Interior insulation

from Wikipedia, the free encyclopedia

The term interior insulation or interior thermal insulation summarizes insulation measures for buildings in which the insulation material is attached from the inside to external walls and ceilings that border on cold external areas.

There can be various reasons why this more complex measure is preferred to other forms of insulation such as core insulation and external wall insulation :

  • The facade is preserved.
  • Rooms and apartments can be insulated individually so that this can also be done by individual tenants and owners in communities.
  • Targeted insulation of individual surfaces is possible, for example to repair mold damage.
  • No scaffolding is necessary.
  • Gradual renovation is possible.

Interior insulation faces two major challenges. The interior installation of the insulation reduces the living space. The reduction of the base area can, if necessary, limit the use of high-performance insulation materials such as phenolic resin foam panels or vacuum insulation panels . Furthermore, it is important to control the moisture balance of the walls and prevent the formation of moisture accumulations through the choice of a suitable insulation material and a professional implementation.

Moisture nests and the resulting mold are favored by thermal bridges . Internal insulation can eliminate thermal bridges and reduce the risk of condensation on the wall surface. Through the targeted application of insulation strips on the inside of building corners, geometrically related thermal bridges are avoided. Many manufacturers of interior insulation materials offer insulation wedges so that a barely visible connection of insulation strips to the adjacent wall surface can be achieved (instead of a shoulder).

The internal insulation increases the temperature of the internal surface of the external walls, which means that less moisture condenses in these areas.

Building physics peculiarities

After the installation of interior insulation, the temperature of the inner surface of the exterior wall drops sharply in winter, as the exterior wall is now shielded from the heat of the interior by the insulation and can therefore almost assume the exterior temperature with large insulation thicknesses. The Fraunhofer Institute for Building Physics calculates a minimum temperature of 4 ° C for a typical wall structure. The dew point of the room air is often assumed to be 10–12 ° C on average. With a typical temperature of the inner wall surface of the outer wall of 17 ° C, the dew point temperature at cold outside temperatures is reached roughly in the middle of the cross-section of the interior insulation.

To prevent air humidity from diffusing into the insulation and condensing there, a vapor barrier is often installed on the room side . Just like the vapor barrier, the wall structure behind it should also be made airtight so that in the event of leaks in the level of the vapor barrier, moist indoor air cannot flow through the level of the insulation material. Since the dew point is here in winter, condensation of larger amounts of moisture would otherwise be expected.

From timber frame construction comes the rule of thumb that with planked cavity walls the value of the inner planking should be a factor of 7 to 10 higher than that of the outer air seal. This means that no condensate can form even under the most unfavorable conditions. Corresponding values ​​can usually not be achieved with the sole use of OSB panels for the interior paneling. A vapor control membrane would then have to be used.

Even if the use of vapor control sheets or foils is often practiced, there is a certain risk in the event of damage. If there is a leak in the inner airtight layer or if moisture collects in the wall as a result of water damage, the vapor control membrane prevents the inside from drying out. The same applies if the outer walls on the weather side of a building are frequently soaked in driving rain in winter, so that there is increased material moisture in the entire wall cross-section. The use of moisture- adaptive vapor control sheets can reduce the risk of moisture penetration, but not completely mitigate it.

Version without vapor barrier

In recent decades, interior insulation systems without a vapor barrier have been increasingly used, which offer greater tolerance to unplanned moisture penetration of the wall (for example in the case of burst pipes, damaged roof cladding or leaky rain gutters) and are generally easier to install in angled wall structures with many penetrations. Since the airtight laying of vapor control membranes often does not work perfectly in everyday construction and the membrane is prone to being accidentally perforated later, the variant without a vapor control membrane also offers increased security against structural damage.

