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Ask Mr. Tight-Watt: Insulate when replacing siding  Smart Choices Archive

Ask Mr. Tight-Watt: Insulate when replacing siding

Mr. Tight Watt says that adding insulation is a good thing.

Ask Mr. Tight-Watt

Q: We are going to have to have some siding work done and we are thinking about beefing up the insulation when we do the siding replacement/repair. One insulation company told me by using their product, I can decrease energy use by 30–60 % and have a payback in 2 to 3 years. This sounds too good to be true. What do you recommend doing?   — Joe D.

Mr. Tight Watt asked insulation professionals Shannon Moe and Andy Seiler, Kinzer Company, Ames, to give Joe and our other readers, some sound advice on insulating your home’s sidewalls, whether you are replacing siding or not.

Normally, reinsulating walls requires drilling though existing siding on the outside or drywall/plaster on the inside. Both are messy and can leave unsightly holes. Insulating sidewalls on a house in conjunction with siding work makes great sense—by eliminating the need to drill through a finished surface you’ll end up with a better looking final product. You also have the ability to tighten up the building envelope by installing housewrap or another air barrier when residing.

 Here are three ways to add insulation to your exterior walls:

  1. Most commonly, in a process known as a “drill and fill,” roughly 2-inch holes are drilled into each wall cavity, a tube or nozzle is inserted through the hole, and the cavity is packed full of blown fiberglass, blown cellulose, or foam. (This approach can be used with the siding removed or holes may be drilled through siding or drywall)
  2. Alternately, strips of sheathing material can be removed in bands around the perimeter of a house to provide access to the wall cavities for a spray foam gun.  Polyurethane foam is sprayed into the wall cavities using the expansion of the foam to ensure a complete fill.  (Old siding must be removed)
  3. The third common method for insulating is to add a rigid insulation board overlaid on the sheathing.  (Old siding must be removed)

All three methods for insulating existing walls, executed correctly, are effective at adding insulation.  Paybacks vary, based on initial cost, the price of energy, and specifics of the structure. Typically though, a simple payback ranging from three to five years is common when considering adding insulation to a previously uninsulated wall.

Evaluating claims from installers
When looking at claims about any particular product, be somewhat skeptical about claims regarding energy savings percentages and payback in large part because it is difficult to assess such claims without comparative data. 

You can look at the information on the manufacturer's website and ask questions of potential installers. For example:

  • Does the product work through commonly accepted physical processes (resistance to heat flow through conduction as well as radiation)?
  • What does test data indicate about wall system performance?

Also, keep in mind:

  • If the wall is already insulated (fiberglass or cellulose in the wall cavity), the payback for adding additional insulation stretches way out. 
  • Careful attention needs to be paid to the overall design of the wall system when adding insulation to an existing wall.  Adding materials which alter the temperature in the wall cavity or change the resistance of the wall to the movement of water vapor can create conditions under which condensation occurs and can result in moisture damage. If in doubt, consult an engineer or other design professional.

Information about our experts:
Kinzler Construction Services is a full line insulation solution provider with locations in Ames, Ankeny and Cedar Falls. The company offers customized insulation packages using fiberglass, cellulose, and foam insulations. Website: Shannon Moe runs KCS’s Building Solutions program, providing building performance testing and energy ratings. Andy Seiler specializes in retrofitting insulation in existing structures.

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