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Wall Insulation

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General info

  • Insulation is required in all external walls to prevent heat loss in winter or heat gain in the summer.
  • Insulations ability to insulated is stated in R value. The higher the R number the better the insulation.
  • Insulation placed in walls is covered by a warm side vapor barrier to prevent moisture from settling in wall cavities.
  • If moisture gets into the wall cavity mildew and rot can result.
Method
Insulation is placed between the wall studs in external walls after the wiring, plumbing, HVAC and framing inspection. After the insulation is placed a plastic vapor barrier is placed over the insulation. Some types of insulation have a barrier attached to the insulation. Fiberglass insulation with a kraft paper backing is an example.
There are several different types of material that can be used to insulate the walls. Fiberglass, cellulose are common. Fiberglass batts are stapled into the cavity and cellulose is blown into the cavity. Urethane foam is also becoming more popular because of its high R value, and its ability to stop air infiltration. Urethane foam however is much more expensive than tradition fiberglass batts.
Most exterior walls are constructed of 2x4 or 2x6 stud walls. The thickness of the wall determines how much insulation can be placed in the wall. Here are typical R values for exterior walls:

Before insulation is installed, it is important to fill all cracks gaps in the walls, top and bottom plates, around pipes wires and ductwork and any other penetrations in the exterior shell of the structure. Urethane foam in a can be used for this purpose. If outside air is allowed to infiltrate the insulation cavity, the effectiveness of the insulation is significantly reduced. Caulk is a good barrier where the gaps are less than ¼".

R-values of wood framed walls

Insulation Type 2x4 Framed Wall 2x6 Framed Wall
Fiberglass batts 11-13 19-21
Cellulose fill 14-16 21-23
Urethane foam 16-17 22-25


Fiberglass batts are the best option for the Do-it-yourselfer. If you decide to pay extra for cellulose or urethane the extra money spent will probably not pay for itself in lower heating bills for many years.

Items that are typically in a subcontractor agreement:
  • Price for the job
  • Price per square foot
  • Hourly rate for work not covered in the contract
  • Cost for change orders
Contract Specifications:
  • Type and R-value of the insulation to be installed.
  • Sealing crack and penetrations in walls around windows and doors.
  • Sealing penetrations through top and bottom plates around pipes wires and ductwork.

Inspection

  • Usually an insulation inspection is required by the building inspector.
  • Check that the insulation cover the entire cavity with no bare spots.
  • Check around doors and windows for light leaks.
  • Expanding foam that is installed around windows and doors can cause them to bind. Special low expansion foam that is specially made for doors and windows should be used.
  • Many Building jurisdictions require that a Building meet the national energy efficiency requirements. The national model is adapted for each state and city in the country. The code is called the Model Energy Code check or MECcheck. Check your local building department to see if you are require to meet this standard. You can download the MECcheck software (free) from www.energycodes.org
Money saver
  • Consider installing wall insulation yourself. The job is not too difficult, and you could save some money.
  • The return on investment (ROI) for cellulose and urethane insulation is 5-10 years.


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