It is accepted that condensation forms in the insulation in the winter months. Only materials are used that are capable of capillary transport. These conduct the resulting moisture to the inner and outer surface of the outer wall, where it can evaporate. If the humidity in the interior is at a constantly high level, the humidity must be able to reach the outside of the building quickly enough. If capillary transport to the outside is not possible or if the water vapor diffusion resistance of the layers outside the insulation is too high, the insulation layer can become moist for a longer period of time. As the moisture content rises, so does the steam or moisture flow. At the same time, however, the dampening increases the thermal conductivity of the wall building materials, as a result of which the temperature of the inner wall surface drops and the formation of condensation accelerates, which leads to a self-reinforcing effect. Even greater dampening of the insulation layer does not always have to lead to structural damage. Capillary-conducting building materials in particular usually offer a sufficiently high level of protection against the formation of mold. However, heating costs increase due to the increased heat transfer.

It can be calculated whether the moisture absorbed in the winter months can dry out completely over the summer . In addition to the Glaser process , programs such as WUFI and Delphin (software) are available for this. The COND program is offered by the Institute for Building Climatology at TU Dresden specifically for hygrothermal assessment and proof of moisture protection for interior insulation systems with condensation.

The evacuation of the condensate to the outside of the outer wall cannot be ensured in every special case, for example in the case of frequent ingress of moisture from driving rain in exposed locations. It is therefore important to ensure that capillary transport to the inside of the wall is not interrupted.

Since every layer of air and every inclusion of air prevents capillary transport, the insulation material should be glued with mineral mortar or pressed onto the outer wall by dowelling. The same applies to any wall paneling that may be provided. If a vapor barrier is not installed, plastering the wall is generally preferred to paneling.

Vapor control membranes are also available that are capable of capillary drainage of moisture, provided that intimate contact with the adjacent building materials can be established (for example by screwing and pressing or by mineral adhesive mortar with a low synthetic resin content). This variant is useful when interior insulation is to be installed in rooms with consistently high levels of humidity, such as poorly ventilated or commercial kitchens and bathrooms, as well as in unheated rooms into which warm, humid air can enter.

If vapor-permeable cladding materials such as clay panels are used, a full-surface mineral filler or an adhesive and reinforcement mortar with synthetic resin content can act as a vapor barrier. If the inner wall surface is to be plastered, the wall plaster itself or an additionally applied slurry can form the vapor barrier. The diffusion resistance can be varied by adjusting the synthetic resin content. Manufacturer of dry mortar usually give the water vapor diffusion resistance (μ-value) or S d - to value most in the data sheet.

At least one manufacturer of wood fiber insulation boards integrates a mineral layer with a vapor-retarding function into the structure of the interior insulation boards , which does not interfere with capillary transport.

The security of a wall construction with internal insulation against moisture penetration depends in particular on the water vapor diffusion resistance of the existing outer wall. An outer wall clad with ceramic tiles or dense natural stone is less suitable for inner wall insulation. Facade cladding should always be installed with rear ventilation. Synthetic resin-based facade coatings can also act as a vapor barrier. When repainting, attention should be paid to the lowest possible water vapor diffusion resistance.

execution

Particularly when installing interior insulation without an internal vapor barrier (or if there is a risk that the installed vapor barrier will be perforated during later work), it is important to ensure that the insulation material is integrated into the wall structure without large cavities.
The main danger arises from larger cavities, in which air circulation develops, which absorbs large amounts of water vapor from the damp insulation material or from the inner layers of the outer wall and allows it to condense at the coldest point on the opposite outer wall. The greatest damage occurs when the cavities are connected to the interior, so that moist interior air can flow in constantly in winter.
Since every cavity interrupts the capillary transport of the moisture condensing in the insulation material, efforts should be made to keep the size of the individual cavities and their total area as small as possible.
If the wall surface is uneven, you can:

  • first to provide a leveling plaster, or
  • to press a soft insulation material to the wall surface by dowelling, or
  • Apply adhesive mortar in sufficient thickness to the wall and insulation material and ensure that the adhesive mortar is distributed over the unevenness by moving the insulation panels back and forth as well as pressing or knocking on them.

