Posted by: SherlockHomesSY | 28 Sep 2011

Handling Basement Mold in the SouthEast

Basement-Crawlspace Mold

Help, Everything in My Basement has Mold On It!

I’ve received several phone calls since returning to Atlanta, GA in February 2011 essentially complaining about mold in unconditioned basements.  I’ve also found this condition in various kinds of inspections of new & existing homes.  The problem is quite simple really.  At a minimum, humidity levels in outdoor air are high enough to support mold growth inside the house with natural air exchanges due to holes in walls, floors, and ceilings.  The solution is equally as simple: seal up the holes and dehumidify the air.

There are a variety of unfinished basements—all with the same problem.  They include poured concrete basements, walk-in basements, and wholly framed basements.  Some of these basements have vented crawlspaces opening into them.  When a crawlspace is also present, the problem increases many fold.

Basement Moisture Physics

It really doesn’t matter whether the basement is considered air tight or leaky if a dehumidifying system isn’t present for the area.  Water vapor (humidity) is a gas that will go through almost all building materials.  It’ll come in through walls and concrete foundation walls and floor slabs.  However, an air tight basement has far less problems than an air leaky one.

The physics is rather simple.  Warm, humid air flows through holes and building materials into a cooler basement.  The basement temperature is often close to the dew point.  In any case, the relative humidity rises.  When it exceeds 60%, mold begins to growth.  After that, 50% relative humidity will sustain it.  When there are fewer and smaller holes, there’s less moisture vapor.  In all cases, some way to lower the relative humidity is needed.

Air conditioners help reduce humidity when they’re running.   However, they aren’t much good when they aren’t used to condition the basement.  They’re also useless when it’s not summer time.

Due to the way house air and vapor pressures work, it’s easier for the moisture vapor to get in than it is to get out.  Also, insulation, wood, wall board and personal items soak up humidity.  Don’t expect moisture that gets in to just as rapidly leave.

Basement Only Solution

Use these procedures to control humidity in a basement.  We’ll handle the complications of a crawlspace later in this blog post.

  1. Seal all holes in walls, floors, and ceilings
  2. Seal ductwork (if any)
  3. Weatherstrip windows & doors
  4. Add a dehumidifier

Seal Holes. Holes in basements are sneaky.  The largest air leaks are through the rimboards—the outer band of the floor overhead.  The best way to deal with area is with spray foam in most cases.  It goes on a whole lot faster than caulk.  Besides, doing so also insulates the area.

The next largest hole is between concrete and wood, whether at a sill plate or bottom plate.  Sometimes a foam gasket is placed between them when the house is built.  In theory, the gasket seals all the holes, but they don’t because the concrete is uneven.  They make a great capillary break to keep moisture from wicking out of the concrete in the wood.  What is needed is a bead of sealant where the concrete meets the wood.

The building trades don’t mind punching holes through the wall to install plumbing, gas pipes, air conditioner linesets, outlet boxes, ventilation fans and other utility penetrations.  In addition, the basement is unfinished right?  Therefore, rough openings around windows and doors are left unsealed.  Almost all of these holes can be filled using cans of spray foam available at your local building supply store.  When holes go through concrete, hydraulic cement or sealant may be appropriate.

There are holes in the overhead floor assembly over the basement too.  Plumbers leave the biggest ones to install tubs, showers, and toilets.  HVAC contractors typically don’t seal the joint between the floor and a register boot.  Electricians, plumbers, and HVAC contractors make holes through the floor to run pipes and cables.

Don’t forget to deal with any holes in the floor too.  There is supposed to be a vapor barrier between the ground and concrete.  If so, cracks aren’t usually a big deal, but they can be filled with concrete sealant.  However, the vapor barrier was punctured to install rough-in plumbing pipes for the future bathroom.  There may also be backwater valves.  Find and fix these holes too.

Seal Ductwork. Sometimes, there is ductwork running through the basement—usually insufficiently sealed.  When the blower fan runs, whatever is in the basement is drawn into the house: humidity, mold, and odors.  Leave duct sealing to an HVAC contractor, unless you plan to have one come out to retune your system immediately after you’re finished.  Sealing ductwork can make bad airflow problems worse, shortening the life of the equipment.

Weatherstrip Doors & Windows. After filling holes and sealing ductwork, check the weatherstripping around doors and windows.  Often, pets have destroyed it.  It’s also not uncommon for window frames and door slabs to warp.

