What I'm Seeing Now


Which Way Is Up? An Insulation Lesson.

Often I go into attics and see that people have put in extra insulation.  They usually make two mistakes - they use the wrong kind of insulation and install it wrong, OR it is put in the wrong direction.

The purpose of insulation is to provide a thermal barrier.  The amount of insulation gives it a resistance value, commonly called the R-value.  The more R-value, the better the thermal resistance.

Heat seeks cold.  Heat can go up or DOWN to seek this cold.  So in an attic space, the insulation is there to keep the heat out of the house in the summer and inside the house in the winter.  That is as simply put as possible.

Lesson over...

Often people add insulation to an attic, as I said.  And often it can be done better.

The initial reaction to this picture is that the vapor retarder is backwards.

A vapor retarder can be plastic, foil or paper and is attached to insulation to use it in certain applications where moisture needs to be kept out of a space.  The exterior walls of your house likely have the insulation you see here, with the paper facing the interior of the house.

To be effective, the vapor retarder should be on the "warm" side.  While on a scale of 1-10, with 10 being real bad, this application here is probably a 7 or so. It might even retain some moisture underneath and contribute to molds on the ceiling drywall.

Effectively placed, this insulation should be upside down, with the paper TOUCHING THE DRYWALL.  But here it is laid over the previous stuff that was there.  Not the best way.

If you add insulation to your attic, it would be most effective if:

1.  The desired number of extra inches is blown in over the existing insulation.  For fiberglass, a good rule of thumb is an additional R-value of 3 for every inch or so of blown in.  In new homes in VA they are putting in R-38 now (until recently the recommended value was R-30).  The "super-insulated" houses have R-48 here! 

A cellulose insulation, derived from chewed up newspaper and treated with boric acid so bugs won't eat it, is also a very effective "top coat" over what is there.  It has a slightly higher R-value per inch, so less depth is needed.

2.  If you add rolled, or batt, fiberglass, rolling it the opposite direction of the trusses, at a 90 degree angle, is best practice.  This helps seal up any gaps or holes in the layer underneath.  Everywhere must be covered.

3.  Be certain not to place the insulation so close to the edge of the roof that it covers the soffit vents, if there are any.  Ventilation is ESSENTIAL to this space above.


My recommendation:  BIG HINT -- measure the length and width of your space.  Determine the number of inches of insulation you want.  The hardware store can tell you how many bags or rolls of insulation you will need to pull that off.  You can wait to buy it when it is on sale.

If you employ a company to add the insulation for you, when they are done, BE SURE they used the number of rolls or bags they have "estimated" you would need!  The price of your job was based on that!  Hint, hint, wink, wink...

P.s.  Until the end of the year there is a tax credit for extra insulation added to your home. And it is something you can do yourself. Keep that in mind!



Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


Comment balloon 37 commentsJay Markanich • October 30 2010 08:36AM
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