Who does green building benefit?

by David Braddy LEED GA

In the 19th and early 20th century Architects and Urban Reformers set out to radically change the way we lived  by improving buildings, streets, neighborhoods and clean water systems to drastically reduce the spread of infectious disease and generally improve public health.  Can you believe there were people back then that thought it was just a fad and that we didn’t really need all that new technology.

My Grandmother was born in 1900 and when I was a young kid I still remember her saying she didn’t understand why people needed to have the toilet inside the house. I remember her resisting when her son’s added one to her house; she said “I have lived this long without it”.

Sometimes we have to change and adapt to preserve our way of living, whether we want to or not. We are in a different world today. We have VOC’s in building products that didn’t even exist back then; we have air conditioning and central heat and air. Many things changed, but homes were built the same and didn’t adapt to accommodate these new compounds and technologies.

Well here we are now in the 21st Century and some things never change, there are many who believe green building is a fad or not needed and simply an unnecessary expense. The fact of the matter is green building is a necessary and needed progression in building technology. We do not have to look very far to find sick homes and homes that make people sick.

I was in a home this week, you know, one of those homes that breathe naturally through the walls using the same building technology from the early 20th century that we are still using today, but this home was only built a few short years ago.  This home was un-inhabitable due to the amount of mold in the walls and was being totally gutted and rebuilt. Many have mistakenly believed this is from poor workmanship or an unqualified builder. This is not always the case.  I have seen many homes with mold issues that were built with excellent craftsmanship; the fault was with the technology not the builder.

Let me give you a tip; if your home smells musty it has mold. Do not ignore it.

This is why green building technology is the fastest growing segment in the building industry. Green building is not a fad or gimmick or something a slick marketer came up with to charge you more money for.  It is simply a better way.

A green built home is much cheaper to live in and much healthier if built correctly. So the person that benefits is you the homeowner.  No one has ever built an energy efficient home that’s more comfortable and healthier and regretted it, but many have cut corners and regretted it.

Cutting corners in something as important as the place you are going to be doing most of your breathing is never a good idea.

I know there are many that are still not convinced, just as there were a hundred years ago with technology that we now accept as the norm. Change and new ideas are never accepted without some resistance, this is simply human nature.  There will always be a way to save some money or do something cheaper.

An outhouse is much cheaper than indoor plumbing, but how many of those do you see today?  

For ideas on how to make your home more energy efficient and healthier visit http://LakeEcoGroup.com

One product with many benefits

by David Braddy LEED GA

Make your home stronger, energy efficient and healthier with one product

Imagine a building product that will make your home stronger, more energy efficient and healthier.

The product is closed cell Spray Polyurethane Foam (SPF), which is changing the way we build as more benefits are being discovered. A report released last year by the National Institute of Standards and Technology detailed the effects of Hurricanes with compelling evidence about the performance of spray foam insulation. When it comes to protecting roofs and walls from natural disasters SPF shows remarkable resistance to high wind uplift and blow off. This is attributed to its excellent adhesion qualities, lack of need for fasteners and no joints or edges for the wind to get under. As a matter of fact, laboratory test of closed cell SPF found the wind resistance exceeded the capacity of Factory Mutual and Underwriters Laboratory testing equipment. Another report by the NRF (National Roofing Foundation) discovered another unique feature of SPF roofs; they are not in danger of immediate leaks if penetrated by hail or other projectiles, provided the penetration does not go all the way thru the foam.  And most roofs could be repaired rather than replaced. This is why spray foam played a significant role in the construction of nation’s largest re-roofing project which was the 9.7 acre hurricane resistant Louisiana Superdome after Hurricane Katrina.

Wall assemblies that incorporate SPF in the cavities also have an increased racking strength of 300 – 400 percent in NAHB test as well as providing a superior air and moisture barrier.

The bottom line is that SPF is gaining more and more attention from contractors and building designers because of its high level of adhesion and resistance to wind uplift and blow off. The structural qualities and added strength alone make this a superior building product, but let’s look at the next benefit; Energy Savings.

You can have the most efficient HVAC system on the market but it will do you no good without a properly sealed building envelope. It is like having a cooler that keeps ice for 3 days. That may be true if it is sealed properly or air tight, but what happens if you fill it with ice on a hot day and leave the top open?   The ice won’t last and you will still be replacing ice quickly. Your house is no different.  With spray foam you are encasing and sealing your home with air tight insulation, imagine it being like that 3 day cooler. If sealed properly it will take very little to heat or cool, regardless of the HVAC system you choose. And don’t buy into the old myth, your home has to breathe, it is simply a myth and dangerous to you and your homes health. You do need proper ventilation, but not thru the building envelope itself, this causes mold and moisture issues. If you have any doubts about this simply look at the results. There are hundreds, if not thousands of homes and buildings right here at the lake that are full of mold or have moisture problems because they breathe. You will be hard pressed to find a SPF home with mold or moisture issues.

This brings us to another benefit of closed cell spray foam, it eliminates air and moisture movement thru the building enclosure eliminating mold and moisture issues, and it is also inert, which means there are no concerns of off-gassing VOC’s, so the air quality is also much better.  It’s hard to beat an SPF home.

