Impact of Envelope Structure on the Solutions of Thermal Insulation from the Inside

K e y w o r d s : Prussian wall; Insulation from inside; Water content. 4/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 123 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 4/2018 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 8 0 5 9 B . O r l i k K o ż d o ń , A . S z y m a n o w s k a G w i ż d ż al solutions allow to effectively improve the thermal condition of building envelopes through internal insulation, provided that the existing condition is subjected to correctly carried out calculations preceded by detailed analyzes, taking into account the actual conditions of external climate or conditions involving the use of rooms [8, 9, 10]. An individual approach for such solutions should be adopted for buildings with inhomogeneous wall construction, e.g. walls made as a wooden frame with a brick filling, the socalled Prussian walls. Such structures were used at the turn of the 19th and 20th centuries also in the present areas of Upper Silesia [11, 12]. The objective of this publication is to present some selected elements of thermal diagnostics of historic buildings. In the form of a short review, the authors present the selected in-situ tests which were conducted for the building in question and its elements, i.e.: measuring surface moisture of the wall, its mass humidity, defining capillary absorption, thermographic diagnosis. Such a form of hygrothermal assessment before the start of thermal insulation works allows to optimize the selected thickness and the type of thermal insulation material. Basing on the modeling in the WUFI 2D program, water content in the selected wall elements was predicted, depending on the type and thickness of the insulation material. Also selected details of wall connections were presented, treated in this work as thermal bridges for which linear heat transfer coefficient and the risk of surface condensation were determined 2. DESIGN METHODOLOGY OF THERMAL INSULATION FROM THE INSIDE 2.1. Analyzed envelopes The subject of the authors’ research involves timberframed wall structures with a ceramic brick filling, referred to as Prussian wall. An example of such a half-timbered structure is the building of the existing State Music School, dated the beginning of the 20th century, located in Gliwice (Fig. 1). The frame structure was applied in the walls of the first floor, and the ground floor was made entirely of a brick wall. The rooms on the first floor contain a library and music rooms for students to practice. The structure of the envelopes made in Prussian wall technology in Silesia depended on where they were placed in the building. Residential and utility floors of multi-family buildings and public utility buildings (further floors) were made with the thickness of one brick. The timber frame (the most commonly used cross-sections of studs: 12/12 cm – 16/16 cm) visible from the façade’s side was filled with bricks and covered from the inside with a layer of bricks laid flat. The thickness of the envelope was approx. 25 cm. In unused attics or staircases, the walls were made with the thickness of 1/2 brick (12 cm). The fields within the wooden frame were left as brickwork structure or they were covered with layered plaster, often textured. Due to the historic character of many buildings, thermal insulation must be placed from the inside. Such a solution is not efficient in view of building physics. High thermal resistance of thermal insulation brings about a significant drop in the temperature of the wall from the inside and increases the risk of interstitial condensation of the diffusing water vapor. The research shows that with the mass moisture of wood at the level of over 20%, being persistent over longer time periods, there is a risk of biological corrosion [13, 14]. The extent of such moisture significantly increases insulation thickness [12, 13]. It is assumed that in the climatic conditions of Poland, the insulation thickness should not exceed 8 cm. The optimal thickness is 3 cm [13, 14]. 2.2. Classification of insulation methods from the inside When using interior wall insulation, we can choose three main solution concepts (Fig. 2): • Insulation from the inside, preventing the development of condensation. The literature [15] recommends that the value of the diffusively equivalent air layer thickness sd of the thermal insulation or the applied vapor barrier 124 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 4/2018 Figure 1. Prussian wall in the building of State Music School in Gliwice [11] I M PA C T O F E N V E L O P E S T R U C T U R E O N T H E S O L U T I O N S O F T H E R M A L I N S U L AT I O N F R O M T H E I N S I D E should exceed 1500 m. • Insulation from the inside, minimizing the development of condensation (Fig. 2a) The standard DIN 4108-3 [15] permits the use of diffusion resistance materials for which the