Attic and Basement FAQ

Attics, basements, and crawlspaces are the least frequented areas of a home, which is one of the reasons they often cause the most problems. A regular inspection can catch potential problems—like leaks, condensation, termite activity, or the growth of mold—before they become a major headache.

Attics can become virtual ovens in the summer, so work in the early morning or wait until a cooler time of year. Inspect basements after a heavy rain to catch any leaks. And don’t neglect the crawlspace under your home if it’s built off the ground on piers. While it’s not the most inviting place to spend an afternoon, early detection might save you thousands of dollars in termite damage or rot that would otherwise go undetected.

Here are some of the most common questions concerning problems with attics and basements:


Q: Is it necessary to install a separate vapor barrier between the living area of a house and the attic or crawlspace?

A: No, a separate vapor barrier is usually not needed since any condensation should be able to escape from a properly vented attic or crawlspace. For more information, see our article on Vapor Barriers.

Q: Should the facing on insulation in the attic or under the floor go up or down?

A: Install insulation with the facing toward the heated living area of the house. In the attic the facing should go down against the ceiling while under the house it should be up next to the subfloor.

Q: Should you install a layer of faced insulation in the attic on top of the insulation that is already there?

A: No, always put unfaced insulation on top of existing attic insulation. Since the facing acts as a vapor barrier, it could trap moisture in the insulation. For more information, see our article on Attic Insulation.

Q: If I install a second layer of insulation in the attic on top of the existing insulation, which way should it run?

A: If the existing insulation is even with or higher than the top of the joists, the new layer should run perpendicular to the joists. If the existing insulation is lower than the joists, lay the new layer between the joists.

Q: How much venting does an attic require?

A: A typical house should have one square foot of vent for every 150 square feet of attic floor space. Ideally, half the vents should be located in the soffit at the bottom of the roof and half in gable or ridge vents near the top to create a flow of outside air into the attic. For more information on venting your attic, see our article on Adding Soffit Vents.

Q: What size should an attic vent fan be?

A: An attic vent fan should be large enough to completely replace the air in the attic every six minutes. To determine the size needed, calculate the volume of your attic in cubic feet and divide by 6. This will equal the rated capacity of the attic vent fan in cubic feet per minute (CFM). For more information, see our article on Attic Ventilation.

Q: Can you cover electrical wires and boxes in the attic with insulation?

A: While recessed ceiling fixtures should not be covered, wiring and ceiling boxes for surface mounted or hanging light fixtures can be covered by insulation.

Q: How can I prevent condensation in my attic?

A: Condensation can occur when heated air from inside the house condenses on cold surfaces in the attic. This can usually be prevented by removing any sources of moisture in the attic, and making sure there is adequate ventilation in the attic. Always vent dryers and bathrooms fans outside rather than in the attic, and check to be sure that soffit vents under eaves have not become blocked by insulation.

Basements and Crawlspaces

Q: How can I prevent mold and termites in of the crawlspace under my house?

A: Mold and termites can be a problem under homes, particularly in warm humid climates. Since both need water to thrive, start by checking for any plumbing leaks, condensation from ductwork, or rainwater seepage. Cover the crawlspace with sheets of 6 mil black plastic, overlapping them a foot and taping all seams. Run the plastic up the sides of the foundation walls with holes cut for the outside vents. Use a flashlight to inspect the joists and the subfloor periodically for signs of mold. Check the piers and foundation walls for mud tunnels make by termites. For more information, see our articles How to Prevent and Remove Mold, and Formosan Termites.

Q: How can I add a bathroom or laundry room in a basement?

A: Since plumbing uses gravity to drain, you will have to install what is known as a “grinder pump” or “lift station” to pump waste water up to the level of the drain pipe leading away from your house.

Q: What can I do to keep my basement walls from sweating?

A: Start by taping a one foot square piece of plastic to the wall and sealing it around all fours sides with tape. If moisture appears on the outside of the plastic, the problem is condensation due to excess humidity in the air. If water forms behind the plastic, then water is seeping in through the walls. To prevent condensation, start by reducing the humidity in the air as much as possible by venting dryers and bath fans to the outside and eliminating any plumbing leaks. If problems persist, consider insulating the exterior walls or installing a dehumidifier. See below if the water is coming from outside the basement.

Q: How can I stop a basement from leaking?

A: Start by being sure the land around your house is graded so rainwater is diverted away from the house. Install gutters and put extensions on existing downspouts. If that doesn’t help, you may have to excavate around the basement and waterproof the walls from the outside. For more information on basements, see our article Basement Refinishing.