Open Cell Spray Foam vs. Closed Cell Spray Foam

Closed vs. Open Polyurethane Spray Foam

By David Braddy LEED GA

Last month we discussed the benefits of a hot roof system using either open or closed cell spray foam. If you missed it you can read it at http://LakeEcoGroup.com

Let’s also keep in mind that insulation is the key to energy savings and a cornerstone of an eco-friendly building.  Sustainable building practices require that we reduce the heating and cooling loads as much as possible. Many of the guidelines and codes used just a few short years ago simply do not cut it anymore, and the excuse “we have always done it that way or that’s how I was taught” doesn’t cut it either.

Central Heating and Air Conditioning Systems changed building methods forever, we are now starting to understand how this contributed to unhealthy homes by the formation of rot and mold in the building envelope.

Insulation has always been the thermal barrier of the building and we have typically focused on the R-Value of the insulation material only. This is simply the resistance of heat flow through the building envelope. Unfortunately this can be very deceiving because it is only part of the equation. How effectively insulation blocks the flow of air and moisture is equally important and R-Value means very little if you do not have an effective air and moisture barrier.

Most of you would be very surprised at how little energy it took to heat and cool a properly insulated and sealed home, and yes there are now ways to fill and seal existing wall cavities.

Energy Efficiency is why spray foam has become so popular, there are 2 types open and closed cell.


They are both superior products to conventional insulation methods, both are great air barriers. The major difference is in the R-value per inch and moisture permeability. The R-Value per inch of open cell is approximately 3.8 and the R-Value per inch of closed cell is almost double that at approximately 6.8 per inch. Closed cell spray foam also adds to the strength of a structure because it bonds to and becomes part of the structure. Closed cell is a true air and moisture barrier at 2 inches.

Do not believe any salesperson, trying to sell you open cell that says, “Since closed cell is solid, normal building movement will make it break lose”. This is simply not true, if applied correctly closed cell will greatly improve the structural integrity of any building and becomes part of the structure, it will not break lose.  Also do not believe a salesperson trying to sell you closed cell when he tells you that “open cell will wick water because it is sponge like”, it will only wick water when the cell structure is damaged. These are both sales tactics to sell one over the other.

Here is a comparison of moisture perm rating, the higher the rating the more moisture can pass through

  • Closed Cell has a perm rating of 1 for a 2” thickness
  • Open Cell has a perm rating of 10 for a 5” thickness
  • An unfaced fiberglass batt has a perm rating over 100

So which one is better? As you can see closed cell wins hands down for structural integrity and moisture resistance, but it will also be the more expensive of the two, they are both superior to conventional batts.  There is really no way to tell you which one is better for your particular situation. I am partial to closed cell as the better product, but it is more expensive. For sound control I would opt for open cell as the better product. Now if moisture was not an issue and I didn’t care about adding strength to my structure I would probably again opt for open cell. Climate will also play a role in this decision.

The people you consult should have a thorough understanding of local climate and building science, unfortunately many people in the industry do not have this expertise or are very resistant to change. This is why we still have musty, moldy, rotting homes. A properly sealed building envelope will not have these problems.

Hot Roof vs Cold Roof

What is a Hot Roof System?

By David Braddy LEED GA

 

Building science is changing rapidly and some of those changes are challenging traditional building methods. One of the most beneficial changes is also one of the most controversial, which is the hot roof system or the unventilated sealed attic.

A hot roof is a properly sealed unvented attic, instead of a traditional vented roof which consist of an insulated attic floor and open soffits where air enters and then leaves through the top of the roof.

 

A few years ago, the scientists at the Oakridge National Laboratory in Tennessee tested properly vented and totally sealed attics. They found that proper venting only reduced the roof deck temperature by 3 to 5 degrees Fahrenheit.

 

But, when an attic was insulated using the Hot Roof Theory, the attic temperature adjusted to within 10 degrees of the ambient temperature of the house. Because the attic is heated or cooled by air that would normally escape from the house, it does not raise the load on the heating and cooling system.

However a vented attic typically reaches 130 -140 degrees, when the attic temperature exceeds outside temperature shingle failure can occur and if you have duct work or HVAC equipment in an attic it has to operate in extreme conditions causing excess energy to be used. This also creates the perfect opportunity for moisture damage due to condensation forming on equipment and duct work.

 

Spray foamed attics have foam applied directly to the roof decking, and the attic space isn’t ventilated.  The lack of ventilation is why they are called hot roofs.

In a standard insulation system, ceiling insulation reduces the transfer of heat from the attic to the living space (in the summer). Attic temperatures often approach 140F during the day. Solar energy warms the shingles and sheathing and then transfers heat to the attic. The 140F temperature of the underside roof surface drives the heat transfer process.

 

By insulating the roof surface with spray foam, the surface temperature exposed to the attic (the temperature driving the heat transfer) is reduced dramatically.

 

The benefits of including the attic in the insulated space are:

 

* Duct leakage and heat loss/gain from ducts is much less of an issue.

* Air sealing is easier in the roof than in the ceiling.

* Dust and loose insulation are less likely to migrate down to the living space.

* Tests show energy costs are lower when the attic is sealed.