When air sealing and weatherstripping is complete, for all practical purposes, the moisture vapor expressway is shutdown.  The path for moisture getting into the house now is through building materials, typically concrete, brick, OSB, and plywood.

Install a Dehumidifier. For the purposes of this article, the goal of air sealing is to reduce the amount off “easy” humidity getting into the basement so the smallest dehumidifier can be installed to do the job.  Dehumidifiers are power hungry, so you don’t want them running all the time.

When choosing a dehumidifier, the thing to watch for is dehumidification per Watt.  A 150 pint is probably more energy efficient than two 75-pint ones.  Look for the ENERGY STAR label.  Also, when choosing one, make sure it’s durable.  Most dehumidifiers available at local building supply stores are no longer functioning a year later.  A good place to look for basement dehumidifiers is at this website.

Mini Basements: Crawlspaces

When you think about it, crawlspaces are mini basements.  Ideally, in the Southeast, they should be air sealed and insulated and treated like any other basement.  Unfortunately, in most cases, they’re not.

Typical Crawlspace Construction. The usual crawlspace has big holes in the foundation for vents.  Sometimes, these vents are closed, even in the summertime. They also have dirt floors, and foundation water proofing is often neglected.  If there was any consideration for moisture coming through the foundation wall, most builders chose to dampproof, rather than water proof walls.  Dampproofing membranes break after several years.  To make matters worse, concrete blocks, instead of poured concrete, are often used.  Finally, footing drains may have been left out.

Crawlspace Moisture Vapor Sources. Moisture vapor typically comes into the crawlspace in three directions: through the dirt floor, foundation walls, and vents.  Water comes in through all three places in addition to spills and drains through the floor above.

The dirt floor is often uncovered or loosely covered with a vapor barrier.  Water may not come through it, but water vapor sneaks around edges and lap joints.  From moisture vapor’s point of view, the vapor barrier isn’t there.  For whatever reason, termite folks think loose sheets of plastic covering 70% or more of the crawlspace is enough.  I’ve seen enough termites to know better.  When the vapor barrier is present, the edges need to be sealed to walls, columns, and other foundation supports.  Any lap joints also need to be sealed.

Ductwork Condensation. Insulated ductwork in a crawlspace needs special handling too.  In addition to air sealing the ducts, the insulation jackets need to be sealed to each other.  When joints are open, humid air comes through them and condenses on cold ductwork—perhaps soaking the insulation.  In the Southeast, insulation jackets around ductwork need a vapor barrier around them.  Typically, it’s metal foil to act as a radiant barrier for attic heat.

Crawlspace Only Solution Summary. Handling a crawlspace then is everything mentioned for a basement, laying a sealed vapor barrier, and sealing the vapor barrier around any ductwork.  The problem with a dehumidifier in a vented crawlspace is that it is energy inefficient.  Dehumidifiers cannot dry outdoor air.  It’s better to use ducted duct fans instead.  One end is open to the crawlspace.  The other goes outdoors.  The downside is that this approach can increase condensation in the crawlspace, but may be better than nothing at all.

Crawlspaces Open to Basements

Crawlspaces open to basements is an indoor air quality disaster happening everyday in the Southeast for houses that have them–unless the crawlspaces are air sealed and insulated.  Moisture vapor levels are already high.  There are several problems to consider.

Crawlspace Ventilation. First, there are probably not enough vents.  People up North in the 1940s told the Southeast to put vents in around the perimeter of the foundation in the form of the building code–Nationwide.  Until a crawlspace study project in North Carolina was undertaken, people thought this was a good idea.

Crawlspace Moisture Vapor Physics. The law of physics for moisture is that it goes from areas of high concentration to low concentration.  The thought is that high moisture would push its way out the vents, and it does. Unfortunately, they forgot wood is sponge!  Tree cells are made to hold water.  In addition, when the humidity comes in, it converts to “rain” to condense all over everything.  Now the moisture is soaked up by the ground, ready to evaporate again another day.  When unsealed duct insulation is present, it’s likely to become damp or soaked.  It’s no wonder moisture levels in usual crawlspaces are high and stay that way.

