Light shafts are usually designed with prefabricated concrete or plastic elements. They are primarily used to illuminate and ventilate rooms in the ground. Numerous manufacturers also offer special system solutions for basement light shafts, e.g. for light shaft drainage, building waterproofing and thermal insulation in the area of the shaft.
The planning goal should be to make the basement waterproof on its own (e.g. as a black or white tub) and to attach the light shaft to the sealed structure. In this way, the light well does not have to meet its own requirements for waterproofing. If the soil is highly permeable (k > 10-4-4 m/s according to DIN 18130-1) and free of strata water and pressing groundwater, the shaft can be planned at the bottom open or with a simple drain. Rainwater penetrating the shaft seeps into the subsoil or is fed into a drainage system.
Regardless of the nature of the soil, the parapet of the basement window should be about 30 cm above the light shaft floor in order to prevent the water from penetrating through a non-waterproof basement window even in the event of unexpected water in the light shaft (e.g. blocked drain, heavy rainfall).
Material: Common materials for light shafts are concrete and plastic.
In principle, concrete light shafts have a particularly high stability. They can be manufactured in practically any size and are heavy-duty, up to the point of being passable by trucks. They are also UV-resistant and have a particularly long service life. Their high dead weight makes the assembly correspondingly complex, and a lifting device (construction crane) is required. The visual design corresponds to fair-faced concrete quality. During the construction phase, the concrete light shaft is correspondingly insensitive to heavy construction equipment, for example when backfilling and compacting the excavation pit.
Plastic light wells have the advantage of their low weight. For example, assembly on the shell or subsequently on the finished house can usually be carried out without a construction crane. Their dimension is limited due to the lower stability of the plastic compared to concrete. The color of the plastic light well is white, its geometry is curved, which makes the luminous efficiency large.
Load capacity: Concrete light shafts on reinforced concrete walls have a high load capacity. They are reinforced and dimensioned according to the requirements and traffic loads. Usually, car passability (up to 500 kg wheel load) is achieved, truck passability in special cases.
Concrete light shafts on brick basement walls are usually only accessible without their own foundations. Plastic light shafts are accessible, car accessibility is only achieved in special cases and with the corresponding load-bearing capacity of the basement wall. A separate foundation is not possible with plastic light shafts.
Pressure watertightness: If the basement wall of a house is constantly or temporarily stressed by pressurized water, the light shaft must be watertight to prevent the basement from flooding over the window, unless it is designed to be watertight. In addition to the light shaft itself, the connection to the basement wall must also be watertight. This is done via sealing tapes, sealing lips and bonds, which vary depending on the manufacturer.
A version without drainage is only recommended in rain-protected areas where there is no risk of surface water penetrating the light shaft from above.
If the light shaft is not connected to a drain system (via lifting pump), it is absolutely necessary to set a drain with a backflow valve. In particularly dangerous situations, watertight basement windows are also advisable.
In areas without constantly pressing water, but with the risk of flooding events (backwater level is above the basement window sill), it is possible to place a standpipe vertically on the drain in the watertight light shaft, the upper end of which is above the backwater level. In this way, a column of water can rise in the pipe (usually transparent) without flooding the light shaft. Once the flood event is over, the standpipe is removed manually and water that has penetrated above ground can seep away or be discharged into the sewer system. The light shaft must be protected against penetrating surface water, as this cannot drain off in the light shaft when the standpipe is in place, e.g. by a rain cover, an inclined driving rain protection, terrain modelling or an elevation of the light shaft above ground.
Insulation in the light well: A light well without requirements for waterproofing can be placed on both an uninsulated and an externally thermally insulated basement wall. The fastening anchors, with which the shaft is attached to the basement wall, bridge the insulation layer applied on site by means of spacers.
In addition, numerous manufacturers offer prefabricated insulation elements that are optimally adapted to the respective system light well (format, prefabricated holes for fastening). The shaft body is anchored to the outer wall by the insulation, and in the case of small plastic shafts, it is also possible to attach it directly to the insulation board (thermal bridge avoidance).
Prefabricated insulation is particularly important for waterproof light shafts. Since a watertight connection on the perimeter insulation applied by the construction company cannot be achieved, it must be left out in the area of the light well. With the help of the prefabricated insulation element, which is matched to the waterproof light well, the connection of the light well to the basement wall is watertight and is made by thermal separation of the mounting brackets without major thermal bridges .
Light well covers: For standardised light wells, all manufacturers offer customised, mostly hot-dip galvanised steel grates in the same format.
A wide-meshed 30/30 mm grate favours the incidence of light. In the area of sidewalks, a narrow mesh size of 30/10 mm is advantageous, which reduces the risk of shoe heels or walking sticks getting stuck. If the luminous efficacy requirements are high, the shaft can also be covered with a walkable and rear-ventilated acrylic glass.
If the light well is also to be protected against penetrating surface water, insects, mice and dirt, the manufacturers also offer covers tailored to the shaft that are placed on the load-bearing grate.
Light shaft head: The light shaft head can be designed with or without a rebate, see also sketches in the lexicon article ► Light shaft head, execution.
Concrete light shafts are usually manufactured with an inner rebate into which the grating is inserted. Shaft heads with an outer rebate or without a rebate can usually be ordered. These make it easier to pave directly on the metal rust frame. The circumferential concrete ring of the shaft is then no longer visible.
Plastic light wells are provided with an inner rebate. Direct paving is possible due to the low material thickness and the manhole body that often cantilevers in the upper area. Especially with larger dimensions, plastic light wells must have a stiffening metal frame as the upper end that also protects against mechanical stress. The plastic frame of the shaft body is therefore no longer visible.
