BUSI401 CHAPTER 4

Question 1

An understanding of the building envelope is important for real estate professionals for multiple reasons:

Answer 1

1. To properly inspect and analyze the market appeal of a commercial building you need to understand its basic construction and perform¬ance goals.

2. The observed state of the building envelope offers clues about the overall condition of the building and can be an indicator of possible deferred maintenance and the need for major repairs.

3. The effectiveness of the building envelope is also an important factor in determining the mechanical and electrical system requirements and overall energy efficiency of the building.

Question 2

Symptoms of a poor building envelop?

Answer 2

1. Conspicuous water staining on the ceiling of upper floor levels may indicate a progressive failure of the roof system, which could be very costly to repair.

2. Poor sealing around window glazing may indicate serious issues with moisture infiltration within the building envelope cavities.

3. Exterior doors and windows that are difficult to open or close may indicate excessive differential settlement.

4. Poor interior air quality may compromise tenant comfort, leading to leasing issues.

Question 3

Main purpose of the building envelope?

Answer 3

Provide protection from the elements, such as temperature fluctuations, solar radiation, air pressure, wind, and humidity. The building envelope is designed to resist transfer of water, air, water vapour, and sound from exterior to interior environments. In order of mention, this resistance is provided by the cladding, air barrier, vapour barrier, and insulation. The envelope must also transmit adequate levels of light to the interior through proper placement of windows. Finally, the envelope contributes to the building’s aesthetics, forming much of its external appearance. The architect’s goal in designing the envelope system is to achieve all of these goals at a reasonable cost.

Question 4

Examples of the urban or built environment impacting the building envelope are as follows:

Answer 4

Examples of the urban or built environment impacting the building envelope are as follows:

Smoke or emissions from industrial activities

Heat sinks associated with the concentration of large buildings in a downtown core area

Wind patterns created by buildings of different height, mass, orientation

Solar shading from adjacent structures

Pollution and noise from heavy vehicle traffic

Question 5

In addition to resisting external natural and other local influences, a building envelope must also satisfy _ _ _ _ _ LIST 3

Answer 5

In addition to resisting external natural and other local influences, a building envelope must also satisfy safety needs, aesthetics, and architectural-design goals.

Question 6

Discuss serviceability of the
building envelop

Answer 6

The serviceability of the building envelope must be considered at the design stage.

For example, access to windows for cleaning, to cladding for painting, to the roof for repairs, and so on, should be a consideration at the design stage to avoid future costly renovations.

Question 7

SOURCES OF ENERGY LOSS

Answer 7

There are many sources of energy loss.

The flow of heat is one, while air loss is another factor.

Other areas of energy loss are related to the efficiency of the heating and cooling systems which contain a multitude of electric components such as motors and pumps.

Question 8

How heat travels . . .

Answer 8

There are numerous ways that heat can flow through the building enclosure. Heat travels by:

conduction, between two touching solids such as a pot and an element on the stove;

radiant flow, heat waves flowing off hot objects to cooler zones, such as soup left out to cool; and

convection, hot liquid or gas rising to be replaced by cooler liquid or gas, such as with boiling water.

Question 9

Explain conduction heat flow in a building

Answer 9

Conduction allows heat from the building to flow through a continuous path of wall materials that connect the indoors to the outdoors.

Consider a wall framed from 2 x 6 studs: the interior surface will normally be gypsum wallboards screwed to the wall studs; the exterior has plywood sheathing nailed to the stud; and then the exterior finishes such as siding or stucco are fastened to the sheathing.

While there is a cavity between the studs, the studs themselves create a “thermal bridge” connecting the interior and exterior environments.

Question 10

Explain radiant heat flow across the cavity between studs

Answer 10

Within the same 2x6 wall assembly, radiant heat flow can occur across the cavity between the studs.

Without insulation, heat can radiate from the warm side to the cold side. Just like the way you can feel the heat radiating away from the hot element on a stove.

Similarly, occupants can lose heat by radiant flow such as when standing next to a single-paned window on a cold winter day.

Question 11

Continuing with the 2x6 wall assembly example, convection will also occur within the cavity between the studs.

EXPLAIN

Answer 11

Continuing with the 2x6 wall assembly example, convection will also occur within the cavity between the studs.

Again, if left uninsulated, convection currents will develop because the air adjacent to the warm side will rise while the air on the cold side will drop.

Thus the air will follow a circular path, as air rises past the warm side it will pick up heat and as it drops down past the cold side it will lose heat.

Question 12

Explain convection in the building as a whole

Answer 12

Convection can also occur on a larger scale in the building as a whole. Heat carried in the interior air rises to the top floor and cold air rushes in through leaks at the base of the building; this causes a stratification of temperatures horizontally within the building and is called the stack effect.

Question 13

Explain thermal conductivity

Answer 13

Thermal conductivity is the term that describes the ability of the building enclosure to moderate heat flow. It can also be thought of as measuring the building envelope’s ability to protect the occupants from daily and annual fluctuations in outside air temperature.

