Wall Insulation

Wall insulation is essential and required when you are building from scratch or doing a major renovation and opening up a section of wall.  However, it is rarely a priority for an existing home.

Top 3 Reasons not to add wall insulation to your existing home:
  1. You won’t see dramatic improvements in your energy bills! Experts estimate it takes 10 to 20 years or more to see a payback
  2. It is usually a messy, tricky project
  3. You can unwittingly create problems with condensation, dampness and mold

But my energy auditor told me to do it…

We have lost count of the times that a customer has called, saying they just had an energy audit and were told to have wall insulation added.  Stop right there, we say.

Some energy auditors – particularly if they are measured or rewarded by how much follow-up work they generate – are often quick to recommend wall insulation.

wall-insulationBut not so fast! While many existing homes – especially in areas of the country with older houses – do not have any, wall insulation should not be high the list of steps to take to make your home more energy efficient.

Wall insulation is expensive and the savings are small.

As experts from the National Association of Realtors point out, models suggest that if you live in an average 2200 square foot home and you insulate your walls, you can expect savings on your heating and cooling bills of between $130 and $300 per year.

Not bad, but the cost of the work is likely between $3,000 and $4,000: so the time it will take for you to earn back your investment is between 10 and 30 years.

So what to do instead? Invest first in attic air sealing and insulation, basement insulation, weather stripping doors and windows, chimney pillows and a high efficiency or a renewable heating and cooling system before you think about wall insulation.

Did we mention that wall insulation is messy?

Assuming your walls are not completely open to the studs, as in new construction or a major renovation project, it is hard to get the insulation into your walls.  Generally, it means drilling holes every 12 to 24 inches in either the outside or inside walls and pumping the insulation in and then patching the holes – and if the holes were drilled from the inside, you then typically need to repaint the wall surfaces so that the hole patches do not stand out.

wall insulation holesIt’s not simple to completely fill the gap in your walls with insulation, either. Obstacles such as pipes and bracing can block off the flow of insulation and create voids. Voids are bad news not just because you are not getting any insulation benefit, but also because you will have “cold spots” on your interior walls, which may attract condensation.

The only way to ensure that there are no gaps in your wall insulation is to use a thermal camera to see through the walls.  And if there are gaps in the wall, then you need to drill another hole and pump that gap full of insulation. Combined, this can become time consuming and expensive.

Condensation, Damp and Mold

The final issue to consider is the risk that your wall insulation could get damp and become a wet mass at the bottom of your wall cavity. Not good for many of reasons! Wet insulation no longer insulates; it can cause problems with paint finishes and be a breeding ground for mold and insects. 

So, many advocates for historic houses are hostile to wall insulation. Be particularly careful if you have a brick wall with exposure to wind-driven rain. The rain will find its way through the brick!

How much does wall insulation cost?

Expect to pay between $3,000 and $4,000 for an average 2,200 square foot home. In some areas of the country there are generous rebates to assist homeowners with insulation.

Installation Matters!

Make sure you get a reputable, local insulation expert to insulate your walls.

Local is preferred because knowledge of your local housing construction styles and materials is an advantage in getting the job done right – and your local expert’s business depends on building word of mouth amongst friends and neighbors: if there are any issues, you can have a reasonable expectation that you will get satisfaction.

Check how your installer plans to validate that there are no voids in the walls: they should offer an infrared inspection at no charge and encourage you to look over their shoulder.

And if your project involves drilling holes into your interior walls in order to pump in insulation, make sure the quotation includes re-plastering and refinishing to the original specs!

Behind the Walls
Innovation Center
One Broadway
Cambridge, MA 02142