How To Protect A House From Wind And Moisture: Construction Films And Membranes

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How To Protect A House From Wind And Moisture: Construction Films And Membranes
How To Protect A House From Wind And Moisture: Construction Films And Membranes

Video: How To Protect A House From Wind And Moisture: Construction Films And Membranes

Video: How To Protect A House From Wind And Moisture: Construction Films And Membranes
Video: Principle of Avoiding Condensation Explainer 2024, March
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  • How membranes work

    • What is the insulation afraid of?
    • Special properties of films and membranes
  • Types of building membranes
  • Frequently asked questions about the installation of building membranes

    • On which side of the insulation should the membrane be attached?
    • Which side to lay the membrane on?
    • Is there a ventilation gap near the membrane?
    • What should be the overlap of the canvases?
    • Do I need to glue the joints? If so, how?
    • How to fix the membrane?
    • How long can the membrane be left open?
  • Instead of an epilogue
How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

Every year, modern dwelling is becoming more complex and technologically advanced. It is not surprising, because recently the requirements for insulating materials, characteristics of almost all elements of buildings and structures have increased significantly. The issues of thermal insulation of residential buildings, in particular, in many countries have become the subject of government regulation. As a result, multi-layer structures with the use of fiber insulation have become widespread. These are frame external walls, ventilated facades, insulated pitched roofs and ceilings.

However, an insulator based on mineral wool itself needs reliable protection. The fact is that wind pressure, atmospheric moisture, vapors from the premises significantly reduce the thermal characteristics of mineral wool and the building as a whole. The use of construction films and membranes allows to preserve the design efficiency of multilayer structures, to avoid the formation of condensation on the building elements. At one time, membranes became a real breakthrough in building heat engineering, now it is impossible to imagine a residential building built without the use of this material. The membranes have proven themselves in practice, and they continue to be improved.

How membranes work

What is the insulation afraid of?

It is believed that rock wool does not absorb water, but it contains many pores and air channels, so that moisture can move inside the material and stay inside it. The mass of stone wool insulation can increase up to 5% of its own weight. Moisture displaces air from the fibers - the thermal insulation characteristics fall (by 20-30% even with one percent humidification, many technologists say), cold bridges are formed. With significant temperature fluctuations, the water repeatedly freezes and melts, expanding, destroying the internal structure of the insulation. If the enclosing and drainage structures are working properly, water can diffuse into the cotton wool from the premises, as a product of human activity, or outside - with humid air.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

In insulated facades and roofs, and then into rooms, air can penetrate from the outside under the influence of wind and temperature pressure. The wind not only pushes against the walls, but also creates swirls. Somewhere cold and humid air is forced into the structure, somewhere it is sucked out of the insulation, taking heat with it. This is how unplanned infiltration of structures occurs with a deterioration in their thermal resistance.

Ventilated roof and facade structures have air gaps that act as convection channels. The air, passing through the ventilation gaps, even at a low speed of movement, "draws" heat from the unprotected cotton wool, which immediately reduces the thermal insulation of the building as a whole to 30–40% of the design values. Moreover, convective air currents are capable of "weathering" binders, as well as fibers of most types of cotton wool, also destroying the structure of the insulation.

Special properties of films and membranes

The main task of building membranes is to protect building structures from wind and atmospheric moisture. But at the same time, the films used on the outer walls and roofs must pass water vapor through themselves from the premises to the outside. From the point of view of physics, any membrane is a semi-permeable film, a shell that separates two media, regulating the unidirectional transport of substances from one zone to another.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

The main feature of most building membranes is the presence in their structure of diffusion layers with microperforation and micropores, which are able to conduct water vapor in one direction. Most often, vapor permeable membranes have one thin functional layer and one or more protective layers that provide physical and chemical stability.

Some membranes (often called construction films) do not allow steam or water to pass at all. They consist of several non-perforated polyethylene layers, usually on a mesh backing. This is the so-called "vapor barrier".

When choosing construction films and membranes, special attention should be paid to two main consumer properties:

  • vapor permeability
  • moisture resistance

Construction membranes are made from synthetic fibers (polypropylene, polyethylene) in the form of textile woven or non-woven fabrics. Depending on the tasks, construction membranes can have a single or multi-layer structure, including with a reinforcing mesh made of polyethylene fibers or an additional aluminum coating. With a small thickness, the membranes have very high strength and low elongation. They are resistant to ultraviolet light for a certain time, they are not affected by fungi and microorganisms.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

Some manufacturers offer membranes that not only regulate humidity conditions, but also have their own resistance to heat transfer, which makes it possible to compensate for heat losses in the area of air spaces. These are multilayer needle-stitched materials with a thickness of 10-15 mm, made on the basis of polypropylene.

