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Building System

Building products that allow for extremely well insulated building envelope are already available.

Thermal bridges need to be included into the thermal design of the building envelope, but they should be avoided as far as possible. (PHI)

Internal floor connection that is practically impossible to be build air tight. The detail solution need to be redesigned for better airtightness.(VTT).
Wind barrier protects the thermal insulation layer from cold winds. Wind barrier is required in structures with ventilated facades, or withair permeable facades.

U-values

  • U–values of building components according to climate, including thermal bridges:
    • Wall 0,09 – 0,15 W/m2K
    • Floor 0,08 – 0,15 W/m2K
    • Roof 0,07 – 0,15 W/m2K
    • Window 0,8 – 1,0 W/m2K
    • Mounted window 0,6 – 0,85 W/m2K
    • Door 0,4 – 0,8 W/m2K
  • Air tightness n50 < 0,6 air changes per hour at 50 Pa pressure difference
  • Window solar transmittance g > 50%

The lower end U-values concern detached houses in Northern climates and the high end values Central European row or apartment houses.

Thermal bridges
Minimum amount of thermal bridges is crucial for the performance of the building. A thermal bridge is typically a building part that penetrates thermal insulation and that has substantially higher thermal conductivity than the thermal insulation. The window or door to wall, wall to floor, and wall to roof connections may have thermal bridges, and these details should be considered carefully. A thermal bridge increases heat loss through the structure, and in some extreme cases this may cause surface condensation or interstitial condensation into the structure. Surface mold growth or wood rot may be the consequences of a thermal bridge.

Linear thermal conductance in these connections should not exceed 0.01 W/mK. The relative effect of a thermal bridge increases according to increasing insulation level.

The design team should consider window dimensions and frame structure distances. If the window dimensions do not fit the dimensions and the distances of the frame system, extra studs are required for window support and inner boarding installations in wooden structures. Architect and structural designer should together decide the window dimensions to find effective solutions. Also, in a wooden building envelope a number of frame studs are unnecessary, e.g. in corner details, and window and door connections. Especially in corner details an easy solution is to add frame members for fastening of inner and outer boards and other structures. These extra frames are thermal bridges that should be avoided.

Air tightness

  • A material layer that has an air permeability of 1 x 10-6 m3/m2 s Pa maximum, including all joints perform as air barriers, e.g., plastic film vapour barrier, building paper, concrete element structures with sealed joints, or fair-faced inner brick walls with plaster. Air barrier needs to be continuous over the whole building envelope.
  • Electrical installations should be surface installations, or in any case inside the air barrier. To help for electrical installations the air barrier may locate not more than 50 mm inside the insulation layer. In general the use of conduit spaces in front of the air barrier can be recommended (either insulated or not).
  • Window or door frame to wall connection should be filled with insulation, and sealed from both sides. Use of positioning systems help for installation of heavy windows and to provide good connection with the structure, or to integrate the windows in a prefabricated wall system.
  • Ventilation ductwork installation should be inside the air barrier. Only fresh air and exhaust air ducts need to penetrate the air barrier
  • The HVAC and sanitary installations and service penetrations of electricity, water, gas, and etc. systems should be sealed using flanges or other means of tightening

Wind tightness

  • A material layer that has a air permeability of 3 10-6 m3/m2 s Pa maximum, including all the joints
  • Wood fibre, gypsum or other board with sealed joints on top of the framing
  • Exterior insulation composite system with rendering
  • Wind proof mineral wool or EPS insulation with sealed joints
  • Fair-faced brick wall without air gaps between insulation and brick wall