Save Energy and Money – Insulate Your Crawl Space Properly
Our home was built in 1941 with no basement, just a crawl space. Being a first-time homeowner, and being the neighbor of frugal people, I learned something valuable this past week:
Insulate your crawl space to block drafts and energy loss.
Since buying the house 2 years ago, we’ve noticed drafts coming from certain parts of the home, but we’ve focused on trying to block the air from within the home itself. However, the true problem was our crawl space vents. If you do not have a basement, you probably have noticed vents all around your home leading into the crawl space.
These vents have a single purpose: To allow humidity to escape from under your home.
Why would you need to vent the humidity under your home? Where does it even come from? Well, thanks for asking! Let me answer those questions for you!
Where does the humidity come from?
Unless you live in the Sahara, and never get a monsoon season, you need to worry about the water stored in the ground. On any spring, summer, or fall day, place an empty can, with both ends removed, on the ground. Cover that can with plastic securely. On a hot day, you’ll soon notice condensation forming on the underside of the plastic. It may take longer on a cooler day, but it’ll form. What does this tell you?
It tells you that the ground is always releasing water into the air. There’s physics or something behind it, and I’m sure there’s saturation levels involved, but rest-assured that this affects your crawl space. This leads us to our next question…
How does this affect me?
If you own a crawl space, and it is not properly vented, the moisture from the ground will go directly into your insulation and floorboards. Mold will form and your flooring will begin to rot. I don’t mean to scare you, but I hope you get the point that this moisture NEEDS TO GET OUT! (or at least be contained…read on)
What can I do to my crawl space?
Well, this answer comes in two parts.
First, make sure your vents are open in warm months. Oh, and make sure you have vents. We found that in our home the vents had metal flashing that was partially closed even in the summer months. For now, we kept them closed, and even insulated them, but I’ll get to that later.
In your case, make sure your vents are covered with mesh to prevent small intruders, and ensure there is proper flow on both the inside as well as the outside of the vent (i.e. make sure nothing is blocking either side).
Second, make sure your dirt is covered with heavy plastic. When we re-insulated our crawl space a few years ago, we laid down a good plastic covering, but not enough (we needed a break from the confined space). We need to add more, and that will happen this spring.
The images below illustrate the before and after of a properly covered crawl space. Note, though, that the ceiling is not yet insulated:
And now the last question:
But what about all that cold air in the winter???
Good question. There are vents that automatically close depending on the temperature (non-electric and electric). However, their seals may not be the tightest, and if these vents are on the windy side of your home, you may still feel a draft.
In our case, we decided to stuff R-13 insulation into plastic garbage bags, then into each vent. We noticed an IMMEDIATE and CONSIDERABLE change in temperature and draftiness (or lack of) inside our home. Nick did the same, and now notices his hardwood floors are not nearly as cold anymore.
However, we must make sure we remove the insulation before the beginning of spring so we can vent out the humidity from the crawl space.
If you have proper plastic covering on your crawl space floor, you can tend to wait longer to remove any covering or insulation from your crawl space, but it’s always good to protect yourself on all fronts.
Summary
- Make sure your crawl space is vented and the vents are not blocked
- Cover your crawl space floor with heavy plastic sheeting
…all the way up the foundation walls. You’ll need to get the big stuff, something like 10 x 25. It needs to be heavy duty so it won’t break down. For example check this roll on Amazon - Close or insulate the vents in the winter to save heating costs and you and your family from cold tootsies
- Remember to remove or unblock the vents before the temperature begins to stay above freezing for extended periods
- Be careful when working with fiberglass insulation. Wear goggles, a mask, and thick plastic or rubber gloves. Also, cover all exposed skin when working with it in your crawl space. Those little particles can lodge in your lungs and skin, and be very hard to remove
Photo Credit: Krystle.
