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home page » passive solar design chapter » wing insulation detail page ... you are here
Bermed foundation wall and frost-protected shallow foundations alike should be given at least basic frostwall concrete waterproofing along with wing insulation.
The home pictured throughout our site was bermed to help it stay sustainable through our long and harsh Rocky Mountain winters ... and the property was already sloping to the south.
In most climates, an underground home is more of an aesthetic choice than a sustainable design necessity.
Above ground HTMs with a shallow footer wing insulation design function worlds better than any conventional home.
Please note that bermed homes are ones which have been backfilled to the top of the first floor.
Add a Swedish sod roof and wrap soil around to the front of an HTM, and it becomes an underground home.
The Underground Space Center at the University of Minnesota did some excellent research in the late 70's and early 80's pointing to the fact that horizontal "wing" insulation was preferable to vertical foundation wall insulation.
Wing insulation was shown to keep the earth near foundation walls dry, greatly increasing the insulation's efficiency.
Expanding greatly upon this concept, John Hait published Passive Annual Heat Storage (PAHS) in 1983.
This work was dedicated to a basic concept, ignored by too many architects: keep the ground under and around foundation dry and it retain energy better.
Water transference problems aside (the classic wet, moldy basement), leaving uninsulated foundation walls in direct contact with wet earth is a huge, senseless energy loss.
Frost-protected shallow foundations (wing insulation) protect the area under and around footers, allowing for a lower foundation "frostwall" depth, making it perfectly suited for slab on grade (monolithic slab) construction.
Installing at least two foot width of 2 inch thick foam board insulation in a horizontal wing around the perimeter of ANY home for frost protection is wise.
The technique has apparently been a standard since the 1950s in cold-climate Scandinavia countries.
click here for the main chapter of our free Passive Solar Design eBook
One of the most important design factors for sustainable, high thermal mass (HTM) construction is this frost-protected shallow foundation wing insulation around the perimeter.
As the shallow footer monolithic slab sketch above outlines, we stress the need for waterproofing and insulating up to a 20 foot perimeter around the home.
Should your site and/or budget dictate less than twenty feet of wing insulation, 4 feet is bare minimal in any climate.
Sheets of foam board insulation typically come 2 and 4 feet wide by 8 feet long (48 sheets of 2 inch thick, 4 foot by 8 foot per unit/pallet).
To save money when purchasing, always get a wholesale bid on "units or bunks" 4' by 8' by 8' tall on a pallet and ignore the per-piece cost at building center.
Wet earth near your foundation acts as a constant drain pulling energy away from your home.
This is a mistake you simply cannot afford, literally, when buidling a sustainable home.
And once you have it dry, insulating your foundation is always a good energy investment.
Always insulate the exterior of any home design and break ground contact at every opportunity.
HTMs do not employ any exotic building materials or methods.
Construction details are more common commercial, if anything.
Electrical wiring in conduits and pipe in chaseways is the norm.
Thankfully, there's not alot of wood framing to drill through.
A single story, bermed, concrete block home is the easiest to build and the most efficient passive solar design for many reasons.
The key to a single story HTM's often total sustainability is having the floor grounded directly to the incredibly large heat / cooling storage mass that the Earth underneath provides.
This is the main reason why a two story home is inherently not as sustainable.
Two story homes are HTM hybrids and will likely always need some type of mechanical heating/cooling system to service the floor above.
And they're more technically difficult to build ... special skills are needed to build a two story home that the average homeowner-builder does not possess.
Skills like perching on top of a 30 foot roof comes to mind for me.
If a key interest is being energy independent, never build an attached garage with any type of home (home and garage share a door). When the two structures share concrete footers/foundation/walls, energy flows easily and the garage constantly drains heating/cooling from the home. Thermally separating walls and foundation by heavily insulating underneath garage floor and between the two structures helps, but the physics works against you. There is a finite amount of passive solar gain potential - why use stored energy resources to indirectly heat/cool the garage and ground around it? We always recommend detaching the garage by at least 12 feet, preferably 20 feet, or more from the home. The integrity of the home's wing insulation is key to thermal mass performance. Allowing energy to be drained off and escape through garage foundation is not sustainable. A covered breezeway between the two structures is very common design element to span the gap. These breezeways are often enclosed against the weather (covered patio), adding to the integrity of the wing insulation (ground above warm and dry). A greater separation of public and private areas goes along with stretching the layout with a breezeway. And, the cost of building the garage portion is greatly reduced.
The drawing below, outlines a conventional poured-in-place frostwall foundation footer design. You can build an HTM with poured-in-place walls - it requires special equipment and is more technically difficult the first time than stacking blocks, but concrete is more common from local contractors. If you don't plan on building your own home, we can work with you on a poured-in-place design instead of surface bonded, stack block walls. The main advantage of dry stack block construction is its ease by the average homeowner / builder and their friends. Putting up your own walls will save you a lot of money and make it a more personal project. When labor amounts to around two-thirds of your home's total cost, it is an important consideration.
