Mauerlat: calculation, installation, waterproofing and insulation

 Mauerlat: calculation, installation, waterproofing and insulation

The supporting element for the roof truss system is the Mauerlat. It is placed along the perimeter of the outer walls of the building and is a wooden bar or log. If a log is used, then trimming is done on one side to make it fit more tightly to the wall surface. When creating a metal rafter system, the Mauerlat can be made from a channel or an I-beam. Some builders, trying to save money, do not use a Mauerlat or install it only under the rafter legs. This cannot be done, since the required rigidity and strength of the structure will not be provided.

What is Mauerlat

The roof protects the house from the negative effects of external natural factors; various external loads act on it. It must withstand large wind and snow influences, so that the roof does not "go", it must be securely fixed. The correct device of the Mauerlat allows you to reliably connect the walls of the house and the roof to each other and thus ensure its reliable and strong fixation.

Words such as a wall, foundation or plinth are known to any man in the street, but when hearing the word "mauerlat", not every person can explain what it is and why it is needed. Mauerlat is an element that is fixed along the perimeter of the outer wall of the building, the entire rafter system rests on it. In other words, we can say that the Mauerlat for the roof is the same as the foundation for the house, and you cannot do without it, otherwise you will not be able to firmly fix the roof.

The main functions of the Mauerlat:

  • compensation of the bursting force created by the rafters;
  • secure fixation of the roof to the walls of the house.

When snow accumulates on a pitched roof, the force of gravity caused by it will have a component directed along the slope and create bursting loads that must be compensated.

Snow lying on a sloped roof creates a load directed along the slope and exerts a bursting effect on the walls of the building

The bursting force can be very large, and if the roof construction technology is not followed, then it can cause partial or complete destruction of the walls. To prevent this from happening, a Mauerlat is installed along the perimeter of the outer walls of the house and thus a solid frame is created on which the rafter system is fixed.

Although the presence of a slope reduces the windage of the roof, it still remains quite high. The Mauerlat also allows you to compensate for the breakout forces that occur during strong gusts of wind.

What materials can be used to make a Mauerlat

In houses made of rubble stone, bricks, adobe and aerated concrete, the Mauerlat is a separate structure that is securely fixed along the perimeter of the outer walls. In a wooden house, its role is played by the last crown, which is firmly fastened to the previous logs. It is better that the rafter beam is for the entire length of the wall, and if joining of the logs is required, then this must be done in such a way as to ensure a reliable and strong connection.

You can make a Mauerlat from the same material that was used to create the rafter system. For these purposes, you can use the following products.

  1. Wooden bar or log. The cross-section of the timber depends on the weight of the roof - standard sizes are used 100x100, 100x150, 150x150 and 80x180 mm. When choosing a material, you need to look at its quality. If there are knots, then their size should not exceed 2/3 of the thickness of the timber, otherwise in these places under the influence of loads the timber will begin to crack. If a log is used, then its diameter should be at least 180 mm, the bark is removed from it, and the lower edge is sawed to ensure a snug fit to the wall surface.

    Most often, a wooden beam is used as a Mauerlat.

  2. Bonded boards. This option is suitable when a light frame house is being created and the load on the roof will be small. It is enough to take boards with a section of 50x150 mm and lay them in two layers.
  3. Metallic elements. There are situations when a metal rafter system is created. In this case, the rafter beam can be made of a channel, which is a U-shaped section profile, or an H-shaped I-beam. Depending on the load on the roof, they usually take brand profiles from No. 10 to No. 14.

    If the rafter system is constructed of metal, the Mauerlat is made from a channel or I-beam

How to correctly calculate the dimensions of the rafter beams

Since the Mauerlat serves as a support for the roof, it is important to correctly calculate it.

The dimensions of the rafter will depend on:

  • the perimeter of the outer walls of the house;
  • roof structures;
  • weather conditions in the region where the construction is being carried out;
  • the purpose of the attic or attic space.

The main indicator for calculating the Mauerlat is the type of roof of the building - it can be one-, two-, three-, four-slope, flat hipped, spherical, etc.

There are general rules that must be followed when calculating the Mauerlat for any type of roof.

  1. The minimum cross-section of a beam that can be used for a rafter is 100x100 mm.
  2. To determine the length of the Mauerlat, you need to measure the perimeter of the outer walls of the house.