Mike is the original Clever Dude, starting the site in 2006 because his wife said “you need a hobby”. Mike loves helping others to avoid the silliness and stupidity that got him into extreme debt, but also learning general life skills and hacks along the way. Mike and his wife “Clever Dudette” are DINKs (Dual Income, No Kids), travel the country in an RV from their home base in DC and are passionate about their respective careers in technology (him) and nutrition (her).
We’ve actually had to put a dehumidifier in our crawl space. We have a good vapor barrier and all, but we live in the South, and the ambient humidity in the summer is just too high. Even with proper ventilation, we often get condensation under the house because it’s cooler down there and, well… When warm, wet air gets cool, it condenses. And when you get condensation, you get mold. Not good. So… I installed a high performance dehumidifer in the crawl space complete with a condensate pump, and then closed the vents.
That’s actually a great idea for warmer temps. For the Northeast US, it really depends on the cost of running such a unit (or even a smaller version) versus insulating and covering your crawlspace.
Next year just buy some hay bales to set in front of or block the vents, its great insulation and you can use it for mulch in the spring, plus it’s cheap. Old farmers down here do this every year in some cases all around the foundation if it’s just up on blocks
Bad advice. Winter air is drier, summer air is moist. If you open the vents in the summer and close them up in the winter, you have let in moist air and trapped it there which is exactly what you don’t want. If you want to insulate your crawl space that is ventilated, insulate the floor above the crawl space. If your crawl space is not ventilated, then make sure all penetrations and holes are sealed and insulate the foundation walls. Also, there should be a vapor barrier on the dirt under the house (usually sheets of plastic).
@Kevin, you have no idea what you’re talking about, nor did you read the article fully. In the summer, the ground AND air are so saturated with moisture that if you don’t have ventilation, the moist air under your house can’t get out and will begin condensing on your joists. Hot air rises, so it will go out through the vents, not come IN!
And I did say that you need to add plastic across your dirt floor. It’s in bold italics. Not sure how you missed that.
Question: i have a A-Frame in nothern AZ with no insulation under the flooring of the crawl spase,As far as vents,it has metal siding all around the side touching the ground(no vents) Should i lay the plastic down on the ground?is R19 sufficient enough to install between the floor joist? We dont use the A-frame that much in the winter but when we do it is very cold when we get there.Thanks
@mike, Since I’m more familiar with the swampy climate here in Washington, D.C., I’m not quite sure what you would need in a dry area like Arizona. The ground probably doesn’t hold as much moisture as it does here, but I would still say lining the ground with plastic is generally a good idea (even if it’s to discourage bugs from multiplying under your house).
As for insulation, I recommend asking your local Home Depot or Lowes professional (or other professional), given the higher average temperature and lack of humidity in your area compared to mine.
Help,
I’m not sure what to do next. I have put down heavy plastic on the ground under the house. I want to put spray insulation under the house next to stop drafts, improve R-rating, block possible rodents, (We live on a horse farm.) and save some money. If good insulation rodents won’t chew and does mold, do I need a vapor barrier to use with the spray insulation, or is the spray foam enough. We have condensation in the morning year around in this region of the southeast.
We have a vented crawl space, and use a dehumidifier in the summer. We are considering insulating the ceiling, and may put heavy plastic on the floor. I’m concerned about the plastic, because when we get heavy rains we get water in the crawl space. The water usually drains out within a couple of hours.
Great post. thank you. I have a 110 year old building with vents in there and no insulation. I’m trying to be a little more efficient this year, so I’m going to suggest to my HOA that we do exactly this. Has anyone also done some spray insulation?
When insulating the floor above a craw space, should the vapor barrier be up or down?
@Greg, the plastic vapor barrier is meant to be laid on the ground.
Not the plastic vapor barrier, the paper barrier attached to the insulation
@Greg, ah, the paper should be down and the insulation faces up.
