Diffusion membranes: types, characteristics, application

Recommendation points

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

The article will tell you about a modern material for vapor waterproofing – diffusion membranes. You will learn about what hydro barriers are and in what cases each of them is applied. Also in the article there is a table with an analysis of market prices for diffusion 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 a 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 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. Laying 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 there are, the higher the membrane’s ability to drain water..

Vapor permeability is the main property of the membrane

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

1. Low diffusion – spend less than 300 mg per 1 m² in 24 hours. This canvas is suitable for dry rooms and interior partitions..
2. Average diffusion – from 300 to 1000 mg / m²/ 24 h. This type of membrane is suitable in most cases – in average and temperate climates.
3. High diffusion (superdiffusion) – more than 1000 mg / m²/ 24 h. It is used with a significant thickness of insulation, in areas with a harsh climate and fluctuations in humidity.

This interesting effect is also successfully used in plant growing – for planting in greenhouses that do not like humid air. The membrane drains 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 is impossible to call it 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 onto 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.
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, it provides for gaps to communicate the air channels with each other..
6. The hydro-barrier blades must be reliably glued to each other, observing an overlap of 50–100 mm. The extreme abutments to the crate are also glued.

A properly mounted 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. The 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 m2, r	Water vapor permeability, mg / m2/ 24 h	Roll area, m2	Roll price, cu e.	Price 1 m2, at. e.
BRANE SM	Russia	75	1000	70	26.5	0.37
Ondutis SA115	Russia	115	1100	75	thirty	0,4
Rufizole SD	Russia	one hundred	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% (stop atmospheric moisture) and will spoil the whole thing by 150%. 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..