Crawl Space Insulation-

The Details No One Will Tell You and Most Do Not Know!

 
 


Written by: Matt Leech
Date: January 2011

Photos courtesy of crawlspaceinfo.com


When it comes to crawl space insulation there is very little useful information written that will guide someone towards the results they seek. Agree? Well then, this article is for you. I will list nearly every way there is to install insulation in a crawl space and what you get for it. I will even discuss the wrong ways so that you will know why it will not work.


Let’s get started.....


Floor Joist Insulation-

I want to discuss what’s wrong with insulating the floor joists (crawl space ceiling) first. Most homes in the U.S. have the floor joists insulated with a fiberglass insulation. This method was thought to be correct since the beginning of time, and still does to a lot of people. The biggest factor that brought homeowners to believing this was the correct way was the building code. The building code left little choice in the matter of insulating a crawl space since the 40’s. The code required R-19 fiberglass insulation installed in the floor joists with the kraft paper facing the conditioned side of the space. The conditioned space is your heated and cooled home, which means 80% of the floor joist insulation is installed wrong. It was most likely installed
correctly at the time the home was built, but then replaced due to getting wet and/or falling out of the joist cavity. Installed correctly means to the code at the time it was installed not the way it should be. To clear the air, it really does not matter which way the kraft paper faces on the fiberglass insulation when it comes to performing better in a crawl space. The fiberglass insulation in an open crawl space had its days numbered right from day one.


The number one complaint about crawl spaces in the winter is cold floors. So, crawl space insulation is the number one topic in the colder months. And there are many websites out there that tell you to do what we have always done. One of the big problems with our building industry is there is no requirements to get continued education in order to stay working in this field. This causes a “always do what we have always done” construction blunder. Which then slows, if not entirely halts, implementing new construction technologies that were researched to improve our safety and health. Even the fiberglass insulation companies (in my opinion) won’t set the record straight because they sell so much fiberglass insulation to people installing it wrong. In short, you will search the internet for answers and end up more confused than you were before you started, so be prepared.


Fiberglass, Floor Joists and Poor Performance.....

In order for fiberglass to work properly it needs to be in a clean, dry space and an open crawl space is not that place. Fiberglass insulation works as an insulator because it traps air in the fibers of the insulation and slows the collision of warm and cold air. If the fiberglass insulation gets wet or very damp it will begin to collapse, get heavy and fall from the floor joists rendering it useless to trap air and be an insulator. For this type of insulation to work properly it has to remain “fluffy”, dry and clean.


Picture this,
warm air is on one side of the insulation and cold air on the other, they are not allowed to come into direct contact with each other which would cause the cold air to absorb the warm air. As you get closer to the center of the fiberglass insulation it is more of a mixture of both warm and cold, in theory anyway. How well this insulation works depends on how much colder the cold is compared to how warm the warm is. For example, if the temperature outside is 20° F and the home is 70°F a higher R value will be needed to slow the cold air from absorbing the warm conditioned air in the home. If the outside temperature were 40°, the R value requirements would be far less due to the lessened amount of cold air. That is the first part of the equation.


The next part has to do more with the forces of nature than anything else. We all know heat rises and cold falls, and this is a very important part of the solution to cold floors in a home. When the heater, furnace or heat pump comes on to heat the home the heat immediately rises to the ceiling. The rising warm air is replaced on the floor by falling cold air. So, since the heat rises away from the floors and the cold falls toward the floors your feet will always be in the coldest part of the room. Insulation in the floor joists will not change this.


However,  without insulation in the floor joists, your floors will be colder than with insulation. Here’s why; We know cold absorbs heat and lack of heat is cold. The next failure by design is the foundation vents. These allow the cold winter air to penetrate the homes envelope (your crawl space) which in turn absorbs the heat from your home via your floors. The cold temperatures from outside cool the homes structure, water lines (threatening frozen pipes) and subfloor. Like putting these items in a freezer (or outdoors) they will change temperature throughout and radiate the cold from all sides (your home being one of those sides). The structure and subfloor system will then begin to remove the heat from your home, remember cold absorbs heat. When you touch these floors with your bare feet- Oie! As you can see the insulation will slow this problem, but not stop it. Add to it the fact that the heat is rising away from the floors and you have some really cold floors. This of course affects your heating costs.


The Real Problem!

The real problem is we have been fighting the battle at the wrong front. The battle is and has always been between the inside and the outside, but we have (in the past) made it between the home and the crawl space. Those days are over, if you want them to be.


