Planeación

The first class distinction is made for houses constructed before and after 1956. This distinction represents the introduction of mineral wool as common thermal insulation material in new houses.

The transition to better insulated constructions occurred gradually over a time period of almost ten years. However, for practical reasons, it is assumed to have taken place at the turn of the year 1955/19568. Thus, houses constructed before 1956 are for modelling purposes presumed originally constructed without mineral wool in the outer

constructions.

There were three main reasons for the transition to the better insulated constructions in the middle of the 1950s:

• reduced production costs for constructions with mineral wool as thermal insulation material,

• favouring of wood saving constructions by the authorities,

• lending terms in the Norwegian National Housing Bank.

These three factors are discussed more detailed in the following sections. Reduced production costs for constructions with mineral wool

The production of mineral wool in Norway began in 1935 (glass wool) and 1945 (rock wool). The quality of these insulation materials gradually improved, especially after the introduction of new production processes in the beginning of the 1960s (Granum and Larsen, 1989).

When introduced, mineral wool was rather expensive used as thermal insulation material. However, the price of mineral wool compared to alternative insulation materials became favourable in the 1950s. From the beginning of the 1950s, it was considered profitable to use mineral wool in both tier of beams and timber framed walls. Granum and Lundby (1952) established in 1952 that the most used thermal insulation materials in tier of beams at that time were rock wool felt and glass wool mats, and that old filling materials as clay and sawdust were totally outclassed as thermal insulation materials.

In 1953, 24 000 tons of mineral wool were produced in Norway, and in 1959, the amount had increased to 32 000 tons (Granum and Lundby, 1961). Of the total utility floor space in all buildings completed in 1953 and 1959, dwellings represented 68% and 56%, respectively (NOS C188, 1995). Since large buildings at that time were commonly constructed without mineral wool in the outer constructions, it can be assumed that a large share of the total volume of mineral wool produced these years was used in the construction of dwellings.

In the end of the 1950s, most houses were constructed with mineral wool in the outer constructions. If the entire production of mineral wool in 1959 is divided by the 26 600 dwellings completed that year, an average of approximately 1.2 tons of mineral wool per dwelling is obtained. For 1953, the corresponding numbers are 35 000 completed

dwellings and an average of 0.7 tons of mineral wool per dwelling. These numbers indicate that also a large share of the dwellings constructed in the beginning of the 1950s must have been constructed with mineral wool in the outer constructions.

In the beginning of the 1950s, only 50 mm and 100 mm of mineral wool were commonly used as insulation layer in floors. The thickness of the insulation layer soon increased, and around 1960 it was recommended to fill the entire cavity with mineral wool; normally implying 200 mm of mineral wool. As shown in Table 3.12, the insulation levels recommended by the Norwegian Building Research Institute have shown a steady increase over the period from 1952 to 1980.

For walls, the transition to mineral wool did not happen as rapidly as for tier of beams. Traditional uninsulated hollow-space framed walls with two layers of cladding and two layers of cardboard on each side of the cavity were still in use in the end of the 1950s, despite the poor thermal insulation performance of these constructions (U-values between 0.8 to 1.1 W/m2K).

The U-value of 100 mm (4") light timber framed walls with 100 mm mineral wool is around 0.4 W/m2K and thus notably better than the U-values of the traditional

uninsulated constructions. In addition, from the autumn of 1955, the production costs of light timber framed walls with 100 mm mineral wool were lower than the production costs of the traditional constructions (NBI anv. 7, 1958).

The reduced production costs and higher thermal insulation level of the insulated 100 mm light timber framed walls made these constructions more profitable as compared to the traditional constructions. Therefore, from the end of the 1950s, 100 mm light timber framed constructions with mineral wool were totally dominating as wall construction in Norwegian houses. In addition to the better profitability of the light timber framed

constructions, favouring of wood saving constructions by the authorities in the 1950s, and also the lending terms in the Norwegian National Housing Bank, influenced the spreading of these constructions.