The fire resistance of construction films is also a rather urgent issue, which is solved in two ways. There are membranes, the polymeric materials of which contain fire retardants in bulk, the second option is the impregnation of finished cloths or the application of protective compounds to their surface.

Another important nuance is the service life of the membrane. Obviously, the membrane should work as long as the enclosing structure as a whole. You should not use materials whose manufacturers are silent about the service life, or limit it to 10-15 years.

The performance of the membranes is significantly reduced due to the aging of the material at high temperatures. Common declared indicators "up to + 80 °" are not always enough, especially in an insulated metal roof, where temperatures can reach much higher values.

So, a building membrane is a film that lets in or out vapors, but always stops water and wind. This is the basis of film technology.

Types of building membranes

Depending on their purpose and, accordingly, some structural features, building membranes are divided into:

  • vapor barrier
  • vapor permeable

A vapor barrier is installed from the inside of the insulation, it should isolate the cotton wool from moisture vapor that occurs in the premises of the building. An example of an application is a heat-insulated roof or an overlap of the “attic” floor, where the cotton wool from below must be covered with a film. Also, a vapor barrier is necessarily used when insulating walls from the inside. The vapor barrier membrane has no pores and perforations, the lower its vapor permeability, the better. These materials are either reinforced or unreinforced polyethylene film, sometimes with a layer of aluminum foil. Note that the use of vapor barrier significantly increases the level of humidity in the building, so special attention will have to be paid to ventilation of the premises.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

Films with an anti-condensation coating can be considered a separate type of vapor barrier membranes. They are used under roofing materials that are afraid of corrosion - corrugated board, galvanized iron, some types of metal tiles without an inner coating. Such a membrane does not allow vapors to pass to vulnerable metal elements. The anti-condensation film is laid with a rough textile (adsorbent) layer downward, where moisture accumulates and is gradually removed without flowing back into the insulation and without contacting the metal. There must be a gap of 20–60 mm between this membrane and the cotton wool.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

Vapor permeable (vapor release) membranes are used on the outside of the insulation. They serve as protection against wind pressure on the enclosing structures and are an auxiliary waterproofing layer in pitched roofs, as well as facades with leaking cladding elements. Due to the fact that such films are a buffer between the insulation and the environment, it is necessary that they freely pass moisture from the cotton wool into the ventilated space. A certain vapor permeability of these materials is ensured by the presence of microperforations and micropores. Naturally, the more active the diffusion of steam outward, the better, the drier and more efficient the insulation will be. In accordance with the degree of vapor permeability, membranes are divided into:

  • psevdodiffuzionnye (up to 300 g / m 2 per day)
  • diffusion (300-1000 g / m 2)
  • superdiffusion (1000 g / m 2)

Pseudo-diffusion membranes have good waterproofing characteristics, therefore they are often used as external under-roofing, and with the organization of a mandatory ventilation gap under them. The use of such films as external vapor barrier for the facade is a mistake due to the minimum permissible throughput. The fact is that in dry weather, the micropores can become clogged with dust from the ventilation gap. As a result, moisture is not completely removed from the insulation, and condensation is possible.

Diffusion and superdiffusion membranes are free from this disadvantage. Here the vapor permeability characteristics are presented, as they say, "with a margin". In addition, vapors are discharged through larger perforated micro-holes that are not subject to clogging. These materials do not require an additional ventilation gap at the bottom, so there is no need to mount all kinds of counter battens and additional battens.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

A special type of vapor release material is volumetric diffusion membranes. Due to its volumetric structure (the height of three-dimensional mats made of polypropylene filaments is 8 mm), this membrane is a specific separating layer that itself forms a ventilation gap and facilitates the removal of condensate from the metal roof. In fact, it performs the same function as a vapor barrier film with an anti-condensation coating, only it releases moisture from the insulation. The fact is that on sheets of metal roofing with a small angle of inclination (3-15 °), the condensate that has fallen from below does not flow down and does not drip down, but is in direct contact with the zinc coating, destroying it. The volumetric membrane is fastened with nails to a solid base.

The main manufacturers of diffusion membranes for roofs and facades produce products that are relatively similar in their technical and operational characteristics. The differences concern only functionality, cost and quality of their films. This is due to the peculiarities of technological processes, the type of raw materials and additives, the type of insulating films, the number of layers and methods of their bonding.

Frequently asked questions about the installation of building membranes

On which side of the insulation should the membrane be attached?

On the insulated facade, mineral wool is covered with steam films only from the outside.

In insulated roof structures, diffusion, anti-condensation or volumetric membranes are mounted on top of mineral wool, similar to installation in ventilated facades.

Roof elements without insulation are protected with vapor barrier membranes from the bottom of the rafters.

