The following pages journal a journey in designing and building a truly “Passive Solar” house. We looked to the past successes and failures of solar projects, and we utilized the tools that modern technology has given us. Focusing on Solar Shading, Therman Mass and Solar Heat Gain, we were able to accomplish a Modern Pasive Solar Solution. Thank you Robert, Deb & the Wadsworth family for sharing in this passion and making this project possible. Steve M. Homa
Form Follows Function
Passive Solar homes require special attention to the elements. Obviously, southern exposure is a key principle, but simplicy is also a key factor. In this particular design, all of the main living areas – living room, kitchen & dining- were kept to the southern half of the house. Setting them up in a linear fashion allowed for equal distribuution of the solar gain across the southern exposure. A 4 foot band of free space was kept at the south wall to allow a buffer for excessive light that can be created when trying to bring in as much sunlight as possible. This buffer zone was also intended to be an indoor gardening area. The two bedrooms and baths were kept to the northern half of the house to allow them to stay cooler both in the winter and summer. The simplicity of design created dramatic sloping ceilings, reaching heights of 16 feet in the bedrooms and 11 feet in the living area. Sunlight spills in from the transom windows, washing the bedroom and bath walls with indirect light. The rear exposure in the lower level allows for a large rec area, bedroom and full bath.
Extensive solar shading studies were done using modeling software. June 21st proudces full shading, while on December 21st we have full sun exposure on all the southern windows. Sunlight comes almost all the way into the back wall of the front living area, allowing the 4 inch concrete floor to collect the maximum amount of solar energy and store it for later
Before the design begins, careful evaluation of the proposed site is done to insure proper exposure. Excavation and foundation work begin. Sandy soil proves challenging and requires stepped grading.
Foam, Foam, Foam,
Polystyrene foam is the building block for PEA homes. Polystyrene foam will not degrade below grade or when protected from sunlight and maintains it’s 3.7 per inch R-Value for its life with no off gassing. It is bulk water-resistant yet is semi-permeable for vapor.
8 Inch Foam Applied to the North Wall
Due to the half-exposure we had as a result of the steep slope of the lot, we opted to increase the thickness of the foam on the half-exposed northern walls. 6″ foam was used on the other exposures of the foundation.
Foam Installation Techniques
6″ & 8″ foam is large and required some extra thought about how to attach it to the foundation. 10″ masonry screws are hard to come by, and glue alone just doesn’t do the trick. We’ve used duct tape in the past to hold the panels in place while the glue dried and before backfill, but it was difficult to work with an, well, just not very professional. So we created a new fasterner…. Using the metal ties that the masons use to hold their concrete forms together (making sure they didn’t knock these off), we developed a simple system. Tying rebar wire to tehse metal ties and then pulling it through the foam, we were able to pull the foam tigtht to the foundation while the eps glue dried. It’s so easy, a 15 years old girl can do it. No, really! Thanks to my daughter for her help on those hot days.
4 Inch Foam
4″ high density polystyrene foam is used below the basement slab. Our foundations are dug flat, which allows 4″ of stone with room for 4″ of foam. This brings us flush to the top of footing, where we can install our 6 mil. vapor barrier and 2″ high density foam over the top of the footing. This way, almost all thermal bridging is accounted for.
Fresh Air Intake
Before backfill, the external connections for the septic, well & external fresh air intake must be made. From past experience, we have found that every house needs to have an ERV (Energy Recovery Ventilator). This brings fresh, controlled air into an otherwise tightly sealed environment. Direct intake through a side wall is good but does not address the exterior temperature of the fresh air. By burying a 6″ sewer pipe in the ground, we are able to, in effect, pre-heat the air in the winter and pre-cool it in the summer. Ground temp stays about 50 degrees all year round (a little warmer next to the foundation). so it’s the perfect fresh air conditioner. A slight slope helps potential condensation drain.
Suspended Concrete Flooring System
A unique concrete flooring system that uses lightweight stamped galvanized steel joists to support a concrete deck. It is engineered and sent to the site ready to install using standard carpentry tools. A plywood deck is suspended between the steel joists and later dropped out after the concrete has cured. This system allowed us to easily incorporate radiant heat into the 4 inch slab. Precast concrete was considered, but due to the remote location of the site and the desire to have the optimum thickness of thermal mass, Speedfloor was chosen.
Radiant Pex Tubing
Pex tubing tied to a wire mesh grid. Pre-locating penetrations in the floor means less drilling and keeps the pex tubes safe. The 4 inch extension of the foundation foam became the form for the concrete.