Crawlspace Water Physics. To add insult to injury, water is often present.  Water running along slopes at the foundation or draining down them comes right through.  Downspouts often discharge water close the foundation.  Splashblocks are largely ineffective as the water needs to drain at least 5 feet away.  Soil wicks up water 16 feet.  How often do you see houses closer than this near lakes, ponds, rivers, and streams?   In our region, ground water also runs through aquifers, often close to ground level.  Sometimes, septic system drain fields are close to the house.  Before there is any hope of control moisture vapor, any water intrusion must be stopped!

Crawlspace-Basement Wall. The wall between the crawlspace and basement needs to be effectively isolated from each other to avoid the high moisture levels in the crawlspace from invading the basement, unless the crawlspace is air sealed and insulated.  To do that, any openings need to be closed and wall joints need to be air sealed, just as they are at exterior framed basement walls.

Closing the entrance to the crawlspace isn’t as easy as it sounds.  Often, large duct runs through the openings.  The way most of them are created, anyone wanting into the crawlspace has to crawl around them.  I suggest creating a separate door for people to crawl through—one that can be weather-stripped.  If it were my house, I’d cut the duct where it goes through the wall, install a wall panel, attach sealed opposing duct collars to both sides of the panel, then seal the cut ends of the duct to collar.  Some folks just spay foam around the duct.

Limited Crawlspace Ventilation. Typically, when a basement is connected to a crawlspace, ventilation is limited.  Someone erroneously thought big holes into the basement were the way to solve the ventilation issue.  Unfortunately, they cause indoor air quality problems for the basement instead.  There is no real moisture ventilation.  In this situation, ducted duct fans can be used to move air where there would normally be vents.

Covering the Cost

My heart goes out to clients.  Many homeowners either don’t know or live in denial until the buyer’s home inspector comes around.  The problem was usually there when the sellers bought the house.  Now, they’ve fallen in love with another house and don’t want to fix their current one.  The buyer, on the other hand, doesn’t want to inherit a problem.  The fault for this situation rests with the builder, but they’re long gone.  What to do now?!!

Facts. Let’s face these facts.  Mold should not be cleaned up until moisture issues are resolved.  The moisture issues are now known.  The buyer isn’t going to purchase the house unless the mold is removed.  The buyer doesn’t want a problem house.  The seller doesn’t want to spend money that doesn’t increase their equity in the house.  In addition, they don’t want to spend money for benefits they won’t enjoy. The solution is for the parties to acknowledge these facts and create a plan.

If there is only a basement, perhaps the seller can air seal and remove the mold in the basement.  The buyer could and should choose the dehumidifier because cheap ones don’t last long.

If there is only a mini-basement (crawlspace), perhaps the seller can air seal it and address any water issues.  If there are substantial mold colonies, they should be removed.  The buyer should consider encapsulating the crawlspace with insulation and a durable vapor barrier, and then install a good dehumidifier.

If there is a crawlspace connected to the basement, both options could be used.

Energy Efficient Mortgages. There is a better way!  Air sealing and insulating a crawlspace is an energy improvement.  Another way to handle it is with an energy efficient mortgage.  The cost of encapsulating the crawlspace is funded over and above the purchase price of the home and paid for with the monthly energy savings.  The energy savings should pay for the additional mortgage increment—essentially making the upgrade “costless”.  This option is available for current homeowners too.

Posted by: SherlockHomesSY | 6 Aug 2011

Why Not to Use Powered Roof Ventilators


I’m in the unenviable position of having to tell a builder the house they’re building can’t be certified for one of a variety of green building programs.  I have no problem doing it when the reason is solid.  However, enforcing a provision I don’t understand is difficult to do.  Such was the case with powered attic ventilators (PAVs).

This episode started when a new Georgia homeowner, originally from the tropics, decided to require the builder of a green energy home to install powered roof vents.  Unfortunately, I found them installed when I did the required pre-drywall inspection.  It’s obvious the homeowner did his homework and I applaud him!  He knows ventilation is used to cool the attic and remove moisture in the winter.  A review of the available literature on line shows this to be the widely held view.  Unfortunately, he, like most Americans, thinks more is better.  Now I have to explain why it’s not wise to use powered roof vents!

No PAV Policy. I have to say no to powered roof ventilators because the program requirements say so.  I could hide behind the rules and just refuse to certify the house with no further explanation required.  I don’t like to be treated that way and try to refuse to treat others that way too.  The “I’m the mommy, that’s why” argument never did sit well with me.

