- Performance characteristics of window systems
- Heat transfer resistance of the window
- Soundproofing properties of windows
- Frame mechanical strength
- Light transmittance of window blocks
- Tightness of windows
- What determines window prices
To understand the criteria for choosing windows, we propose to understand in detail the principles of the window system. Let’s also talk a little about the cost of window blocks. This is the first article in a series of publications about glazing..
A window is a fencing element of a building, which is intended for natural illumination of the interior space, as well as for ventilation of premises. Over several hundred years of evolution, translucent structures have changed beyond recognition, going from a hole in the wall with a stretched bull bubble to the most complex multifunctional product with an impressive price tag. Against the background of widespread tightening of building codes regarding the thermal insulation of buildings, window systems have made a rapid qualitative leap in recent decades. For this reason, almost every renovation now starts with replacing windows. Fortunately, our services are currently provided with the best materials and the most advanced technologies..
Depending on what materials are used for the manufacture of the window frame, there are several types of window profile systems..
1. PVC systems are currently the best sellers. Low cost and practicality do their job. Do not forget about the rather good thermal and sound insulation characteristics of the plastic profile. Within this class there is a classification by the number of isolated chambers (three-chamber, five-chamber …) and by the thickness of the inner and outer walls (classes A, B, C).
2. Wooden windows (Euro windows) account for a little less than 20% of the market. They have two drawbacks – high cost and mandatory maintenance of the paintwork. They are made from hardwood and coniferous species, the profile is obtained from laminated veneer lumber. The filling of the skylight is carried out with single glasses and double-glazed windows. The tightness of the rebate zone is ensured by elastic seals located in two or three circuits. Within the class, windows are divided into those that have single, double split, double paired sashes. The opening of wooden windows can be either swing or swing-out.
3. Aluminum structures are mainly used for glazing large areas (balconies, winter gardens). The main disadvantages are high thermal conductivity and cost. The profile is hollow, inside there can be a polyamide insert (thermal break, thermal bridge), which divides it into several chambers and increases the resistance to heat transfer. Depending on the presence of polymer in the profile, the systems are divided into warm (about 0.55 m2* ° С / W) and cold. Cold frames are used for glazing unheated rooms, balconies, loggias. The opening of aluminum windows can be absolutely anything. Cold sliding designs are gaining great popularity, which are distinguished by their ergonomics, low weight and an affordable price..
4. Combined windows use the advantages of different materials. They are subdivided into: wood-aluminum, wood-plastic, aluminum-wood, plastic-aluminum. In fact, these profiles are made of a specific material (the first in the name), which has internal or external lining of a different material. “Wood-aluminum / plastic” – metal or polymer linings protect the wood from the weather. “Aluminum-wood” – a lining made of wood decorates the aluminum frame, improves its thermal insulation properties. “Plastic-aluminum” – for decoration the PVC structure is finished with metal plates.
By the number and location of the sashes, the windows are divided into systems:
- with single (as in traditional PVC products);
- with paired (there are two of them, they are combined and close / open at the same time, controlled by one fittings);
- with separate sashes (there are two of them, they work independently, as in Soviet windows).
By the nature of the movement of movable canvases, windows are classified into:
- hinged (the sash moves around the vertical axis, opening is carried out outward or inward);
- folding (the upper part of the window opens);
- suspended (the lower part of the window opens);
- swing-out (a combination of swing and folding method);
- sliding, parallel-sliding … (the sash moves along the frame);
- deaf (no moving elements).
Modern window systems with the same components are used quite widely, but the design of specific products (depending on the purpose) has a number of features. Therefore, let’s outline the main areas of their application:
- production of room windows;
- manufacturing of doors (for example, for balconies);
- glazing of balconies and loggias;
- manufacture of roof windows;
- creation of interior partitions (usually office).
The type of profile system, double-glazed windows, fittings and accessories, the configuration of the window, the type of opening of the sash – everything is subject to certain laws, everything matters. The choice is very difficult: either you need to figure it out, or you have to trust the sellers. What is the difference between 21st century windows? What are we paying for? What are the criteria for choosing a product that will fully solve the assigned tasks? To answer these questions, first of all it is necessary to understand what processes occur in the area of window openings, and to understand the principles of the window unit operation..
Performance characteristics of window systems
First of all, it should be understood that any window is a technical compromise, even with supertechnologies existing today. Will explain. We want to: let daylight into the rooms, have a panoramic view from the window, be able to quickly ventilate the premises. But window openings (as well as doorways) are in many ways the most vulnerable part of a building. In fact, the window, being a building envelope, does not so much protect the house as it needs to be protected in order to do less harm. Actually, the efficiency, durability of the window and, of course, its price depend on how much the manufacturer has succeeded in combating the inherent shortcomings of translucent structures. There are many problems, let’s look at the main ones in order..
