How to properly Ventilate a crawl space: Basically, every traditional home built a long while ago or of recent, is designed and built with a basement which has become an essential part for experiments and storage purposes, or basically whatever you want to use it for asides storage. However, basements are pretty expensive to build and are sure to take a chunk of your building budget or add more, to say the least and is why the crawl space was invented.
Crawl spaces are generally a cheap option to having basements in the home and are easily made by leaving a few inches spaces off the ground before starting the actual flooring of the house. Though this invention would save you a chunk of money, lack of proper maintenance could also cost you more, and not only in money but in environmental hazards.
Crawl spaces most times, harbors, piping, and HVAC outputs in the home, and when there is not enough attention, an environmental condition like moisture is sure to ruin stuff or create a home for mold and pests to dwell in and climb up the house eventually.
Moisture control is one of the biggest challenges faced in maintaining a crawl space, especially on how to vent it without letting more moisture in. The old-fashioned way of leaving the space open has been found to only let in more moisture content from the atmosphere than remove preexisting ones.
In all, it is a wrong solution, which is why in this article, we would be discussing all you need to know to work and maintain effectively.
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Do you need to vent a Crawlspace?
Crawl spaces are generally prone to different harsh atmospheric conditions at several times throughout the year. The result of not dealing with moisture in a crawl space is numerous, and most of it results from a vast quantity of moisture that has gathered up in the enclosed space over time.
Venting the space was initially seen as the best way to dealing with the problems of moisture accumulation (why not just leave it open and let air move the moisture), but as simple as that sounds, it doesn’t just work that way.
Venting the crawl space by letting open to the air, in a nutshell, would instead do more harm than good, exposing the area to more moisture rather than taking away the preexisting one.
Automated louvers have long been touted to do the venting job accurately, being able to open and close, allowing air to pass through and shutting it some other times depending on the climate condition (opens when the temperature drops below freezing point and closes otherwise). However, these louvers have been known to be not durable, therefore sure to get stuck not too long after installation.
For this reason, they aren’t the most preferred solution for venting crawl spaces. In simple terms, it is important to vent the space reliably to avoid moisture build-up that could cause damages and contaminations.
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Should crawl space vents be opened or closed
Since it is already discussed and agreed on that the dangers of crawl spaces are easily eliminated by proper ventilation that removes moisture contents, it now becomes a question of the way and manner to vent the area with maximum impact effect and effects on backfires.
There are two ways by which crawl spaces can be vented; it could be in an open way, allowing air breeze through and out, hence removing moisture or completely sealing the area and controlling the aeration and moisture condition inwardly.
Know that trying to rid moisture by exposing it to more moisture is just kind of counterproductive and doesn’t make much sense. Though it seems like the air from outside is colder than high moisture air in your crawlspace, but in the real sense, it isn’t.
Ventilation and consequentially moisture is rather rid of by completely sealing the area, and controlling the atmospheric condition inwardly. Don’t vent to open air, but rather achieve proper ventilation by controlling it, most times by making use of an exhaust vent or a dehumidifier.
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Crawl space ventilation calculations: knowing the needed amount of ventilation
Knowing how and the specific way to ventilate a space might quite tricky. Get a device that’s too much above the required, and it’d be a waste of money. Purchase one that’s too small in capacity, and it would still be a waste of money, as it wouldn’t be able to do the job required of it.
For this reason, it is essential you get a spot-on, the required amount of exhaust vents necessary to get the job.
This is achieved by calculating the requirements necessary to pull ventilation off, and is we have put the calculation together to make it easier for you. Follow closely.
1) Calculate the total area of the crawl space to be vented
This is estimated by measuring the length and width of the total space to be vented, and multiplying the two values,
putting it in the formula, Area= length X width in feet.
2) Divide the area of the space by 150sqft
This is done in order to find the total square feet of vent space needed.
In formula, vent space = area ÷ 150sqft.
3) Divide the total vent area by two
This is done in order to determine the soffit vent area.
In the formula, soffit vent area = Vent space ÷ 2
4) Determine the vent area in sq.ft
Many manufacturers today would use indicate the net free area the venting exhaust can serve, taking into account the actual open area of the vent rather than the total vent size.
In a case when the net free area is available, use it in calculating the soffit area. This method is done by multiplying the length and width of the vent space in inches, then dividing by 144.
In formula, vent area in square feet = (length x width in inches) ÷ 144
Taking an example now to calculate the vent area in square feet for a crawl space of 50ft in length and 60ft in width.
Total vent area needed = length x width= 50 x 60 = 3000sqft
Soffit vent area = area ÷ 150 = 3000 ÷ 150 = 20sqft of total vent space needed.
Soffit vent area = vent space ÷ 2 = 20 ÷ 2 = 10sqft soffit vent area.