We associate warmth with insulation,
so it only makes sense that if we install insulation or even more insulation the space will be warmer. To some degree this is true, but only to some degree. Every modern walk-in freezer uses insulation to keep in the cold and every coffee thermos uses insulation to keep in the heat. The point is, the purpose of the insulation is to help maintain a desired temperature not create it. If a space is cold it is because it lacks heat and it may lack heat because cold air has entered the space, nonetheless it lacks heat. So where is the cold air coming from? In crawl spaces it mostly comes from the foundation vents, plain and simple. It does not matter if they are open or close (mechanically). The only real improvement is to stuff fiberglass insulation in the foundation vent opening. But you can’t do that because there will be no way for the moisture from the earth to escape the crawl space, at least not without doing damage to the home.


We didn’t learn from doing it right!

Like most any other subjects related to building construction, it seems as though it has to be done wrong before it can be done right. If a building collapses, it would be investigated to find out why. We then use this information to improve building codes so that we don’t make the same mistakes. The shortcomings of the old crawl space design have succumb to the same investigation and improvement strategies.


Improving the Results

Now that we have identified where the battle really is, lets look at how to improve the results.


Cold Floors-

Now we know what causes the cold floor problem; we also know installing fiberglass insulation in the floor joists will not fix it. The battle is between the inside and the outside of the home. So then, it only makes sense to insulate between the inside and the outside like we do for the rest of our home. However, this will do little good with foundation vents, which will allow the cold air to pass right by the insulation. The foundation vents are there to allow excess moisture to escape the crawl space. Unfortunately, they don’t consistently work that way in reality, but that is what they are there for. Back to what the code allows in 2010- We can eliminate the vents in the foundation if we handle the moisture from the earth a different way. Regardless of how much moisture you think you have coming from the ground you must put in place a way to control the ground moisture and it must be done a certain way or you will cause more problems than you fix.


Control Moisture Coming From The Earth....

Click here for the longer more detailed description on how to seal a crawl space - watch installation videos or learn about soil gasses otherwise here is the short description:

A continuous vapor barrier (or vapor retarder)must be installed to cover the entire crawl space floor then sealed to the concr
ete foundation. The vapor barrier must then be taped at all seams and sealed around all supports, plumbing and protrusions.


If you are going to go through all of that work, select a vapor barrier like the DrySpace™ brand crawl space vapor barrier to ensure it will last.


Back To Cold Floors...

Now that the ground moisture is sealed out to prevent major structural damage to the home, you can proceed with removing the foundation vents. Notice I said removing the vents and not closing them. Just closing the vents, as stated earlier, does not work and neither does installing vent covers. Now that the “windows” are no longer open you can put heat and the proper crawl space insulation to work and fix the cold floors.


Proper Crawl Space Insulation

There are a few kinds of insulation that you should use in a crawl space and a few kinds you should not. One of the kinds you should not is polyurethane closed/open cell spray foam insulation. The spray foam guys will tell you different and they will tell you their foam will seal all air penetrations in the foundation and sill plate. http://www.squidoo.com/cooler-insulation





What they won’t tell you is:


  1. Bulletcarpenter ants are known to nest in it (Photo courtesy of Justin Nickelsen from Nickelsen Home Inspections LLC)

  2. Bulletit makes it impossible to inspect for damage caused by insects and/or water

  3. Bullethas had mold growth issues

  4. Bulletit is the most expensive of all the options

  5. Bulletits messy and hard to control

  6. Bulletbecause of its make up, it will absorb moisture causing a drop in R-value performance within the first year

  7. Bulletit looses 75% of its R-value in 5 years.



The fact is, there is a better and more cost effective option in rigid polystyrene foam insulation (pink/blue). The pink or blue rigid foam board offers:


  1. Bulletlower installation costs

  2. Bulleta DIY project

  3. Bullettreated with a fire retardant - Flame Spread = 25 / Smoke Development =<450 (which will be important in the cold floor solution as you will learn later)

  4. Bulletlooses only 25% of its R-value in 5 year

  5. BulletDoes not absorb moisture


Installing rigid insulation on the crawl space foundation wall is both cost effective and the most energy efficient, when installed correctly.


Back To Cold Floors....

Now that we have the crawl space foundation walls insulated the last thing to address is the lack of heat. conditioned crawl space is a crawl space that is both heated and cooled like a basement or any other part of the home. By supplying heat to the crawl space you greatly improve the temperature of the homes floors. The heat that is being delivered to the crawl space will act like the heat in the rest of the home, rising to the ceiling. This time the ceiling is your floors and the heat is not lost into the attic. This process does not cost more in your heat bill either. Actually it costs less and for many reasons; you do not have the cold air entering the homes envelope which robs the home of heat, the heat stays inside your home (if properly insulated) by leaking into your living area and the warm air that passes from the crawl space into the living area will help cause the furnace to run fewer cycles. In its simplest form, you are turning your old nasty crawl space into a mini basement.



