Category Archives: Building Science

Home Energy Magazine

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If you like this blog, then you’ll really like Home Energy Magazine!

Here’s their promo for the latest issue:

If there’s one thing contributing editor Steve Mann learned while attending the 2010 Passive House Conference in Portland, Oregon, it’s that the Passive House approach is anything but passive. In this issue of Home Energy, Steve explains the history of the Passive House standard, where it stands today, and what its future holds. Steve is a HERS rater, Green Point rater, LEED AP, Certified Energy Analyst, serial remodeler, and longtime software engineer.

Read the excerpts below to learn why senior building science consultant John Tooley says we need to Raise the Bar for Home Performance, and how a standard retrofit package can save a homeowner money in The Robo Retrofit House. This issue also features real-life horror stories from the field of energy auditing and a look into how students at Syracuse University experienced a Multifamily Performance Program in on-campus housing.

Click here to access the current issue. If you are a current online subscriber to Home Energy, click here to log in.

Cathedral Ceilings – Mold and Moisture – Problems and Solutions

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Rotten roof deck

Disclaimer: while I think all the information presented here is accurate and scientifically valid, you are advised to consult a *professional before changing your home. This article covers just one component of your home. Your specific home may have conditions that override the comments contained herein.

*By professional, I mean an experienced building scientist, not your local carpenter or roofer or even a structural engineer or architect. While many of these people are artists in what they do, most have no training in building science or engineering and cannot be trusted to properly design a roof assembly. Likewise, you wouldn’t hire a building scientist to swing a hammer and build your roof!
Cathedral ceilings are very popular – they give rooms a feeling of openness and an added aesthetic dimension. At the same time, they are responsible for a variety of building problems and homeowner heartbreak. What causes these problems and how do you avoid them?

There are a variety of climate zones. The south-eastern United States is hot and humid, while the north east is cold. The mid-Atlantic states, where I live, is mixed – during the summer it is hot and humid, during the winter it is cold. The south west is mostly hot and dry and the northwest is moderate in temperature but very humid! Each of these climate zones has its own particular building details. However, all must follow the laws of physics.

Physics tells us that moisture moves from areas of high humidity to areas of low humidity. If it’s more humid outside, moisture wants to come in. And when it’s more humid inside, the moisture will move toward the outside. Simple!

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Videos on insulating and sealing a crawlspace

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Here’s a handy, albeit highly incomplete, video on insulating your crawlspace:

Insulation installed upside-down

The positives:

  • They installed it with the vapor barrier put firmly up against the floor of the room above – this is actually correct. Most people install it upside-down and staple the paper vapor to the floor joists – this is totally incorrect. When you do that, you end up with moldy insulation like shown here.
  • They stressed the importance of air sealing and even showed the band joists (technically called the “rim joist”). Kudos for that!

The not-so-good:

  • They noted the importance of installing a vapor barrier on the floor, though they should have mentioned that you typically only do that for a dirt floor. They should also have mentioned that just laying plastic on the floor won’t do much to stop moisture from coming up. Any place air can flow, water vapor will go!
  • They used fiberglass (of course) on the rim joists. Unfortunately, this can lead to moisture damage. See this excellent article in Fine Homebuilding (PDF file) on insulating the rim joist.

Superb video on a crawlspace sealing system

The next (commercial) video presents the situation in crawlspaces accurately and proposes a solution that appears to be done thoroughly and professionally. Note that I have no personal experience with the company that produced the video. Regardless, it is well worth a view.

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Here’s a very nice article on insulating your crawl space by the Dept. of Energy. They get the rim joist insulation wrong though…

Fine Homebuilding article showing the proper way to insulate the rim joist.

Family Handyman article on installing a vapor barrier in your crawlspace.

Types of insulation: part 3-Insulations compared

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Signs of moisture and air flow in fiberglass insulation

When you climb into an attic and see this, you know something is seriously wrong. In fact, if your home isn’t very old, your insulation should be clean like when it was installed. The reason you get black insulation like this is because air and moisture are moving through the insulation, and it’s acting like an air filter.

The reason I’m showing you this picture is because it’s an example of the wrong insulation being used for a job. I feel pretty strongly about this because I’ve seen numerous homes where fiberglass has been installed in open walls like this and in almost every case, the insulation was seriously compromised – it was buckling under its own weight or simply falling out of the wall cavity. Or, in cases like this, it was hiding a big hole in the wall that should have been air sealed.

