Thursday, February 11, 2010
What is an attic? This may sound like a silly question, but it isn't. I didn't know what it really was until I was about to buy my first home. I grew up in a home without an attic.
The simple answer is, the space under a roof. Many buildings have attics, such as homes, low or mid-rise apartments, town homes, offices, restaurants or schools. There are also many building types without attics. For this conversation we'll be talking about only buildings with attics.
An attic space is almost certain for buildings with pitched roofs, but there also can be attic spaces in buildings with flat roofs. I'll be discussing both new and existing buildings. I'd like to classify attic spaces into 2 categories.
2. Vented or Open
You might think the attic isn't that important. Either it's just above you on the other side of the ceiling or floors above you in the building you live in. You may not even know if there's an attic? The saying, "Out of sight, out of mind" is very true. You should really take notice of attic spaces. Do you live in a building with an attic? Most single-family homes have attics. So do many town homes and low or mid-rise apartments. No matter what type of building you live in, you should know if there's an attic.
Why is the attic space so important when it comes to Green Building? At one level, you might think of an attic as you would the foundation of a building. If a foundation fails, or is poorly designed,…what can happen? All kinds of things, none of them good.
What if I told you that your attic is designed incorrectly? I'm sorry to report that in all likelihood, it is. The vast majority of attic spaces are designed, built and renovated incorrectly.
Yes, I know. A bold statement? Actually, not bold enough. If I could take a magic wand and have every attic space in America designed and built correctly, my belief is that we would …
Before I give you my list of benefits, I want you to think about 'associated economic costs' a bit differently. As a matter of course the first thing we think about is money. For this discussion I'd like environmental and human impacts to be the first things to think about. Economics are omnipresent; I'm not going to put them aside, just rearrange priorities for a moment. Also, consider the many layers behind the percentages I'm about to pose. For example, reduction of the use of energy includes extraction, production, distribution, waste streams, pollutants, and land use.
With my magic wand…
Reduce 10-15% Energy usage with their associated costs
Reduce 6 – 9% Construction waste with their associated costs
Reduce 3 - 8% Healthcare costs
Individually – Dwelling by Dwelling
Increase 40 - 80% indoor air quality
Reduce 40 – 70% Heating/Cooling Energy with their associated costs
Reduce 10 -20 % healthcare and associated costs
Reduce 80 – 98% presence of, or necessity to, Renovate/Mitigation from insect intrusion with their associated costs
Reduce 80 – 98% presence of, or necessity to, Renovate/Mitigation from mold intrusion with their associated costs
Green Building Consulting and LEED Project management is my second career. Upon entering the field more than 15 years ago with a naive perspective, I was surprised and shocked to discover an array of fundamental building design elements that were flawed, some profoundly. One of which, is the design and construction of attic spaces. What continues to surprised me, is that the attic space conundrum still persists and is maintained by the design and construction industries as well as building codes.
This flaw is evident throughout the country, and is profoundly acute in warmer, humid climates like Southern Texas, Florida and the Caribbean. As I mentioned earlier, nearly all buildings with attic spaces are open or vented. This is the flaw, they should all be closed, with insulation on the underside of the roof decking, not the top of the ceiling.
No building with mechanical heating/cooling should have a vented attic. The attic space needs to be part of the conditioned building envelope. After all, an attic is inside the building.
The concept of a non-vented attic space may be met with resistance and pessimism. But I assure you, whether you're in cold, dry or warm and humid climates, the approach is sound. When you finish this article, I encourage you to do additional research.
Vented attic spaces are commonly designed with:
Open vents on the roof itself. Turbine, goose neck, and ridge.
Soffit vents. Openings on the underside of an overhanging roof's eave.
Insulation on the top of finished ceilings, usually laid between and sometimes covering ceiling joists.
The recipe for the non-vented, closed attic.
Spray foam insulation on the underside of the roof decking.
Calculated amount of conditioned air brought into the attic space.
Cool roof measures.
That's it. If you do only the first measure, you'll achieve benefits. The additional measures elevate those benefits dramatically. The intension of bringing conditioned air into the attic is not to heat/cool the space, but to maintain a temperature and humidity close to that of the living spaces.
In a typical single family home you can expect:
40 – 60% Energy Savings
o Interstitial condensation
o Drywood Termites. ( You will still have to protect the dwelling from subterranean termites if wood is used as a construction material. )
How is so much energy saved? It's simple. In a typical vented attic on a midsummer day with an air temperature of 85˚F and 80% humidity, the temperature inside the attic space can be between 100˚ and 130˚F or more. Hopefully there'll be insulation on the top of the ceiling. At minimum R19, hopefully more. For argument sake, the air conditioning system is set to 74˚. There's 110˚, near 90% humidity in the attic. Factor in the insulation and you have a mechanical system that is working to move the temperature down about 30˚ and humidity down 25%. If we're talking about a dark roof, like asphalt shingle, the temperature in the attic could be more like 140˚.
With the non-vented recipe, complete with a cool roof, the temperature in the attic should be about 80˚ to 85˚ with 70% humidity. In this scenario, the cooling system works to bring the temperature down only a few degrees.
Remember, the energy efficiency is just one of the dramatic benefits. The overall indoor air quality is also enormously improved. With a vented attic, hot, humid air is just above the ceiling but it also fills the spaces inside ALL the wall cavities. This is another place where mold can grow and insects can nest.
For those of you with respiratory or allergy issues, this can have a profound benefit to your quality of life. For homes in regions with high or moderate susceptibility to drywood termite infestation, the problem is virtually eliminated.
The scenario for cool, dry climates is the same, in reverse. The non-vented recipe is applicable everywhere.
If you're considering renovation, this recipe should be on the top of the list. To further add to the energy efficiency and improved indoor air quality, apply spray foam or other environmentally preferable insulation ( No Fiberglass ) to the interior side of the exterior walls, and install efficient windows and doors. My perference is spray foam insulation, as it also seals as well as insulates the building's envelope.
The costs to enact these measures in an existing building can be expensive and varies from region to region, vendor to vendor. If you're building new, the costs can be minimal. No matter what the costs to follow the recipe, it pays for itself over and over, with savings in energy, improved well being and termite infestation prevention.
One of the big questions I'm sure you're asking is, "If a non-vented attic is so much better than one that's vented, why isn't it done more?" The simple answer, entrenchment. Before mechanical cooling and heating systems, it was better to vent an attic space. Since architects and builders had been constructing vented attics for decades, it seems they saw no reason to change.
Have you ever heard an builder say, "I've been doing it that way for twenty years, just like my father taught me and it works fine"?
Welcome to my Performance Green Building - LEED Certification Blog. This is the place where you can follow my Green Building Consulting work, News about the Green Building movement as well as important information and strategies.
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