Heat transfer resistance of the window
The main unpleasant phenomenon is heat loss. If we compare the available reference data, it can be seen that the materials themselves, from which the windows are made, are not always inferior to the materials of the outer walls in terms of the degree of heat transfer. But in this case, we have a completely different thickness of the enclosing structure (glass is much thinner than brick). Closed air gaps become a way out – this approach is implemented in multi-chamber profiles and glued glass units with several glasses, which can have a reflective energy-saving coating. In addition to this, in order not to let cold air into the room, the porches of the window frame are equipped with several contours of elastic seals.
The second moment, aggravating the heating situation, is the small distance between the street and the interior space, since modern profiles cover only a small part of the outer wall. We are talking about the slopes of the opening subject to freezing and condensation, including under the windowsill. There is a real tug-of-war (internal heat / outside cold) near the frame, our task is to bring the dew point further out of the room. You have to carefully insulate the opening and protect the heat insulator from moisture. For this, the window is considered as a system of several functional elements, very strict requirements are imposed on the design and technology of its installation:
- mounting gaps and slope cavities are filled with polyurethane foam, only polymer wedges and linings are used;
- cladding of slopes is made with materials with good insulation (for example, sandwich panels);
- if possible “warm” window sills are installed;
- from the inside, the abutments of all elements are sealed;
- outside are used ebb, sealing tapes, cover strips.
The latest revisions of regulatory documents indicate the minimum allowable heat transfer resistance. For the north and center of Russia, the window block is supposed to issue stability from 0.5 to 0.75 m2* ° С / W. Energy saving programs are also being adopted for buildings under construction, here the bar is at the 0.8 m mark2* ° С / W. These figures indicate that for glazing in our latitudes, it is necessary to switch to a triple glass bag with gas filling and applying a reflective coating. If we use a PVC profile, then at least five-chamber (width from 70 mm), if aluminum – then only with a thermal insert (inside the profile there is a polymer insulating gasket). In any case, it is necessary to have at least two sealing circuits..
Keep in mind, over 80% of insulation problems are the result of poor installation..
Soundproofing properties of windows
The window is a source of street noise penetration. Sound is easily transmitted through thin homogeneous obstacles, glass (which occupies most of the area in the window block – more than 80%) can generally act as a resonator. Air gaps and cameras also help to delay sound waves. Naturally, the more cameras there are in a double-glazed unit, the less noise will enter the room, packages with three glasses are about 30% (reduction is up to 40 dB) quieter than those with two. If the windows face a noisy street or, for example, a busy road, this may not be enough. Then you can order an asymmetrical filling – this is when spacers of different widths are used between the glasses of the same package. According to the same principle, the fight against noise is realized if the glasses themselves differ in width. Definitely, a plus for ensuring sound insulation is the use of any polymer films – it does not matter, shading or shockproof.
Frame mechanical strength
In order for the window to remain airtight and to close / open normally, it must at all costs keep its shape. The structure is subjected to loads from the weight of the glazing and the movable sash acting on the hinges like a lever; significant operational problems are created by sudden temperature changes, due to which the window profiles expand and contract. Of course, correct installation, assembly quality and competent design of the unit are very important here (correct size of doors, choice of fittings, location of bulkheads …), but a lot also depends on the profile itself. Aluminum frames are assembled with self-tapping screws, they are champions in strength, so their sections can be 30% larger than wooden ones and more than twice as large as plastic ones. They are very successfully used in the glazing of balconies, the creation of winter gardens and verandas. Wooden structures do not suffer from active thermal expansion, but their outer paint and varnish layer needs regular renewal (otherwise there is a risk of wood moistening and subsequent deformations). For this reason, combined profile systems have appeared, when a timber profile is closed from the outside with aluminum or polymer strips..
Plastic profiles have the highest coefficient of thermal expansion – up to several millimeters per running meter. To curb this change in length, metal box inserts (galvanized, wall thickness from 1.5 mm) are integrated inside the PVC profile, which play the role of restraining reinforcement. They are also the basis for a reliable installation of anti-burglar fittings. Also, to compensate for the expansion, there are restrictions on the minimum size of the mounting gaps; to assemble the front part of the balcony frames, a special H-shaped connecting profile is used, inside which the sections have a small stroke. Also, the minimum distance between the fixing points of the window in the opening is regulated, by the way, the color profile, which can heat up more in the sun, is fixed with a large number of anchors.
