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Residential Energy Efficiency Blog

Thursday, November 19 2020
What Should You do with Your Crawl Space? Here is Why You Should Seal It!

 

Let’s face it – you want nothing to do with your crawl space.  You just assume that it does not exist.  You ignore it.  You board it up, lock it and put it out of your mind! 

But, it keeps reminding you it’s there.  In the summer when you go down to wash the laundry and you get a whiff of that musty odor that only comes out when it is humid. 

A few years ago you poked your head in the crawl space for one reason or another and you noticed several pieces of insulation falling down.

And, you’re not quite sure, but winter is probably the worst time of year when it comes being comfortable.  The last thing you can do on a cold winter morning is walk barefoot over the floor above the crawl space.  It never really seems to get warm. 

In fact, you avoid the whole area altogether during the cold months.

But here is a tip:  You do not need to accept this way of life.  You do not need to bow down to the demands that your crawl space is putting on your comfort and energy bills.  Encapsulating a crawl space can turn it into one of the most consistently temperature controlled areas of your your home.

 

Old School Thinking:  I See Insulation Everything is Fine

If you live in a home on a crawl space there is a very good chance that you think that this just is the way it is and there is not much you can do.

When you first moved in you ambitiously went into the crawl and you saw insulation below the floor.  Everything seemed fine.    

Maybe you have never looked in the direction of your crawl space, or any crawl space for that matter, and have no ideas on what one may look like.

If that is the case, have a look at this video taken during a BGE energy audit of a typical open crawl space.

 

What is the Reason Your Crawl Space is a Problem?  Open Vents for Starters

Open Crawl Space Vent Example

Creating vent openings in the foundation wall were designed to allow "fresh" air into the crawl space for ventilation.  Millions of homes have been built using this method.

The problem is that you can't control what air moves into the crawl space and when it turns hot and humid or cold and dry, the open vent solution is not the best for climates that have seasonal changes like Maryland.

You cannot count on enough dry, average temperature days in a row to sufficiently dry out the crawl space.  Additionally, considering the vents are typically not nearly large enough or often times obstructed, your crawl space does not stand much of a chance for success and as a result, your indoor comfort and air quality suffer and your energy bills are high.

 

Two Seasonal Pitfalls of an Open Crawl Space
 

Summer Humidity

Inside look at a crawl space vent.Open vents allow humid air into the space, or worse streaming water, which tends to get trapped and migrate to unwanted places. 

So many of us plug up our dehumidifier in the summer to keep the basement dry. 

Those with open crawl spaces likely have two machines working and they may not be able to keep up with the high humidity. 

Open vents in a crawl space can have a significant impact on indoor air quality and are main factors in high indoor humidity levels.

Eighty percent of crawl spaces in humid climates have insulation that has fallen. Wood structural flooring components should not be subjected to moist, humid conditions for long periods of time.

 

Winter Issues and How Physics Plays a Role

During winter months, cold winter air is actually pulled into the vents due to physical dynamics that are at play - known as the stack effect, or chimney effect.  Insulation is unable to prevent infiltration through the floor.

Negative pressure is created in a crawl space when it is connected to the living space above.  As warm air rises and finds places to escape, it tugs the cold air from below right on in as seen in the diagram to the right.

Unconditioned cold air that migrates into the crawl space through the vents is than conveyed up through the floor and walls and into your living space.  

Therefore, as a result of this physical characteristic of most buildings, having an open crawl space is not a good solution if you live in a location with a cold season.

 

 

If You Have a Crawl Space – You Have an Energy Efficiency "Point of Weakness"

Big problems with comfort and high energy bills stem from irregularities in the building shell.  Twists and turns in a home’s design create more complex treatment solutions in locations such as:

  • Porches
  • Roof Overhangs
  • Shafts for Chimneys & Pipes
  • Protruding Windows & Doors
  • Indented Windows & Doors
  • Cantilevers
  • Garages
  • Knee Walls
  • Open Basements
  • Open Crawl Spaces

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 and it requires a team that knows home performance techniques and solutions to do it right.

