ᐅ Wall Construction – Timber Frame – Service Cavity – Questions
Created on: 17 Sep 2018 19:12
S
scooter121S
scooter12117 Sep 2018 19:12Hello,
we are currently planning the renovation of a typical prefabricated house from 1978 by Nordhaus.
The existing exterior wall construction is as follows (from inside to outside):
Gypsum plasterboard – chipboard (V100 – 13mm (0.5 inches)) – 100mm (4 inches) mineral wool insulation – chipboard (V100 – 13mm (0.5 inches)) – 16mm (0.6 inches) air gap – 8mm (0.3 inches) chipboard as cladding with plaster
Since we want to upgrade the electrical and building services installations, I am considering adding an installation cavity from the inside. My idea was to later insulate this cavity additionally with wood fiber boards (60mm (2.4 inches)). According to dew point calculations, this should not be a problem. My question is whether it is advisable to apply a vapor retarder before the "old" wall from the inside (i.e., in front of the first chipboard layer), or whether this could be counterproductive. The OSB board already acts partially as a vapor retarder. Or would the wood fiber insulation absorb moisture over time?
In another forum, I received responses suggesting there would be condensation with my proposed design (see below). However, no further replies have come in there. That’s why I’m trying my luck here.
The rule that the interior should be more airtight than the exterior should apply here. Could someone clarify what might be wrong with my approach? I have researched multiple times and always found wall assemblies similar to what I have planned:
Planned construction (from inside to outside):
Gypsum plasterboard – OSB3 18mm (0.7 inches) – installation cavity (filled with 60mm (2.4 inches) wood fiber boards) – chipboard (V100 – 13mm (0.5 inches)) – 100mm (4 inches) mineral wool insulation – chipboard (V100 – 13mm (0.5 inches)) – 16mm (0.6 inches) air gap – 8mm (0.3 inches) chipboard as cladding with plaster
Thanks in advance!
we are currently planning the renovation of a typical prefabricated house from 1978 by Nordhaus.
The existing exterior wall construction is as follows (from inside to outside):
Gypsum plasterboard – chipboard (V100 – 13mm (0.5 inches)) – 100mm (4 inches) mineral wool insulation – chipboard (V100 – 13mm (0.5 inches)) – 16mm (0.6 inches) air gap – 8mm (0.3 inches) chipboard as cladding with plaster
Since we want to upgrade the electrical and building services installations, I am considering adding an installation cavity from the inside. My idea was to later insulate this cavity additionally with wood fiber boards (60mm (2.4 inches)). According to dew point calculations, this should not be a problem. My question is whether it is advisable to apply a vapor retarder before the "old" wall from the inside (i.e., in front of the first chipboard layer), or whether this could be counterproductive. The OSB board already acts partially as a vapor retarder. Or would the wood fiber insulation absorb moisture over time?
In another forum, I received responses suggesting there would be condensation with my proposed design (see below). However, no further replies have come in there. That’s why I’m trying my luck here.
The rule that the interior should be more airtight than the exterior should apply here. Could someone clarify what might be wrong with my approach? I have researched multiple times and always found wall assemblies similar to what I have planned:
Planned construction (from inside to outside):
Gypsum plasterboard – OSB3 18mm (0.7 inches) – installation cavity (filled with 60mm (2.4 inches) wood fiber boards) – chipboard (V100 – 13mm (0.5 inches)) – 100mm (4 inches) mineral wool insulation – chipboard (V100 – 13mm (0.5 inches)) – 16mm (0.6 inches) air gap – 8mm (0.3 inches) chipboard as cladding with plaster
Thanks in advance!
OSB boards do act as vapor retarders, but not at the joints, and with the numerous openings for light switches and sockets, a significant amount of moisture can still pass through.
A vapor retarder with a low sd-value installed between the old wall structure and the installation layer is unlikely to cause any damage if the insulation is intact. With the division of 60/100 mm (2.4/4 inches) inside/outside, there should be no risk of dew point occurring. However, in a 40-year-old house, I would recommend checking the wall structure at a suitable location to ensure it is free of damage.
Otherwise, no one can guarantee that retrofitting without a vapor retarder on the interior side will not cause problems, and a solution without thermal bridges is, of course, to replace and double the existing insulation from the outside. Generally, this is not cost-effective with the existing wall structure.
A vapor retarder with a low sd-value installed between the old wall structure and the installation layer is unlikely to cause any damage if the insulation is intact. With the division of 60/100 mm (2.4/4 inches) inside/outside, there should be no risk of dew point occurring. However, in a 40-year-old house, I would recommend checking the wall structure at a suitable location to ensure it is free of damage.
Otherwise, no one can guarantee that retrofitting without a vapor retarder on the interior side will not cause problems, and a solution without thermal bridges is, of course, to replace and double the existing insulation from the outside. Generally, this is not cost-effective with the existing wall structure.
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