  1. Hi!

    In my “cold room” where the water pump, sump pump and water filter is located, I’m getting condensation on the concrete ceiling, which is also the floor of the front porch. This only happens in cold weather. There had been a moldy, rotten piece of plywood there, probably left from forming the slab ceiling/floor, of which I removed. I’ve had a floor fan directed out of that room all winter, but am still getting condensation.

    I’m considering using Nansulate thermal barrier paint. What do you think of this solution?



  2. I have a home that was built in 1927. I have batt type insulation in the attic crawl space which has been installed with the vapor barrier toward the crawl space rather than toward the living area -It’s been that way for over 30 years. I would like to overlap some nonfaced insulation over the top but I’m wondering if it’s worthwhile to pull the existing insulation first.

  3. Hi, I have a Home (built new in 2000), that has an exposed North Basement wall (8 ft tall x 28 ft wide). In the colder days of Winter we have a problem with that wall sweating. I think it needs to be sealed on the outside. Can you give me directions for best way to do this or how do I fix the Problem? Thanks Don

  4. I have basically a flat roof in Florida with no attic crawl space. I want to insulate and they told me it could be done through the fascia board by drilling 4 inch diameter circles in the fascia. Then they would insert a 3 inch pipe and blow insulation all through the house in each roof trust cavity. I went to home depot and they only had 3 inch round vents for the fascia. Could you tell me where I could get about 80 of the 4 inch diameter round vents for my fascia so I can insulate. Thank you

  5. My basement framing was installed 9″ away from the wall. I want to finish the basement but Im not sure if it is wise to install insualtion as it wont be flush against the wall.Any suggestions?

    • Hi John,
      I don’t see a problem with having a gap behind the insulation. If anything it would be a good thing since the air gap would have an additional insulation factor and if there was any condensation on the wall it wouldn’t soak into the insualtion.

  6. Thanks Ben,its the best news I have so far. One more question. Should I place a film barrier behind the Insulation in order to help keep it in place?

    • John,
      Assuming the insulation (fiberglass?) has a facing that is stapled to the studs, I wouldn’t think a barrier behind it is necessary.

  7. my home was built in 2006 . the roof has ridge vents. would i be helping any thing,like my energy costs or the life of the roof shingles by having power vent fans installed ? guy robinson

    • Hi Guy,
      The most efficient system is to combine soffit vents with a ridge vent (using the natural flow of hot air rising) or soffit vents with a power vent, but not to use all three together. Using a power vent with a ridge vent disrupts the natural air flow of cool air coming in the soffit vent, rising, and going out the ridge vent. When you add a power vent to an attic that has a ridge vent, it tends to reverse the air flow and pull air (and possibly rain) in through the ridge vent.

  8. I built my SIP (structural insulated panel) home in NH,in 2005, with a full foundation,(6 feet below grade). I have no leaks in the basement, as I did install a perimeter drain after they poured the foundation. I can smell a musty odor when I enter the home, both upstairs, and down in the basement. In the Summer, the pipes in basement sweat a lot.I am in the proces of insulating all the pipes in the basement. Even if I run a dehumidifier, I can still smell the odor. House is quite “tight”, along with energy efficient windows. Did I “overkill”, and what can I do?

  9. Ron,
    Sounds like you have a mold problem somewhere that needs correcting. You might want to consider adding an air exchanger that lets in fresh air from outside without losing your heat or cool.

  10. When my 20 year old house was built, it was built with gable vents in the attic. When a new roof was put on recently, the roofer added a ridge vent. Someone told me that the gable vents now have to be closed up. That you couldn’t use both gable vents and a ridge vent as they work against each other. Is that true? Should the gable vents be closed off?

    • Hi George,
      Gable and roof vents together should be fine, the more ventilation the better, what can cause a problem is combining a ridge vent with a power vent, since the power vent can reverse the natural air flow through the attic as heat rises and draw air (and possibly rain) in the ridge vent rather than expelling it through it. For the most effective attic cooling, you should also have soffit vents under the eaves to draw outside air in as the heat rises. More info is available in our articles on Combing an Attic Vent Fan and Roof Ridge Vent and Attic Ventilation.

  11. Hi Came home from vacation and have rust stains on ceiling, which is under attic crawl space. We had a blizzard and lot snow on roof. Last years blizzard got this staining too. we have 2 gablevents, ridge vent almost whole length of a roof, and power attic fan, and a continous soffit vent, on this side of the crawl space. With the A roof and this crawl space has no circulation to the attic. small Mold has appeared on closet wall that shares this wall with crwal space. Husband has plugged in fan and has dried everything up. he has added more insulation to floor. Do we need another type of vent to vent this area and what else can we do. only seems like when we get these long cold spells and lots snow, the lack ventilation is a problem. Help!