Typical Reasons. There are three well known valid reasons for saying no to powered roof ventilators.  I’ve known these arguments for years.  The Natural Florida Retrofit and Advanced Energy Corporation Applied Building Science Center reported results of their research in 1994, The Unplanned Impacts On Houses By Powered Attic Ventilators.

1.    They can backdraft combustion appliances
2.    They can pull conditioned air through holes in the ceiling into the attic
3.    They use more energy than they save

In this case, there are no combustion appliances to backdraft, the ceiling will be sealed tighter than a drum, and a solar powered PAV is installed.  What’s the problem?

Principles of Attic Ventilation. I went on-line in search of white papers.  I found a very solid article about attic ventilation by Air Vent, Inc. published in Dec 2010: Principles of Attic Ventilation:  A Comprehensive Guide to Planning the Balanced System for Attic Ventilation.  Sure enough, they convincingly argued for the use of a powered roof vent.  My next step was to discover the flaw in their argument.  I didn’t have to search long only because I got help on where to start looking.

Preferred Practices. Before revealing what I learned, I need to discuss what the preferred options are to avoid using a powered roof ventilator.  In general the principles are as follows:

1.    Use balance ventilation between the soffits and ridge
2.    Provide adequate ventilation openings
3.    Use a ridge vent rather than a gable vent
4.    Install a radiant barrier
5.    Use lighter color roofing materials
6.    Air Seal the attic ceiling
7.    Seal all ductwork in the attic to make it leak as little as possible

I did all this to my house and I have a much cooler attic.  Currently, I’m sitting in my office during the hottest three weeks of the year in Georgia without air conditioning supplied to the room.  I could not be in this office without the room air conditioner running full blast in years prior.  (Another major reason is that I fixed my attic kneewalls too.)  Even then, I had to abandon my office after 4 PM.

Informal Survey. I found it interesting to see the results of this informal study someone did just a few days ago.  Someone measured the temperature of attics with various ventilation strategies on a 105° F day.

1: Ridge vent house: 155° F
2: Power vent house: 145° F
3: Attic turbine house: 145° F
4: Radiant barrier stapled to underside of roof: 125° F

In researching the topic of attic ventilation in the past, I figured out the building code rules worked well for roof pitches up to 6/12.  After that, a different level of thinking is required.  I’ve been in several houses since then with roofs with greater roof pitches that had ridge vents and continuous soffit vents.  However, their attics are incredibly hot.  I knew not to recommend powered attic ventilators, so I frequently recommended turbine vents instead—with great success!

Ridgeless Roofs. However, I often wondered what I would say to a homeowner with a hipped roof, especially for a house that didn’t have much in the way a ridge and the roof pitch was greater than 6/12.  It’s a known fact that a hip roof withstands high wind events better than houses with gables.  Structurally, I prefer them.  I can certainly recommend turbine vents and static vents (turtlebacks), but they may not be enough.  The folks at Air Vent advocate the use of a powered attic vent in this case.  I’d opt for a foamed roofline instead, which takes the question of ventilation completely off the table.

No Cooling Savings Evidence. After spending the day researching, I came across this finding: houses with powered roof vents don’t perform any better in terms of heating & cooling costs than houses that don’t.  Perhaps the informal survey reinforces the point.  I had to ask, Why?

I found this in an on-line article reprinted by permission: Danger Above, Brendan Reid, Contracting Business, March 1998

•    3. Even with a perfect installation, PAVS still don t work significantly better than passive ventilation. Scientists at the Florida Solar Energy Center have proven that infrared radiation is how heat primarily gets from the underside of the hot roof sheathing into the insulation on the attic floor below. The invisible radiant energy waves pass right through the attic air without warming it, and are absorbed by the top surface of the insulation. Once the top of the insulation is hot, it in turn transfers heat to the air. It turns out that instead of the hot attic air heating the insulation, it s actually the insulation that s heating the air. Removing the hot attic air at this point is like shutting the barn door after the horse has escaped.

Case Closed. The argument for using a powered attic vent to reduce cooling costs is flawed.  There is little benefit to increasing the air exchange rate beyond what occurs naturally through passive vents.

