As more and more crawl spaces have issues with moisture and high humidity, homeowners are discovering the proven benefits of the Sealed Crawl Space.
Also called a Conditioned Crawl Space or an Encapsulated Crawl Space, thousands of existing homes every year are converted to a sealed design, and thousands more are built from scratch to never be a vented crawl space!
As with any major project, you should become familiar with your State Codes. We strongly suggest you contact local companies that specialize in this type of work (not your termite guy or insulation contractor).
Crawl Spaces are designed to be vented to the outside air - allowing the air to circulate beneath the home and help clear out the built-up humidity and moisture that can come from walls, the ground, or simply the humidity in the air.
It gets complicated, as sometimes it's truly circulation that is the problem (tight crawl spaces, lots of HVAC piping affecting airflow), but it's often a temperature/dew point issue. Simply put, the air from outside cools in the crawl space until the humidity comes out as dew. Just like when you have a cool drink outside in the summer, the moisture will condense right on it.
When handling the obvious issues (excess moisture in the soil, etc) have been exhausted, (beyond the scope of this lens, and why we strongly recommend you contact a contractor!) - you can be left with a Sealed Crawl Space as the option.
In short, a Sealed Crawl Space stops your home from letting air circulate beneath it.
The vents are sealed, a thick poly covers the floor and walls, and the space is conditioned.
While originally conceived to combat high moisture levels, there are several other benefits for homeowners!
Originally conceived to control moisture in crawl spaces, Sealed Crawl Spaces have 3 over-arching benefits.
1. Give the homeowner control over the humidity and moisture levels beneath their floors. Sagging, stringy insulation? Molds? Rot? Sweating HVAC? All caused by moisture and controled by a Sealed Crawl Space.
2. Improved efficiency - Studies show that up to 50% of the air in a home comes from the crawl space (it's called the "stack effect", just like a chimney, air below moves UP into the home). When that air is humid air from outside, your HVAC has to start with more moist air to cool or heat your home. Sealing the crawl space allows the air in the home to be dryer to start with - letting your HVAC system run approximately 20% more efficiently!
3. Allergies - If outside air, with it's dust, pollen, etc. is moving beneath your home - and 50% of the air IN the home is coming from the crawl space, all those allergens are coming up with it.
The International Building Code recognizes sealed crawl spaces, but State Codes modify to meet their specific requirements. In cooler climates, insulation may be required on the floor, or the walls - or both! Options to Condition the space vary as well. Read your State's code and/or contact your local Code Enforcement division to get additional information!
Your options to consider, whether a contractor is going to do it for you or you're going to try to DIY it:
Thermax is a rigid insulation board that comes in 4x8 sheets and is lined with a metallic face that many Code Enforcement divisions recognize allows it to be used in buildings (again, check with you local and state municipality!)
This board can be cut-down to the size of the vent openings and when the opening is plugged, it is caulked ito place.
while I've seen sealed crawl spaces with the vents sealed with cheaper non-code compliant foam boards, or with poly caulked into place, they seldom perform as well as one with the vents truly plugged. Take the extra effort and do it right!
The plastic or poly you use is key.
While most codes recognize as little as 6mil (thousandths of an inch) poly, most quality contractors will recommend between an 10 and 20 mil poly. These can come in all colors, but you want one that is a vigin polyethylene MADE for crawl-space applications! They'll not break down when in contact with the floor, and have less chance of off-gassing or releasing smells.
While codes will frequently recognize sealing the vents and covering the floor with a very well installed poly, this typically makes for a less-efficient Sealed Crawl Space that needs to work harder to stay 'conditioned'. I ONLY recommend this option when a home has poured concrete walls.
Block, brick, and mortar can all absorb moisture from the air, driving rain, or exterior soil built up and will release this moisture as a humidity into the crawl space - often leaving behind efflorscence on the walls.
Running the poly up the walls, fastening it to the walls, and caulking the entire top edge blocks this humidity and makes your new sealed crawl space substantially more efficient!
