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Is adding insulation a good investment?

Monday, 30 April 2012 17:12
Published in News

Is adding insulation a good investment?If you've airsealed your attic properly, the next step is to add insulation.Better Building Works is working with RCClear (Roanoke County Community Leaders Action Roundtable) to provide energy audits (energy checkups) for County businesses and homes. We make recommendations for energy efficiency upgrades in a checklist. We were recently challenged about one of our recommendations, to add additional insulation to an attic that already had R19 insulation.

The argument was that if airsealing was done, the majority of the gains were accomplished and that the additional insulation was not cost effective. This may have been the case when energy prices were low - but today, things are quite different. Just in case you don't want to read all the way to the end:

If you first airseal properly then you are likely to achieve close to a 20% return per year, every year, if energy prices stay the same.

Here is the full text of our answer (get ready to geek-out on building science):

"Calcs are below, but I think the major difference is that energy prices in the early 80's were a lot lower than they are today and the cost of insulation, while also more expensive, has not gone up as much. You are right that there is a diminishing return (R value and u-value relationship). But:

With respect to energy loss at the attic (heat lost to the attic in the winter and heat gain from the attic in the summer), it's all about the dynamic interactions of heat and the stack effect. We want to hit that 'sweet spot' where adding more insulation stops making sense, cash wise.

  1. Heat moves in three ways - convection, conduction and radiation.
  2. Air sealing solves the convection problem - this is the biggest gain because without it, the existing insulation is not performing.
  3. Insulation solves the conduction problem - it will not function as a thermal barrier without air sealing. Assuming that air sealing has been completed and that it is continous and in contact with the air barrier, if it is insufficient as a thermal barrier, then conduction still occurs.
  4. If conduction occurs through the materials, then radiation will occur at the 'hotter' surface. In the winter, heat will radiate from the inside of the home to the attic and in the summer from the attic to the interior of the home. Sometime just for fun, when you are in friends' homes this summer on a hot day, feel the surface of the ceiling to the attic - if it's hot, there are insulation issues.
  5. 6" of insulation is R19. Code since 2006 has been R38. Energy Star is R49. For this reason alone, we recommend it and would be lax not to do so given our BPI certification, ASHRAE Standards, 2009 Energy Code, etc. Note that the 2012 Energy Code will be even stricter. The reason the DOE cares is that insulation saves btus - and btus mean expensive infrastructure.
  6. Insulation is inexpensive - around $.50 per attic square footage. (for blown in, say, if we did it). For a ten year payback (yielding a 10% return per year over the life of the home), that means that a 1000 sf house would need to save $50 per year by installing additional insulation to R38 (another six inches). This is probably the outer limit that we'd go to 'justify' an investment.
  7. But, there are other reasons to do it, such as health, safety, home value, comfort of babies, health problems or older folks who are much more sensitive to heat swings.
  8. Heating and cooling days (added together) for Roanoke is about 5100 per year (based on the past several years) - locations in our area will vary a lot, though, and these numbers are conservative - based on a setting of 65 in the winter and 78 in the summer. Very few people actually use these settings! More typical is 68 / 72.
  9. Use the handy online calculator below - according to this, depending upon the energy source and condition of the equipment (and remember that older equipment is not functioning at its original EER):

The return on our hypothetical Roanoke City 1000 sf house with R19 blown in insulation, a heat pump EER of 10 and in 'AEP' land, is 18% per year ($89.87). If the 'typical' settings are used, then this jumps to $100 / year and 20% return per year. (Try that with a $500 investment in the stock market! In fact, try to get half of that.)

Answer: yes - it is cost effective. And, often the insulation that exists needs to be optimized if there is windwashing, uneven coverage, etc. All of these things should be fixed, regardless, but the cost of the additional insulation usually includes that."

Several sources:

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