Technical-Economic Research for Passive Buildings

Ruta Miniotaite

#### Abstract

The Energy Performance of Buildings Directive (EPBD) 61 requires all new public buildings to become near-zero-energy buildings by 2019 which will be extended to all new buildings by 2021. This concept involves sustainable, highquality, valuable, healthy and durable construction. Foundation, walls and roofs are the most essential elements of a house. The type of foundation for a private house is selected considering many factors. The article examines technological and structural solutions for passive building foundation, walls and roofs. The technicaleconomic comparison of the main structures of a passive house revealed that it is cheaper to install an adequately designed concrete slab foundation than to build strip or pile foundation and the floor separately. Timber stud walls are the cheapest wall option for a passive house and 45–51% cheaper than other options. The comparison of roofs and ceilings showed that insulation of the ceiling is 25% more efficient than insulation of the roof. The comparison of the main envelope element efficiency by multiple-criteria evaluation methods showed that it is economically feasible to install concrete slab on ground foundation, stud walls with sheet cladding and a pitched roof with insulated ceiling.

Keywords: passive house, foundation, walls, roof, technological solutions, multiple-criteria evaluation

#### 1. Introduction

A passive house is not a new method of construction. It differs from ordinary houses by good thermal insulation, high-quality windows and heat recovery ventilation system. All these features lead to the lower demand for thermal energy. The Energy Performance of Buildings Directive (EPBD) 61 requires all new public buildings to become near-zero-energy buildings by 2019 which will be extended to all new buildings by 2021 [1]. A passive house becomes a standard for energyefficient buildings [2]. The problem in modelling a passive house occurs when investment into construction is estimated and the payback period for investment is calculated. The payback period depends on thermal energy price, which is difficult to forecast. Therefore a house of lower energy efficiency class is a less risky investment for an individual builder [3–5].

A passive house is the building with very low energy demand and uses only onefourth or even less energy compared to the conventional buildings. Usually, passive houses do not have separate heating systems. Regenerative ventilation system is enough. The primary idea of such a house is to reduce the energy demand and at the same time maintain comfortable microclimate inside. The effectiveness of a passive house is based on the efficient thermal insulation and higher tightness of envelope components. A passive house is the concept (method) of construction applied in practice. A passive house is a standard widely used in constructing energy-saving buildings. A newly constructed passive house must save 80% of heat resources; otherwise it is not a passive house. The heating energy demand of a passive building is less than 15 k Wh/m2 per year. However, a passive house is something more than just an energy-saving house [5–9]. This concept involves sustainable, high-quality, valuable, healthy and durable construction. Features of a passive house are the following: high insulation of envelope components, high-quality windows, good tightness of the building, regenerative ventilation system and elimination of thermal bridges. The recommended architectural solutions are simple forms, less angles in order to avoid the development of thermal bridges at the joints. The most effective form of the house is the one with the smallest area of external walls. For these reasons it is easier to build a house of bigger floor area meeting the passive house criteria because the area of external wall and thermal bridges is smaller than the useful floor area of the building. A passive house should have no basement; otherwise the basement must be well insulated. Besides, it is recommended to plan as many windows on the southern façade in order to use more natural solar energy. Windows must be made of special frames filled with double-chamber selective glass units. The site also has a significant effect on the energy demand by the building. Shadows from the neighbouring buildings must be considered when building a house in the district where tall buildings prevail. Water may be heated by electricity; however solar panels are recommended. Combination solar wind power generation units are recommended to produce electricity for lighting and regenerative systems as well as for household needs [10, 11]. This article examines technological and structural solutions for passive buildings' main structures.

of foundations (e.g. pile foundation), which is necessary while building a house on weak, expanding or watery soil. Strip foundation is generally selected due to simple

Pile foundation distributes the load of the building via pile cap and sides; therefore the stress propagates across the big volume of soil. Pile foundations do not sink much and have a high load-bearing capacity; thus they are suitable for buildings

As the piles are driven deep into the ground, it is impossible to fully insulate the entire foundation. Thermal bridges occur at the pole and grade beam joints, and

A monolithic slab is a one-piece load-bearing foundation structure. Concrete is poured into special polystyrene foam forms that completely isolate the foundation slab from direct contact with the soil. It is the single type of foundation where the load-bearing monolithic slab has no contact with the soil and has the highest thermal resistance value. The thermal resistance value R of this foundation may be as high as 9.7 (R = 9.7 m<sup>2</sup> K/W) and higher. Thus, thermal bridges, frost and foundation deformations are avoided. The monolithic slab bears the load of the building across the entire plane rather than individual segments. The monolithic slab has from 3 to 20 times bigger supporting area than conventional foundations. For this reason it is less susceptible to movement and is firm and stable. All traditional foundation structures create thermal bridges because there are no structural possibilities to avoid them. Monolithic slab is the only exception where the entire concrete slab can be thermally insulated at 100%. A properly installed slab has no thermal bridges, and the main advantage of this foundation is high thermal resis-

Estimate calculations of strip, pile and monolithic slab foundations are done. A private two-storey house is selected for the calculation. The calculated foundation

Double-stud wall structure significantly decreases the formation of thermal bridges and enables to diminish the weight of the entire structure. Thermal insulation layer is installed inside the double stud without an additional frame. The insulation layer thickness may vary depending on the required heat transfer factor U value. Thermal insulation made of PAROC WAS 25t sheets simultaneously serves as a wind barrier. This layer is fixed onto the studs. It is one of the best structures for a passive house (Figure 1a). An auxiliary frame on the internal side is required to install a tight vapour insulation, which in this system also serves as an air barrier. The vapour insulation is installed between the auxiliary internal frame and the thermal insulation layer in the middle. For this reason the engineering systems installed in the wall structure will not damage the tightness of the insulation layer. Four hundred and twenty millimetres of thick thermal insulation layer enables to

. Labour, materials, machinery and total costs for foundation installa-

construction method, regardless the longer time required to build it.

they deteriorate the heat conservation capacity of the building.

2.1.2 Pile foundation

2.1.3 Monolithic slab

tance and tightness.

tion are calculated.

2.2 Alternative solutions for walls

2.2.1 Timber stud wall with sheet cladding

achieve the U value ≤ 0.09 W/(m<sup>2</sup> K) [12].

area is 110 m<sup>2</sup>

107

that are sensitive to subsidence.

Technical-Economic Research for Passive Buildings DOI: http://dx.doi.org/10.5772/intechopen.85992