 

Further information is available from ASHRAE (8700-527-4723) in a publication titled ‘Vented and Sealed Attics in Hot Climates’.

 

For more information check out this video


 

The next question is what type of spray foam is best for a hot roof system; there are two types open and closed cell.

Both of these can be used if properly applied, but there are big differences between the two. Open cell is moisture permeable and should not be used in a hot roof system without a vapor retarder. It has a R value of approximately 3.5 per inch; on the other hand closed cell is moisture impermeable has an R value of 6.8 per inch and is a vapor retarder. Closed cell has excellent adhesion qualities as does open cell, but closed cell actually becomes part of the roof structure making it much stronger.

We will have more on the differences between open and closed cell foam next time.

 

 

Diagnosing Moisture Problems in Wall Assemblies

Building Science Digests

BSD-108: Investigating and Diagnosing Moisture Problems

By Joseph Lstiburek
Created: 2006/10/27

Introduction

Water is supposed to be easy to understand.  It only comes in four forms or states [1]. And the rules governing water movement are straightforward:

  1. Water runs downhill due to gravity.
  2. Air carrying water vapor goes from areas of higher air pressure to areas of lower air pressure.
  3. Water in the vapor form diffuses from warm to cold driven by the thermal gradient.
  4. Water in the vapor form diffuses from more to less driven by the concentration gradient.

    Ok, not always straightforward:

  5. Water in a porous material diffuses on pore surfaces from more to less along the concentration gradient in the form of adsorbed water. When there is a lot of it and it fills the pores it is sometimes referred to as capillary water. In this way it can move upwards against the force of gravity – or sideways long distances. Just remember that porous materials “suck” and you’ll be ok.

Water always changes its behavior, because its form is never constant. Evaporation, condensation, capillary suction, gravitational flow, vapor diffusion and mass flow of moist air are all happening at the same time inside building cavities and inside materials.

Water plays clever tricks on us by changing forms and methods of movement along its flow path.  It’s devious and treacherous and laughs at us simple-minded humans whenever it can get away with it. We have to fight it by knowing its tricks. We’ll begin with some simple stuff – diagnosing and finding rain leaks. Then we’ll get into some clever tricks water can play on us.

Rain, Rain Go Away…

Rain falls out of the sky, mostly straight down. Sometimes the wind smacks it against the walls. Diagnosing rainwater leaks is not that complicated. If things get wet after a rain, it’s probably the rain. Start at the wet spot and work backwards and upwards. This gravity thing is pretty predictable. Now, there is a catch – water likes to stick to things and it can run horizontally quite a long ways because nothing is ever completely flat. And that pesky wind can blow it uphill a ways – sometimes over things that are an inch or two high – like sills, flashings and ledges.

The best time to diagnose rainwater leaks is when it is raining. Duh. And unless you are superman and can see into walls, you should be prepared to make lots of holes to see inside of assemblies. Now, it doesn’t always rain when you are asked to look. So you can make your own rain when you need to. A garden hose works real well. Consultants get embarrassed when they charge lots of money while using a garden hose so they use a spray rack instead to make it seem more “technical” and “scientific.” But a leak is a leak whether the water comes from a hose or a calibrated spray rack spraying calibrated water at a calibrated air pressure.  In fairness to consultants, standardized tests can come in real handy once you know the flow path and you want to know if the leaking window you found meets industry standards. Just remember to be “gentle” when you use a hose – you don’t want the momentum of the water spray forcing water into the building. The secret is misting the surface and letting gravity do the dirty deed. So fire hoses are out.

Sometimes a building only leaks rainwater when it is windy. And there isn’t always wind around when you need it – like when you are on-site looking for the leak. So make your own wind.  Instead of blowing against the building from the outside, suck air out of the building from the inside to simulate wind driven rain. Turn off the supply air, and crank up the exhaust. You should probably only do this with adult supervision, but you get the picture.

Most of the time rainwater leaks are straightforward to diagnose, but sometimes finding moisture due to rainfall is not such an obvious process.

Clever Water Tricks I – The Old Rain on the Brick Sun Trick

Up to now, the story has been pretty simple. Let’s complicate it by splashing rainwater on a brick veneer. Brick is a sponge. Brick wicks water into itself because it is porous. The mortar in the joints between bricks is also a sponge.  Mortar wicks water into itself because it is porous. There are also cracks between the brick and the mortar. These cracks are also “pores” and they also wick water. Remember, porous materials suck. Think of a brick veneer as a moisture reservoir that is filled during a rainstorm. So now we have this wet sponge on the outside of your building. The sun comes out. The sun beats down on the wet brick on the southwest side and makes the water in the brick hot. How hot? Probably 120 degrees F? Let’s go to the psychometric chart. Find where 120 degrees F crosses the saturation curve (100 percent RH). Hey, we’re off the chart.  We have to go to the steam tables. Wow. Any guesses what direction the water in the brick wants to go? Did I mention the building this brick veneer is enclosing is air-conditioned?

