Retrofit of Drainage Plane in Old House

by Julie

Creation of a drainage plane from the inside:

  • To catch the bulk moisture, we installed a rain screen between the studs on the inside. It ran down from the top plate, below the floor joists and draped the outside of sill.
  • Blocking was placed between the studs at the floor level to close off the opening under the house.
  • Behind the rain screen, we fit 1″ rigid foam board tightly between each stud. At that point, there was an overall R-value in the walls of about 10.38.
  • For additional thermal benefits and to seal any air gaps, we sprayed open-cell spray foam which raised the overall R-value of the walls to 19.
  • Paperless drywall was then installed.

This approach solved most moisture intrusion issues as well as providing for a good thermal barrier.  By creating a tight air barrier it allowed us to correctly size the HVAC equipment using Manual J. Since the HVAC equipment and ductwork were located within a semi-conditioned, un-vented attic space we were able to decrease the size of the units even further.  This will also help prevent any condensation issues.

Special Products and techniques used in building envelope:

  1. The spray foam used was Sealection Agribalance foam insulation, manufactured by Demilec USA as an agri-based renewable water-blown product.
  2. Rain screen by www.HomeSlicker.com

Balloon Framing

Step 1:Existing, open to sill. Typical balloon framing in place

Step 2:  New wall assembly with rain screen and foam board.

Step 2: New wall assembly with rain screen and foam board.

Step 3:  New bottom plate, sealed off.

Step 3: New bottom plate, sealed off.

Step 4:  Spray foam behind rigid foam board.

Step 4: Spray foam behind rigid foam board.

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