The requirements in Building Regulations for Small Dwellings can be met by choosing construction elements with U-values lower than or equal to those listed in table 10 and at the same time ensuring that the total area of windows and external doors does not exceed 22 per cent of the total heated floor area of the house. Examples of constructions fulfilling these U-value requirements, are shown in the previous chapters.
Table 10 Building Regulations for Small Dwellings: U-value requirements for construction elements surrounding heated rooms.ψ-value requirements acc. to DS 418
Usually it is assumed that all rooms in single family houses are heated to a minimum of 18oC. Exempted from this rule are rooms in basement, porches and enclosed patios.
When rooms are heated to temperatures between 5 and 18oC the minimum requirements concerning thermal insulation are applicable, see table 11. There are no limitations as to the areas of windows and external doors in such rooms.
The heated floor area is calculated as described in the following.
External walls with a mass below 100 kg/m2 are termed “light external walls”. All other walls are termed “heavy external walls”. When calculating the mass of the external walls only the part of the construction that is placed on the inside of any
Table 11. Building Regulations for Small Dwellings: Requirements to minimum thermal insulation of all heated rooms. ψ-value requirements according to DS 418
Figure 83. The area of windows and external doors is calculated on the basis of the dimensions of the wall opening. The dimension of the window or the door is smaller than the opening.
When calculating the area of windows and external doors only the area of windows and doors towards the outside is included. The area of windows and doors facing unheated or partially heated rooms is not included.
Construction element U W/m2K External walls
with mass below 100 kg/m2 0.20 External walls with mass above100
kg/m2 and basement external walls
under ground 0.30
Partition walls and storey partitions
adjacent to unheated rooms 0.40 Ground supported floors, basement
floors, storey partitions towards the
outside and ventilated crawl spaces. 0.20 Ground supported floors, basement
floors, storey partitions towards the outside and ventilated crawl spaces
with floor heating.
0.15 Attic and roof constructions
Including walls between attic and
wasted attic space 0.15 Flat roofs and sloping walls
directly against roof 0.20 Windows and external doors, sky
lights, glass walls and hatches. 1.80 ψ W/m K Foundations
Foundations surrounding floors with floorheating
0.25 0.20 Joint between external wall and
windows/ext.doors, glass walls, gates or hatches
Joint between roof construction and windows in roof or skylights
0.03 0.10 (There are no specific U-value requirements to ventilation openings, smaller than 500 cm2).
Construction element U W/m2K External walls
with mass below 100 kg/m2 0.30 External walls with mass above100
kg/m2 and basement external walls
under ground 0.40
Partition walls and storey partitions
adjacent to unheated rooms 0.60 Ground supported floors, basement
floors, storey partitions towards the outside and ventilated crawl spaces
irrespective of floor heating 0.30 Attic and roof constructions
Including walls between attic and
wasted attic space 0.25 Flat roofs and sloping walls
directly against roof 0.25 Windows and external doors,
skylights, glass walls and hatches. 2.90 ψ W/m K Foundations, irrespective of floor
heating 0.60
Joint between external wall and windows/ext.doors, glass walls, gates or hatches
Joint between roof construction and windows in roof or skylights
0.10 0.30
SBI Direction 189
KLJ 72
porches and enclosed patios. In Building Regulations for Small Dwellings there are no requirements for heating. Consequently it is possible to include or exclude unheated and partially heated rooms when calculating the heated floor area – provided they are thermally insulated as if they were heated rooms.
The heated footprint is calculated as the projection of the heated floor area on a horizontal plane, see figure 84.
The heated floor area of a building is calculated as described under “floor area” in Building Regulations for Small Dwellings, enclosure A. The heated floor area of a building shall be calculated by adding the gross areas of all heated storeys including heated basements and attics. The gross floor area shall be measured in a plane defined by the topside of the finished floor to the outer surface of the surrounding external walls. In habitable attics the area to be included shall be measured at a horizontal plane 1.5 m above the finished floor, to where the plane meets the outer surface of the roof covering. In the case of partition walls between rooms whose areas are to be included in their respective storey areas, the areas shall be measured to the middle of the wall. A room that stretches through several storeys shall only be included in the storey in which the floor of the room is situated. However, stairs and stairways are included in each storey.