Wrong. Vapor Barrier on the insulation that is between floor joists needs to be towards the warm side which in this case would be up towards the floor sheeting not down towards the cold dirt.
http://energyaudit-sdge.sempra.com/library/basement.asp
Not only was “clever” dude wrong about that but he’s a little misguided about crawl space thinking in regards to ventilation. It’s common old school science. Check this out to learn more…
http://www.basementsystems.com/crawlspace/crawlspace_ventilation.php
“We now know that venting is not a great solution for keeping crawlspaces clean and dry. Indeed, venting will only help increase crawlspace moisture levels if the outside air is dryer than the air in the crawlspace, or when enough hot outside air enters and warms the crawlspace. New studies have shown that as air enters the crawlspace through the foundation vents and comes in contact with surfaces that have been cooled by the cold air in the ducts, the dew point is reached and condensation occurs. And when condensation forms on various surfaces within your crawlspace, you have the ideal environment for mold, mildew, and the accompanying problems they create in your home.”
Taken from Your Crawl Space.
The crawlspace under half my house is only about 15 inches to 6 inches .Not enough room to crawl under.the other half (an addon) is about 3 feet.I have vents that open and close all around the house.I am told that lying plastic on the ground will cause vaper to condense till you have puddles of water on the plastic.I used insulation in all vents untill I replaced them this year.Last spring I took out the insulation and found one corner (under an unused room) was so wet I ran my hand up to the flooring and came away with water in my hand.I had to replace the 2×6 that lies on the cement foundation and some of the flooring.I left the opening off to dry for a week. I checked and all had dried up . So what is the right way to insulate the crawl space? I am really confused.HELP!!!
Did anyone comment on Glen Boehme’s April 26, 2009 posting? I have the same issue with my old house…I can’t get in there to install a vapor barrier – do I have to remove all the floors in my house to do this???
Regarding the post from the person who lives in the south (back a couple of years ago unfortunately). You said you installed a dehumidifier and closed the vents…would I still need to install the vapor barrier is I did this? Where can I get the dehumidifier? I live in central Texas and it’s VERY humid here.
I read all of these comments and have been through all the gyrations. I’ve owned a ranch style home in Maine since 93; it was built on ledge and has a 4 foot crawl. The insulation was sopping and you could have floated a canoe under it along with adding fish. Fixing the broken sump pump fixed the water problem, but I will had an open pool of water in the crock.
I tired a dehumidifier, plastic, fans, sealing the vents opening the vents, all to know avail.
I bit the bullet and just had a fully encapsulated system installed with a submerged sump pump with battery back up. Guess what, no cold drafts in the house this morning! First time in 16 years. It was worth every penny. The vents were completely seal over, the foundation walls were covered with 2″ dense blue wall insulation and then covered over in a heavy lining, the pea stone floor received what I call a waffle pad and a 20 mil liner. the joist bays were sealed with 2″ spray insulation, and the crawl space plug was removed and a thick plastic sealed panel was installed that is weather stripped lined.
I wish this system would have been around back in 93, I have spent more TIME and tons of money trying to slay this beast. I am going to monitor my energy savings to see what cost savings are realized.
I have a situation with a customer of mine that has major moisture issues under his house. Add an air handler under a house with floor insulation and you will have a mess. I guarantee you that. The only way to completely get rid of moisture under a house is to totally encapsulate underneath and have a dehumidifier installed.Its costly, buy effective. The combination of thick schrubbery around a house, and an air handler blocking air from entering and escaping from under a house, will cause insulation to act as a sponge when humidity rises and dew point is met. With the system off I read 72% humidity under this house. When the system turned on- humidity rose to 85% in a matter of seconds. In my opinion- dont install an air handler under a house or have floor insulation installed if you live in the south. I have seen too many insulated floors rot under bathroom and kitchen cabinets. The idea of having floors insulated where humidity levels are high is long gone and shouldnt be done. The insulation will eventually fall from between the rafters onto the ground anyway- even if installed correctly. If air cannot cross breeze under a house without any obstruction such as ductwork or an air handler- you will experience major moisture problems. I cant stress enough. Dont install floor insulation.