Sealing the crevices that matter most!

In existing homes, it is not out of the ordinary to find components of the heating and cooling duct configuration to be disconnected, loosely connected or connected and leaky due to old methods of installation.  If the problems are in ducts that are located in the attic or in a crawl space the loss is greatest and should be high priorities.

Duct leakage points located inside the conditioned area of a home are less costly than those that are outside, but there are examples where leakage inside the envelope can cause pressure dynamics in the home that actually can force conditioned air out or pull it in, so it should not be overlooked.

An energy auditor can find disconnected ducts that are quite costly
 

Cracks in the ducts that are under the greatest pressure leak the most and therefore are higher priorities.  An example of this would be the ducts closest to the air handler.  In this area of the system, the pressure is greatest.  The good news for many homeowners is that many opportunities exist to seal near the air handler.

It is always best to target all ducts in an HVAC duct system, but it is worth noting that supply ducts are more important to seal than return ducts.

Consider getting a duct diagnostic test performed to determine how leaky your ducts are overall and isolate those that are outside to see how much they are leaking compared to the system as a whole.

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Written by Eric Gans
I have over 1000 energy audits under my belt in Maryland.  I like to take my personal experiences with each of my audit customers and try to get the things that concern them out into the world so others can make good home improvement decisions - in the right order - according to their needs.
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In Maryland, it is recommended that our attics are insulated to R-49

No matter where you live, if you are having comfort issues in your home a good place to start when looking for answers is the attic.  You must identify what insulation material exists and measure the insulation level in inches to see if you are meeting the latest building codes.  Determining these two things will provide you with enough information to figure out the R-value of your insulation. 

R-value is the conventional method by which the performance of insulation is measured.  Insulation has one job - to resist heat flow.  The higher the R-value, the better the insulation resists the transfer of heat.

Missing insulation, as you will see below, is quite impactful and should be fixed ASAP!

Insulation is very important because in summer, it is responsible for stopping the hot attic air from coming inside (it gets 150 degrees in attic!!) and in the winter it keeps the warm conditioned air from going outside (through the ceiling mostly, due to pressure). 

The attic is the most important place to check first, however there are other areas that should also be considered such as the basement, overhangs and crawl spaces.
 

Insulation R-Value requirements in the State of Maryland

LOCATION - REQUIRED R-VALUE MARYLAND

Typical Places You will Find Insulation 

Attic Flat - R49
Attic Slope - R38
Vertical Wall (basement, crawl space, knee wall) -  R13
Crawl Ceiling - R25
Below Cantilever - R25
Rim Joist (top of foundation wall in basement) - R19

1st - Determine what Type of Insulation You Have

Different attic insulation materials yield different R-values based on how many inches are in place so one important piece of information to determine insulation R-value is to identify the type of insulation that was installed in your attic. 

Fiberglass batts, loose fill fiberglass, loose fill cellulose, mineral wool and two-part spray foam are all insulation materials that you might find in your attic.

Need help with this?

Pop your head up in the attic and take a photo of your insulation or if you live in Maryland get a comprehensive home energy audit through BGE or Pepco. 

You can also call or email it to me so I can take a look and identify it for your eric@hometrustremodeling.com or refer to the photos below to try and figure it out.

Identifying Different Insulation Types
 

Cellulose Loose Fill - Grey in color, more dusty and clingy than fiberglass loose fill, has bits of newspaper in it

Fiberglass Batts - Typically referred to as rolled insulation, has the kraft paper or aluminum foil on one side.

Fiberglass Loose Fill - You might see it in your attic in white, yellow, pink or grey.  Much less dusty, but not as good as cellulose!

2nd - Determine a Reasonable Insulation Level in Inches

Insulation levels in an attic are rarely the same everywhere.  In order to gain an true perspective on how much insulation an attic needs will depend on the cumulative amount in inches an attic has.  So, as an example, if you have an attic that has 8" of insulation at the highest point and 2" at the lowest point and after surveying the attic floor, you can conclude that the level is approximately split 50/50 between the two heights then you can average things and call it 5".  Of course, it is never quite that easy and it take a bit of a trained eye, but another alternative is to simply take measurements in five locations (corners and the middle) and get your number that way.

3rd - Convert the Number of Inches of Insulation into R-Value

Once you determine your type and level, it is time to figure out how to calculate for R-Value.  I won't get into it too much here, but R-Value is sometimes misleading.  This must be said for this reason:  several factors including, installation integrity, the presence of untreated thermal bypasses (cracks/crevices where air can flow through below the insulation) and overall insulation coverage (evenly distributed) all play into the overall R-Value.   

For each of the three types of insulation shown in this article (prevalent in Maryland attics), the following R-Values can be multiplied by the number of inches to see where your attic falls on the scale.

