*3.4. Equivalent Energy—Building materials*

In order to develop this section, just one dwelling, the "wigwam", was considered. The original materials, which are summarized in Table 4, were assigned to it, and it was placed in the locations of New Mexico, where the pueblos were built.

This approach has made it possible to see that the elm bark sheets (from *Ulmus americana* L. or from *Ulmus rubra* Muhl.) which covered the Iroquois longhouses were the material that implied the highest amount of energy (Figures 8 and 9). The most abundant building material the natives who inhabited the forests of the Great Lakes region had at their disposal was wood. These forests, located both in Dfb and Cfa zones, according to Köppen scale, were full of coniferous trees, such as *Tsuga canadensis* (L.) Carrière or *Picea rubens* Sarg., and deciduous trees, such as *Quercus rubra* L or *Betula alleghaniensis* Britton. Besides, this region is characterized by a high ambient humidity, against which the bark tree provides a quality solution thanks to its waterproofing capacity.

**Figure 8.** Thermal characteristics of the original building materials. They were assigned to the same dwelling, whose openings were removed.

**Figure 9.** Indoor conditions in a dwelling whose openings were removed. All the analyzed building materials were assigned to it, and it was placed in the New Mexican locations.

Due to have the lowest thermal resistance of all of the materials that were analyzed, the bark sheets provide the most stable difference between the outdoor and the indoor conditions throughout the whole year. Unlike the other building materials, whose thermal resistance or effusivity is higher, this material neither stores heat nor offers a great resistance to its passage. Because of these reasons, it achieves a practically constant difference between the indoor and outdoor conditions throughout the year.

By observing Figures 5 and 8, it can be concluded that the amount of energy the wigwam envelope is equal to that of a timber frame superinsulated template (Figure 5) and is lower than the values obtained for the traditional materials in the same dwelling (Figure 8). The only exception is the case of wooden planks. This means that, contrary to the results obtained in previous researches about traditional architecture [79], traditional materials would have achieved better results than the present ones, if taking into account the energy they are equal to.

As can be seen in Figure 10, the transmittance (14) is the thermal characteristic more closely related to the equivalent energy (10 and 11). The second characteristic most related to it is the diffusivity (13). However, it is practically opposite to the effusivity (12). This means that the highest values of Δh (10 and 11) correspond to the highest values of transmittance (14).

**Figure 10.** Scatter graph. Links between the building materials and the equivalent energy.

Moreover, in this graph, it can be seen that the tree-bark envelope (V), the one used for coating the longhouses and the roofs of the plank houses, is influenced by both the effusivity (12) and the thermal transmittance (14). However, the grass house (GH) and the tipi (T), which have the next highest values of Δh (10), are related exclusively to the transmittance (14). Its location in the graph indicates definitively that this is the factor that influences Δh the most (10 and 11).

The envelopes composed of several layers, or with a high presence of earth, offer a higher resistance to the heat transfer. The consequence of this circumstance is that indoor temperatures are lower in summer, as are their differences with respect to the outdoor temperatures. Since these differences are lower, the amount of energy these envelopes are equivalent to is usually lower during the summer too.

However, the building material that is equivalent to the lowest amount of energy is the one that covers the plank house walls, the cedar planks. Again, it is a dwelling built in a region with high humidity levels due to its proximity to the coast. This territory corresponds to a region classified as Cfb by the Köppen scale, and there are four most abundant tree species in this rainy climate, located in the northwest of the United States: *Pseudotsuga menziesii* (Mirb.) Franco, T*suga heterophylla* (Raf.) Sarg., *Thuja plicata* Donn ex D. Don and *Fraxinus latifolia* Benth. Specifically, it was *Thuja plicata* Donn ex D. Don, or Canadian Western red cedar, the wood used for building, since it is coated with a special type of oil that makes it resistant to water, preventing it from rotting [80].

The wood planks correspond to one of the lowest values of heating speed (diffusivity), similar to the one of the bark sheets which comprise the envelope of the longhouse. Their capacity to store heat is very similar. The biggest difference between them concerns their thermal resistance, since the value corresponding to the plank house almost triples the one of the longhouse. Their heating speed is also reflected in the thermal lag that characterizes both materials (Table 4). The dissimilarity among them provokes that the size of the difference between the indoor and the outdoor temperatures depends on the period of the year.As can be seen in Figure 11, the tree bark keeps the indoor temperature higher than the outdoor temperature during the summer, whereas the temperature achieved by the wooden planks is almost the same as it. The thermal resistance of the wooden planks, higher than the one of the tree bark, ensures that the indoor temperature takes longer to change. This means that the indoor ambient is less vulnerable to the weather changes inside a plank house and that its thermal lag reaches a higher value.

**Figure 11.** Comparison between the outdoor and the indoor conditions generated in the same dwelling by the envelope of a longhouse and by the envelope of a plank house.

However, the higher speed the thermal wave passes through the bark strip at ensures that the difference of temperature between the outdoors and the indoors is almost constant throughout all the year. At the same time, the humidity level changes, since it decreases when the temperatures rises and rises when the temperatures decrease.