Most codes give you the choice of insulating the joists or the walls, but require at least one option be taken.
My general rule of thumb is if you have joist insulation in good condition - leave it.
If it's in poor condition and in need of replacement, take it out and insulate the walls.
If you're interested in a sealed crawl space primarily for the efficiency aspect, the insulated walls will be your best choice by far.
When insulating the walls, codes require a 3 or 4 inch gap left at both the top and bottom - the top for a terminte inspection zone and the bottom to prevent wicking of moisture into the insulation.
Wall insulating can take several forms - most use a rigid insulation like Thermax, but as you can see in the pictures in this lens some contractors have a 'wrapped' insulation available which is a fiberglass batt wrapped in a thick poly. Less expensive and easier to manipulate in a crawl space, this can be a real money saver.
Code allow you several different options to condition the space once it's sealed. 'conditioning' the crawl means to remove humidity from the air, keeping moisture levels under control!
Dehumidifier - this is the most common (depending on your area). It will run as needed and typically only needs to be checked every 6 months - to clean or replace the filters. Santa-Fe builds dehumidifiers that are designed for crawlspaces and basements - specifically to work better at the cooler temperatures. They're not cheap, but you'll get much better results than with a cheap-o walmart special.
HVAC air - you can have your mechanical contractor to modify your HVAC system so that when the heat or AC in your house kicks on, it blows into your crawl space as well. Effective, but be aware you'll be REQUIRED to insulate the walls - and often this can make it a more expensive option overall than the dehumidifier. Also, consider than this puts an extra load on your HVAC system and it may perform less efficiently overall.
House air - I don't ever see this option taken, but it's available. Opening(s) are cut into your floor, forcing the air in your home into the crawl and conditioning the space. Most homeowners are simply not interested in cutting into their floors!
Also called a Conditioned Crawl Space or an Encapsulated Crawl Space, thousands of existing homes every year are converted to a sealed design, and thousands more are built from scratch to never be a vented crawl space!
As with any major project, you should become familiar with your State Codes. We strongly suggest you contact local companies that specialize in this type of work (not your termite guy or insulation contractor).
What is a Sealed Crawl Space?
Crawl Spaces are designed to be vented to the outside air - allowing the air to circulate beneath the home and help clear out the built-up humidity and moisture that can come from walls, the ground, or simply the humidity in the air.
It gets complicated, as sometimes it's truly circulation that is the problem (tight crawl spaces, lots of HVAC piping affecting airflow), but it's often a temperature/dew point issue. Simply put, the air from outside cools in the crawl space until the humidity comes out as dew. Just like when you have a cool drink outside in the summer, the moisture will condense right on it.
When handling the obvious issues (excess moisture in the soil, etc) have been exhausted, (beyond the scope of this lens, and why we strongly recommend you contact a contractor!) - you can be left with a Sealed Crawl Space as the option.
In short, a Sealed Crawl Space stops your home from letting air circulate beneath it.
The vents are sealed, a thick poly covers the floor and walls, and the space is conditioned.
While originally conceived to combat high moisture levels, there are several other benefits for homeowners!
What are the advantages of a Sealed Crawl Space?
Originally conceived to control moisture in crawl spaces, Sealed Crawl Spaces have 3 over-arching benefits.
1. Give the homeowner control over the humidity and moisture levels beneath their floors. Sagging, stringy insulation? Molds? Rot? Sweating HVAC? All caused by moisture and controled by a Sealed Crawl Space.
2. Improved efficiency - Studies show that up to 50% of the air in a home comes from the crawl space (it's called the "stack effect", just like a chimney, air below moves UP into the home). When that air is humid air from outside, your HVAC has to start with more moist air to cool or heat your home. Sealing the crawl space allows the air in the home to be dryer to start with - letting your HVAC system run approximately 20% more efficiently!