  12. I grew up with an attic fan or whole house fan. I can remember that when it was turned on in the evening that it would cool the attic off. Thinking about this and the heat of my attic that I have now made me wonder if installing a whole house fan on my back porch would be a good way to push the hot air out of my attic on hot summer days. Is this a good idea? It seems that it would be a good way to bring air in from the bottom of the attic and push it to the top.

  13. I have a bedroom addition thats built 3 ft. over dirt. There is rolled insulation under the floor. The floor is very cold in the winter. Nothing on the cement walls. What cn I do to warm up our floor. We live in the northeast.

  14. My church bought the house next door a few years back. For the past year there is a really strong mold odor in the house, and the underside of the carport roof has turned from white to black. Isn’t this hazardous ot our health? We hold Sunday school classes in this house for 45 min every Sunday. I live in Burlington, N.C. What should we do?

  15. The floor is very cold in the winter. Nothing on the cement walls. What cn I do to warm up our floor. We live in the northeast.

  16. Hello Danny,
    We are currently dealing with a 12% moisture reading on a wall that our clients wants wood paneling applied. This paneling is bubbling & cracking due to the moisture or sweating of the wall itself. How would you go about rectifying this issue? Any advice is greatly appreciated.
    Naples Florida

  17. Hello Danny I have a question on the basement walls of my 100+ year old home. The walls have a parging material on them now that is crumbling off to the touch. I have cleaned this up a few timesover the 20+ yrs that we have owned the home. Iwould like to know if the why to solve this is to apply some type of crystalizing product or if it has to be a lime based product to let the wall breath The wall is a flagstone type.

  18. We have a heated basement that I’d like to put sound/insulation in the basement ceiling area. Can I put insulation with craft paper backing and use the craft paper backing to staple the fiberglass insulation in between the floor joists?

  19. We tore down and old garage, kept the foundation and built a family on the slab as well as built a new garage with new foundation next to it. We “built” up the old garage floor to be flush with level of the existing house (there was a step down into the old garage) , and before we put the plywood down on the “frame” that was built, we had the whole thing spray foamed with closed cell insulation. Then plywood was put on top. The hardwood flooring guy had his materials delivered a week before installation and he use black “tar” paper before laying the flooring down. ( I think that’s what its called) Anyway, it looked great for a few weeks but now we noticed the boards are cupping. We see water was getting in under 2 sets of french doors where the snow is piled 3 feet high outside. could this water be the culprit? Could it wick all across the room (25’x25′ room size.) Most people that see it think not. They feel there is a moisture problem from underneath. How can we tell? Could it be too insulated somehow? Does this area need to vent? Do we wait until spring and see if it gets worse.? Or is there something we can do now to uncover the problem?

    Any help would be greatly appreciated. I feel like $6,000 just went down the drain and I don’t want to throw good money after bad until I can get down the actual problem

  20. Hello, my question is what would cause my basement floor and certain walls to be pink in color? On the walls it appears to look like it dripped out of a drill holes and around the electrical box … And the floor I don’t know if it is coming up from the ground???? could it be iron or a mineral? The house has well water and septic….the water is treated for being hard water…..I am puzzled … Hoping it’s nothing serious…I personally haven’t noticed this….it was pointed out by a potential buyer……thanks for your help.

  21. Hello – I have a leak in the basement from the shower drain. I will need to replace the “j” and the section of the pipe right above it. The problem: the first section of pipe is about 4-6 inches up into the rafter and other cords are pretty close to it. The pipe to be replaced is 1 1/2in around, I have tried to find a telescoping basin wrench to fit this pipe but I have had no luck… PLEASE Help!

  22. i did a coat of concrete at the outside basement entrance brick walls after i did it my basemant leak when a heavy rain happen this did not happen before i leave at the house for 11 years. this happen this year. thanks

  23. hi,

    I would like to create a venting system that pulls hot air from attic during day time into crawl space. what effect on a house it will have? any moisture problems, etc?

  24. Danny,

    We want to insulate our basement walls, but the previous owner put studs (14 1/2 inches apart) up against the concrete with with plastic sheathing between the studs and the concrete wall. My wife said she saw on one of your shows, insulation that fits between the suds. We can’t seem to find it online. What Brand is it? Should we rip out the plastic in-between the studs before we install it? We don’t want moisture or mold issues.

    Thank you in advance for any help you can give us.

    Richard and Marie

    • Hi, Richard!
      Rockwool was the featured product.
      Just make sure you get the size made for 16-inch stud walls.
      Good luck with your project!


Please enter your comment!
Please enter your name here