How thick should the roof insulation be?

Roof insulation is an important step in the thermal insulation of the entire house. A large amount of heat can escape through it, and precipitation can increase humidity and cause mold. To avoid negative consequences, roof and roof insulation is done. To do this, it is necessary to select the material in advance and calculate the thickness of the insulation.

How to calculate the amount of material

Thermal insulation of the roof improves comfort and indoor climate. Also, insulation improves the thermal resistance of the structure, reduces heat losses. Thermal insulation does not heat the building, but only keeps the heat inside the house. Therefore, it is important to calculate how many layers of insulation are needed for the roof, what width is needed and what material to buy.

All design work is carried out at the design stage. It is necessary to take into account the individual characteristics of the structure, climatic conditions, characteristics of the heat insulator and the purpose of the rooms. Calculations are made in advance, taking into account the type of roof and its dimensions.

The roofing heat insulator is laid on the rafters. It is necessary to calculate how many slabs will be placed along and across the roof slope. To do this, it is necessary to take into account the distance between the rafters, the number of steps and the length of the ramp.

An example of calculating the amount of mineral wool for a gable roof

The roof is symmetrical, the number of rafters is 7, the distance is 60 cm, the length of the slope is 5 m. For laying, slabs with dimensions of 1.17 × 61 × 25 cm are chosen. You can also take rolled mineral wool.

First of all, the number of slabs that will be stacked in a row is determined. To do this, the length of the slope (5 m) is divided by 1.17 and the result is 4.27 pieces. This value is multiplied by step (7) and the total is 29.89 slabs for one slope and 59.78 for the entire symmetrical roof. The result is rounded up and a margin of 15-20% is added. As a result, about 70 slabs are required for the entire roof.

Insulation selection

The choice of material depends on the insulation requirements and availability. It is necessary to take into account the cost of the heat insulator itself, its transportation and installation. Also, the insulation should not be heavy so as not to create unnecessary stress on the logs.

Extruded polystyrene is a popular insulation for roofs. It has good thermal conductivity, so that a thin layer is sufficient for high-quality thermal insulation. Expanded polystyrene is lightweight, easy to install and attach to the roof surface. It is more expensive than other materials, but the cost of installation, shipping, and service life is worth it.

Glass wool is one of the most economical materials. Its production technologies have been improved, so it has improved characteristics and properties. Glass wool is not subject to combustion and does not emit harmful substances. Has a low thermal conductivity, good steam permeability.

Mineral wool is obtained from mineral fibers. This is a standard insulation that is laid in slabs. Its main advantage is its ability to maintain high temperatures for a long time.It is often used for thermal insulation of the bath roof.

Polyurethane foam is applied by spraying. For internal insulation, a soft method is used, for an external one, a hard one. The installation of such an insulator can only be carried out by professionals with special equipment. The advantages include cost-effectiveness and the ability to apply to complex structures.

Primary requirements

Thermal insulation for the roof must meet the following parameters:

• High degree of fire safety. The material must not be burned.
• Soundproofing. The insulation must additionally protect the room from external noise.
• Water vapor permeability. Allows you to create an optimal microclimate.
• Compliance with GOST and SNiP standards, as well as environmental and sanitary safety.
• Strength and durability.
• Resistant to deformation.
• No shrinkage.
• Low weight.

It is recommended to take insulation with a thickness of about 250-300 mm for the mansard roof. Double and triple layers are created to remove cold bridges at the joints of the slabs.

Parameters affecting the thickness of the insulation

The main criteria that determine the thickness of thermal insulation are the characteristics of the material and the roof. Calculations are carried out at the design stage and take into account the following:

• Specific thermal conductivity. The lower it is, the thinner the heat insulator is required.
• Climatic conditions of the area.
• Roof and roof construction. No bulky materials are used on multi-pitched roofs.
• The weight of the insulation itself. The heavier it is, the more powerful the rafters are needed to hold it.

The correct selection of material reduces heating costs and allows you to create comfortable conditions in the house.

Thickness calculation

You can calculate the required thickness using the following formula:

αout = (R0priv-0.16) λout

In it, the symbol αut the thickness of the insulator is indicated in meters, R0 priv. - reduced resistance to heat transfer, λut - coefficient of thermal conductivity.

Determination of thickness when insulating an attic

The room under the roof can be used as residential or non-residential. For a non-residential attic, it is enough to insulate only the covering that separates the ceiling of the house from the room itself. In the case of residential attics, thermal insulation of the side walls and slopes, if any, is required. In mansard roofs, there are three types of enclosing structures - overlapping, ramps and gable walls. They need different widths of insulation for the roof. A thick layer is required for the ceiling, and a small one for the walls. Calculations for each surface are carried out separately.

Insulation of ceilings with a cold roof

If the attic is not used during the cold season, the attic floor can be insulated, leaving the roof without thermal insulation. Then the material is placed on top of the ceiling and covers the ends of the walls. If an insulating layer is installed inside, the walls will give off heat to the outside.

Insulation of only floors greatly simplifies and speeds up the work. Laying on a flat surface is easier than fixing the material on the slopes.

Calculation using online calculators

Many services offer construction calculators that allow you to perform approximate calculations of the amount of materials, its thickness and the cost of the entire process. There are several options for calculating the size of the insulation for the roof:

• By the total area of ​​the building. It is necessary to enter the linear dimensions of the building, the number of floors, the selected insulation. The result is a value with a large number of errors, since the characteristics of the house and climatic conditions are not taken into account.
• By project type. The architectural, structural and engineering plans of the building are taken into account.
• Universal calculator.It takes into account the type of floor, materials and other important features.

The exact figures, how many cm of insulation is needed for the roof, can only be given by a specialist who will conduct an overall assessment of the house and take into account all the nuances. The calculator makes it possible to roughly estimate the level of spending when using one or another type of heat insulator.

Stages of insulating the inner part of the roof

An important function of roof insulation is protection from atmospheric precipitation. To do this, you need to do the laying on the logs. Step-by-step thermal insulation algorithm:

• Design. The material is selected here, the required values ​​are calculated.
• Laying waterproofing on the rafters. It is fixed with bars of 3-5 cm, which can be placed parallel or perpendicularly. It is necessary to clarify in advance which side you need to lay the film, since on some varieties you can lay it with any part up. The contact points are connected with tape.
  
• Installation of a counter-lattice. It is done using boards or OSB boards. Next, you can do the installation of the roof.
• Insulation laying. It is better to take the width of the slabs with a margin of 2-3 cm for a snug fit into the cells from the rafters.
• Vapor barrier. It protects the roofing cake from moisture ingress. The contact points are glued with tape so that water does not get through the cracks.

When creating the structure, it is important to make ventilation gaps. Through them, excess moisture will be removed to the outside.