Separately, it should be said about the wall thickness of PVC products. According to GOST 30673–99 “Polyvinyl chloride profiles for window and door blocks”, there are three classes of PVC profiles for wall thickness. “A” is the most durable profile with an outer wall of 3 mm, “B” is the middle version (2.5 mm), “C” is not standardized. Despite the fact that this indicator is indirect for determining the dimensional stability of the system, tests show that the welded joint of the corners of class A profiles is about twenty percent higher than that of a similar product from class B. Naturally, the cost of windows from a profile of different classes will differ significantly.
Light transmittance of window blocks
Interestingly, the main function of the window (to provide natural light) conflicts with the methods of solving basic technical problems. Let’s start with the fact that glass reflects part of the visible light, something is absorbed – in total we lose about 10 percent. A package with one chamber (2 glasses) will allow about 80% to pass through, a two-chamber filling (3 glasses) is already 70%. Also, the height of the profile and the width of the imposts affect the light transmission. The lower the profile, the more light we can get, but by reducing the cross-section of the frame, we have to use thinner reinforcing inserts, which inevitably affects the spatial rigidity of the structure. Wooden euro-windows and metal-plastic structures are close to PVC products in profile height, aluminum profiles with a thermal break are also somewhere nearby (although they can form sections and a light opening larger in area). But products made of cold aluminum, and especially sliding systems for balconies and loggias, have a minimum area of shading details.
Tightness of windows
Low air permeability of a modern window block is the key to effective thermal insulation. However, by blocking the path of drafts, we often disrupt the natural exhaust ventilation, which worked successfully with old wooden windows. As a result, the flow of air from the street to the rooms stops, and the flow of air masses towards the exhaust ducts stops. As a result, the humidity in the room rises sharply, and water in the form of condensation falls on relatively cold glass and on the slopes. It is worth noting that this also applies to wooden euro-windows, which, according to the assurances of managers, “breathe well”.
The problem is solved by the use of slot (winter) ventilation, when the sash leans back a few millimeters from the vestibule. Another option is to install a special valve on the frame or sash that can let air through when the window is completely closed. Summer ventilation can be carried out through sashes, vents and transoms, but here a system of stepped opening, limitation and fixation of moving elements should be organized.
The situation is somewhat different with sliding aluminum systems, which are actively used to implement cold glazing of balconies and loggias. The movable sashes do not form an airtight vestibule, since a brush element is used instead of elastic seals. This is a good option if you actively use the balcony, for example, for drying clothes..
What determines window prices
The price of modern windows, first of all, is formed from the cost of basic components, such as profiles, double-glazed windows, fittings. Of course, you should consider the costs of installing and purchasing accessories. Preliminary calculations to roughly calculate your costs can always be done using the window calculators that manufacturers post on their websites. To obtain accurate data, you must call the master measurer.
PVC profiles are the most inexpensive, the average price per square meter of high-quality metal-plastic windows is about 4-6 thousand rubles. Much depends on the width of the profile (70 mm is 20% more expensive than 60 mm), the number of chambers, and wall thickness. The division into “budget” and “elite” classes is, of course, a convention.
The cost of wooden windows ranges from 10-30 thousand rubles per square. It is important where the profile is produced (domestic is half the price), what kind of wood is used (oak is twice as expensive as pine), solid or spliced lamellas (-20%), single or double doors (+ 20%).
Structures made of warm aluminum are 3-4 times more expensive than plastic ones, but cold products without a thermal bridge will be an order of magnitude more profitable than PVC.
Combined frames “wood-aluminum” are about 30-60% more expensive than wooden ones, the option “wood-plastic” – by 25-30%.
Painting or color lamination of profiles increases their price by 20-30 percent.
A window divided by an impost is more expensive than a blind one without bulkheads, since one more profile is added, glazing beads, a double-glazed window is divided in two (more spacers, sealant, work). Windows with sashes are even more expensive (sometimes more than 2 times), since it is necessary to apply profiles to create a frame of a movable canvas, fittings, handles. In general, the hardware significantly affects the cost of the window (it is believed that a unit equipped with branded fittings can become one third more expensive), it takes into account how many opening / closing cycles it will allow to do, what are its anti-burglar characteristics, what type of sash movement it provides.
As for double-glazed windows, a two-chamber product costs 30% more than a single-chamber one (about 900 rubles per m2), the cost will also increase by a third if the single-chamber package is filled with an inert gas and one glass with a low-emission coating is used.
Do not forget that about 3000 rubles will be delivered and installed one window unit. A low tide with a window sill will cost about 400-700 rubles. You will also have to pay a little for the mosquito net. However, with a large or non-urgent order, as well as when buying a standard window (especially important for wooden structures), you can get a discount of up to 20%.
Today we examined the general features of modern window systems, we hope that the main current issues were highlighted. In the following articles we will talk in more detail about plastic, aluminum and wooden windows..