Let’s walk through the different insulation types and compare their main attributes: R-value, ability to reduce air movement, suitability for retrofit applications, and other characteristics.

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Building Science vs. B.S.

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This video is a promo for my upcoming video series, Building Science vs. B.S.

You hear B.S. every day….

***B.S.***

houses need to breathe
too much insulation causes roofs to rot
furnaces dry out your house
cold water boils faster than warm water
green building is always more expensive
ridge vents always help cool your roof and reduce moisture

***B.S.***

Unfortunately, B.S. like this gets spread by supposed experts, further perpetuating these damaging myths.

The problem is, people are really bad at reaching proper scientific conclusions. Our brains are wired to look for patterns, and research has shown that we create patterns where none really exist. For example….

  • Did you ever buy a new car, then suddenly notice that model everywhere?
  • If you’re a woman who has been pregnant, didn’t it seem like there were lots more pregnant women around?

It’s called “perceptual vigilance” and it leads to all sorts of incorrect conclusions. It causes people to think something in their environment has changed, while in fact, it is only their brain that changed!

There’s another favorite term among scientists: “correlation is not causation.” This is a related cousin to perceptual vigilance. What they’re saying is that just because two events appear to be correlated, it doesn’t mean that one caused another.

Insulation  does not cause roofs to rot!

Let’s start with a simple piece of B.S., usually spread by poorly informed contractors.

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Guest post: How I dealt with water problems and saved the house

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Crawlspace walls after foaming

My good friend Jerry takes to the keyboard today, telling us the trials and tribulations of having a house adjacent to a hill….

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We bought the house not knowing the backyard had really bad water retention issues (note: never buy a house when there’s snow covering the yard).  After heavy rain in the spring, the back yard would essentially be an unmowable mudpit for several weeks.  We had French drains installed which greatly alleviated the issue.  With the remodel, we figured we’d further address the wet yard by channeling the downspouts from the gutters in the back of the house into an underground collection pit (a dry well), which would run off into a rocky bed leading to the street.  This also worked well.

Unfortunately, during construction they built an open crawlspace under what would later become the kitchen extension.  Open to the sun and the stars…and the rain.  The first rain after they built it happened on a weekend.  The carpenter/job manager came over without us even calling, luckily, and build a makeshift cover out of plywood.  But it was a heavy rain and we had to run and get a pump as well to keep the crawlspace from filling up and coming into the basement.  Eventually they built the kitchen over it, and that was the end of that.  Or so we thought.

Types of Insulation: Part 2 – Where does insulation go?

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In part 1 of this series, I gave you an overview of the different insulation materials and the various forms they come in. This article covers where insulation goes and why. Knowing this helps you understand why you’d want to use a particular type of insulation for specific applications in your home.

Where do you use insulation?

  • On the attic floor
  • In attic cavities
  • On an attic knee wall
  • On the attic ceiling
  • In the walls
  • Around the windows and doors
  • Around pipes and other holes in the wall
  • In the basement and crawlspace ceilings
  • On the basement and crawlspace walls
  • Under the slab
  • Outside the foundations

Each of these areas really deserves an article of its own. In fact, if you look on the Building Science website, you’ll find highly detailed articles doing exactly that.  If you want to go straight to the source, consult these references.

Let’s look at some photos to get an idea of several of these cases…

Continue reading →

Q&A – Types of Insulation

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Bonded Logic Denim Insulation

When you insulate your house, you’re going to be confronted by a dizzying array of choices. How do you know which one to use? How much do they cost? Are some better than others or is it all hype? In this article, I’m going to do my best to sort through the options and help you make sense of them. Be warned – there’s a LOT of material here, so I’m going to have to break this into several articles.

First, let’s survey the types of insulation that you’re likely to encounter. I’m also going to provide links where appropriate.

  • Fiberglass – batts
  • Fiberglass – dense batts
  • Fiberglass – compressed
  • Fiberglass – shredded / loose fill
  • Fiberglass – Johns Manville Spider – sprayed in
  • Cellulose – loose fill
  • Cellulose – damp sprayed in
  • Cellulose – dense packed
  • Spray foam – open-cell, Icynene
  • Spray foam – open-cell, soy based
  • Spray foam – high-density closed-cell
  • Spray foam – high-density closed-cell, soy based
  • Board foam – expanded polystyrene
  • Board foam – extruded polystyrene
  • Board foam – polyisocyanurate
  • Board foam – foil faced polyisocyanurate
  • Denim – Bonded Logic batts

This list is long enough. There are other insulation materials that have been used over the years, from vermiculite to horse hair to rice hulls to straw bales, but I’m not going to touch on anything that isn’t commonly available in the United States. Sorry!