Structural Insulated Panels ( SIPs )
The backbone of the PEA building system. 8″ SIPs were used on the first floor walls of this house, with 12″ SIPs on the roof. This produced a very airtight house that tested at 325cfm @ 50 pascales, one of the lowest ever tested by our Energy Star rater. SIPs rate at about 3,7 R-value per inch, so our 8″ walls with an additional 1″ foam on the exterior rate at about R-35. This gave us a very low heating and cooling load of less than 20,000btu each. That, in turn, allowed us to put in a a smaller solar heating system which only required a 4500 watt internal backup heat coil. SIP walls can be pre-cut at the factory as these were, which allows for quicker construction at the jobsite. The whole shell and roof of this house was assembled in just 2 days. Typically, SIPs are anywhere from 3-4 times stronger than a stick framed wall. They easily meet any shear wall loading, since the entire wall is sheathed on both sides, creating a sort of engineered I-beam.
Before the siding goes on, the surace of the SIPs needs to be protected. We have chosen to use a hybrid system of 1″ polystyrene foam. We glue the joints and caulk all the gaps to make it waterproof. Polystyrene foam has the unique characteristic of being bulk water resistant and semi-permeable, so water vapor can escape from it. Muck like “Tyvek”, but with an added R-5.
The lower level was not forgotten in the design of this house. Ample light from large egress windows create a bright rec area and future bedroom. A full bath rough-in and lots of storage finish it off. The walls and concrete floor act as “thermal mass” and give a spot to dump excess heat in the summer. Temperature is consistently comftorable at around 70 degrees.
Drywall week; the rooms start to take shape. SIPs are easy to work with as they have no studs. All items, including kitchen cabinets, can be screwed directly to the osb skim of the SIPs.
After drywall and the first coat of paint, the floor protection is removed to reveal the acid stained floors. A dark color is preferred to maximize the captured solar energy. A 4″ concrete surface can collect enough energy on a sunny day to raise the temperature in the room by several degrees.
Solar Thermal & Hot Water Storage
The main source of heat for the house is direct-gain solar energy from the sun onto the concrete floors. Extra heat is stored in the concrete as the temp of the floor is raised by the sunlight. This energy is then later distributed to the room as the air temperature drops below that of the floor. This is the main principle of “thermal mass” and what drives the design of this house. The floor is further heated by the “solar thermal” hot water panels on the roof (previous page). They reach temperatures of 165+ degrees on clear winter days. That heat is stored in two hot water tanks in the basement. The larger 120 gal, tank stores hot water for domestic use and the smaller 80 gal, tank supplies heat to the radiant floor throughout the house and basement. 4500 watt elements in the tanks serve as back-up just in case. These run on a set-back system, so they use cheap nighttime electricity. Each tank holds more than enough heat for a full day’s needs.
Every house we build incorporates some type of Energy Recovery Ventilator (ERV) or Heat Recovery Ventilator (HRV). When homes are built to a standard as tight as ours, fresh air control is a key ingredient in a home’s health.
So why not just build a leaky house? ERV’s and HRV’s have special filters that allow them to draw fresh air in from the outside and pass through the exhaust (stale) air from the inside to collect up to 80% of the heat. So we can control the air quality and not lose energy.
On this house, we have the air exchange system tied to the bathroom vents,,, so we choose to use an ERV, which has the capacity to vent moisture. Our unit, the “Ultimate Air” has the added feature of a summer switch which bypasses the heat exhchange feauture to exhaust only. This results in the ability to cool the house naturally when the outside temp drops below the indoor temperature.
This house is further cooled by the radiant tubing running through the floor. We used a potable valve system that allows us to reverse the cold well water through the floor to reduce the floor temperature by as much as 20 degrees. The cool floor then pulls heat from the indoor air as it tries to equalize temperature. It’s enough to drop the indoor temp by about 5 degrees.
Exterior Insulation Finishing System (EIFS)
“EIFS” is the perfect material to cover the 6″ & 8″ foam that insulates the foundation. It’s a stucco-like material that is designed to adhere to a fiber mesh embedded over the polystyrene foam surface. We designed the top ledge profile out of foam to mimic a brick ledge and, more importantly, to eliminate the thermal bridging that could at the sill.
Indirect natural light washes in from the high transom windows in the rear rooms.
Natural light is so important to the comfort of the inhabitants. One might consider a well insulated house to function better with no windows. But wthat would eliminate the natural benefits of the sun. The sun essentially provdes us with “free” light to do daily tasks and can be the main source of heat, as it is in this house.
With the use of transom windows, we were able to light bathrooms, bedrooms, and even hallways. Since this light comes from above and bounces off walls to its desired places, it is soft and unobtrusive.
For nightime, we utilized indirect LE-5 fluorescent tubing. These are very efficient, producing a soft, even light. We mounted them behind crown moulding, so that the light would bounce up toward the ceiling and fill the room.
A HIGH PERFORMANCE HOME
- Super Insulated Foundation
- Structural Insulated Panels
- Triple Pane Fiberglass Windows
- Passive Solar Design
- Thermal Mass
- Solar Hot Water
- Passive Shading
- Controlled Air Exchange
These are the ingredients that make up a “High Performance Home”.
Building better takes great commitment. But the rewards are just as great.
Comfort & Peace of mind.