 

What to Look for In Order to Prescribe the Proper Treatment for an Open Crawl Space

No general rule should be applied to how to treat a crawl space. 

These three factors should be considered first:

1. Climate
2. Ground Dampness
3. Presence of Ducts in the Space

In Maryland we tend to have hot, humid summers and sometimes it can be damp well into the fall.  The winters bring cold snaps, some longer than others, that can put a significant load on any HVAC system. 

Seasonal changes make sealing crawl spaces in our region a good option.  Typically, ducts are in crawl spaces in homes where this foundation type exists.

Crawl space inspections will require defining the best place to establish or re-establish the thermal boundary.

The thermal boundary can be described as the location that divides the inside living space from the outside, unconditioned space of your home.

Most crawl spaces are outfitted with insulation at the ceiling.  And, most crawl spaces are sources of energy loss and comfort problems.

 

If I Have Insulation in My Crawl Space Ceiling, Why is it Such a Problem?

In order to understand any high-performance crawl space insulation retrofit, you must first understand the three key things that getting results are dependent upon:

  1. Proper Installation of an Air Barrier
  2. Proper Installation of a Sturdy Vapor Barrier
  3. Proper Installation of Insulation

Typically, all three key factors are missing in a crawl space.

If not properly sealed, penetrations at the crawl space ceiling (floor inside) will lead to communication of air between the two areas.

A vapor barrier is only good if it is 100% sealed, otherwise moisture will still migrate up and into your living space.

Fiberglass batting insulation is difficult to install in almost all applications.  The thermal performance of batt insulation is heavily dependent on proper installation.  To attain maximum R-value, the batt insulation should be in continuous contact with all the surround cavity surfaces where they are installed.  They need to be cut exactly to length because if they are too long they bunch up leaving the area to be insulated exposed and if too short, spaces are created that promote convection.

 

Open Crawl Space vs. Encapsulated Crawl Space

Past research has shown that a conventionally vented crawl space that has been converted into an non-vented and conditioned space tends to operate similarly to houses with basements, with several benefits for the homeowner: 

• Energy savings
• Comfort
• Moisture control
• Long-term durability
• Healthier air quality


Open crawl space with insuation at the ceiling and an improperly installed vapor barrier.

Completed crawl space project with sealed walls, rim joist, floor and HVAC ducts.

 

Reasons Maryland Homeowners with Crawl Spaces Might Not Choose to Encapsulate

  • Significant efforts can be made with ease to seal and insulate ducts, air handlers, water heaters, pipes etc.
  • Lacking any paid heat source, the crawl space is consistently between ground temp and outdoor temp which is typically above 32 degrees
  • The floor has had significant air sealing and insulation work performed already; some investment has taken place
  • The cost to seal and insulate the floor is considerably less then encapsulation for some reason

 

A Big Opportunity That Often Gets Overlooked

Too often the ducts that are running through crawl spaces are asked to do way too much. 

Not only do they need to carry conditioned air to the furthest reaches of your home, but in some cases they are expected to transport 90 degree air through a duct that is super cooled to 25 degrees on the coldest of days.

Sealing a crawl space from the outside can drastically improve the performance of your HVAC system and will contain duct leakage because the immediate barrier outside of the ducts also plays into the amount they leak.

For example, ducts that run through an open crawl space will leak much more due to the pressure dynamics compared to an encapsulated crawl space.

 

How to Properly Encapsulate a Crawl Space

It is important to not begin a foundation insulation retrofit project until it is well drained and dry.  Drainage should be the priority if the crawl space recurring takes on water.

Next, the crawl space should be free of debris and items that might impede the ability to install a vapor barrier.  A thick plastic vapor barrier should always be installed in crawl spaces with dirt floors.

The vapor barrier should be sealed to the walls, piers and any other penetration from the ground.

Crawl space walls should be air sealed and insulated (typically by using a rigid foam board with high R-value) all the way up to the rim joist.  The rim and band joist should be air sealed and insulated.

 

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