Representation of a thermally insulated building frame
When the thermal insulation is embedded in the exterior or the interior shell of the building and it is independent of the structural frame’s construction, the solution is clear and most of all effective. However, when the thermal insulation is placed on the exterior or the interior surface of the structural frame as part of the total thermal insulation as, for example, in buildings with masonry walls, various issues arise. These include thermal bridges but also constructional matters regarding earthquake resistant behaviour.
External blind wall with 2 bull stretchers
In masonry infills, thermal insulation is usually placed inside the masonry walls. A typical bond beam reinforcement is stirrups Ø6/150 and 2 to 4 Ø10 bars (depending on the bond’s width) in both the upper and lower part of the beam. The steel class may be B500A.
External blind wall with 1 bull stretcher and 1 stretcher
The most practical way to anchor the bond beams’ rebars inside the columns is by creating holes to the column sides and implanting starter bars by means of resin adhesives.
Eternal blind wall with 2 stretchers
The 120 mm thick wall when compared to the one with a thickness equal to 90 mm, has disadvantages such as higher cost, higher weight and a 120-90=30 mm reduction of the interior space. On the other hand, it has advantages such as better brick fitting, higher heat capacity (of the layer towards the inner face) and the possibility to embed electrical piping.
External wall with sliding frame
A simple way to create channels in the support faces of beams and columns is the use of a board or an extruded polystyrene strip 20 mm thick by 100 mm long.
Rules for choosing the correct thermal insulation thickness for the structural frame
An optimal technical solution is to use 30 mm thick thermal insulating boards in the columns and 50 mm thick boards in the beams. Moreover, the masonry should be built externally with a thickness equal to 120 mm.
Constructional problems
When a floor does not require thermal insulation e.g. pilotis or basement, extra attention must be paid to the vertical centring of columns to avoid having the columns of one floor placed outside the perimeter of the columns that belong to another floor. The next figure shows two columns that have a total cross-section 400/400, however, on the upper floor, the column has a 370/370 cross-section and a thermal insulation board with 30 mm thickness.
1st Solution: Construct a column larger in size and with larger stirrups
Drawbacks: The drawback in following this solution is the eccentricity of the column’s rebars and the need for bending them up at a large angle, something that entails a high degree of constructional difficulty.
2nd Solution: Repositioning of the column’s fixed spot to the edge of the thermal insulation thickness
Drawbacks: It requires constructional attention and may have possible architectonical side-effects due to the formation of an edge.
3rd Solution: Placement of unreinforced concrete (plain concrete) with a thickness equal to the insulation thickness
Drawbacks: A large concrete thickness with no reinforcement. This problem can be partially solved with the use of surface reinforcement and completely solved with the use of wire mesh when combined with the basement shear walls.
