How to Insulate

Insulation is just like any other project. And for small jobs it can even be a DIY project. Whether you hire a contractor or tackle this your self, knowing what needs to happen is critical. But, let me start with why you should consider a reputable Contractor;

  1. It is surprising how inexpensive they can do the job, they pay much less for the materials and are much faster than most of us would be.
  2. They know what steps need to occur and in what order.
  3. They know which products to use in each application.
  4. It is a dirty job, often in hot attics or other tight spaces.
  5. Insulating is usually a multi-person job.
  6. The insulation at the big box store is often not what you should be using. The best option is friction fit batts, these will likely have to be special ordered at a big box store. Definitely don’t get the plastic wrapped stuff, you’ll struggle to get a grade one install with it.

If you are talking to an insulation contractor, let them know you expect grade one installation and plan on third party certification from an Energy Auditor, HES Assessor or HERS Rater. The difference in performance for insulation that is not grade one can be as much as 75% for the same insulation purchased.

The map below shows the recommended R-values for each region of the country. Here in Birmingham we are zone 3 and as of 2017 our codes for new homes are still lower than the recommended. Our 2017 codes are R-30 for ceilings, R-13 for walls and R-19 for floors. In addition, attic doors and stairs only require R-5, though attic hatches require R-19. This means even new homes have opportunity to improve insulation.

What is R-Value? Simply an object’s ability to resist the flow of heat. The higher the R-Value the better it resists the flow of heat. I use the term flow, because heat flows like water. It will take the path of least resistance. If you insulate a wall to R-30, but leave 10% of the wall at R-1, you actually get R-8 for the whole wall. So 100% coverage is king, also it means consistent coverage is your best return on investment. One last important topic for R-value, insulation MUST be fully enclosed on all six sides and filling the cavity to get the rated R-values (horizontal applications only need five sides enclosed).


How much insulation does it take to get an R-value? Take a look at the next image to see for blown-in insulation in an attic:


So what do you do with this information for your plan. First consider what you can practically get to. Walls are generally not worth opening up to add a few points of R-value. But consider a foam board under siding if it is going to be replaced. The one type of wall we will address is Attic Knee Walls; they’re so bad, they desire their own write-up (see link for more details). Cathedral ceilings is another area we can’t do much with, without ripping apart your home. Most cathedral ceilings we see only have R-19 with no deck vents or R-13 with deck vents. Honestly I’d take the R-13 with deck vents, the moisture control on the under side of the deck is too important to neglect. The best improvement for Cathedral ceilings would be to seal the bottom and top where accessible (allowing the deck vent to still function). Often you can double the effectiveness of the existing insulation.

So now we are left with is ceilings and floors. Your biggest bang for your buck is ceilings, with proper air sealing and deck venting, additional attic insulation can make a huge comfort and energy savings impact. Pay special attention to attic doors, stairs and hatches, anything you can do to seal and insulate them equivalent to the rest of the ceiling will pay huge dividends.

Your next opportunity is floors. Though not spelled out here, the rim joist is a key component of floors. With proper air sealing and installation, insulation can be very effective under your floor. Though in zone 3, rarely does it pay to add insulation, only if none previously existed.

The following three videos from NAIMA show (1) what to look for when planning for insulation, (2) how to insulate, and finally (3) what to look for to a get Grade I Install.

For more great information visit The Insulation Institute.

Written by askefficiency

Owner / Operator of ASK Efficiency, LLC.