Innovative Energy Engineering



Enclosure

The enclosure separates the inside (comfort) from the outside (rain, light, heat, cold, wind, moisture). It can get damaged from the inside (i.e. vapor) and the outside (frost, water, light). A good enclosure consists of all "control layers" (not a stopping layer!). No enclosure in real life is be 100% tight and we account for that. Each layer should be continuous throughout slab, wall, and roof including all elements inc. windows and doors. This presentation by Dr. Joseph Lstiburek gives an overview. Before any enclosure materials, methods and details are selected, the shape of the building should be functional and efficient. Large Floorspace-to-Enclosure (F/E) Ratio reduce up-front cost and reduces energy consumption.

Moisture goes from warm to cold and from wet to dry. Air goes from high to low pressure and gravity acts down. This simple science is often ignored and that is when buildings fail. How can it be acceptable that we travel to space, but have roofs that last 20-30 years only, while medieval roofs lasted hundreds of years? Maybe the old master builders knew something.

Walls

Wall material is exposed to rain water, wind and temperature extremes. Water exposure can be reduced by large roof overhangs, which also serve as shading devices. Colors should be light to reduce expansion, contraction, material deterioration and heat gain. Brick, metal or cement board are good outside materials that can last as long as the building. Plastic siding and wood don't last long.

Thermal bridges often happen around wall openings, where floors or partition walls meet the perimeter wall, at outlets, or any other penetrations. All studs typically create a thermal bridge. To eliminate thermal bridges, continuous insulation is needed.

Roofs

Roofs keep water out by diverting water before it can penetrate the roofing material. Steep roofs with long-life roofing materials (slate, copper, or other corrosion-protected metals) can last many decades with minimal care.

Typical flat (low slope) membrane roofs with exterior membrane only last 20 - 30 years with occasional leaks. This is due to the membrane exposed to sunlight and temperature extremes. If a flat roof is required, an inverted, or protected membrane, roof should be used. This membrane is protected from sun and temperature extremes.

Asphalt shingles, plastic membranes and other modern materials are not resistant to sun light and deteriorate. In addition, those roof materials are made of crude oil, which is expected to be expensive at time of replacement and are combustible. Disposal also is a concern since recycling of those is not easy.

Roofs should always be vented above the thermal and vapor barrier. This will allow any moisture (whether from rain, or vapor leaks) to dry out over time. If insulation is not sufficient, the heat escaping will cause snow to melt. This water will flow to the (non-heated) overhang, freeze, and will create an "ice-dam" that keeps water standing in a paddle on the roof. This water will penetrate the roof and damage it.

A reflective roof is beneficial from an energy point as it reduces summer cooling load. Buildings without AC also benefit from less overheating. Longevity of a reflective roof also is extended because the roofing material does not get too hot. On older roofs without vapor barriers, the black roof helped in heating up the membrane and drying out the insulation that got wet from condensation. Some roofs without vapor control layer that got a white roof failed. But they failed because of the lack of a vapor control layer, not because of the white roof. The roofing designer should understand how the roof works and adapt the design appropriately. Unfortunately many institutions wrongfully claim black roofs would be beneficial in heating regions.

Foundation, Slabs and Basements

Unlike walls, foundations and slabs are not exposed to sunlight and large temperature extremes over short periods of time. However, they are constantly exposed to moisture and ground water. Water should be diverted by trench drains and sump pumps. To break capillary effect, coarse gravel has to be beneath the slab and the foundation has to back-filled with coarse gravel as well. The foundation wall has to be covered with an epoxy sealant. On top of the sealant an additional capillary breaking plastic plane should be installed.

Most basements appear moist. Often this is not caused by leaky foundations, but by condensation on cold surfaces. Often this problem is worsened by ventilating basements. Bringing in new warm and moist air actually introduces more water to the basement. Even with a de-humidifier, this infiltration constantly introduces water to the basement. Mechanical equipment in basements often creates negative pressure, "sucking in" even more outside air. This can be prevented by insulating the foundation walls and slab, which increases the temperature of the basement.

Heat escapes through the foundation and the slab in 2 ways. First, it conducts to the outside. This depends on the distance from the surface to the outside. For example, more heat is transmitted from the foundation wall that is just below grade and less from the center of the slab. Foundation insulation has to be installed on the vertical foundation walls and additional insulation "wings" at the foot of the foundation slow down heat transfer from the slab. The second way to lose heat is directly lose it to the ground. The ground is a huge heat sink with an (almost) constant temperature. While this temperature is warmer than ambient air in heating climates, it still creates a heating load, even after a long time. Heat lost to the ground can't get recovered!

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