The brick is wetter than the rest of the wall and wetter than the inside. The brick is hotter than the rest of the wall and hotter than the inside. The water in the brick is driven inwards out of the brick into the airspace where it turns into a vapor. Some of the water also goes to the outside, because the brick is also wetter and hotter than the outside. But let’s go back to the airspace behind the brick. It’s not likely that the airspace is free from mortar droppings and vented at the bottom and at the top so that ventilation air can flush the water vapor driven into the airspace out of the brick to the outside. Even if the cavity is clean it’s rarely vented.  It may be drained, but it is seldom vented – at least not by design – although it should always be [2]. It may be vented accidentally – and this accidental venting saves a lot of buildings.  It seems that we are more often lucky rather than smart.

So inwards goes the water vapor, traveling along the temperature gradient and along the concentration gradient.  How far it travels depends on what’s in its way.  If it runs into something impermeable like foam sheathing or a rubber membrane on the backside of the cavity behind the brick veneer, the vapor won’t travel far.  If it hits foam sheathing or a rubber membrane the vapor condenses, turns back into a liquid and runs down the back side of the airspace, hopefully to a flashing where it is directed out of the wall to the outside.

But what happens if it runs into a building paper or a housewrap that breathes? The heat driven vapor blows through it like a hot knife through butter. What is the building paper or housewrap installed over? Probably a gypsum sheathing – highly permeable to vapor. So vapor diffuses right through it. Next comes fiberglass cavity insulation, which can’t stop the vapor – it’s permeable too. The vapor goes all the way in until it hits the plastic vapor barrier. Not a good idea to put a plastic vapor barrier on the inside of a brick veneer wall that sees rain and sun.  The vapor condenses on the plastic vapor barrier and runs down the wall to sit in the bottom plate track (Photograph 1). Now we have a full range of problems to choose from: corrosion, mold, odors or staining. You can get the same effect by installing a vinyl wall covering rather than the plastic vapor barrier (Figure 1). Just ask the hotel industry about this practice (Photograph 2).

photo_01: interior poly

Photograph 1: Interior Polyethylene Vapor Barrier – Condensation from inwardly driven moisture

figure_01: inward moisture drying

Figure 1: Inward moisture drive due to solar radiation

photo_02: vinyl wallcovering

Photograph 2: Vinyl Wallcovering – Mold due to inwardly driven moisture trapped by the vapor impermeability of the vinyl wallcovering
In this example the water started out as a liquid governed by gravity (the rain on the brick veneer) and was pulled into the porous brick veneer by capillarity. It was driven from the brick veneer and converted into a vapor in the airspace behind the brick by the energy added by the incident solar radiation [3]. Once in the cavity it traveled along the concentration gradient and thermal gradient through the wall assembly materials by the process of vapor diffusion until it condensed back into a liquid at the interior of the exterior wall assembly. Once in the liquid form again, it ran down the wall to the bottom plate. Two rules can prevent this common problem sequence:

Rule Number One: Never install a vapor barrier on the inside of a wall assembly, which has a moisture reservoir cladding and a vapor permeable combination of sheathing and building paper.

Rule Number Two: Always vent claddings, especially reservoir claddings. Remember, that in order to vent the cladding you need an air gap behind the material along with an air inlet, an air outlet and a clear path connecting the two.

This is important to your homes health!

When Sunshine Drives Moisture Into Walls

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Helpful? 0

When Sunshine Drives Moisture Into Walls

Because of inward solar vapor drive, vapor diffusion from the outside inward is often more worrisome than vapor diffusion from the inside outward — so you need a good vapor barrier strategy

Posted on Jul 2 by Martin Holladay, GBA Advisor

Image 1 of 4

Forgetting the air space behind the bricks sure didn’t help. After only 10 weeks of occupancy, some new homes built by Zaring of Cincinnati were so wet that most of the brick veneer, sheathing, insulation, and drywall had to be removed and demolished. A portion of the defective walls were sheathed with Celotex fiberboard, which is so vapor-permeable that moisture held in the brick veneer was easily driven into the wall cavity when sun shone on the bricks.

Builders have worried about wintertime vapor diffusion ever since 1938, when Tyler Stewart Rogers published an influential article on condensation in the Architectural Record. Rogers’ article, “Preventing Condensation in Insulated Structures,” included this advice: “A vapor barrier undoubtedly should be employed on the warm side of any insulation as the first step in minimizing condensation.”

Rogers’ recommendation, which was eventually incorporated into most model building codes, was established dogma for over 40 years. Eventually, though, building scientists discovered that interior vapor barriers were causing more problems than they were solving.

Interior vapor barriers are rarely necessary, since wintertime vapor diffusion rarely leads to problems in walls or ceilings. A different phenomenon — summertime vapor diffusion — turns out to be a far more serious matter.

Something is rotten in Denmark
During the 1990s, summertime vapor diffusion began to wreak havoc with hundreds of North American homes. This epidemic in rotting walls was brought on by two changes in building practice: The first was the widespread adoption of air conditioning, while the second was one unleashed by Rogers himself: the use of interior polyethylene vapor barriers.

Rogers conceived of interior vapor barriers as a defense against the diffusion of water vapor from the interior of a home into cold wall cavities. Rogers failed to foresee that these vapor barriers would eventually be cooled by air conditioning — thereby turning into condensing surfaces that began dripping water into walls during the summer.