• Loose Fill Cellulose - 3.13 R-Value Per inch (Example: 6 inches of loose fill cellulose = R19)
• Fiberglass Batt Insulation - 2.10 R-Value Per Inch
• Loose Fill Fiberglass - 2.73 R-Value Per inch 

Most attics in Maryland are insufficiently insulated and are a big contributor to comfort problems, high energy bills and in some cases, poor indoor air quality.

Un-insulated Areas Play a Heavy Hand in Poor R-Values

Now lets go a little deeper and explore the impact an un-insulated surface has on the entire area when it comes to overall R-value.  If you go in your attic and see any area that does not have insulation, you should really pay attention to the information below.

To demonstrate this, I am going to use a common set of circumstances in a typical Maryland attic.

For this example, the attic area is 975 square feet and flat.  The home is pictured above.

At the attic floor (drywall surface of the ceilings below) there are 2" of loose fill fiberglass insulation (white).  On the top of that there is 6" of rolled fiberglass batting. 

Total calculated R-Value for this attic = R17

There are two major un-insulated areas in this attic.  The 3' x 3' push up hatch was not insulated and there is a 3' x 3' whole house fan that was un-insulated for a total of 18 square fee of un-insulated area at the attic floor.  This equates to just about 2% of the overall attic area.

The hatch has a plywood cover (seen in background)

When calculated in the handy Home Energy Score Averaging Calculator it is apparent how much of an impact un-insulated surfaces can have on the overall performance of your insulation.  This calculator performs basic reciprical calculations to convert and then average the R-value in a weighted fasion.  It gives you an accurate value for the performance of your insulation and can also be used to more precisely measure the R-value for a home energy audit where getting the R-value correct is important.

Calculating the actual area with insulation in combination with the areas that are not insulated yields a significant reduction in overall R-value as seen in the two scenarios above.

Conclusion: if as little as 2% of your attic surfaces are un-insulated it can have as much as a 25% negative impact on the overall R-Value.

What is a Knee Wall?

A knee wall is best described as a vertical wall that touches living space on one side and it also touches the "outside" on the other side.  The difference between a knee wall and an exterior wall is that the knee wall typically has one side to the inside living space and one side to an attic area. Notice here how the attic is referred to as the outside. Knee walls are created in houses where the inside living space is more complex.  For example, vaulted ceilings, spaces over garages, lofts, skylights, bulkheads, dormers and other interior designs create the need for a proper understanding of a knee wall and how it can quietly cost you comfort and money.

Different Types of Knee Walls

Vaulted Ceiling Knee Wall.  One classic knee wall is created when a portion of the upper floor has a traditional eight foot ceiling and perhaps a bedroom or hallway has a vaulted ceiling that rises up at the highest point to thirteen feet.  The vertical wall area that transitions from thirteen down to eight is the knee wall area.  This is very common in newer homes built between 1980-present.

This knee wall is created by the vaulted ceiling with 8' ceiling on other side
 

Basic Attic Knee Wall.  A basic attic knee wall is created in a Cape Cod style home where the upper floor is built into what a traditional attic space might be in a home of different construction type.  If you can imagine being in a house with an A-frame style roof and your head is about 3-5 feet from the apex of the roof. Considering where your head might be in a house with a traditional attic, the idea can take shape.  A big sign of a knee wall in a living space like this would be a sloped ceiling.

Bulkhead Knee Wall. A bulkhead knee wall is mostly found in upper floor bathrooms and bedrooms, but occasionally this will be found in kitchens and other areas of the home, particularly if the home is only one story.  A house could be two stories, but the kitchen could be built in a one story section of the home in which case a bulkhead could be considered a knee wall.  The main point to consider is that a change in ceiling height (lowering) in a location that is connected to an attic should get attention for proper insulation.

Thermal imaging reveals incorrectly installed insulation at the bathroom bulkhead
 

Skylight Knee Wall.  The drywall areas that create the skylight "tunnel" rise up through the attic and are joined to the framing almost directly at the decking underneath the roof so that the skylight can be installed and it will allow the natural light into the living space below.  The walls inside the skylight cavity are dynamic knee walls in that they are outside to inside surface on all four sides.

Most Maryland houses with skylights have inadequate knee wall insulation
 

Dormer Knee Wall.  Dormers come in all shapes and sizes and as a result can add a nice structural feature to the front or rear of a home and they also serve a practical purpose by adding more area to the inside of a home.  The biggest challenge for Maryland homeowners that have a dormer is how to properly insulate the area and making sure the pressure and thermal boundary are properly aligned.

Knee Wall Created by an Addition.  A knee wall is sometimes created by an addition depending on how the existing structure is built, where the addition is going to be built and what is the most economical solution which sometimes creates knee walls that could have otherwise been avoided.  Not that there is any issue with having a knee wall, more so the issue comes into play with how to properly seal and insulate the knee wall to maintain comfort and energy efficiency in the new area of living space as well as the existing conditioned area.

