High Thermal Mass Envelope

The massive walls comprising the conservative component of the prototype engage the larger part of the envelope. The high thermal mass envelope was developed with the aid of the Trees and Timber Institute (IVALSA) of Trento, Italy. Local, “green” certified building materials were used: cross-laminated (X-Lam) panels made out of spruce wood, and wood based insulation.

Thermal inertia is a key attribute that confines the thermal capacity of the envelope. Good lagging preserves the interior conditions: conserves heat during the winter and prevents from excessive heat during the summer.

The interaction of the thermal properties of the building materials, their dissimilar response in unexpected temperature swings and user preferences, greatly affect the overall energy performance.

Calculating the thermal capacity of the different material parts of the envelope (base, walls, roof, etc.) enabled to determine the optimal pattern of heat flow in the interior. We thus simulated how heat is stored in the house components during the day (from solar gain or HVAC system) and use the information to calculate how we can maintain the desired thermal comfort levels during the night.

The house envelope is prefabricated, using a system of cross-laminated (X-Lam) panels for the load-bearing parts. The X-Lam timber is a rigid yet lightweight product that meets industrial standards and it is sustainable.

This structural system demonstrates how it is possible to use wood, a natural material, to build contemporary, prefabricated, high-tech structures, in a way that is more economical, light, and environment-friendly than conventional construction.

The prefabricated, modular envelope, includes the modules of the base and the modules of the house.

Base
The base is a massive, void, wooden container, filled with insulating material. It insulates the house interior, it conserves heat, and it transfers the loads of the structure to the ground. The base includes 3 transportable modules that are joined with threaded bars and 2 side components.

The structural material of the base is X-Lam panel of 174 mm thickness. The side components are exposed to the natural elements, and are constructed with Glulam GL28 class. The side components are connected to the X-Lam panels of the two extreme modules with hold-down elements and the tightening is made with screws of type HBS.

X-Lam panels of 51 mm thickness, cover all the parts of each base module and function as a support for the remaining structure. On the top of each base module, rests a house module, and on the overall base rests the whole house.

House
Each house module is approached as a structurally independent, self-standing box, with its sides oriented towards north, south, east and west, respectively. It is open from south, west and east, and it is closed from north, top and bottom. The structural components of each module (floor, north wall and roof) involve three X-Lam panels of variable thickness.

The bottom structural panel, which rests on the base of the house, is made of an X-Lam panel of 174 mm thickness. The vertical structural panel, of the north wall, is made of an X-Lam panel, of 135 mm thickness. The structural panel of the roof, is made of an X-Lam panel of 105 mm thickness.

The north wall is further enforced by vertical elements in Glulam, 140 x 180 mm in section. The Glulam is joined to the X-Lam panel with angular steel plates and hold-down. The X-Lam panels of the wall, floor, and roof, are connected by means of metal angles, ringed annular shacked nails and self-drilling screws.

The thermal conservation features of the envelope are of paramount importance for the performance of the house. They are assured by a multi-layered system of materials, where each layer serves a specific purpose.

The walls are 72 cm in thickness to secure high-level heat transmission resistance. Both the house walls and roof have a theoretical calculated value of U equal to 0.150 W / m^2 K, thus making the house envelope complying to the standards of a passive house.

The interior side of the vertical wall is covered with a double layer of fiber gypsum panels. This material improves the acoustic insulation and augments the collapse time, in case of fire. The air gap between the fiber gypsum slab and X-Lam panel improves the acoustic and thermal insulation.

The next layer of materials includes a double sheet of insulating panels made of fiber wood. Each of these sheets has different density. The first layer of lower density panels improves the thermal insulation, and the second layer of higher density panels improves the acoustic insulation.

A breathable barrier film ensures the protection from the external humidity, while it remains permeable to air and humidity from the inside out. This film guarantees the natural transpiration of the wall and prevents the formation of interstitial condensation during the winter.

The exterior layer of the wall is a cover of ventilated double board warping and larch trapezoidal cladding. The cover of the roof has the same insulation with the wall. Above the ventilation chamber, is placed a wooden Osb panel on which is nailed a corrugated, pre-painted aluminum sheet. This plate collects the rainwater into the gutter.

The roof cover is made of Larch wood similar to the external skin of the house. The roof tiles are spaced appropriately, to ensure the good ventilation of the roof and the collection of the rainwater.

Reference
Kotsopoulos, SD, Farina, C, Casalegno, F, Briani, A, Simeone, P, Bindinelli, R, Pasetto, G, 2012, “A Building System for Connected Sustainability”, Proceedings of the World Conference on Timber Engineering (WCTE2012), University of Auckland, New Zealand Timber Design Society, pp. 270-279.

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