Question 14

U-Value

Answer 14

The heat transfer coefficient of building envelope materials is referred to as the U-value.

The U-value is an indicator of how well a material conducts heat. It is measured as the amount of energy lost over a given area for a given temperature difference, described in Watts per square metre per Kelvin. A high U-value means the material is a good conductor and a poor insulator. A low U-value means the material is a poor conductor and a good insulator.

Question 15

The overall thermal resistance of the building envelope components is referred to as _ _ _ _ _

Answer 15

The overall thermal resistance of the building envelope components is referred to as the R-value.

Question 16

NOTE ONLY

The higher the R-value, the greater the thermal resistance of a material or the overall building wall system. In Canadian climates, the recommended R-value for commercial construction wall assemblies ranges from 18 to 31, depending on the region

Answer 16

NOTE ONLY

The higher the R-value, the greater the thermal resistance of a material or the overall building wall system. In Canadian climates, the recommended R-value for commercial construction wall assemblies ranges from 18 to 31, depending on the region

Question 17

An R-Value of 27 is a U-Value of . . . .

Answer 17

An R-Value of 27 is a U-Value of 0.037 (the inverse of the R-value, U = 1/R).

Question 18

Insulation may consist of _ _ _ _ _

Answer 18

Insulation may consist of mineral or glass fibre batts, various types of rigid insulation such as polystyrene and polyurethane, or formed in place insulation such as polyurethane.

Question 19

Explain convection

Answer 19

Convection, hot liquid or gas rising to be replaced by cooler liquid or gas, such as with boiling water.

Question 20

Thermal Gradient

Answer 20

The thermal gradient is the gradual change in the temperature within the wall that results from one side being warmer and one side being cooler.

For example, in winter the outside of the wall is cold and the inside is warm - the temperature gradient illustrates how this temperature change occurs within the wall.

Question 21

A high U-value means _ _ _ _

Answer 21

A high U-value means the material is a good conductor and a poor insulator.

Question 22

The thermal gradient for a wall could be graphically plotted. This will show the temperature at any given point within the wall. This can be used to determine the exact location of the _ _ _ _ _ within the wall.

Answer 22

The thermal gradient for a wall could be graphically plotted. This will show the temperature at any given point within the wall. This can be used to determine the exact location of the dew point within the wall.

Question 23

Dew Point

Answer 23

The dew point in the wall reflects the temperature at which the water vapour in the air condenses into water.

Question 24

Vapour Barrier

Answer 24

A vapour barrier, as its name implies, prevents the movement of vapour and is typically comprised of a polyethylene sheet.

Question 25

Explain conduction

Answer 25

Conduction, between two touching solids such as a pot and an element on the stove

Question 26

The vapour barrier should be located _ _ _ _ _ _

Answer 26

The vapour barrier should be located on the “warm side” of the dew point.

Question 27

NOTE ONLY

In a typical residential wood frame wall assembly, the vapour barrier should be attached to the wood studs on the interior side (under the drywall finish).

Thus, warm moisture laden air is prevented from entering the wall cavity where it may be cooled sufficiently to form condensation within the batt insulation.

Answer 27

In a typical residential wood frame wall assembly, the vapour barrier should be attached to the wood studs on the interior side (under the drywall finish).

Thus, warm moisture laden air is prevented from entering the wall cavity where it may be cooled sufficiently to form condensation within the batt insulation.

Question 28

__________ is the term that describes the ability of the building enclosure to moderate heat flow. It can also be thought of as measuring the building envelope’s ability to protect the occupants from daily and annual fluctuations in outside air temperature.

Answer 28

Thermal conductivity is the term that describes the ability of the building enclosure to moderate heat flow. It can also be thought of as measuring the building envelope’s ability to protect the occupants from daily and annual fluctuations in outside air temperature.

Question 29

Define radiant flow

Answer 29

Radiant flow, heat waves flowing off hot objects to cooler zones, such as soup left out to cool

Question 30

List other factors can affect thermal performance of building envelopes:

Answer 30

• Thermal mass
• Thermal bridging
• Radiant barriers
• Convective transfer resistance

Question 31

Explain Thermal Mass

Answer 31

Thermal mass:

Building components that absorb excess heat and radiate it back to the space when the external heat source has been removed. All parts of the building contribute to its thermal mass. However, more dense and massive components such as concrete walls and floor slabs will have greater thermal mass effects. For example a south-facing concrete wall will absorb heat during the day, reducing the heat build-up inside the building. In the evening, when the air cools down, the concrete wall will release the stored energy as radiant heat.

Question 32

Explain Thermal Bridging

Answer 32

Thermal Bridging

Building components with higher thermal conductivity that conduct heat more rapidly through an insulated building assembly, such as a steel stud in an insulated stud wall. Insulation reduces the effects of thermal bridging. However, thermal bridging cannot be entirely avoided. For example, insulation must be fastened to the structure using metal screws or nails; these fasteners will act as thermal bridges due their high thermal conductivity.

Question 33

Discuss Emissivity

Answer 33

The ability of a material to radiate energy is known as emissivity.