    To calculate the length of the Mauerlat, you need to measure the perimeter of the outer walls of the house

  3. To determine the mass of the beams, the formula m = r ∙ V is used, where m is the mass of the Mauerlat, r is the density of the tree, V is the volume of the rafter beam.
  4. The calculation of the volume of the material is carried out according to the formula V = S ∙ L, where S is the section, L is the length of the bar.
  5. Regardless of the size of the Mauerlat, it must be located at a distance of at least 5 cm from the outer edge of the wall.
  6. The rafter beams are laid along the entire perimeter of the outer walls of the house, while their width should not be less than 1/3 of the wall thickness. Too large a beam creates an additional load on the walls, and a small one does not provide the necessary reliability and strength.
  7. It is desirable that the length of the beam matches the length of the wall. If this is not possible, then it is necessary to lay two beams as equal in length as possible and connect them together in half a tree.

    Half-thickness grooves are cut at the end of each beam, after which the beams are applied and connected with nails or bolts

Practice shows that for most cases, the standard values ​​of the main parameters of the Mauerlat, indicated in the table, are suitable.

Table: standard Mauerlat parameters

ParameterValue
Widthnot less than 100 mm
Optimal cross-section100x150 mm
Materialantiseptic treated larch timber
Mass and volumecalculated by the specified formulas
The location of the timber from the edge of the wallnot closer than 5 cm
Distance between barsthe same along the entire length

How to install the Mauerlat correctly

The installation of the Mauerlat is quite simple, so any home craftsman can cope with such work. Please note that this element for the roof is the base of the roof, therefore, its installation must be treated very responsibly.

Before proceeding with the installation, you need to decide on the method of attaching the timber to the wall, for which one of the following options is chosen.

  1. With a wire. This is a simple and affordable way, fixation is performed using steel wire with a cross section of 4–6 mm. To provide the necessary strength, it is twisted several times and laid into the wall 5-6 rows below the location of the Mauerlat. The masonry must dry, after which the bars are securely fixed with a wire harness. Please note that the length of the wire should be enough to wrap around the beam, tighten and secure the ends well. The wire should be embedded in front of each rafter leg, usually in 60–70 cm increments.

    For fastening the Mauerlat, a wire with a cross section of 4–6 mm, twisted several times, is used

  2. For construction studs. This method is used for light roof loads. L-shaped construction pins are used, which are reliably embedded in brickwork to a depth of 450 mm. Above the beam, the ends of the studs should protrude at least 3 cm. For a more reliable fixation of the fastening element, you can make a concrete pad, but during pouring you need to be careful not to contaminate the threads. To determine the place for the passage of the studs on the bar, you need to put it on top and hit it lightly. The marks will remain on the tree, along which holes are made.

    The studs are tied to the reinforcing cage prior to pouring concrete so that their ends protrude above the timber by at least 3 cm

  3. On anchor bolts. This method is used when the Mauerlat is mounted on an armored belt. During the creation of an armored belt, anchors are inserted into it, after which a rafter beam is fixed on them. The bar is put on the bolts and fixed with a nut through a washer, after which the lock nut is tightened. Since the cost of anchor bolts is quite high, reinforcement is sometimes hammered into the armored belt to a depth of 200–250 mm instead of them, after which the edge is bent.

    For reliable fixation of the Mauerlat, anchor bolts with a diameter of 12-14 mm are sufficient

In each case, the owner himself decides on the choice of one or another method of fixing the Mauerlat.

Depending on the chosen installation method, the sequence of work will be slightly different, but in any case, it is based on a number of standard actions.

  1. The place where the timber will be installed is cleared of dirt and debris.
  2. To protect the wood from decay, a layer of waterproofing is laid between the Mauerlat and the wall, for which a polyethylene film or roofing material is used.
  3. For the installation of studs, anchors or wire, appropriate holes are made in the beam.
  4. Fixing of the wire, pins or anchors in the wall or in the armored belt is carried out. It all depends on the chosen installation method - we have already considered how to do it correctly above.
  5. After securely fixing the studs or anchors, a bar is pushed onto them through the holes made.

    In order to put the bar on the studs, it must be clearly fixed in the working position and hit with a hammer or an ax on the upper side, then there will be marks from the bottom in which holes of the required diameter must be drilled

  6. The Mauerlat is being fixed. In the case of studs or anchors, a nut with a washer is tightened from above, and the wire simply twists well and bends to the side.

    After laying the timber, it is fixed with nuts screwed through wide washers

Video: installing the Mauerlat on studs

Fastening the Mauerlat to various types of walls

Depending on what material the walls of the house are made of, the method of fixing the Mauerlat will differ.