Thermal bridges arise in particular:

  • on window and door reveals, as a lower insulation thickness is often chosen here in order not to restrict the incidence of light too much in existing buildings. Ideally, the insulation thickness should be as large as possible directly on the window or door frame. On the other hand, the insulation material can be beveled towards the inner edge of the reveal without hesitation in order to allow a better view and better light diffusion. At inner corners (in contrast to outer corners) there is no strong heat dissipation due to the area ratio of the inner to the outer wall. However, this geometrical advantage is reversed within the reveal when the door or window frame is approached, since there the heat flow to the nearby cold surfaces on the outside of the frame predominates. The use of insulation wedges is recommended here.
  • on sockets of the electrical installation
  • at the connections between ceilings and interior walls and the exterior wall. Flank insulation should be provided in the corners of the room facing the outer wall, especially in the case of the unfavorable combination of thin outer walls with solid inner walls . An insulation thickness of 20 to 40 mm on a 20 to 50 cm strip is usually sufficient to prevent condensation from forming. By using insulation wedges, steps within the wall and ceiling surfaces can be avoided. (Flank insulation). The thermal bridge effect of wooden beam ceilings and half-timbered walls is low, so that no special measures are generally necessary here. In rooms with very high levels of moisture, it makes sense to open the wooden joist ceiling near the outer wall so that the interior insulation can also be carried out in the ceiling level. The parts of the wooden beams that are in the immediate vicinity of the outer walls can be coated all around with clay so that this removes any moisture that may condense in or on the wood to the surrounding building materials.

Attachment of objects

Light objects such as pictures and bathroom cabinets can be attached simply by screwing in chipboard or drywall screws with a coarse thread (without pre-drilling). If necessary, a perforated plate with several screws should first be screwed on, which supports the actually load-bearing screw. Alternatively, special insulation dowels are suitable for increasing the load capacity, as are the many dowels for use in aerated concrete and gypsum building materials . To carry larger loads, the dowels must be anchored in the ground. To distribute the compressive stress that occurs, a wooden board can be placed on the wall surface or embedded in the insulation.

It is also easy to drive in fine pencils. Driving in nails with a larger diameter or blunt point is made more difficult by the wood fibers.

materials

The following insulation materials are offered for interior wall insulation and have sufficient capillary moisture transport capability in order to avoid moisture accumulation from driving rain and to be able to do without a damage-prone vapor barrier in the construction.

plates

Lime and cement-containing insulation boards generally have a higher pH value, which provides additional protection against the formation of mold. When properly carried out, any type of interior insulation prevents the formation of mold, so this is only a decisive criterion in exceptional cases. For example, in rooms with extremely high humidity or in door and window reveals with reduced insulation thickness, where condensation has already formed if this is not yet the case in the rest of the wall area.

Pourings

for filling up cavity walls or for throwing on or spraying on as a moist mixture:

Flexible insulation materials

Flexible insulation materials that require support from expanded metal or cavity wall constructions:

Insulation materials that are open to diffusion but not capable of capillary water drainage (e.g. mineral wool ) must be protected from the ingress of moisture by an internal vapor barrier . If the insulation thickness is limited to around 35 mm, it may be sufficient to provide it with a vapor-retarding reinforcement or plaster layer in order to keep winter moisture within a tolerable range.

Vapor retarders

  • Foils are usually not able to carry on planned or unplanned moisture in the wall structure.
  • Cardboard or papers are capable of capillary transport if the synthetic resin content is not too high.
  • Not for the capillary-capable vapor retarders water present to variable Dampfdiffusionbeiwert in liquid form evaporates back to a limited extent on room side can
  • Wood-based panels as well as slurries , adhesive and reinforcement mortars, plasters and paints can serve as vapor retarders, as their diffusibility depends mainly on the synthetic resin content. The ability of these materials to transport capillaries usually decreases as the µ value increases. From a certain synthetic resin content, the moisture transport is generally completely prevented.

planking

  • Uncoated plasterboard and clay building boards are capable of capillary transport without restriction
  • In the case of HWL and cement-bound drywall , the capillary transport is significantly restricted by cavities that are too large or by the dense structure
  • Due to the high synthetic resin content of OSB panels , capillary transport is restricted compared to uncoated wooden panels and plywood panels . Despite the high proportion of synthetic resin, chipboard allows moisture to pass through somewhat better, as there are fewer two-dimensional barrier layers in the disordered chip structure.