Zaring Homes goes bankrupt
As with many scientific discoveries, it took a series of disasters to fully illuminate the phenomenon of summertime vapor diffusion.

One early victim of this type of diffusion was Cincinnati builder Zaring Homes. In the mid-1990s, Zaring Homes was a thriving mid-size builder that completed over 1,500 new homes a year. But the company’s expansion plans came to a screeching halt in 1999 when dozens of its new homes developed mold and extensive rot.

The first signs of the disaster surfaced in July 1999, when homeowners at Zaring’s Parkside development in Mason, Ohio, first began complaining of wet carpets. These moisture problems emerged only ten weeks after the first residents moved in to the new neighborhood. When inspection holes were cut into the drywall, workers discovered 1/4 inch of standing water in the bottom of the stud cavities. “We were able to wring water out of the fiberglass insulation,” said Stephen Vamosi, a consulting architect at Intertech Design in Cincinnati.

Consultants concluded that water vapor was being driven inward from the damp brick veneer through permeable fiberboard wall sheathing (Celotex). During the summer months, when the homes at Parkside were all air conditioned, moisture was condensing on the back of the polyethylene sheeting installed behind the drywall.

“Zaring Homes went out of business because they had a $20 to $50 million liability,” said building scientist Joseph Lstiburek. “Hundreds of homes were potentially involved. To fix the problems would probably cost $60,000 to $70,000 per home. It was a spectacular failure, and they are out of business.” (For more on Listiburek’s view of inward solar vapor drive, see Solar-Driven Moisture in Brick Veneer.)

Inward solar vapor drive problems require four elements
The phenomenon that destroyed Zaring’s walls came to be known as inward solar vapor drive. The classic disaster requires four elements:

  • A “reservoir” cladding — that is, siding that can hold significant amounts of water;
  • Permeable wall sheathing like Celotex or Homosote;
  • A polyethylene vapor barrier on the interior of the wall; and
  • An air-conditioned interior.

Reservoir claddings include brick veneer, stucco, manufactured stone, fiber-cement siding, and (to a lesser extent) wood siding. Although wall failures with permeable sidings like Celotex are particularly spectacular, inward solar vapor drive is also a factor in the failure of walls sheathed with less permeable types of sheathing, especially OSB.

Problems with inward solar vapor drive show up first on elevations that get the most sun exposure; north walls are usually immune to the problem.

Whenever a wall separates environments at different temperatures and moisture conditions, the direction of the vapor drive is from the hot, moist side toward the cool, dry side. After a soaking rainstorm, the sun eventually comes out to bake the damp siding. When it comes to driving vapor, the sun is a powerful motor.

The heat of the sun easily drives the moisture in damp siding through housewrap and permeable wall sheathing. The first cold surface that the vapor encounters is usually the polyethylene behind the drywall. That’s where the moisture condenses; it runs down the poly and pools at the bottom of the wall cavity. It doesn’t take long before mold begins to grow and the walls begin to rot.

Once the phenomenon of inward solar vapor drive was well understood, it was identified as one of the main mechanisms causing a cluster of wall-rot problems in EIFS-clad homes in North Carolina. Inward solar vapor drive is also blamed for many of the “leaky condo” problems in stucco-clad multi-family buildings in Vancouver, British Columbia.

Moisture and temperature probes confirm the phenomenon
Data from a 2003-2004 wall-drying study by building scientists John Straube, Eric Burnett, and Randy Van Staaten confirmed the phenomenon of inward solar vapor drive.

“Inward vapor drive resdistributes moisture quite dramatically,” said Straube. “Some people have said, ‘Summer condensation on the interior does not occur.’ But summer condensation does happen, even in Ottawa.”

Worry about diffusion from the outside in, not the inside out
For decades, builders have worried about vapor diffusion into walls from the indoors during the winter. But if a home has air conditioning, vapor diffusion into walls from the outdoors is a much bigger problem.

According to Straube, “Solar-driven vapor is much more important” than winter diffusion from the interior. He continued, “The moisture is coming from the other side of the assembly.”

Avoiding problems caused by inward solar vapor drive
If the components of a wall assembly are poorly chosen, as they clearly were at the Parkside development built by Zaring Homes, there may be no faster mechanism for destroying a house than inward solar vapor drive. After only 10 weeks of occupancy, some of the Zaring homes were so wet that most of the brick veneer, sheathing, insulation, and drywall had to be removed and demolished.

But once you understand inward solar vapor drive, it’s relatively easy to choose building details to avoid problems. Here are a variety of ways to reduce risks; of course, you’ll probably only need to adopt one or at most two of the following measures to avoid problems.