diffusively equivalent air layer thickness sd is contained between 0.5 and 1500 m. Such large variation in the value of sd affects ambiguously the assessments involving the suitability of the applied thermal insulation. • Insulation from the inside, permitting the development of condensation, with provided justification or proof that the condensate formed during the unfavorable period evaporates during the calculation year (Fig. 2b) DIN 4108-3 [15] permits the use of materials for which diffusively equivalent air layer thickness sd is lower than 0.5 m. The thermal insulation materials used in such solutions are capillary-active and enable the developed condensate to accumulate in the material structure, without deterioration of their physical properties. The systems with vapor barrier from the inside prove most effective in buildings with high humidity. Since the diffusion of water vapor through the surface is completely blocked, possibly the highest efficiency of the ventilation system should be ensured. The envelopes in the Prussian wall system are characteristic of the presence of gaps between the frame and the adjacent elements, allowing the penetration of rainwater into the wall (Fig. 3). Studies have shown [17] that it can penetrate the wall to the depth of 20 cm. Such a phenomenon was described by Kozakiewicz [18], who also pointed to the aging processes and slow losses in the cross-section of wooden elements. C I V I L E N G I N E E R I N G e 4/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 125 a) Capillary-active method b) Method with vapour barrier Figure 2. Selected insulation methods from the inside for the Prussian wall [16] (1 – summer vapor diffusion flux, 2 – winter vapor diffusion flux, 3 – flux of slanting rain) Figure 3. Moistening with lashing rain and drying-out of the non-insulated Prussian wall c B . O r l i k K o ż d o ń , A . S z y m a n o w s k a G w i ż d ż The properties of external wall coatings in terms of rain protection are defined by their water absorption coefficients, equivalently thick layer of air sd and the product of both these quantities CRP [17]. Initially, the suggested CRP value was to be 0.1 [kg/m h0.5] [19]. However, most products and materials were not able to meet such criteria, and therefore the value was increased to 0.2 [kg/m h0.5]. For envelopes insulated from the inside, WTA guidelines recommend that CRP should not be higher than 0.1 [kg/m h0.5] with the Ww value not higher than 0.2 [kg/m2 h0.5] and sd lower than 1 m [17]. The explained earlier limit values and requirements for Ww and sd refer to water-resistant plaster and paint systems as defined in part 3 of the standard DIN 4108 [15]. In 2009, the document WTA – Merkblatt 6-4 2009-05 [20] has been published in which selected issues concerning the design of thermal insulation from the inside were presented. Such solutions lead to coolingout of the structural part of the wall, and hence they reduce the drying-out process of the existing structure. The presented procedure allows, in a simplified way, to estimate the correctness of the choice of a material solution, in terms of water absorption of the existing envelope and its outer layer. The first element of the procedure is to determine the impact of rain on the outer coating of the wall, i.e. to determine its water absorption expressed in Ww [kg / m2 h0.5]. If there is sufficient protection against rain in accordance with DIN 4108 [15], (part 3), it is usually sufficient. If the condition is not met, the following diagram is applied (Fig. 4) [20]. However, the diagram – methodology [20] can only be applied if: • the existing rain protection of the façade is efficient, the existing external wall has the thermal resistance of at least R 0.39 [(m2 K)/W] ; the normal climate prevails in the room, according to the definition given in WTA [20]; the average annual temperature of outside air exceeds 7°C, and the improvement of resistance ΔR should not exceed 2.5 or 2.0 [(m2 K)/W]. If one of these requirements is not met, detailed analyzes and calculations are required. 2.3. Material tests of wall elements The envelopes insulated from the inside require a detailed assessment of their interaction with additionally designed thermal insulation layers in terms of durability of the entire structure. 126 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 4/2018 Figure 4. Minimum requirements involving thermal insulation layer, depending on the thermal resistance of insulation for substrates characterized by different capillary activity [20] Figure 5. a) Making opencasts and collecting material for the wall from the room side; b) Measurement of surface humidity; c) Measurement of water absorbency of the wall a b c I M PA C T O F E N V E L O P E S T R U C T U R E O N T H E S O L U T I O N S O F T H E R M A L I N S U L AT I O N F R O M T H E I N S I D E The preparation of project documentation should be preceded by a tho