If in doubt, the capillarity can be tested by sprinkling the building material with water droplets. If the moisture is initially absorbed and within a few hours it is distributed in the material in such a way that no accumulation of moisture can be recognized, sufficient capillary transport should be possible. If the moisture takes a long time to absorb or not at all, this may be due to a hydrophobic surface. The experiment should then be repeated after removing the top layer. If the moisture does not absorb even then, it can be assumed that the porosity necessary for capillary transport is not given. If the moisture is absorbed but not distributed, then it is likely that the pores contained are too large or the internal material structure does not allow moisture to be transported for other reasons.

literature

Individual evidence

  1. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, pp. 78 and 80; accessed in January 2017.
  2. ↑ Martin Krus, Klaus Sedlbauer, Hartwig Künzel: Interior insulation from a building physics point of view. Fraunhofer Institute for Building Physics; accessed in November 2016.
  3. ↑ Characteristic data of building envelope and heating load , data pool IfHK, FH Wolfenbüttel; accessed in November 2016.
  4. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, p. 68; accessed in January 2017.
  5. ↑ Peter Cheret, Kurt Schwaner: Holzbausysteme - an overview ; accessed in December 2016.
  6. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, p. 74; accessed in January 2017.
  7. ↑ Technical sheet for interior insulation , Claytec.de; accessed in November 2016.
  8. ↑ Interior insulation with and without vapor barrier , part 2: Innovative systems - experience with processing and first moisture measurements. In: Timber construction - the new Quadriga. Issue 4/2008; accessed in November 2016.
  9. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, p. 81; accessed in January 2017.
  10. ↑ See section Planning aid for flank insulation in the application brochure "Interior insulation of the outer wall" from GUTEX wood fiber board plant, Waldshut-Tiengen; accessed in January 2017.
  11. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, p. 84 ff; accessed in January 2017.
  12. ↑ In the event that the outer wall is also to be insulated in the ceiling level of a wooden beam ceiling, it is recommended in some places to only choose a low insulation thickness of 20 to 40 mm. This is to prevent the wooden beams near the wall from assuming a significantly lower surface temperature than the surrounding wall surfaces, which would result in the risk of condensation forming there. If, on the other hand, the insulation is completely dispensed with, a permanently increased air humidity can in turn lead to so much condensation water condensing on the masonry in the ceiling level that the moisture also leads to moistening of the wooden beams again via the masonry. In general, it is advisable to make the floor, but especially the underside of the ceiling, as airtight as possible in order to limit the inflow of moist room air into the ceiling level in advance. In order to avoid the convective transport of moisture to the joist heads lying in the masonry, it is recommended to first fill the gap between wooden joists and masonry about halfway with densely packed darning wool (e.g. made of hemp or flax) and then to spread the joint filled with darning wool generously with clay . Darning wool and clay together provide a sufficient seal against the entry of moist indoor air. The clay buffers moisture peaks and ensures quick drying of the wood in the event of (unplanned) moisture penetration of the masonry. See also the guidelines for interior insulation 2.0 , DBZ editorial team in collaboration with the interior insulation working group in the WDVS eV, special issue at Bauverlag BV GmbH, 2015, p. 48 (accessed in January 2017), and Claytec worksheet for interior insulation , as of January 2019.
  13. ↑ Claytec internal insulation worksheet , p. 10, as of January 2019.
  14. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, p. 69; accessed in January 2017.
  15. ↑ Modernization of old buildings with passive house components. Passive House Institute, 2009, p. 71; accessed in January 2017.
  16. ↑ Guideline for interior insulation 2.0 , DBZ editorial team in cooperation with the interior insulation working group in the WDVS eV trade association, special issue at Bauverlag BV GmbH, 2015, p. 74; accessed in January 2017.