  • Never include interior polyethylene or vinyl wallpaper in an air-conditioned home. If your building inspector insists on a vapor retarder that comes in a roll, choose a smart retarder like MemBrain.
  • Avoid high-permeance sheathings like Homosote or Celotex. Instead, specify foam sheathing — especially behind brick veneer, stucco, or manufactured stone.
  • Homes with asphalt felt experience fewer problems with inward solar vapor drive than homes with plastic housewrap.
  • Consider the use of a water-resistant barrier (WRB) that is impermeable to water vapor. The best-known vapor-impermeable WRB is Delta-Dry. Delta-Dry is made of stiff high-density polyethylene formed into a 5/16-inch-thick egg-carton configuration. The three-dimensional WRB creates two air spaces: one between the siding and the WRB, and the other between the WRB and the sheathing. Unlike high-permeance housewraps, Delta-Dry depends on air movement (ventilation) to dry the gap between the Delta-Dry and the sheathing.
  • Walls with a rainscreen gap between the siding and the sheathing experience much less inward moisture transfer than walls without a gap.
  • Ventilated rainscreen gaps are more effective at limiting inward moisture transfer than unventilated rainscreen gaps.
  • More vapor drive problems occur in homes with dark-colored siding than light-colored siding.
  • When specifying stucco, choose a traditional stucco formulation without modern polymeric admixtures, since stuccos with these admixtures dry much more slowly than traditional stucco formulations.
  • Choose a siding (like vinyl siding) that is not a moisture reservoir.

I’d like to thank architect Steve Bostwick, one of the consultants who investigated the Zaring Homes disaster, for graciously sharing his photos. I’d also like to thank William Rose, whose historical research has highlighted Tyler Stewart Rogers’ role in establishing the idea that the warm-in-winter side of wall insulation should be protected by a vapor barrier. Rose is a building researcher at the University of Illinois in Urbana-Champaign.

Last week’s blog: “Using Ceiling Fans to Keep Cool Without AC.”

Can your home be too tight?


By David Braddy LEED GA

We have heard for years that a home can be built to tight and that a home has to breathe. Well a home does not have to breathe; you do and there are ways that are much safer than leaky walls. Before air conditioning, this was never really a problem. As a matter of fact many homes were built without much, if any insulation.

How many homes today do not have air conditioning?

This changed building science tremendously and created a new set of problems that we are just now starting to address and understand. This problem is called Vapor Drive

Here are a few simple facts to help you understand this:

  • All siding  will eventually leak and is not intended to be the air or moisture barrier
  • Water Vapor always moves from warm and humid to the cold and dry side
  • Water Vapor is driven through even the smallest crack or opening, and many building materials themselves.
  • This water vapor is the primary cause of mold & rot, not necessarily an actual water leak.
  • If air can move through a wall so does water vapor.

This is a problem that has caused mold issues in many parts of the country even though builders were following proper building procedures and local building codes. Up until 2007 the International Building Code classified the entire country as a cold climate with only one solution for vapor drive and this caused many serious problems. Unfortunately those outdated codes and methods are still in use throughout many parts of the country.

The standard solution was to put a vapor barrier or poly on the inside of the wall assembly, this is fine in a cold climate with warm humid air on the inside most of the time, as this keeps the moisture from entering the wall cavity from inside, but in our area for instance we do not have that kind of climate. We have hot humid summers and air conditioned homes. Even in the winters we have very little humidity inside of our homes to create vapor drive from the inside out, yet that is what we have been told is proper building method for our area.

In our area Vapor Drive forces moisture from outside to the cool dry inside. This is opposite of the old one size fits all code and the reason for its change.

When you fill a wall with a highly vapor-permeable insulation (fiberglass batts) and cover the wrong side with a non-permeable vapor retarder you can have moisture problems that are unhealthy for you and your home, as this can become a wood rotting, mold feeding liquid, created by Vapor Drive.

Make sure before you build or remodel you are using the proper method for your area, as many local codes have not been updated. A simple discussion with your builder and local building inspector will usually suffice, as there is a plethora of information on this subject.

One last thing; for an air or vapor barrier to be effective it must be continuous, vapor drive can be quite strong and find even the smallest openings in a protective barrier. Pay special attention around door and window openings and use high quality flashing around all openings to ensure a good seal in the building envelope.

Which Type of Insulation is best?

By David Braddy LEED GA

This is a question I am asked on a regular basis, but it is a question that is not as easy to answer as it sounds. Do you want cellulose or fiberglass, batt or blown? What is the difference between the two?

In this area it seems that fiberglass is the insulation of choice, but does that mean it is better? It is probably the most readily available, it comes in batts so it is easy to handle and install in wall cavities. It also creates much less of a mess and is less labor intensive than many other forms of insulation. It can also be loose blown into attic spaces and wall cavities.

But when it comes to choosing the type to use homeowners and builders have two different issues to consider:

1. How well does it perform, in other words it R-value
2. What is its resistance to air and moisture movement

Are you looking for thermal barrier or an air barrier? What’s the difference?

Let’s start with the difference between an air and thermal barrier. Thermal barriers deal with keeping the heat in and cold out of the building envelope in the winter and the opposite in the summer, the higher the R-value the higher the thermal resistance, while a higher R-value will keep more conditioned or heated air in, it will not necessarily keep the air from moving through a wall, this is the job of an air barrier.

Some types of insulation can do both.

Fiberglass for instance, while the most popular insulation is not an effective air barrier. Air can filter through fiberglass, and if air can move through it so can moisture, which creates another set of problems if the wall cavity doesn’t have the proper vapor barrier (and what is proper in one part of the country may not be proper in another), but that’s another issue that deals with vapor drive and mold growth, which is another topic that I will discuss another time, so back to insulation.

What is the best for air infiltration and thermal resistance cellulose or fiberglass?