If the walls are insulated from the inside, a continuous vapor barrier is needed - a non-perforated film is installed over the cotton wool from the side of the room.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

Insulation of the upper floor with the cold attic located above is closed with a vapor barrier from below.

Which side to lay the membrane on?

Vapor barrier films are usually two-sided (no matter which side the material is facing), but there are exceptions. Anti-condensation membranes are fixed inside the room with a textile absorbent layer. Metallized films are also one-sided - the foil should be facing the rooms.

The installation of vapor (diffusion) membranes on one side or another must be carried out according to the manufacturer's instructions. The same company can produce both double-sided and unidirectional films. The reference point is usually the different coloration of different sides of the membrane, one of which most often has a pronounced marking. In most cases, the “colorful” side of the membrane should be facing outward.

Is there a ventilation gap near the membrane?

An air gap (about 50 mm) must be provided at the bottom of the vapor barrier films to ventilate possible condensation. The inner lining is not allowed to touch the vapor barrier.

Diffusion membranes are mounted directly on top of insulation or a continuous coating of OSB, moisture-resistant plywood. But on top of such membranes, it is simply necessary to make a ventilation gap to remove moisture. The ventilation gap in the roof is made with the help of counter-lattice bars; in the structure of the ventilated facade, the required interlayer is provided by pillars or perpendicularly located horizontal profiles.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

The anti-condensation foil on both sides should have an air gap of about 40-60 mm.

What should be the overlap of the canvases?

Construction films and membranes are often marked with a line along the edge of the web, which indicates the size of the overlap - from 100 to 200 mm. For the roof, the membrane performs a waterproofing function, therefore this size can vary depending on the slope of the slopes (from 30 ° - 100 mm; 20-30 ° - 150 mm; up to 20 ° - 200 mm).

The diffusion membrane in the ridge area overlaps by 200 mm. In the valleys, the material is overlapped by 300 mm, plus, with small slopes, the second layer is laid along the entire length in the form of an additional strip extending 300-500 mm on both slopes.

Note that the membranes should cover not only the total area, but also the ends of the insulation. Roofing membranes are led out onto a drain gutter or a metal drip.

Do I need to glue the joints? If so, how?

The fabrics of building membranes must be glued together. The joint must be sealed. For these purposes, special self-adhesive tapes are used, which are made on the basis of various non-woven materials: polyethylene, polypropylene, expanded polyethylene, butyl, butyl rubber. They can be bilateral or one-sided. These tapes are used to repair tears and damage to the canvases.

The choice of a specific type of connecting tape should be made in accordance with the manufacturer's recommendations.

The use of packing tape (especially narrow widths) for joining construction films and membranes is a common cause of joint failure.

How to fix the membrane?

Wide-headed nails and construction staples can be used as temporary fasteners. However, a truly reliable fixation can only be ensured with the help of counter rails.

How to protect a house from wind and moisture: construction films and membranes
How to protect a house from wind and moisture: construction films and membranes

The situation is somewhat more complicated when equipping hinged facades. After installing the brackets, mineral wool slabs are laid, each of which is fastened with one or two disc dowels. Next, a diffusion membrane is rolled out over the insulation, cut through at the points of passage of the brackets and through a layer of cotton wool is fixed to the wall with the same dowels. The number of fasteners must be at least four per square meter. If there is a choice, you need to drill at the junction of the canvases.

On roof slopes, the membranes are glued to structures along the entire perimeter using double-sided tapes. With the same materials, regulating construction films are fixed to various elements of the building: windows, doors, pipes, ventilation ducts, antenna racks … On rough surfaces, tapes do not help - here they use polyurethane, acrylic, rubber adhesives, "fixers".

How long can the membrane be left open?

The UV resistance of building membranes is limited. Usually it is up to 4–5 months, then the material loses its thermal stability, aging of the material occurs with the loss of most of its useful characteristics. Obviously, it is necessary to minimize the illumination of the membranes, to install the cladding as soon as possible. No matter how hard we try to seal all joints and holes, these roll materials work only in tandem with the finishing outer layers, so heavy rain can cause the heat insulator and structural elements to get wet. That is why it is better to install insulation, films and membranes in stages, and not immediately for the whole house.

Instead of an epilogue

The use of building films and membranes is a prerequisite for the correct functioning of multilayer structures. Only with their help it is possible to ensure the proper temperature and humidity conditions inside the building. In working with membranes, there is usually no particular difficulty, you just need to choose the right material for a particular case and mount it correctly.

Practice has shown that it really makes sense to protect the insulation, especially if you consider that the cost of films and membranes during the construction of a cottage does not exceed 0.5% of the total estimate. But there is a lot at stake - the microclimate of the premises, the durability of the building elements, the level of energy costs.

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