Here's some good basic building terminology to know:
The Uniform Building Code (UBC) is regionally modified to prevent frost heaval of your foundation walls.
In the Colorado high country, the top of backfill (finish grade) extends a minimum of forty inches from the exterior finish grade (your yard surface) to the bottom of the footing (footer).
When floor joists run across the top of a short frostwall, it's called a crawlspace.
When you pour a frostwall tall enough to allow headroom (7'6" minimum), it's a basement.
If the basement floor has a door that leads directly outside (no steps up) it's a slab-on-grade walkout basement.
Slab-on-grade construction refers to pouring the concrete floor (slab) directly on the ground (grade).
In the picture above, the floor slab will be poured directly on the top of footer elevation.
You'll find it very handy to know the vernacular when talking with builders and architects.
With any foundation design, it is key to note:
As noted above, roof runoff should be gathered and directed away from the foundation.
Moisture under and around your foundation creates an amazing heat sink that results in a lot of energy loss during both the heating and cooling seasons.
We always suggest connecting the gutters to underground pipes and taking the roof runoff at least 20 feet away from the foundation and disposing of it in underground drywells.
Please see drywellinstallation.htm for details on these drywells.
The most important factor to successful earthtubing is DRY EARTH.
As the sketch below outlines, we stress the need for waterproofing and insulating up to a 20 foot perimeter around the home.
Wet earth acts as a constant heat sink pulling energy away from your foundation walls.
Dry earth under and around an HTM stores an amazing amount of energy.
Earthtubes utilize this energy by allowing fresh, incoming ventilation air to passively gain or lose heat energy before it enters your home.
This sustainable ventilation system exchanges indoor air more often, keeping your home's environment fresh without the drawback of "losing all that energy".
All exterior foundation walls should be insulated with 4 inches (minimum) of EPS ("blueboard") foam to prevent energy loss. You need to make the foundation energy efficient - we would most highly recommend wing insulation. Your house plans should call for a minimum 2 percent grade away from the foundation for at least an 8 foot perimeter (minimum) up to 20 feet. We normally suggest 2 inches of EPS foam and three waterproofing layers as shown in the sketches above. Wing insulation keeps the perimeter of the home dry and insulated. This is critical to creating a viable heat sink under and around the home. Dry earth stores heat/cool; wet earth steals energy form the foundation and footers. A French drain should be placed along the far edge of the wing insulation to direct ground runoff to the drywells 20 plus feet away from the foundation. This wing insulation concept is critical to high thermal mass housing and will pay off in the long run. It is not common to conventional construction yet, so don't let yourself get talked out of it. Topsoil above wing insulation is one foot minimum or go with a xeriscaping design with sand, rocks and stone. You can adjust this as needed to fit the site's needs and the availability of backfill. We suggest one foot as a minimum only.
click here for the main chapter of our free Passive Solar Design eBook
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Whether regarding HTMs specifically or passive solar in general, our initial consultation will address your concerns.
After reviewing the material, we encourage you to drop us an email with your questions.
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First, we email an extended outline of tips, tricks, and technical details, many not found on the website.
Then, we ship you a two inch binder jam-packed with the following printed information:
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$1495* plan review & HTM consultation
This isn't ongoing personal project consultation, and is limited to five or six emails, but we trust the plan review and follow-up consultation puts your project on the right track. |
We request that you start with the initial consultation packet for $195* to ensure a solid feel for HTM principles and get a chance to know each other first. Later, after your construction blueprints are finished, sign up for plan review consultation and send us two complete sets for study. For $1495* we will carefully pick over your plans for possible errors, better flow, wiser use of space, and alternative design possibilities. When pointing out options, we view your whole house as an independent "holistic system" chock full of inter-related, functionally inter-dependent parts from the ground up. With a project as large and complex as a new home, it's extremely easy to save more money than you spend on a good consultant. Building a home is the greatest investment of time, energy, and money most of us will ever make. Having an experienced ally giving you relatively unbiased answers to your questions is priceless. Please note that our plan review and consultation service has never included custom blueprinting, engineering or load calculations. Custom drafting and structural engineering services are best supplied by locally licensed professionals and we do not offer referrals, sorry. Always hire professionals familiar with your area's building regulations and who can physically visit your property to inspect soil, construction and materials. Here is a short biography page: whoweare.htm as way of personal introduction and our standard contract is online at: Terms of Service Agreement. We look forward to being of assistance. |
in-house consultation and personal HTM home tours are no longer available
hourly and flat-fee on-going HTM consultation services are also discontinued
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First half hour walks you through the sustainable design, HTM passive solar earthhome featured on our website. While not a How-To video, the second half does include detailed Infiltrator chamber leach field septic system installation and Sun-Mar composting toilet footage. |
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