Neither is actually the best. The best is closed cell spray foam, it is a true air and moisture barrier at 2 inches thickness, it has an R-Value of 6.8 per inch, and it turns solid when sprayed so it adds strength to the structure. It has no off gassing of VOC’s as some fiberglass batts do (although formaldehyde free batts are readily available, just ask for them) and since it totally seals a wall cavity and air and moisture cannot pass through, it virtually eliminates mold problems. So why doesn’t everyone just use closed cell spray foam? Unfortunately it is the most cost and labor intensive, while it will pay for itself in the long run in several ways; it has the most upfront cost.

Next would be open cell spray foam, which has an R-Value of approximately 3.9 per inch, it is not solid and does allow some air infiltration, but since it is sprayed you still get a very good seal & coverage. While not quite as costly as closed cell, it is still much higher than cellulose or fiberglass.

Following very closely with an R-Value of approximately 3.4 to 3.8 per inch is loose fill cellulose which is blown dry (or wet, but I don’t recommend unless you allow ample time for drying) into a wall cavity behind a special fabric or loose in the attic. Cellulose is a much better air barrier than fiberglass and the loose blown is comparable in price to fiberglass. So cellulose has a slightly higher R-Value per inch and is a better air barrier, but blowing the walls is more expensive than fiberglass batts and very messy. I would actually choose cellulose over open cell spray foam, because the performance is close while the cost is usually not.

Now comes fiberglass at an R-Value of approximately 2.9 to 3.8 per inch of thickness, and it is the worst air barrier. Why is it still the most popular? If your walls are properly constructed with the proper vapor barriers in place or with a good sealant package, you can still enjoy a good performing energy package and still use fiberglass batts, which are very economical.

Keep in mind without a properly constructed, energy efficient wall to begin with you can lose up to 15% of the R-Value in a wall assembly due to thermal bridging of framing components, regardless of the type of insulation you use, so call a professional to consult with if you are unsure of the proper methods. The last thing you want is a drafty wall full of mold.

Believe or not there are more insulation options but these are the most common.

So as you can see there is no easy answer to which insulation is best for you, it depends on several factors, but you need the proper air barrier and thermal barrier to insure a healthy, comfortable, energy efficient living environment.

One of the most overlooked areas of home health is under your house

U.S. Department of Energy – Energy Efficiency and Renewable Energy

Energy Savers

Crawl Space Insulation

If you properly insulate your crawl space—in addition to air sealing and controlling moisture, you will save on energy costs and increase your home’s comfort.

Before insulating or deciding whether to add insulation to your crawl space, first see our information about adding insulation to an existing house or selecting insulation for new home construction if you haven’t already.

How to insulate a crawl space depends on whether it’s ventilated or unventilated. Traditionally, crawl spaces have been vented to prevent problems with moisture; most building codes require vents to aid in removing moisture from the crawl space. However, many building professionals now recognize that building an unventilated crawl space (or closing vents after the crawl space dries out following construction) is the best option in homes using proper moisture control and exterior drainage techniques. There are two main reasons for this line of thinking:

  • Ventilation in the winter makes it difficult to keep crawl spaces warm
  • Warm, moist outdoor air brought into the crawl space through foundation vents in the summer is often unable to dehumidify a crawl space. In fact, this moist outdoor air can lead to increased moisture levels in the crawl space.

Insulating an Unventilated Crawl Space

If you have or will have an unventilated crawl space, then your best approach is to seal and insulate the foundation walls rather than the subfloor. The advantages of insulating the crawl space are as follows:

  • You can avoid the problems associated with ventilating a crawl space.
  • Less insulation is required (around 400 square feet for a 1,000-square-foot crawl space with 3-foot walls.)
  • Piping and ductwork are within the conditioned volume of the house so they don’t require insulation for energy efficiency or protection against freezing.
  • Air sealing between the house and the crawl space is less critical.

The disadvantages of insulating a crawl space include the following:

  • The insulation may be damaged by rodents, pests, or water.
  • A radon mitigation system will require ventilation of the crawl space to the exterior. Not planning for radon-resistant construction may necessitate air sealing the floor to mitigate the radon through ventilation.
  • The crawl space must be built airtight, and the air barrier must be maintained.
  • The access door to the crawl space must be located inside the home through the subfloor unless an airtight, insulated access door in the perimeter wall is built and maintained.