In Conclusion

Back to the house that started this investigation.  The house has a 12/12 pitch roof with a great passive ventilation system on it already.  I’ve already told you that all the traditional arguments for not using a powered attic vent have been answered.  This house is in Atlanta, Georgia, so ice damming will never be an issue.  In my experience here after inspecting over 1000 houses, I’ve never seen an attic severely moisture damaged by moisture venting into the attic.  It’s also obvious that an attic with a fan is somewhat cooler.  So I’m left with the argument of reducing cooling cost by using the PAV.

Here’s what I’m going to do for this house.  I’ll recommend replacement of the powered attic vents with turbine vents or complete removal.  The house may need the benefit of turbines on really hot days, but I don’t think so.

Here’s my recommendation for all new houses where the roofline is not foamed.  Add a radiant barrier, especially if the roof pitch is over 6/12.  If there is any ductwork, I’ll strongly encourage it under all conditions.

I now have 3 reasons to recommend radiant barriers.  First, they lower the HERS Index by up to 3 points.  Second, my attic is cooler in the hottest part of the year.  Finally, cooling off the attic after the radiant energy has heated the attic ceiling below is pointless.  The message is to stop the radiation in the first place with a radiant barrier.

Oh yeah, I’m not going to certify the house with operational powered attic vents present!

Posted by: SherlockHomesSY | 7 Feb 2011

51 Attic Holes: Scuttle Holes

Scuttle Hole Cover

Click to DOE Home Energy Savers


A scuttle hole is usually a 2’ x 2’ entrance hole to the attic, covered by a panel.  Often, the panel fits badly and rarely insulated.  The result is probably the biggest air leak in the house with a 20% reduction in attic insulation value over 1000 sqft.

I still haven’t air sealed and insulated my scuttle hole because I haven’t found a solution I liked.  I’ve been designing it and redesigning it since 2007.  (The picture is typically found.)

I been through a lot of scuttle holes: some are easy to work with and others are a pain because of the construction details around the scuttle hole.  I’ve searched in vain for an easy DIY project or off-the-shelf product that does both the air sealing and insulating job it’s supposed to do.  Most of them are under-insulated or deny the realities of the abuse they must endure while getting in and out of the attic.

Our next post is the DIY Attic Scuttle Hole Cover, where you’ll find the a-ha moments leading to  how I’m going to build mine.  It’s one I can easily recommend and adapt to almost all attics!  It wasn’t until I wrote the requirements for this post that it occurred to me what to do.

What We’re Trying to Do (Objectives). The goal is to make the entrance as air tight as possible and ideally, insulate it to the same value as the rest of the attic.  Not easy to do because people have to get in and out of the attic without ruining it.  And, it’s got to be easy to put back.

What Needs to Happen (Requirements)
1. The panel, when closed, needs to create a tight seal, much like a refrigerator
2. Use rigid insulation to avoid having insulation fall out when the panel is moved
3. No air leakage around supporting trim is allowed
4. Avoid air movement around the ceiling panel insulation
5. Have an easy place to put the panel out of the way when removed, without messing up the finish
6. Ensure the largest piece of heating and air equipment can fit through the hole
7. Don’t leave foam exposed in an attic with a gas furnace or water heater in it
8. Insulation against the scuttle hole frame  isn’t allowed to fall out

What to Look for When Finished (Test)
1. Put a light around the entrance in the attic and close the door.  No light leaks allowed.
2. Look for rigid insulation tightly fitting against the ceiling panel
3. Confirm air does not easily circulate around the insulation
4. Remove the panel, crawl in and out of the attic, and put the panel back.  It should be easy to do quickly without falling apart
5. Determine whether the hole is big enough to get heating and air equipment in and out

Basic Idea (Process). To build an insulated scuttle hole cover, the main problem to solve first is how to get the lid the off the opening.  That depends on design, particularly if truss chords (roof deck support boards) are in the way.  Where will you put it when you take it off?  Make sure there’s enough space for the lid and the entrance isn’t covered in anyway.

The frame around the scuttle hole needs to be built tough.  A ladder may lean on it.  It will surely have to carry a person’s weight as it is crawled over and kicked.  May I suggest at least 300 lbs for man and tools?

If an air handler (inside unit) needs to go in the attic make sure there is a way to take the frame apart, if necessary, to get it out!

Somehow, air circulation needs to be limited around insulation, usually with one or more air-tight seals.  The sealed surfaces need to be in alignment with each other, usually level.