Heat Loss Frame.
Construction elements may have a higher U- value then the ones stated in table 10, and the total area of windows and external doors
towards the outside may exceed 22 per cent of the heated floor area provided the total design heat loss through transmission falls within the so-called Heat Loss Frame.
This means that the design heat loss (through transmission) shall be less than the heat loss from a similar reference house where the U- values of the construction elements fulfil requirements in table 10 and where the window and external door area constitutes 22 percent of the heated floor area.
The U-values shall, however, not be higher than stated in table 11.
In the subsequent paragraphs some essential extracts and rules from DS 418: “Calculation of Heat Loss from Buildings” are reproduced. The rules are used when calculating the Heat Loss Frame for single family houses.
Temperatures
A constant room temperature is used when calculating, usually 20oC – also in bathrooms and behind radiators. In rooms with floor heating the temperature in the floor construction is normally set at 30oC in the plane of the heating source but in principle it depends on the dimensioning of the floor heating system. The same temperature is used when determining the heat loss through foundations surrounding constructions with floor heating. It must be stressed that the temperature in the plane of the heating source is somewhat lower than the mean temperature in the supply pipes for the floor heating system.
The design outside temperature is usually -12oC - also for basement walls. The design soil temperature is 10oC and is used e.g. when calculating ground supported floors and basement floors. The design temperature in ventilated crawl spaces is set at -5oC. In unheated rooms the temperature may be set by estimation or calculated by the use of the heat balance.
Figure 84. Calculating the heated footprint area
Transmission areas
Transmission areas for external walls, floors and roofs are determined pretending partition walls are non-existent.
The transmission area for external walls is measured from the top side of the ground supported floor to the topside of the insulation in the ceiling or in the roof. In the existence of an unheated basement or a crawl space, the measurement is from the underside of the floor partition. At the corners the measurement is calculated from the external side of connecting walls.
In ground supported floors the area is calculated based on internal measurements (the inside of the external wall). In ground suspended floors above basements and crawl spaces and in ceilings and roofs the transmission area is calculated based the measurements from outside wall to outside wall. When calculating unheated attics the area of the ceiling is used. Basement walls against the ground
Figure T4 shows the principles of the mentioned bracing and anchoring possibilities
outside ground level.
Transmission areas of windows and doors are calculated on the basis of the wall openings.
The length of the foundations is determined by the external perimeter. Length of joints between window/wall and door/wall is determined by the perimeter of the wall opening
.
When calculating the heat losses it is imperative that the distribution of construction elements in the house in question corresponds to that of the
house of reference. There must, for example, be a similar distribution of light and heavy external walls, of flat roofs, of sloping walls, of ceiling constructions against attic and of windows towards the open and towards unheated rooms. If, for instance, the Heat Loss Frame is used in order to make a window bigger then, the area of the construction element in which the window is placed shall be made equivalently smaller.
Possibilities and advantages of using the Heat Loss Frame
The Heat Loss Frame can, among other things, be used in order to increase the area of the windows and external doors in excess of 22 percent of the heated floor area normally accepted.
Figure 85 refers to a house with light external walls and shows the relationship between the area of the windows and the external doors as a percentage of the heated floor area compared with the U-values of windows, doors and external walls. In figure 86 the same situation is shown for a house with heavy external walls. The elaboration of the graphs is based on the U-value requirements stated in the Building Regulations for Small Dwellings (indicated on the graph). The figures can be used when evaluating possibilities before calculating the Heat Loss Frame. Interpreting figure 86, for example, it is possible to deduce that the area of windows and external doors may be increased to 25 per cent of the heated floor area, provided windows and doors
U -values of windows and e xternal door s W/m 2 K