Saturday, April 2, 2011

INSULATION

AR-461: BUILDING SCIENCE
By:
RAVINDAR KUMAR
Assistant Professor
Department of Architecture and Planning
NED University of Engineering and Technology
Karachi
LECTURE NO. 09
TOPIC:                                                         INSULATION

INTRODUCTION:[1]
The term insulation may mean variety of themes. For instance Building insulation; which is added to buildings for comfort and energy efficiency; it may also refer to Soundproofing; or acoustic insulation i.e. any means of reducing the intensity of sound. It can be Thermal insulation; which refers to materials used to reduce the rate of heat transfer. Similarly it may be Electrical insulation which means the use of material to resist the flow of electric current and magnetism. Finally the term may also be referred to as Insulated glass which is used for energy saving. Thus; a question may arise what insulation is to be discussed hereunder? In the following all the aforementioned concepts of insulation may be elaborated for the reference of readers.

BUILDING INSULATION:
Building insulation refers broadly to any object in a building used as insulation for any purpose. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation (e.g. for vibrations caused by industrial applications). Often an insulation material will be chosen for its ability to perform several of these functions at once.

THERMAL INSULATION:
Thermal insulation in buildings is an important factor to achieving thermal comfort for its occupants. Insulation reduces unwanted heat loss or gain and can decrease the energy demands of heating and cooling systems. It does not necessarily deal with issues of adequate ventilation and may or may not affect the level of sound insulation. In a narrow sense insulation can just refer to the insulation materials employed to slow heat loss, such as: cellulose, glass wool, rock wool, polystyrene, urethane foam, vermiculite, perlite, wood fibre, plant fibre (cannabis, flax, cotton, cork, etc.), plant straw, animal fibre (sheeps wool), cementitious and earth or soil, but it can also involve a range of designs and techniques to address the main modes of heat transfer - conduction, radiation and convection materials.[2]

The effectiveness of insulation is commonly evaluated by its R-value. However, an R-value does not take into account the quality of construction or local environmental factors for each building. Construction quality issues include inadequate vapour barriers, and problems with draft-proofing. In addition, the properties and density of the insulation material itself is critical.

PLANNING FOR INSULATION:
How much insulation a house should have depends on building design, climate, energy costs, budget, and personal preference. Regional climates make for different requirements. Building codes specify only the bare minimum; insulating beyond what code requires is often recommended. The insulation strategy of a building needs to be based on a careful consideration of the mode of energy transfer and the direction and intensity in which it moves. This may alter throughout the day and from season to season. It is important to choose an appropriate design, the correct combination of materials and building techniques to suit the particular situation. To determine whether you should add insulation, you first need to find out how much insulation you already have in your home and where. A qualified home energy auditor will include an insulation check as a routine part of a whole-house energy audit.[3]

ORIENTATION - PASSIVE SOLAR DESIGN:
Optimal placement of building elements (e.g. windows, doors, heaters) can play a significant role in insulation by considering the impact of solar radiation on the building and the prevailing breezes. Reflective laminates can help reduce passive solar heat in pole barns, garages and metal buildings.

BUILDING ENVELOPE:
The thermal envelope defines the conditioned or living space in a house. The attic or basement may or may not be included in this area. Reducing airflow from inside to outside can help to reduce convective heat transfer significantly.[4] Ensuring low convective heat transfer also requires attention to building construction (weatherization) and the correct installation of insulative materials.[5] The less natural airflow into a building, the more mechanical ventilation will be required to support human comfort. High humidity can be a significant issue associated with lack of airflow, causing condensation, rotting construction materials, and encouraging microbial growth such as mould and bacteria. Moisture can also drastically reduce the effectiveness of insulation by creating a thermal bridge (see below). Air exchange systems can be actively or passively incorporated to address these problems.

THERMAL BRIDGE:
Thermal bridges are points in the building envelope that allow heat conduction to occur. Since heat flows through the path of least resistance, thermal bridges can contribute to poor energy performance. A thermal bridge is created when materials create a continuous path across a temperature difference, in which the heat flow is not interrupted by thermal insulation. Common building materials that are poor insulators include glass and metal. A building design may have limited capacity for insulation in some areas of the structure. A common construction design is based on stud walls, in which thermal bridges are common in wood or steel studs and joists, which are typically fastened with metal. Notable areas that most commonly lack sufficient insulation are the corners of buildings, and areas where insulation has been removed or displaced to make room for system infrastructure, such as electrical boxes (outlets and light switches), plumbing, fire alarm equipment, etc. Thermal bridges can also be created by uncoordinated construction, for example by closing off parts of external walls before they are fully insulated. The existence of inaccessible voids within the wall cavity which are devoid of insulation can be a source of thermal bridging.
Some forms of insulation transfer heat more readily when wet, and can therefore also form a thermal bridge in this state. The heat conduction can be minimized by any of the following: reducing the cross sectional area of the bridges, increasing the bridge length, or decreasing the number of thermal bridges. One method of reducing thermal bridge effects is the installation of an insulation board (e.g. foam board EPS XPS, wood fibre board[6], etc) over the exterior outside wall. Another method is using insulated lumber framing for a thermal break inside the wall.[7]

INSULATION MATERIALS:
There are essentially two types of building insulation - Bulk Insulation and Reflective Insulation. Most buildings use a combination of both types to make up a total building insulation system. The type of insulation used is matched to create maximum resistance to each of the three forms of building heat transfer - Conduction, Convection, and Radiation.

