Frame wall insulation question

[jraabe]

Question from Limey:

I have a query about thermal insulation. I'm assuming that insulating material is placed between the vertical studs of 4x2 or 6x2 and then is sandwiched between plywood on the outside and plasterboard on the inside. Fine and seems efficient. However, surely you'll get 'cold spots' where the vertical studs are because heat conduction will be different at the studs than the insulated cavity. Also, have you encountered interstitiual condensation whereby vapour condenses in the cavity between the external plywood and internal plaster board. Any help or advice would be most welcome.
     

[jraabe]

Yes, the conduction through the studs is greater than through the insulated cavity. This is why a redundant (2nd) layer of insulation such a 1" foam sheathing is such a wise upgrade to a frame wall as it insulates the framing and all those tiny voids that are inevitable when installing batt insulation.

Framing lumber is a bit less than an R-1 per inch. So a 2x4 wall is about an R-3 and 2x6 R-5 at the studs and plates.

[JRR]

Another old trick is to stagger ("offset") the studs creating greater wall thickness.  Strips of filler foam can be attached to the inner edges of the studs, flushing out the cavity thickness.  This will all but eliminate high heat transmission thru the studs.  Then comes the cheaper fibre-glass or cellulose insulation to finish filling the cavity.

If cellulose is used, attic access to the wall cavity must be provided for an occasional "top-off".

[glenn-k]

Your staggered studs also cut down on noise traveling from one room to the next, JRR.

My wife thinks I should use them in the bathroom.  :-/    

[jraabe]

JRR's suggestion is a good one - and time tested for both sound proofing and better thermal insulation.

Here is a quick diagram:



It does use a bit more wood than a standard 2x6 wall and both interior and exterior wall finishes must be able to span the 24" stud spacing.