Study: material effectiveness depending on the installation location of windows and doors, based on their suitability for use in passive houses
The BBS Institute run by Prof. Dr.-Ing. H.-P. Leimer from Wolfenbüttel has completed an extensive study on this topic on behalf of HANNO.
In the introduction to a recently published study on employment impacts and training and qualification requirements in energy and building renovation, the Federal Environmental Agency found the following: 40% of energy consumed in Germany is used by buildings. Through appropriate measures, this energy consumption could be reduced by approx. 20% by the year 2020. Opportunities in building energy renovation, however, have certainly not been exhausted. Currently, building owners are only taking advantage of approx. 1/3 of the potential savings they could achieve through renovations. Because of this, the German federal government has identified building energy renovations as a key area activity, and plans increased funding activity in this area in the future. It is important, however, that such renovations are completed by appropriately trained technicians.
The question of how to seal door and window joints with long-lasting, energy-optimised seals is a key issue, and one that should be answered through scientific investigation. In the past, however, scientific findings on this subject have been lacking. The BBS Institute study undertakes to close this gap.
HANNO commissioned the BBS Institute of Prof. Dr.-Ing. H.-P. Leimer from Wolfenbüttel to answer the following questions from a scientific standpoint:
Optimising or minimising thermal bridges in energy optimised buildings is important. What role does window installation play in this context?
One key criteria is the air-tightness of the building envelope itself. How does this air-tightness change as the building is used over time, and while changing temperature loads impact the building and its joints?
Energy optimised buildings are designed to save energy over the long term. Joints that offer long-lasting functionality are important for window installation. How do these joints behave when exposed to long-term diffusion and convection loads?
Prof. Dipl.-Ing. H.-P. Leimer and Mr. Jan Schneider from the BBS Institute developed a concept to answer this question in collaboration with the Head of HANNO application engineering construction, Dipl.-Ing. (FH) Björn Kethorn, an expert in building damage caused by heat and moisture.
Energy assessments of construction joints
The BBS Institute used guidelines from the ift Rosenheim, ift-Richtlinie WA-15/2: Passivhaustauglichkeit von Fenstern, Außentüren und Fassaden [2] (Suitability for use in passive house windows, exterior doors and façades), specifically section 4.3, in its assessment, then completed calculations to assess the suitability of different products in the Hanno® 3-layer joint sealing system.
To evaluate different structures, the investigators selected two structures - a wall recess with clinker brick and a monolithic masonry wall with a composite thermal insulation system - from the Annex 1 of the ift guidelines WA-15/2. These structures were then each assessed with multiple sealing systems and different installation locations. The surface temperature Өsi, temperature factor fRsi and linear heat transmission coefficient Ψi were used as evaluation criteria.
The results indicate that good planning of thermal bridges can essentially eliminate calculated losses through such areas.
Influence on the thermal conductivity of sealing products with identical construction
The investigators noted differences of up to 0.4°C in surface temperatures Өsi. This is why HANNO indicates the thermal conductivity of all of our sealing materials. Even fractions of a degree can indicate relevant differences. Because of this, we provide the complete λ value of 0.0428 W/(m*K) for Hannoband®-3E - an outstanding result for a multifunctional tape.
Influence of the installation location of construction elements, depending on design
In a monolithic masonry wall with a composite thermal insulation system, the location on the structural wall may have a significant influence on the linear heat transmission coefficient ψi. From an energy assessment standpoint, it may be a good idea to insert structural elements into the insulation layer of the composite thermal insulation system. Thermal conductivity is a key factor in this area as well, although it is more important for the surrounding thermal insulation in addition to the sealing product.
Based on this knowledge, HANNO developed its Hanno® Flashing Tape DUO Easy as a system to fulfil sealing requirements while not restricting the surrounding thermal insulation materials.
Conclusion: all products available in the Hanno® 3-Layer Joint Sealing System are suitable for use in passive houses, thanks to their thermal conductivity properties.
Part 2 of the study investigated permanent air-tightness.
The study considered the following question: How does this air-tightness change as the building is used over time, and while changing temperature loads impact the building and its joints?
In general, window connection joints must be air-tight and sealed against driving rain, in order to prevent moisture from penetrating the structure. Expected movements were determined based purely on thermal expansion based on a defined PVC window with a profile length of 2.18 m, defined as 3 mm per joint side. Specialised test bodies were developed and constructed based on this 3 mm joint movement and fitted with 4 different sealing systems. The joint flanks of the test bodies were made of solid wood and sand-lime brick. Several test bodies were built for each sealing product, to determine the variance in measured values.
Three different products were installed in the window joints:
Joint sealing tape, using Hannoband®-BG1 in the testing.
Joint sealing tapes from stress group BG1 in accordance with DIN 18542, 2009 version, only needed to fulfil requirements for external air-tightness. However, the tape was also tested to determine how an air-permeable product would perform in an exterior seal in terms of air-tightness during joint movement.
Multifunctional tape, using Hannoband®-3E in the testing.
Multifunctional sealing tapes products are used in all three layers of the window seal, and are therefore directly responsible for the air-tightness of the joint itself.
Joint sealing tape, in this case Hanno® Flashing Tape Duo Easy.
Flashing tapes are air-tight by nature. The focus of the investigation was on using an elastic material, installing it “taut”, without the elastic reserve required in non-elastic systems, and therefore investigating its elasticity properties.
PU-based volume adhesive, designed with a product from a competitor.
The test was designed to show how such products behave in response to actual joint movement. Since the measurements used a test structure different from that used in normal joint testing in accordance with EN 1026, the measured values could not be compared with values from the standard testing. However, the investigators were able to compare the systems adequately.
Results show clear differences in stretched joints
While the initial joint of 15 mm showed only minor differences among the individual sealing products, the joint permeability coefficient was 10 times higher for PU-based volume adhesives.
Conclusion: The proven systems fulfilled the requirements easily. The products Hanno® Foil Tape Duo Easy and Hannoband® 3E multifunctional tape can be used in construction applications without restriction to ensure an airtight seal.
The alternative airtight sealing system was not able to fulfil the defined normal movement requirements for the test. It is not suitable as an independent, permanently air-tight seal.
How does this effect impact the joint and its moisture balance?
To answer this question, Prof. Dr.-Ing. H.-P. Leimer from the Wolfenbüttel BBS Institute completed a hygrothermal construction simulation calculation.
First, he completed the calculation for completely air-tight systems, with an a-value of 0.0, to see how the system would behave under only a diffusion load and to obtain a reference value. Second, the air permeability values from part 2 of the study were considered by extrapolating the behaviour of the joint over a period of 5 years.
This complex approach verified the influence of the continuous combination of diffusion and convection on building connection joints.
As expected, simply considering the diffusion effects and the theoretical assumption of 100% air-tightness, no harmful moisture build-up was found in the structure with any of the systems.
However, if the convection values are included in the calculations, systems using Hannoband® BG1, multifunctional band Hannoband®-3E and Hanno® Foil Tape DUO EASY show outstanding results. Material moisture in the joints was even reduced from its initial level. The PU-based volume adhesive seals considered in the study, in contrast, did result in leaks that caused moisture accumulation in the joint over years of use. Therefore, this solution should not be considered a permanent one and is not on its own a good alternative for creating an air-tight seal.