(Hence 10sqft intake net area, and 10sqft exhaust net area is needed)
Now convert to inches to meet manufacturer’s standards,
soffit vent area = 10sqft x 144 = 1440sqin.
Hence 1440sqin intake of net area needed, and 1440sqin exhaust of net area needed.
Now, to determine the number of vents needed, divide the soffit vent area by the Net free area rating of the vent by manufacturers.
Assuming the intake vent is about 5sqin in net free area rating per linear ft. while the exhaust vent is about 8sqin net free area per linear ft.
To achieve 1440sqin of intake net free area would require 1440 ÷ 5 = 288 linear ft.
To achieve 1440sqft of exhaust net free area would require 1440 ÷ 8 = 180 linear ft.
How much does it cost to ventilate a crawl space?
Crawl spaces are actually expensive to ventilate, especially a proper one if you want to get the job done in a proper manner. Many times, these installations cost between $1,500 and $15,000 in total, including suppliers of materials and professional labor.
The ventilation process involves an encapsulation system that consists of a thin, screen-layer plastic liner, and some advanced version using a specially designed thicker liner or a multi vapor barrier, dehumidifier, sump pump or drainage trenches. Of course, deciding to go for all these features would mean more cost.
It is paramount you install a layer of encapsulation with vent inlet and exhaust, to say the least, then decide to negotiate the inclusion of sump pump, dehumidifier or drainage trenches, depending on your budget and how much you are willing to part with.
Also, ventilating after parking or building newly is preferable to doing so later. It is better to prevent the damage than pay a professional to both correct and prevent it from happening again.
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Best methods to properly ventilate a crawlspace
Before taking on the adventure of ventilating your crawl space, there are specific standards you should know and observe, which would help you create natural clean ventilation across space.
This involves using materials with the following specifications;
- Metal sheet plates with holes no less than 0.070 inches thick
- Expanded metal sheet plates of no less than 0.047 inches thick
- Corrosion-resistant wire mesh of at least 1/8-inch thick
- Cast-iron grill or grating.
These materials would allow for the proper flow of air to eliminate humidity accumulation within the space.
Some necessary inspections should be taken in order to ascertain the condition of the space, as well as associated dangers and possible solutions before embarking on the ventilation process.
- Electrical inspection against electrocution
- Mechanical/ combustion systems located in the crawl space should be inspected for adequate venting sources and if none, a proper channel should be created for them.
- Mold infested areas should be investigated and rid of properly by a professional before going on.
- The area should be checked for asbestos contents and professionals invited to get rid of it, as they are really dangerous and able to cause lung diseases.
- Other hazardous materials should be cleared.
- Deal with exterior moisture sources leading directly into the crawlspace like lawn sprinklers, roof drainage, leaking roofs, standing water on the floor, poor access doors, weak grading perimeter around the house, etc.
Now moving unto the actual ventilation options and processes, there are about 4 methods by which you can achieve this, which are;
1) Vent the crawlspace to the outside:
Although this looks easy and the most direct to achieve, it is, however, not recommended to be used in humid climates. This is as a result of the fact the air being vented into the space from outside carries more moisture content than the crawlspace itself.
If you have installations like the HAVC or ductwork system lying in the space, too, it is best you stay away from this option. In essence, this should be your least choice.
2) Supply air from the HVAC system:
This process involves encapsulating the crawlspace and adding a little bit of air from the HAVC system, which helps dry the space.
It is effortless and less expensive to do, especially if there is an HVAC system there already, and if it is as effective, it could keep humidity levels below 70% where you would want it. This method may or may not work well, depending on the nature and conditions of the crawlspace.
3) Exhaust air to the outside:
This simply involves placing an adequately sized exhaust fan in strategic locations around the encapsulated space, which would be responsible for pushing out large quantities of humidity filled the air from the crawlspace to the external environment. Following IRC standards,
“Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic foot per minute (0.47 L/s) for every 50 square feet (4.7m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated.”
This method works most times and is a really reliable way of getting the job done.
4) Install a dehumidifier:
This is basically purchasing and installing an adequate capacity dehumidifier in the already encapsulated crawlspace, setting it to run according to the conditions of the crawl space atmosphere. Dehumidifiers are very efficient in doing the job, and though they are more expensive (especially the high capacity models), it is the most effective way to get the humidity out.
Also Read: Best Dehumidifier for large room
Final Thoughts on proper crawl space Ventilation
Having an adequately vented crawlspace is just as important as designing the house with a crawlspace to save cost at the initial stage.
Houses with inadequate infested spaces over time tend to get a lot of wood rut, consequentially weakening the foundation. And if that’s not scary enough, the thought of molds, pest, and other moisture. We would advise that you get that crawlspace ventilated!!