Steps for Installing Crawl Space Wall Insulation

  1. Review plans for this method of foundation insulation with pest control and local building officials to ensure code compliance.
  2. Eliminate or seal the foundation vents.
  3. Ensure that combustion furnaces and water heaters located in the crawl space are sealed-combustion units equipped with a powered combustion system.
  4. Seal all air leaks through the exterior wall during and after construction, including the band joist.
  5. Locate the crawl space access inside the home or install an access through the perimeter that will remain airtight after repeated use.
  6. Install rigid foam board or batt insulation—exterior foam, interior foam, or interior batt—to achieve complete insulation coverage. Insulate the band joist with batt insulation, as well as the crawl space access if it’s located in the wall.
  7. Install a continuous termite shield between the band joist and masonry foundation wall that covers the wall insulation and extends completely outside (or leave a 2- to 4-inch insulation gap at the top for termite inspection).
  8. Install a supply outlet in the crawl space, relying on the leakiness of the floor to provide the return air path.
Diagram of two options for insulating a crawl space. Option 1 is exterior foam insulation. A protective membrane covers exterior rigid insulation and folds over top course of foundation block. Option 2 is interior foam insulation. Labeled parts include a sill gasket, unfaced insulation in a band joist, and a 6-mil poly vapor diffusion retarder. A protective membrane overlaps and extends down insulation to provide capillary break. Rigid insulation (fire-rated) has joints taped or sealed. A perforated drainage pipe is embedded in gravel, covered with filter fabric, and located at the lower perimeter of the foundation footing to provide drainage.
Diagram of third option for insulating a crawl space. Option 3 is interior batt insulation. The diagram shows R-11 to R-19 batt insulation along the crawl space. Labeled parts include a sill gasket, unfaced insulation in the band joist, and a 6-mil poly vapor diffusion retarder. A protective membrane overlaps and extends down insulation to provide capillary break. A perforated drainage pipe is embedded in gravel, covered with filter fabric, and located at the lower perimeter of the foundation footing to provide drainage.

Steps for Installing Underfloor Insulation

  1. During the early phases of construction, the builder should inform all subcontractors (plumbing, electrical, HVAC, etc.) that they need to keep the space between the floor joists as clear as possible. Run drain lines, electrical wiring, and ductwork below the bottom of the insulation so that a continuous layer of insulation can be installed. For freeze protection, supply plumbing may be located within the insulation. The best approach is to run supply plumbing together in a few joist spaces. The insulation can be split and run around the plumbing.
  2. Seal all air leaks between the conditioned area of the home and the crawl space. High-priority leaks include holes around bathtub drains and other drain lines, plenums for ductwork, and penetrations for electrical wiring, plumbing, and ductwork (including duct boot connections at the floor).
  3. Insulation batts with an attached vapor barrier are typically used to insulate framed floors. Obtain insulation with the proper width for the joist spacing of the floor being insulated. Complete coverage is essential. Leave no insulation voids. The batts should be installed flush against the subfloor to eliminate any gaps, which may serve as passageways for cold airflow between the insulation and subfloor. The batts also should be cut to the full length of the joist being insulated and slit to fit around wiring and plumbing.
  4. Insulate the band joist area between the air ducts and the floor as space permits. Use insulation hangers (wire staves) spaced every 12-18 inches to hold the floor insulation in place without compressing the insulation more than 1 inch.
  5. The orientation of the vapor barrier depends on the home’s location or climate. In most of the country, the vapor barrier should face upward. However, in certain regions of the Gulf states and other areas with mild winters and hot summers, it should face downward.
  6. Insulate all ductwork in the crawl space.
  7. Insulate all hot and cold water lines in the crawl space unless they are located within the insulation.
  8. Close crawl space vents after ensuring that the crawl space and all the construction materials are dry.

For insulating truss floor systems, it’s better to install netting or foam board insulation to the underside of the floor trusses. Then, fill the space created between the netting or insulation and subfloor with loose-fill insulation.

Insulating a Ventilated Crawl Space

Here are some guidelines to follow for insulating a ventilated crawl space:

  1. Carefully seal any and all holes in the floor above (“ceiling” of the crawl space) to prevent air from blowing up into the house.
  2. Insulate between the floor joists with rolled fiberglass. Install it tight against the subfloor. Seal all of the seams carefully to keep wind from blowing into the insulation. Also, adequately support the insulation with mechanical fasteners so that it will not fall out of the joist spaces in the years to come. DO NOT just rely on the friction between the fiberglass and wood joists to secure it in place.
  3. Cover the insulation with a house-wrap or face it with a vapor barrier. The orientation of the vapor barriers depends on the home’s location or climate. In most of the country, the vapor barrier should face upward. However, in certain regions of the Gulf states and other areas with mild winters and hot summers, it should face downward.
  4. Install a polyethylene vapor retarder, or equivalent material, over the dirt floor. Tape and seal all seams carefully. You may also cover the polyethylene with a thin layer of sand or concrete to protect it from damage. Do not cover the plastic with anything that could make holes in it, such as crushed gravel. Be sure the headroom of the crawl space meets local code regulations if you are considering pouring a concrete slab.

Other Considerations

As mentioned above, when properly insulating a crawl space, you also have to consider moisture control measures and air sealing.

Finally, you need to consider radon resistance or control when installing any type of foundation. See the Learn More resources on the right side of this page (or below if you’ve printed it out) for more information about radon and radon-resistant construction techniques.

Learn More

Financing & Incentives

Professional Services

Federal Government Resources

Reading List

  • Radon-resistant Construction for Builders (PDF 46 KB). (2002). Energy Fact Sheet 30. Southface Energy Institute.
  • Crawlspace Insulation (PDF 235 KB). (December 2000). DOE/GO2000-0774. U.S. Department of Energy.
  • “New Crawl Space Data.” (August 2002). Energy Design Update (22:8); pp. 9-11.
  • Crawl Space Ventilation (PDF 223 KB). (July 2004). Forest Products Laboratory.