Wooden walls

If the house is made of glued or rounded timber, then the uppermost crown plays the role of the Mauerlat, which is attached in the same way as the rest of the wall elements. If desired, the base for the installation of the rafter system can be made of a solid wooden beam, which is fixed to the wall with an anchor, before that the wall surface must be leveled.

Brick walls

On brick walls, the beam is mounted closer to their inner edge; outside it is recommended to make a small ledge that will protect the Mauerlat from the negative effects of external factors.

Fixing the rafter beam on a brick wall can be done:

  • with wire that is embedded in the wall, it should be enough to reliably tie the timber;
  • anchor bolts - holes are made in the wall into which special bolts are driven;
  • by laying wooden plugs into the wall, in this case the beam is fixed with metal brackets;

    The plug is laid in the wall, after which the beam is fixed with brackets

  • by hammering reinforcement into the wall, for which it is bent in the shape of the letter "G", a short edge with a length of at least 250 mm is laid to a depth of 3-5 rows, the upper edge is placed vertically, and a bar is put on it.

Walls made of aerated concrete or other cellular material

Since aerated concrete has not very high strength, for reliable fixing of the rafter beam, it is imperative to make an armored belt.

  1. Formwork is made above the end surface of the wall.

    Formwork for armopoyas can be made of boards or plywood

  2. Reinforcement is laid in the formwork and studs are installed. For reliable fixation, it is better to tie them to the frame with wire, and to protect the thread, the working part should be wrapped with masking tape.

    The studs must be installed strictly vertically and securely fixed to the reinforcing cage

  3. Concrete is poured into the formwork.

    After creating the formwork and laying the reinforcement, concrete is poured inside

  4. After hardening of the armored belt, the formwork is removed.
  5. Install and fix the Mauerlat. After 2-3 days, the nuts must be tightened, and then finally fixed in position with the locknuts.

To strengthen the Mauerlat frame at the corners, you must additionally use brackets or plates to securely fix the beam.

To fix the timber in the armored belt, you can use ordinary or wedge anchors, as well as special dowels, but the cost of such elements is quite high. The chemical installation method is less costly. The anchor is fixed in aerated concrete with a special adhesive and ensures reliable fixation of the Mauerlat.

With the help of chemical anchors, reliable fastening of the Mauerlat to the aerated concrete wall is ensured

When using mechanical fixation, a bursting force occurs, which is not very desirable for porous materials. The use of chemical anchors does not have such a disadvantage; they provide a more durable fastening.

If a chemical anchor is installed, it is not recommended to carry out welding work with it, since during heating the glue may collapse and the fixation will weaken.

Video: mounting the Mauerlat on the armopoyas

Mauerlat insulation and waterproofing

In order to prevent damage to the Mauerlat by fungus and mold, as well as the penetration of cold into the under-roof space, it is necessary to properly waterproof and insulate this roof element.

Laying logs on bare walls is not allowed... This applies not only to the Mauerlat, but also to the rafters if they come into contact with the wall or armored belt. For waterproofing, roofing material is used, which is best folded in two layers. You can use other waterproofing materials, for example, polyethylene film, but it is two layers of roofing material that provide the most reliable protection of the tree from moisture penetration into it. This material has a fairly long service life and low cost.

For high-quality waterproofing, roofing material is best laid in two layers.

The waterproofing material must be positioned so that the upper layer does not allow moisture to enter the Mauerlat, and steam can freely escape through the lower layer.

Experts say that about 12-15% of all heat from the house leaves through the roof, if insulation was not performed correctly during the installation of the Mauerlat. The following can be used as thermal insulation materials for this element:

  • sawdust - to scare away rodents, they must be mixed with lime;
  • expanded clay;
  • ecowool;
  • Styrofoam;
  • polyurethane foam.

This type of insulation is considered optimal when ecowool is used outside, since it allows the tree to "breathe", and inside there is mounting foam. Such a solution will reliably protect the Mauerlat from the cold and provide high thermal insulation characteristics for 40 years or more.

From the outside, the Mauerlat is usually insulated with ecowool or slab mineral materials, and a layer of polyurethane foam is laid from the inside

Video: Mauerlat insulation

To understand the meaning of the Mauerlat, it must be borne in mind that this element for the roof is the same as the foundation for the house. Different loads are constantly acting on the roof of the building - wind, snow, the weight of the roofing cake. To compensate for them, it is necessary to correctly and securely fasten the rafter beams. For fixing the Mauerlat, depending on the material of the walls, different installation methods can be used, in each case they must be chosen individually. If, during the installation work, you adhere to the developed rules and recommendations of specialists, you will be able to do everything qualitatively with your own hands.


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