Favouring of wood saving constructions by the authorities

There was a major lack of dwellings in Norway in the post-war years. During the war, 22 000 dwellings had been destroyed, and the need for new dwellings was estimated to be between 80 000 and 90 000 units. This number soon increased. In 1948, the need for new dwellings was estimated to be 100 000 units, increasing to 125 000 units in 1950

(Martens, 1993).

In the years after the war, the construction of new houses was strictly regulated through

Table 3.12. Thermal insulation thicknesses for wooden houses recommended by the Norwegian Building Research Institute and commonly practised thicknesses by year of reference. Based on Granum and Lundby (1952, 1958, 1961 and 1964); Aschehoug et al. (1970) and Edvardsen et al. (1980).

Year Outer walls Tier of beams

towards cold attic

Tier of beams towards basement Recom- mended Common practice Recom- mended Common practice Recom- mended Common practice mm mm mm mm mm mm 1952 100 - - - - - 1958 100 - 150 - 50-100 - 1961 100-150 - 200 50-100 150 - 1964 100 200 - 150 50-100 1970 100-150 - - - 150 - 1982 150-200 - 200-300 - - -

in each municipality (Granum and Larsen, 1989). Not only the construction of new houses was restricted in this period. Because of shortage of resources, building materials were also rationed. However, this rationing was abolished by the end of 1955.

About 50% of the timber produced was exported in the early post war years to help the payment balance. From around 1950, when the Korean-War resulted in prosperous times for the timber-trade, as much as two-thirds of the timber were exported. A result of this export was however shortage of timber for inland use. Timber was therefore rationed until 1953, and the timber prices controlled until 1958 (Granum and Larsen, 1989). The authorities also favoured wood saving constructions by giving new houses constructed with such constructions only 50% weight in the building quotas system.

However, the favouring of wood saving light timber framed walls was removed in 1953. This resulted in a significant shift towards more traditional constructions. It also resulted in a reduced share of houses with high quality thermal insulation. To counteract this effect, actions were taken by the Norwegian National Housing Bank to increase the number of houses constructed with insulated light timber framed constructions. The Norwegian National Housing Bank

The Norwegian National Housing Bank was established in 1946 to help the financing of new houses. The main goal for the bank was to regulate the total consumption of

resources in the housing sector and to ensure the quality of new dwellings. This way the bank became the main housing political tool of the Norwegian Government.

In addition to the Housing Bank, "Noregs Småbruk- og Bustadbank" financed between 10% and 15% of all dwellings constructed between 1945 and 1965. This bank operated in the districts and the directing lines were similar to those of the Housing Bank. The two banks merged in 1966. (Granum and Larsen, 1989).

During the 1950s, these two banks jointly financed almost 75% of all new dwellings in Norway. Between 70% and 80% of the total number of dwellings constructed during these years were located in detached one-family houses or small divided houses (NOS C188, 1995). The dominating part of these houses were wooden houses. The percentage of the wooden houses financed by the Housing Bank which were fully insulated, may therefore be assumed to be representative for the entire dwelling stock in the 1950s. In 1953, the favouring of light timber framed constructions in the building quotas was removed. This resulted in a significant and undesired shift towards more traditional constructions. To compensate for this, the Housing Bank offered larger loans from January 1957 for new houses provided with highly insulating materials. To obtain larger loans, the thermal conductance of walls and roofing had to be below or equal to 0.4 W/m2K (Granum and Larsen, 1989). This rapidly increased the share of houses with insulated timber framed walls. Table 3.13 shows that only 27% of the dwellings in wooden houses financed by the Housing Bank in 1956 used mineral wool in the outer walls. This share increased to 96% in 1961. The Housing Bank also promoted wood

saving constructions by designing a number of standard houses which could be erected using light timber framed constructions.

One of the goals for the Housing Bank was to support construction of houses for families with limited economic resources. Consequently, houses erected by the more wealthy part of the population were not financed by the Housing Bank. The standard of these private financed houses may therefore be expected to be higher, as compared to the general standard of the factual Housing Bank-houses. Some of these private financed houses may have been constructed as concrete or brick houses with limited thermal insulation in the outer walls. However, it is not likely that the insulation of these privately financed houses were of lower quality in average, as compared to the houses financed by the Housing Bank.