Insulated Siding: Should You Do It?

The term “insulated siding” almost invariably refers to vinyl siding with expanded polystyrene (EPS) glued onto the back. First introduced in 1997, it has slowly been gaining popularity since. R-value claims range between R-2.0 and R-5.0. The actual R-values are between R-2.0 and R-2.7.

Insulated Siding pros cons

A Short History of Insulated Siding

Before 1997, insulation was installed behind siding as loose pieces–typically made of EPS or Buffalo Board. It was called backerboard and its primary function was to keep the face of siding pieces flat. Aluminum siding–on which it was first used–and vinyl siding tend to have a concave look. The siding did not have the smooth beveled look of the wood siding it was replacing.

It was represented as adding insulation value but was very thin at the top and the installation practices were inconsistent–to be generous. At least one aluminum siding manufacturer sprayed foam on the backs of siding panels. Consistent R-values only became possible when the process of gluing EPS onto vinyl siding was perfected.


Vinyl siding is the most popular exterior wall finish in North America. Insulated vinyl siding is part of that market. Some of the reasons to consider insulated vinyl siding for your home include:

  • Adds insulation value.
  • Reduces thermal bridging by insulating over wall studs.
  • More impact resistant to hail, stones kicked up by lawnmowers, and balls thrown by kids.
  • Provides a more natural-looking finish by eliminating siding cupping.
  • Can be installed over framing or walls that have already been insulated.
  • Can be installed over relatively smooth stucco or existing siding without the cost of removal.
  • Helps with soundproofing.
  • Damaged panels are as easy to replace as regular vinyl siding.
  • EPS does not absorb water.
  • Siding and insulation do not separate over time.


Insulated vinyl siding use and acceptance are growing slowly. Its acceptance is likely to remain slow for the following reasons.

  • Cost. Uninsulated vinyl siding costs approximately $0.75 – $2.15 per square foot at Home Depot. Insulated vinyl siding costs are at least 50% more. Accessories are also more expensive. Supplied and installed costs can be as high as $12.00 per square foot.
  • Installation. More difficult. Slower. Requires some different tools–cannot just be cut with siding shears–need to use a table saw or hand saw. Also needs extra deep buildup around openings due to the finished thickness.
  • Insulation Value. The effective R-value of R-2.0 – R-2.7 is low for the cost. Better insulation options are available.
  • Inconsistency. The EPS expands and contracts with the vinyl but it is applied short of the ends of each panel to allow for overlapping. On cool or cold days the material contracts leaving uninsulated spaces at each joint. (Each piece of vinyl siding can expand and contract up to 1” between summer and winter.)
  • Availability. Not always available in many locations. Often special order only and non-returnable. Cost and multiple colors and profiles make it difficult for smaller outlets to carry a full line of products.

Other types of Insulated Siding

Some manufacturers like Progressive Foam take insulated siding one step further. They produce insulation that matches vinyl siding profiles that drop in behind the siding. The advantages of this insulation are:

  • Lower Cost. Use regular uninsulated vinyl siding and trims. The insulation fills the cavity behind the siding to produce the same backing and strength as glued-on EPS.
  • Easier Installation. No need for extra tools. EPS foam cuts with a utility knife and the siding with shears. 1 1/4 “ J-trim does not stand too proud of most window and door frames–eliminating the need to build up the frames.
  • Better R-value. The product is slightly thicker. There are no gaps between the insulation at vinyl panel joints because the foam is designed to butt tight together. They produce foam inserts for accessories such as corner posts.

Progressive Foam also manufactures profiled insulation for cement fiber siding and beveled wood siding. These larger sheets are installed on the wall before siding is applied. This adds a blanket of insulation to the house and the profiles provide straight lines for easier siding installation.

Installing the foam before the siding allows for overlapping at the corners and sealing it to window and door frames with caulking compatible with EPS or spray foam. Treat all wall penetrations such as pipes and vents the same way.

The best selling points of insulated vinyl siding are the finished look, strength, and rigidity. Most buyers consider the insulation value of secondary importance.

Wrapping the house with extruded polystyrene at R-5.0 per inch and covering it with uninsulated vinyl siding provides better insulation value and a lower cost.

Insulated vinyl siding and profiled insulation can be installed over rigid foam insulation for added R-value. One inch of R-5.0 extruded polystyrene applied before the siding produces approximately R-7.5 of additional insulation to the house walls and a seamless blanket.