Recommended steps to properly insulate in the different crawl space designs and the expected effect:


Open crawl space Definition- concrete floor or 6 Mil plastic (qualifies minimum permeance rating of 1) laid on the floor (not sealed to the foundation/piers or taped at the seams) lapped 12” at the seams and has mechanical foundation vents.


  1. 1.Most areas in the country will require insulation with an R-Value of 19 installed in the floor joists. Foundation wall insulation is useless in this design.

  2. 2.Options for venting in an open crawl space-

        1. Close (mechanically) in winter/Open in summer

        2. This will allow warm humid air into the crawl space during the summer months which will condensate to cool surfaces likely causing: wet insulation, musty odors, high moisture levels in the structure, high moisture levels in wood flooring and throughout the home, mold, mildew and fungus growth, damage to heating/cooling systems and attracting of insects.

        3. In the winter this will help to fend off the cold winter air, lessening the problems with cold floors, threatening frozen water lines and robbing heat from your home. However, this will also allow the temperature to be higher, which could cause any summer moisture problems to continue.


        4. Close (mechanically) in summer/Open in winter

        5. This will give some defense to combat warm moist air entering the crawl space from the outside. However, it also traps the moisture that evaporates from the earth likely causing: wet insulation, musty odors, high moisture levels in the structure, high moisture levels in wood flooring and throughout the home, mold, mildew and fungus growth, damage to heating/cooling systems and attracting of insects.

        6. In the winter this will allow the cold winter air to enter the crawl space causing heat loss, cold floors and threatening frozen water lines.

  3. 3.This option is the minimum requirements by all building codes in the U.S.

  4. 4.Using a dehumidifier in this environment will do little good because both of the open and close options for the foundation vents will cause a nonstop supply of moisture. Expect higher energy costs and a shortened life of the dehumidifier if running in this environment.


Closed crawl space Definition- concrete floor or 6 Mil plastic (both qualifies as minimum permeance rating of 1) laid on the floor (not sealed to the foundation/piers or taped at the seams) lapped 12” at the seams and does not have mechanical foundation vents. It does, however, have supply air from the A/C (no return air to the home) or a permanently installed crawl space dehumidifier (see below “Encapsulated crawl space” to determine which is best for your situation).


  1. 1.Most areas in the country will require insulation on the foundation walls equal to or greater than an R-Value of 5. This type of insulation allows for conditioned air to be introduced into the crawl space. However the insulation needs to be treated with a fire retardant.

  2. 2.This type of crawl space also allows insulation with an R-Value of 19 installed in the floor joist if the crawl space and has a permanently installed dehumidifier.

  3. 3.If this crawl space has a concrete floor, it may or may not have a vapor barrier under the concrete. A layer of concrete on the dirt floor qualifies as a moisture retarder with a perm rating less than one.


Expected effects with supply air-

    1. -Warmer floors

    2. -No frozen water lines

    3. -Possibly lower moisture

  1. Expected effects with dehumidifier-

    1. -Lower moisture levels

    2. -Lower odor problems

    3. -Lower threat of Mold and Mildew

    4. -Fewer insects


Encapsulated crawl space Definition- concrete floor or high performance plastic (both qualifies as minimum permeance rating of 1) laid on the floor and walls, sealed to the foundation/piers and taped at all seams. Does not have mechanical foundation vents. It does, however, have supply air from the A/C (with or without return air to the home) or a permanently installed crawl space dehumidifier.


  1. 1.Most areas in the country will require insulation on the foundation walls equal to or greater than an R-Value of 5 (in rigid foam R-5 is 1” and R-10 is 2”). This type of insulation allows for conditioned air to be introduced into the crawl space.
              1. -The insulation needs to be treated with a fire retardant if you are going to add supply air only. Owens Corning (Pink) and Dow (Blue) make an extruded polystyrene rigid foam that meets these requirements.

              2. -White foam board is less expensive but does not meet these requirements.

              3. -If you are going to add a return air duct back to the home or use the crawl space as a plenum (this will make the crawl space by NCDOI’s definition- a conditioned crawl space) you will need (by code NCDOI R409.8.2 Exception) to cover the insulation with a thermal barrier such as plywood, cement board or metal sheets.

  2. 2.This type of crawl space also allows, as an alternative, insulation with an R-Value of 19 installed in the floor joist of the crawl space and a permanently installed crawl space dehumidifier. Conditioned air is not an option with this method.