In general, highly reflective materials have a low emissivity and dull darker colored materials have a high emissivity. All materials, including windows, radiate heat in the form of long-wave, infrared energy depending on the emissivity and temperature of their surfaces.

Radiant energy is one of the important ways heat transfer occurs with windows. Reducing the emissivity of one or more of the window glass surfaces improves a window’s insulating properties. For example, uncoated glass has an emissivity of .84, while Vitro Architectural Glass’ (formerly PPG glass) solar control Solarban® 70XL glass has an emissivity of .02.

Question 34

Explain Low Emissivity Glazing

Answer 34

Low emissivity glazing (“Low-E” glass) is a coated glass that reduces the amount of heat transference through a window, keeping the heat out in the summer and restricting loss of interior heat in winter.

Question 35

Explain convective transfer resistance?

Answer 35

Convective transfer resistance: techniques to limit the loss of heat by convection, or the natural tendency for warm air to rise and cool air to settle.

Question 36

Explain how convective transfer resisitence can be achieved?

Answer 36

This can be accomplished by limiting the space between panes in double-glazed windows. If this gap is too large, the air between the sheets of glass may start to move in a loop between the two sheets, creating a convective cell.

This movement increases heat transfer between the cold pane and the warm pane and results in heat loss.

A convection oven works using this principle: a fan moves hot air in a loop through the oven and increases heat transfer to the food, which reduces cooking time.

Question 37

Three Factors Than Influence Water Tightness?

Answer 37

There are three factors that can influence the water tightness of a building: the presence of water; an opening in the envelope; and a driving force. It is impossible to keep the outside of a building absolutely dry, therefore the presence of water must always be assumed.

Question 38

During the design and construction of the building envelope, many forces must be eliminated or neutralized to contribute to a water tight structure. These forces include:

Answer 38

During the design and construction of the building envelope, many forces must be eliminated or neutralized to contribute to a water tight structure. These forces include:

• Gravity: water flows “downhill”; e.g., off the roof down the wall.

• Momentum: once in motion, water has momentum that requires a stopping force in order to bring it to rest; e.g., rain running down a sloped roof may have sufficient momentum to be driven under a flashing. Wind-driven rain is another example of this effect.

• Surface tension: a tension force that builds up on the surface of a liquid (e.g., how insects can “walk” on the surface of the water) — surface tension can “pull” water through small openings in a building envelope.

• Capillary action: water will flow into very small holes or tubes, often in defiance of gravity: e.g., water in contact with the base of a concrete wall can be “wicked” up the wall.

• Vapour diffusion: vapour exerts a pressure similar to air pressure called “vapour pressure” which is proportional to absolute humidity and temperature. Like air pressure, vapour pressure tends to equalize; i.e., there is a flow of vapour from a region of high humidity to low humidity.

• Air pressure: Water vapour is carried by the air in which it is contained. Outside air can be drawn into the building when the exterior air pressure is higher than the interior air pressure. This process also works in reverse, where inside air can be drawn through the walls to the outside. If air leaks through the building envelope and cools due to the “thermal gradient”, the dew point will be reached and some of the vapour will condense into water within the envelope.

Question 39

There are three general approaches to controlling the entry of external moisture into a building:

Answer 39

There are three general approaches to controlling the entry of external moisture into a building:

mass-wall systems, face-sealed systems, and pressure equalized wall systems.

Question 40

Explain how mass wall systems work?

Answer 40

Mass-wall systems are the historic approach that relies on the thickness of the wall to shed or deflect most of the moisture from rain and absorb the remaining surface moisture.

Question 41

Explain Face Sealed Systems to Contol Moisture

Answer 41

They rely on waterproof exterior cladding with well-sealed joints. Such systems require a high degree of ongoing maintenance because sealed joints will inevitably fail, establishing clear pathways for moisture to enter the wall cavity.

In BC’s Lower Mainland, the numerous buildings constructed in the 80s and 90s had face-sealed wall assemblies that ultimately failed, leading to the well-documented “leaky condo crisis”.

Question 42

What’s another problem with face-sealed systems?

Answer 42

Another problem with face-sealed systems in modern insulated buildings is that they are susceptible to changes in exterior versus interior wall temperatures.

CMHC reports that the main problem with these systems is thermal movement and cracking, with failures typically occurring at the joints. Related problems are the deterioration of sealants with the impact of constant humidity, freezing and thawing, and direct sunlight.

Due to the nature of the wall system, moisture entering the wall cavity will often become trapped, amplifying the impacts.’

Question 43

_ _ _ _ _ _ _ are the norm in most modern building enclosures

Answer 43

Pressure equalized wall systems are the norm in most modern building enclosures

Question 44

_ _ _ _ _ _are sometimes referred to as rain-screen wall systems.

Answer 44

Pressure equalized wall systems are sometimes referred to as rain-screen wall systems

Question 45

Explain mass wall system to control external moisture

Answer 45

Mass-wall systems are the historic approach that relies on the thickness of the wall to shed or deflect most of the moisture from rain and absorb the remaining surface moisture.