Exterior wall becomes interior wall; plastic or not?

[Åbacka]

Planning to expand with a large family room. The old exterior wall will thus become an interior wall for this section. The old half brick is to be removed and replaced with studs to allow for some electrical work. The old house doesn't have a vapor barrier in the walls (and hardly any insulation, for that matter). So the question is:

I plan to build the extension in a modern way, with plastic according to all the rules. But can I put plastic on the old exterior wall, i.e., on the plank wall that remains when the brick is removed? The house currently has natural ventilation. Is it enough to install a fresh air vent in the extension? Is any additional exhaust vent needed?

VERY grateful for opinions...

 

[norrbottenstorpet]

Plastic between two connected, open, and heated building sections has no function. The plastic is usually placed on the warm side to prevent moisture transport out through the wall and condensation at the dew point.

How is the natural ventilation currently constructed, a chimney? In such cases, you should reasonably have one or several smaller low-lying intake vents that create a draft and up out through the chimney channel?

 

[Åbacka]

Thank you for the answer. Yes, I have come to the same conclusion. But, low-placed supply air vents? Aren't they usually mounted at the top of a window?

 

[norrbottenstorpet]

Yes sometimes, but even better low behind the radiators. A diagonal flow from low to high provides good natural ventilation.