membranes are divided into three categories:

1. Small diffusion - spend less than 300 mg per 1 m ² within 24 hours. Such a canvas is suitable for dry rooms and interior partitions.
2. Diffusion medium - from 300 to 1000 mg / m ². / 24 h This form of the membrane is suitable in most cases - in the middle and temperate climates.
3. High diffusion (superdiffusion) - up to 1000 mg / m ². / 24 h is used at a considerable thickness of the insulation in areas with severe climate and humidity differentials.

This interesting effect is also successfully used in plant growing - for planting in greenhouses that do not like humid air. The membrane dries out the closed atmosphere of such a "greenhouse".

Membrane assembly

A vapor barrier installed between a roofing material or a ventilated facade and a wall or roof structure is conventionally called a waterproofing or hydro-barrier. This term is conditional, since it reflects not the properties of the material, but its purpose. In this case, the membrane really does not allow moisture to pass through, but it cannot be called a full-fledged waterproofing.

As mentioned above, the manufacturer does everything to ensure that no errors occur during installation, and the membrane was installed correctly. But these are not all the requirements for it. Laying the diffusion membrane sheet requires compliance with the following rules:

1. The canvas is rolled out on the laid insulation with the fleecy side to it and at the same time fits snugly.
2. The canvas is pressed against the rafters or uprights with a pressure bar or counter lattice.
3. Between the hydro-barrier and the finishing material of the roof or wall, there must be 15–50 mm air flow.
4. The channel formed by the pressure bars must be free from the soffit to the ridge (on the roof) or the starting rail or soffit (along the wall).
5. If a counter lattice is used, gaps are provided in it for communication of air channels with each other.
6. The hydro-barrier canvases must be reliably glued together, observing an overlap of 50–100 mm. The extreme abutments to the crate are also glued.

A properly assembled membrane will last a very long time - from 50 years. The absence of this layer in the roofing cake will lead to a malfunction of the insulation.

Special membranes

This category includes high-tech materials that combine the properties of a vapor barrier and insulation.

Metallized membrane. Developed by Tyvek and DuPont. Aluminum, sprayed on each fiber separately, provides partial heat reflection while maintaining diffusion properties.

Foil membrane. Especially relevant for hot areas. Foil reflects infrared heat back into the atmosphere. As a result, the roof is heated several times less. In winter, such a barrier maintains the temperature in the ventilation duct to evaporate condensate.

Diffusion membrane prices

Name Manufacturer Weight 1 m ², g Permeability mg / m ² /24 hours Roll area, m ² Roll price, cu e. Price for 1 m ², cu e. BRANE SM Russia 75 1000 70 26.5 0.37 Ondutis SA115 Russia 115 1100 75 thirty 0,4 Rufizole SD Russia 100 1250 70 35.5 0.5 Stroizol SD 130 Russia 130 1500 70 38.5 0.53 CHESCO SD Russia 115 1200 60 37 0.61 Fakro Eurotop N35 USA 135 1900 75 58.5 0.78 DELTA VENT N Germany 120 1750 75 70 0.93 Tyvek Solid Silver (metallized) Liechtenstein 82 1300 75 110 1.47 Izovek T (foil) Russia 150 1000 60 58.5 0.97

The first thought that comes to mind when trying to save on hydro-barrier is to replace the diffusion membrane with ordinary polyethylene. This option will perform the function by 50% (stopping atmospheric moisture) and by 150% will spoil the whole thing. Steam not released from the insulation will accumulate in it and soak the cotton wool. And cotton wool, as you know, cannot be restored. Therefore, use diffusion membranes to keep the roof and walls always dry and warm.