3. Allergies - If outside air, with it's dust, pollen, etc. is moving beneath your home - and 50% of the air IN the home is coming from the crawl space, all those allergens are coming up with it.
Sealed Crawl Space Options
The International Building Code recognizes sealed crawl spaces, but State Codes modify to meet their specific requirements. In cooler climates, insulation may be required on the floor, or the walls - or both! Options to Condition the space vary as well. Read your State's code and/or contact your local Code Enforcement division to get additional information!
Your options to consider, whether a contractor is going to do it for you or you're going to try to DIY it:
- What to seal the vents with
- Poly - floor only or floor and walls
- Insulation in joists or on walls
- Conditioning options:
- dehumidifier
- HVAC air
- House Air
Sealing the vents
Thermax is a rigid insulation board that comes in 4x8 sheets and is lined with a metallic face that many Code Enforcement divisions recognize allows it to be used in buildings (again, check with you local and state municipality!)
This board can be cut-down to the size of the vent openings and when the opening is plugged, it is caulked ito place.
while I've seen sealed crawl spaces with the vents sealed with cheaper non-code compliant foam boards, or with poly caulked into place, they seldom perform as well as one with the vents truly plugged. Take the extra effort and do it right!
The Poly
The plastic or poly you use is key.
While most codes recognize as little as 6mil (thousandths of an inch) poly, most quality contractors will recommend between an 10 and 20 mil poly. These can come in all colors, but you want one that is a vigin polyethylene MADE for crawl-space applications! They'll not break down when in contact with the floor, and have less chance of off-gassing or releasing smells.
While codes will frequently recognize sealing the vents and covering the floor with a very well installed poly, this typically makes for a less-efficient Sealed Crawl Space that needs to work harder to stay 'conditioned'. I ONLY recommend this option when a home has poured concrete walls.
Block, brick, and mortar can all absorb moisture from the air, driving rain, or exterior soil built up and will release this moisture as a humidity into the crawl space - often leaving behind efflorscence on the walls.
Running the poly up the walls, fastening it to the walls, and caulking the entire top edge blocks this humidity and makes your new sealed crawl space substantially more efficient!
crawl space insulation - joist or walls
Most codes give you the choice of insulating the joists or the walls, but require at least one option be taken.
My general rule of thumb is if you have joist insulation in good condition - leave it.
If it's in poor condition and in need of replacement, take it out and insulate the walls.
If you're interested in a sealed crawl space primarily for the efficiency aspect, the insulated walls will be your best choice by far.
When insulating the walls, codes require a 3 or 4 inch gap left at both the top and bottom - the top for a terminte inspection zone and the bottom to prevent wicking of moisture into the insulation.
Wall insulating can take several forms - most use a rigid insulation like Thermax, but as you can see in the pictures in this lens some contractors have a 'wrapped' insulation available which is a fiberglass batt wrapped in a thick poly. Less expensive and easier to manipulate in a crawl space, this can be a real money saver.
Conditioning your Sealed Crawl Space
Code allow you several different options to condition the space once it's sealed. 'conditioning' the crawl means to remove humidity from the air, keeping moisture levels under control!
Dehumidifier - this is the most common (depending on your area). It will run as needed and typically only needs to be checked every 6 months - to clean or replace the filters. Santa-Fe builds dehumidifiers that are designed for crawlspaces and basements - specifically to work better at the cooler temperatures. They're not cheap, but you'll get much better results than with a cheap-o walmart special.
HVAC air - you can have your mechanical contractor to modify your HVAC system so that when the heat or AC in your house kicks on, it blows into your crawl space as well. Effective, but be aware you'll be REQUIRED to insulate the walls - and often this can make it a more expensive option overall than the dehumidifier. Also, consider than this puts an extra load on your HVAC system and it may perform less efficiently overall.
House air - I don't ever see this option taken, but it's available. Opening(s) are cut into your floor, forcing the air in your home into the crawl and conditioning the space. Most homeowners are simply not interested in cutting into their floors!
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