Warnings & Cautions

If there is a gas appliance in the attic, be sure foam is sandwiched between something like plywood/OSB and drywall.  The issue is the smoke and flame spread indexes.  Foam burns fast while creating a lot of toxic smoke.

If gas appliances are inside the house, be aware that if your house is close to or already considered air tight, any natural draft gas appliances could backdraft.  Be sure to get a combustion safety test done if you’re at all close on the air infiltration numbers.


Professional Recommendations. It took me over 3 years to find a solution that works.  This is not something routinely built for houses.  If it were, many of the construction hindrances around the scuttle hole just wouldn’t be there. Show these requirements and test conditions to your contractor and then ask a lot of questions about their solution(s).  Don’t be shy about showing them ours because the light bulb just might come on for them too!

Hint: The picture in the article is typical, but it doesn’t work very well. The article on Attic Covers is okay though.

DIY Recommendations. Assuming basic tool knowledge and the ability to cut the frame to exact dimensions with a table saw, this is an easy DIY project.  The only special tool you’ll need is a thin-kerf plywood table saw blade to cut the foam.

Expect to use a little creativity to adapt your solution to the construction around the existing attic hole.  This is the major reason there are no real good off-the-shelf products you can buy to do the job.


Here’s a technical bulletin from Soutface Energy Institute on Attic Covers.

In Conclusion

Oh, alright, I’ll give you a sneak preview on what finally occurred to me that makes this project work easily.  I’ve only seen scuttle hole covers to that go into the attic before taking them out.  I’ve also seen hinged scuttle hole covers that drop down.  How about a ceiling cover that drops down  and out while the  lid that pops into the attic?  See our next post: DIY Attic Scuttle Hole Cover.

Posted by: SherlockHomesSY | 4 Feb 2011

51 Attic Holes: DIY Scuttle Hole Cover


I’ve seen a lot of diagrams of what an attic scuttle hole cover looks like and chuckled because they would fall apart when they were used the first time by somebody like me who didn’t know it was there, or it would does a really bad job of insulating the hole.  Most of the time, the air seal solution looks okay.

The solutions I’ve read don’t consider obstructions in the way and forget there are no such thing as plumb and square corners in a house. Read More…

Cripple Wall Instead of Girder

Cripple Wall on Concrete Beam


Since arriving in the San Francisco Bay Area, I’ve marveled at how some crawlspaces can be soaked while others are bone dry during the same time of year.  I’ve come out of several of them looking like mud man.  But, it took getting into one that was bone dry on one side and soaked on the other one to begin to figure it out.  I finally got answers to this mystery after inspecting a house that is tearing itself apart! Read More…

Posted by: SherlockHomesSY | 28 Jan 2011

51 Holes: Air Sealing Attic Ceilings

DIY Air Sealing & Insulation Guide

Click to DIY Air Sealing & Insulation Guide


– Attic Stairs & Scuttle Hole
– Recessed Can Lights
– Electrical Outlets
– Duct Registers
– Exhaust Fans
– Flue Vents
– Walls, Cables, & Pipes
– Chases
– Soffits
– Attic Doors
– Foamed Roofline

Over Christmas 2010, I had a delightful time with my sister.  She bought a new house, and I was dying to check it out as the best present I could ever give her.  I spent all kinds of hours going over it, laughing and trying out all kinds of kool new things I just learned along the way. She had a gremlin and I named it, while providing a full dossier: DUST!

I laughed inwardly as she described how her ghost behaved and where she thought it came from.  A few years back, I would’ve concluded the same thing.  But, I seen this spirit before and it took me a long time figure it out.  After over a 1000 houses, I sorted this one out,  especially when families called me in to discover it from them.

As odd as it seems, a house becomes incredibly dusty when walls and floors are tightly sealed and the attic ceiling isn’t.  I can usually spot the gremlin right away because I can see its signature on a return grill.  It’s usually black, with dust bunnies all over it and all around the sides.

I’ll never forget the day I finally trapped the creature.  I stood at the top of attic stairs in a garage and nearly got sucked out roof vents because air was pulling that hard.  For once I was cool in a hot attic.  The attic was trying so hard to let heat out that it was drawing air in as hard as it could.  It was like trying to suck through a straw pinched tight.  The attic and the air return were sucking so hard that it was pulling dust, and whatever else is in the attic, through holes in the ceiling and into the heating & cooling system, in addition to wherever else cooler air could escape.