Knee Walls are Silent Energy Wasters

Because knee walls are common, but they are not commonly identified, knee walls can sit there for year after year and leak comfort and money away.  The attic is a less then desirable place to visit.  It is stifling in the summer and frigid in the winter.  It is dusty and the insulation is dirty and most people will simply feel itchy when thinking about fiberglass insulation.  As a result, gravity takes over and because of the knee wall insulation methods that were being used over the past sixty years, the insulation begins to sag and fall.

A visit to this attic revealed insulation was missing unchecked for a long time
 

Why Knee Walls Need Special Attention

Insulation is only going to work if it is in good (almost perfect) contact with the surface in which it is meant to insulate.  Unfortunately, due to poor installation, exposure to wind and air flow as well as workers and other visitors to the attic, insulation is rarely in good contact with the attic floor (ceiling of upstairs) let alone the vertical knee wall.  As a result you get insulation slipping.  Gravity is a powerful thing, particularly when it has nothing but time to do it's work.

How to Properly Treat a Knee Wall

Properly treating a knee wall requires three steps.  Step one - air seal all of the cracks, crevices and voids.  Second, add insulation to R13 and make sure the insulation is installed correctly.  Finally, sheathing should be installed behind the insulation so it is snug in the cavity, in good contact with the surface wall and there is virtually not chance the insulation can fall back down.

Common Construction Philosophies

Maryland crawl spaces can be a giant source of comfort issues in summer months.  Crawl spaces are typically intentionally connected to the outside humid air with vents around the foundation wall.  The idea was that installing vents will create ventilation.  Unfortunately, due to pressure dynamics that in many ways are related to meteorology pressure highs and lows, the air in the crawl space becomes more humid and damp and issues are compounded with the steady infiltration of stale, humid air.  If there are ducts running through a crawl space it is more important to consider what measures can be taken to treat the crawl space.  Spending a little money up front on crawl space encapsulation will save much more money in the long run if you consider duct leakage, overworking HVAC equipment and extra infiltration of warm, humid air in summer and cold, dry air in winter. 

Check out this before and after crawl space encapsulation project with blocking and sealing open vents.

Crawl Space Encapsulation Maryland - Smart Thinking
In the simplest terms, to encapsulate a crawl space is cutting it off from the outside air.  When I was young we had the Weather Channel that was just a table with today's temperature and conditions and it would cycle through each city in the U.S.  San Diego, no matter the time of year it seemed, was always 70 degrees and sunny.  We want the crawl space to be 70 degrees all year round - without the sun, of course.  By doing so, you are bringing the space into the "envelope" of your home.  If ducts exist in the crawl space, the ducts don't have to work as hard to service the rooms above. 
 

Overall, the HVAC system is asked to do less as a result of crawl space encapsulation and yet the inhabitants are more comfortable.  

Imagine if that was a formula for everything in life.  Work less and gain more!

Learn more about common sources of home comfort issues.

Hometrust Remodeling recently completed an insulation job in Laurel, MD 20723.  The project consisted of the following measures:

• Air seal the attic floor
• Install soffit baffles at eaves for ventilation
• Cut soffit holes to add air intake for attic ventilation
• Seal 4 recessed lights
• Add 10" of loose fill blown cellulose insulation
• Treat the main attic access hatch
• Treat the garage attic to encapsulate the space
• Sealed accessible HVAC duct connections

For most insulation to be effective it is important to stop the flow of air by sealing up holes and cracks in as many accessible areas as possible. 

Insulating the accessible skylight kneewalls to R13 after sealing smaller crevices/cracks and adding sheathing (air barrier) over the insulation will maximize boundary effectiveness and reduce air communication between the living space and the attic (outside).

                                 
Completed attic insulation & skylight kneewall 20723                                      Garage roof encapsulation in Laurel, MD                   

Most of the largest leaks in homes occur where framing (such as floor joists or wall studs) span from an area inside conditioned space to an unconditioned or vented space, such as the attic,crawlspace, garage, or roof. Appropriate blocking is needed in these instances.

Untreated recessed lights are invisible gateways for air to communicate between the inside (conditioned space) and outside (attic).  Covering and sealing accessible recessed lights will eliminate this issue.

Encapsulation, using open cell spray foam, was completed for this project so that the space below, including the HVAC unit in the garage attic, would become part of the overall "envelope".  The garage is going to be converted to living space (in-law suite) so by encapsulating the area above the space, it will make it easy to complete the job once the work gets done and when the space is changed, the HVAC will also benefit from being enclosed inside the house rather than outside (garage attic).