  3. 3.A crawl space with a concrete floor and no water problems may only need foundation wall insulation and a crawl space dehumidifier, conditioned air or both (depending on if there is an vapor barrier installed under the concrete floor).

  4. 4.Determine if you need Conditioned Air, a Dehumidifier or both:


          1. -Add Conditioned Air if you have problems with:

              1. -Cold Floors

              2. -Low to medium moisture (north of Tennessee)

              3. -High energy bills


      1. -Add Dehumidifier if you have problems with:

        1. -High moisture (All areas)

        2. -Mold, Mildew and Fungus

        3. -Insects

        4. -Odor


      1. -Add both Conditioned Air and Dehumidifier if you have a combination of problems listed above.


Expected effects with supply air-

    1. -Warmer floors

    2. -Lower energy bills

    3. -Lower or eliminated odor

    4. -Fewer insects

    5. -Lower moisture

  1. Expected effects with a dehumidifier-

    1. -No insects

    2. -Lower and more controllable moisture

    3. -Lower or eliminated odor

    4. -No Mold or Mildew

    5. -Cleaner air in the home

    6. -A/C will run more efficient


North Carolina’s Code Definitions NCDOI-

Source- Click Here


     Conditioned Crawl Space – A foundation without wall vents that encloses an

intentionally heated or cooled space below the lowest supported floor.  Insulation is

located at the exterior walls of the crawl space.  “Intentionally heated or cooled” means

air is both supplied to the crawl space and returned from the crawl space by the

equipment serving the dwelling.  Closed crawl spaces become plenums when the crawl

space is used as a means to distribute supply air from the equipment serving the

dwelling to other spaces in the dwelling or as a means to return air from other spaces in

the dwelling to equipment serving the dwelling.

     Closed Crawl Space – A foundation without wall vents that uses air sealed walls, ground and foundation moisture control, and mechanical drying potential to control crawl space moisture.  Insulation may be located at the supported floor level or at the exterior walls of the crawl space.  Conditioned crawl spaces, defined below, are a special case of closed crawl spaces.  Not all closed crawl spaces are conditioned. 

     Wall Vented Crawl Space – A foundation that uses foundation wall vents as a primary means to control crawl space moisture.  Insulation is located at the supported floor level.

     Thermal Barrier – A material that will limit the average temperature rise on the unexposed surface to no more than 250oF after 15 minutes of fire exposure complying with the ASTM E 119 standard time temperature curve. According to Section R314.4 of the Residential Code, ½” gypsum wallboard qualifies as a prescriptive solution for a thermal barrier.


Notable Crawl Space Liner Code Citations from NCDOI ( North Carolina Code)

Source- Click Here



    R409.2.2 Liner. The ground vapor retarder may be installed as a full interior liner by sealing the edges to the walls and beam columns and sealing the seams. Single piece liner systems are approved. The top edge of the wall liner shall terminate 3 inches below the top edge of the masonry foundation wall. The top edge of liner shall be brought up the interior columns a minimum of 4 inches above the crawl space floor. The floor of the crawl space shall be graded so that it drains to one or more low spots.  Install a drain to daylight or sump pump at each low spot. Crawl space drains shall be separate from roof gutter drain systems and foundation perimeter drains.

    R409.2.1.1 Wall liner termite inspection gap. Provide a clear and unobstructed 3” minimum inspection gap between the top of the wall liner and the bottom of the wood sill. This inspection gap may be ignored with regards to energy performance and is not intended to create an energy penalty.


Notable Insulation Code Citations from NCDOI (North Carolina Code)

Source- Click here


    R409.8 Insulation. The thermal insulation in a closed crawl space may be located in the floor system or at the exterior walls. The required insulation value can be determined from Table N1102.1

    Exception: Insulation shall be placed at the walls when the following condition exists:

1. The closed crawl space is designed to be an intentionally heated or cooled, conditioned space.

    R409.8.1 Wall Insulation. Where the floor above a closed crawl space is not insulated, the walls shall be insulated. Wall insulation can be located on any combination of the exterior and interior surfaces and within the structural cavities or materials of the exterior crawl space walls. Wall insulation systems require that the band joist area of the floor frame be insulated. Wall insulation shall begin 3 inches below the top of the masonry foundation wall and shall extend down to 3 inches above the top of the footing or concrete floor, 3 inches above the interior ground surface or 24-inches below the outside finished ground level, whichever is less.  No insulation shall be required on masonry walls of 9 inches height or less. 




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Photo courtesy of CrawlSpaceInfo.com