Best Insulation For Your Home..... Attic, Floor & Wall

 What's the best insulation product for a residential house?

First, what makes me qualified to possibly answer these questions.  I am at the time of this writing a certified BPI Building Analyst and gained an additional certification as an envelope professional. I have preformed dozens of home energy audits with a blower door and thermal camera.  Although I have since left the industry I thought I could put some simple answers together without all the BS you may see from someone offering to sell you products.

First the Attic- Best insulation for your attic 

I highly recommend a two stage approach to insulating a new attic space with an optional kicker for maximum energy efficiency.  If at all possible to start with a fresh un-insulated attic space it is highly beneficial to seal the lid with an expanding spray foam.  The lid is simply the ceiling or attic floor.  Spraying the foam to seal all penetrations including the eletrical wires, and HVAC ducting, lighting fixtures, and of course the entire perimeter is very beneficial - this is mostly to reduce the air infiltration rate or movement of air into the attic.  

Optional: Spray the entire floor in a 1-2 inch layer of expanding spray foam.  This is very beneficial - however it can cause it's own problems down the road when it comes to remodeling.

OK you are done with the spray foam what next.  Well in my opinion you should pile in the cellulose insulation.  It has two advantages 1) It is relatively inexpensive 2) At an R Value of around 3.5 per inch it is a good insulator.  18" or so should max out the Department of Energy guidelines of R-60 in just about any climate.

Cellulose is a great air barrier itself - better than fiberglass insulation in nearly every install I ever saw - I've literally been in over a hundred attics.  It's also easy to replace after a remodel or roof leak.

As long as you have the space it your attic this system is every bit as good as just spray foam coating the whole thing 6-8" thick or so.  You can still get to all your electrical fixtures, fans. etc...

Bonus tip for achieving best attic insulation

Well it isn't exactly insulation but it does help a great deal and that is a perforated radiant barrier.  While traditional insulation materials slow convective heat loss they do nothing for radiant heat loss or gain.

In cold climate:  Adding a sheet of radiant barrier on top of the insulation loosely laid has had dramatic effects and keeping the heat in.  If you are a do it yourselfer it's also very affordable.

In warmer climate:  If this is a new build I highly recommend using an OSB board for your roof that is coated on the underside with a radiant barrier aluminum foil.  The effects at reducing heat gain from the sun are tremendous.  For retrofit situations, simply purchase roll sheets of radiant barrier and attach them the the underside of the roof rafter making sure the leave a gap at the very top to allow excess heat to escape through your roof venting.

Second, Alright attic done, what best for my walls?

This one is simple unequivocally spray foam is your best friend for exterior wall insulation. 

• Primary reason is the limited depth restricts your choices for achieving a great R Value.
• Secondly, The air sealing properties of expanded foam are fantastic, and unbeaten with traditional fiberglass or cellulose fill.(although wet cellulose can do a great job.

The best product to achieve this is a soft spray foam with an R Value of around 7.  No other product on the market can give you this.  So Even with 2x6 construction (apprx 5.5" cavity you can get 38.5 in the walls.  More in a 8" cavity and less in the 2x4 traditional.  Still this is DOUBLE what you get with fiberglass batts or cellulose insulation.

A little cheaper than the best please?

Yep, your right spray foaming all the exterior walls in a house can be pricey.  One popular option is called flash and batt.  You simply spray a 1" base layer on the wall for optimum air sealing qualities than finish with traditional fiberglass batt insulation.

Lastly, the best insulation for cold floors.

Alright normally cold floors are from someone with a crawl space or dirt floor type basement. In these cases a two tier approach seems to work the best.

• Spray foam all but a inch or so of the floor joist depth direcctly to the underside of the subfloor, all of the rim joist onto the transition to the foundation.
• Install a radiant barrier to the underside of the floor joist

This helps in two ways the R Value from the spray foam is great and therefore helps slow convective heat loss.  Also the radiant barrier will reflect back radiant heat towards the floors.

There is also a more traditional approach that works very well I also like because of moisture control aspect.  

1.  A moisture proof membrane usually around 20-30 mil plastic is installed onto the dirt floor with no gaps and then tacked onto the side walls(concrete block, stone, poured walls, whatever is there)
2. Then spray foam(can be done less effective with foam board) the foundation walls and rim joist.  This work very well too and honestly for the health reasons most of the time I would recommend this approach.