The manufacturers of light shafts made of concrete and plastic also offer add-on elements made of galvanized steel or stainless steel, which are used to adjust the height to the terrain (often infinitely adjustable), but also form a visually filigree shaft closure.
Light shaft as a 2nd escape route: The suitability of a light shaft as a 2nd escape route is not regulated by law. In the case of recreation rooms within the meaning of § 2 para. 5 of the Model Building Code (MBO) in the basement, which require a second escape route, it is therefore always advisable to coordinate with the building supervisory authority and, if necessary, to obtain its separate approval. The coordination takes place between the authority, the fire brigade and the architect. The size of the manhole, the quick opening option and the weight of the manhole cover must be taken into account. The manufacturers, especially of concrete light shafts, also offer crampons and escape route ladders as additional components, but their use must also be coordinated with the building supervision in each individual case.
Another important prerequisite for the routing of a 2nd escape route via a light shaft is compliance with the requirements for the affected window according to § 37 para. 5 of the Model Building Code (MBO) in the wording of the respective state building code. In particular, the minimum dimensions of the clear width and height of the window and the maximum permissible height above the upper edge of the floor must be taken into account.
If this is a workplace, the Technical Rules for Workplaces (ASR) A2.3 also apply.
Since self-rescue is always made more difficult by a light shaft, it is generally not suitable for rescuing larger groups of people.
Traffic safety obligation: Light shafts on and in traffic areas must be secured against unauthorised lifting in accordance with § 38 (2) of the Model Building Code (MBO). In this way, accidents are prevented, as the grid cannot be lifted off carelessly, e.g. by children. Unintentional opening is prevented.
A lift-off protection is achieved by means of brackets or chains that are anchored in pairs in the shaft wall. These are often included in the scope of delivery of the light wells.
However, a ruling of the Karlsruhe Higher Regional Court of 22.06.2005 (file no. 7 U 104/04) states that gratings of considerable weight, in this specific case 151 kg, are not to be secured against lifting, since lifting by unauthorized persons is not to be expected due to the enormous weight.
Burglary protection: Effective protection against burglary is not achieved with lift-off devices. In principle, light shafts are popular entry points into a building, because the burglar can pry open the basement window protected from view. Since even a secured light well can never offer absolutely secure protection against burglary, the goal is to increase the break-in time needed to loosen and lift off a grille. The European standard DIN EN 1627 specifies seven different RC classes (RC for resistance-class), which also describe the potential break-in time for the respective grating including fixation.
The burglar protection systems offered by manufacturers on light shafts are usually not classified. The stability of a plastic light well is generally not sufficient to effectively fasten chains or rods against tension. Burglar-resistant security systems can therefore usually only be installed in concrete light shafts, in the case of plastic light shafts, the anchoring should be in the basement wall.
Some manufacturers of concrete light well systems offer so-called burglar-resistant "vault grates" (RC2, RC3, in individual cases also higher). These are gratings anchored in the shaft by means of heavy chains and protective tubes. The cross-sections of the grates are massive, so that cutting is more difficult.
A very effective method of deterring burglars are "rolling rod grilles", which are permanently installed in the light shaft below the light well cover. Additional rods are inserted into the hollow metal rods welded to a frame, which provide a high level of saw protection due to their rotatable bearing. It is not possible to use the shaft as an escape route due to the construction that cannot be opened. In addition to light shaft protection, a special task in burglary protection always has the additional security of the basement window.
Especially in the case of insured properties, the information in the VdS security guidelines must also be taken into account. In addition, when planning burglary protection systems, it must be ensured that they do not contradict a planned use as an escape and rescue route.
Mechanical stress during the construction phase: Plastic light wells are particularly at risk during ongoing construction operations due to their low material thickness. Heavy construction equipment can cause deformations and fractures in the shaft, especially at the corners. If necessary, suitable safety measures must be taken in the form of barriers or covers.
Caution is advised in particular when backfilling the light well. For a short time, enormous earth pressure can arise, for which the shaft wall is not designed. Damage can be prevented by stiffening the inside of the shaft, for example with wooden beams.
Risk of falling during the construction phase: During the construction phase, care must be taken to ensure that light shafts do not remain open. If the grids have not yet been inserted, care must be taken to ensure that the open shafts are covered in a load-bearing manner that cannot slip.
Acceptance of the light wells: When accepting the light wells, it is important to ensure that the lift-off protection has been properly attached. In addition, the shaft was to be inspected for mechanical damage, such as fractures, spalling or cracks.
Manufacturers of pressure-tight light wells in accordance with DIN 18195-6 also offer protective letter inspections with an extended warranty on material and watertightness. Acceptance takes place before backfilling.
DIN 1045‐2, Structures made of concrete, reinforced concrete and prestressed concrete - Part 2: Concrete - Specification, properties, production and conformity - Rules of application for DIN EN 206-1
DIN 18195 Waterproofing of structures - Terms
DIN 18533 Waterproofing of components in contact with the ground:
EN 1627, doors, windows, curtain walls, lattice elements and closures - Burglary resistance - Requirements and classification Note: DIN EN 1627:2011-09 replaces DIN 18106:2003-09
Technical Rules for Workplaces (ASR) A2.3, Escape routes, emergency exits, escape and Rescue Plan
VdS 0691: Security Guidelines for Households
Higher Regional Court of Karlsruhe, Judgment of 22.06.2005 - 7 U 104/04 – (Fall into open light shaft)
Source: bauwion