When I counted all the holes in my sister’s ceiling, I found 51 holes in the main attic.  There were 4 others in the other one.  This series is about how to air seal those holes and others she doesn’t have. thankfully.

It’s appropriate to start here because my first recommendation for just about every house is stop airflow from the house through the attic.  Slowing air movement due to the stack effect solves a lot of problems.  It also creates a few that have to be dealt with too as a result—like adding mechanical fresh air ventilation and ensuring smoke exhausts properly.  If there is only one thing you can do for whatever reason, seal the attic ceiling.

Described here are types of holes we’re about to talk about air sealing.

Attic Stairs & Scuttle Hole. The hole in the ceiling allowing access to the attic is the biggest single open hole in the house.  It also looses the most heat.  Not only does it leak air, it’s usually not very well insulated—if at all.  It usually lowers the insulation value of the entire attic by ~25%.

Recessed Can Lights. Taken together, down lights are probably the second largest hole in the attic.  The old steel ones leak like a sieve and insulation has to kept away—also leaving “a lot” of the attic uninsulated. Even the newest ones, the aluminum air tight ones have air leakage problems.

Electrical Outlets. Except house for houses built in the 1970s, when swag lamps were popular, the most common hole in the ceiling is electrical outlets.  They’re usually for lights and smoke alarms.

Duct Registers. When someone decided the heating and cooling systems should be installed in the attic, it meant at least supply ducts are routed through the attic ceiling too.  They’re good for about a 3 square inch hole each.

Exhaust Fans. Starting in the 1970s, we started air sealing the houses.  When we did, we started tightening up our houses and then needed a way to get pent up moisture out.  Now we have bath area fans through every bath room and toilet room ceiling.  In one story houses, the rangehood fan from the kitchen usually goes through it too.

Flue Vents. If there are gas appliances, the flue vent goes through the ceiling also—unless the appliance happens to be the high-efficiency kind.  Like recessed can lights, they get hot and require special treatment to avoid fire.

Walls, Cables, & Pipes. The most obvious, yet least recognized hole the attic is the top of walls.  It’s where drywall is attached to studs—without caulk or other sealant.  Nobody likes seeing pipe and cables, so they’re hidden in walls.  Sometimes they’re routed out of the top of the wall and through the attic.  Air lost through these holes is felt around receptacles and light switches.

Chases. Sometimes, big pipes, such as ducts, go through hidden cavities (chases).  I’ve seen some really big ones.  Besides loosing incredible amounts of heat because their uninsulated, some allow a lot of air movement—especially when the bottom end is in the crawlspace.

Soffits. To give the house some architectural appeal, sometimes there are changes in ceiling height.  Some of them come in the form of soffits around cabinets, ducts, or lights.  Not only are they missing insulation, some have some pretty big air pathways through them.

Attic Doors. Most attics aren’t heated or cooled, but for whatever reason, the attic doors are installed like an interior closet door.  A full-size door has about a 29 square inch hole around the frame, where the door fits.  Not only that, interior doors have almost no insulation value: around R-1—if that much.

Foamed Roofline. Sealing all the holes may take some time.  If you’re not a do-it-yourselfer and have a lot of holes,  it could run a modest amount of money to plug them up.  In this case, it may be worth leaving them all there and air sealing the roof deck instead.  The heat load on your heating and air system will go down considerably too.


Air sealing is the most cost effective thing that can be done to improve energy-efficiency, comfort, and health.  Air sealing the attic ceiling, in my opinion, the best single thing you can do.

I started with the US Environment Protection Agency’s (EPA’s) pamphlet on Do-It-Yourself Air Sealing and Insulation.  To learn how we diagnose and correct air leakage, see our home performance website.  Before you start, be sure to head our warning in this blog’s second post: Air Sealing.

In Conclusion

In our next post, we’ll start this series.  The ones my sister needs will be written first, so she can beat her dust problem for good.  Air sealing and insulating the attic entrance is first!

Posted by: SherlockHomesSY | 25 Jan 2011

Improving Your Chances for a Healthy House

Example House

Example Mold-Free California House


After experiencing seasonal mold in older San Francisco Bay Area homes, people sensitive to mold have asked what to look for in the next house they either buy or rent.  Many thanks to a current client who’s considering doing just that, who provided me with opportunity and inspiration to write this post! Fortunately, these ideas work just everywhere else in North America. Read More…

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