Insulation Characteristics

Before we go into analyzing all the details of insulation materials, let’s spend a moment defining the basic characteristic of insulation – the R-value.

Continue reading →

Bright Ideas for Saving Energy #4 – Window Dressing

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We’ve all heard the hype – buy new windows and save 35% on your next heating bill. To put it politely, that’s a bunch of hooey. Unless your windows are old, poorly installed, leaky and missing half the glass, you are not going to save 35% on your heating bills. In fact, there are numerous studies showing that replacing windows is among the least cost effective measures for improving your home’s energy efficiency!

That said, windows are among the worst performing parts of your home when it comes to energy efficiency. Did you know that a single, 3 by 5 foot window can double the energy loss for the wall in which it’s mounted? This is why manufacturers often make such outrageous claims about energy savings. But a home loses energy through more places than its walls. It loses energy through air infiltration, walls, windows, doors, ceilings, the foundation and the slab.

Let’s compare a variety of window styles and their relative energy loss. But first, a definition:

U-value: is a measure of the energy transfer through a window. The higher the U-value, the greater the energy transfer and the worse the insulating ability of the window.

  1. Single glazed, clear glass, metal frame. U-value is above 1.0. Metal framed windows are the worst since metal conducts heat so well.
  2. Single glazed, clear glass, non-metal frame. U = 0.71 to 0.99
  3. Double glazed, clear glass, metal frame. U = 0.71 to 0.99. An old wooden, single glazed window is better than a metal framed double glazed window.
  4. Single glazed window with tight storm window. U = 0.50
  5. Double glazed, clear glass. Non-metal frame. U = 0.41 to 0.55
  6. Double glazed, low-e glass. Non-metal frame. U = 0.26 to 0.40 depending upon frame.
  7. Triple glazed, low-e glass. Non-metal frame. U = 0.15 to 0.25

Comparing U-values, we can directly compare the relative energy efficiencies of these different styles of window. For example, if you install a super insulating, triple glazed window with a U-value of 0.20, this will lose 20%-25% as much energy as an old single glazed clear glass window. That is truly substantial. In fact, when I renovated my own home, I went this route. Not because I knew the energy savings will pay off (they won’t) but I was trying to optimize my entire home’s energy efficiency and comfort.

Suppose you have a moderately old wood frame, single glazed window with a tight fitting storm window. This might have a U-value of around 0.50. If you were upgrading to a double-glazed, low-e window, which typically has a U-value of about 0.35, then the new windows would only reduce the energy loss through the window by 30%. Not bad, but not great and probably not worth the investment.

In addition, most new windows are installed poorly. I have seen many instances where a house was less comfortable after installing new windows. Why? Because the installers did not seal around the windows properly and air infiltration is much worse for energy loss than is poor insulation.

If you remove the trim from around a window, you would see something like this. The window unit would be shimmed out and nailed into place. Around the perimeter are big air gaps. Sometimes, you can even see right outdoors.

The problem is, most installers just shove fiberglass in these cracks. Fiberglass is not an air barrier. In fact, when compressed like this, it isn’t even a good insulator!

Please see my website for more detailed information on proper window installation.

For all these reasons, if your windows are in good shape and don’t seem drafty now, then I usually don’t recommend replacing them. Instead, start with some high-quality window treatments.

It’s amazing how much of a difference cellular shades or window quilts can make. At a fraction of the cost and disturbance of new windows, properly installed shades or window quilts can reduce energy loss by anywhere from 50% to 80%, making your home more comfortable and energy efficient.

Practically speaking, usually I recommend that people outfit one room with these initially to see if they yield the desired improvement. However, you really can’t go wrong with these unless you’re planning on renovating anyway and will be upgrading the windows. In that case, I suggest holding off on the window treatments until you get the new windows because often the new windows will be a different size and the treatments might not fit then ew windows.

For more detailed information, please see the links below.

Other links:

Dept. of Energy – Energy Performance ratings for Windows

Dept. of Energy – Energy Saver Tips for Windows

Efficient Windows Collaborative for more technical information on windows.

Florida Solar Energy Center – Windows

Grace-Vycor – Contractor’s Guide to Window Installation

National Fenestration Rating Council – General website