CONDUCTIVE AND CONVECTIVE INSULATORS ('BULK INSULATION'):
Bulk insulators block conductive heat transfer and convective flow either into or out of a building. The denser a material is, the better it will conduct heat. Because air has such low density, air is a very poor conductor and therefore makes a good insulator. Insulation to resist conductive heat transfer uses air spaces between fibers, inside foam or plastic bubbles and in building cavities like the attic. This is beneficial in an actively cooled or heated building, but can be a liability in a passively cooled building; adequate provisions for cooling by ventilation or radiation[8] are needed.

INSTALLATION OF INSULATION:[9]
Insulating buildings during construction is much easier than retrofitting, as generally the insulation is hidden, and parts of the building need to be deconstructed to reach them. Due to the variety of building insulation materials available and the various building elements that may require insulation, there are a number of ways of installing building insulation.

WHERE TO INSULATE?
Where to insulate depends on where the living or conditioned space (the space that is required to be heated and air-conditioned) ends and where the unconditioned space begins. Treat unconditioned space as if it were outdoors, minus the rain and snow. Insulate the living space as if you were insulating from the outdoors. For example, if your crawlspace is unheated, and you want it to stay that way, and then make sure it has adequate ventilation, and insulates the floor above.

If your attic is unheated, and you want it to stay that way, also make sure it has adequate ventilation, and insulate between and over the floor joists. If you occasionally want to heat only some sections of the living space, you should insulate the walls between the sections you want to heat and the sections you don’t want to heat. If the basement space is unheated, it may be best to insulate between floor joists (basement ceiling) instead of around the foundation (basement floor and walls). There is no harm done in insulating both the ceiling, and the floor and walls.
Generally, the insulation takes place at:
  • Attic, especially the attic door hatch
  • Doors and windows
  • Floors over unheated spaces
  • Ceilings with unconditioned spaces above
  • Knee walls and rafters of a finished or conditioned attic
  • All exterior walls
  • Walls between conditioned spaces (such as living room) and unconditioned spaces (such as unheated garage or storage area)
  • Floors over unconditioned or outside spaces
  • Around the perimeter of a concrete floor
  • Around the slab (if present), close to grade level on the outside
  • Walls of finished, conditioned basement
  • Foundation walls above ground area.
  • Foundation walls in heated basements
  • At top of foundation, where foundation meets mudsill.
  • Around perimeter of house at band joist
  • Between rafters, but leave an air space for ventilation between the insulation and the roof deck.
  • Floors above cold spaces, such as vented crawl spaces and unheated garages
  • Any floor section that is cantilevered beyond the exterior wall below
  • Around slab floors built directly on the ground.
  • Foundation walls of crawl spaces (people often insulate crawl spaces so poorly that the insulation is ineffective).
If you are curious what kind of insulation already exists, here are some ways to inspect your walls for insulation:

  • Remove electrical cover plates and look through gap on side of electrical box.
  • Remove piece of siding and sheathing.
  • Drill hole in interior or exterior wall and extract sample.

LOCATION OF STRUCTURAL INSULATION:
Thermal insulation works best on the outside of the structure, as this allows walls, floors and ceilings to stay closer to room temperature, thus preventing condensation in the living area of the house and increasing comfort by the use of the building's structure as thermal mass to dampen temperature swings. A well-insulated house requires a vapor barrier because of the risk of condensation on cold parts of the structure with resulting damage, such as mold and rot. The vapour barrier is usually a sealed plastic film inside the wall and should go on the warm side of the insulation. The difficulty with complete vapour barriers is the quality control of the installation and the risk of piecing the vapour barrier by a following trade. This can allow bulk air flow (and moisture laden) air to enter the structure leading to interstitial condensation (condensation within the structure) and resulting damage. This was particularly evident in numerous building failures which led to an alternative controlled vapour permeable construction method. A vapour barrier may be a film type, board type with sealed joints or a continuous render/plaster with reinforcement fibre / grille at critical junctions and over dissimilar materials with different rates of expansion and contraction. A vapor barrier must be continuous to be effective. Seams must be closed between sheets or panels. In a heated house, the vapour barrier or air barrier goes close to the warm inside of the wall.
In very warm climates, on a well-insulated air conditioned house, the vapour barrier should go on the outside so that the insulation is between the vapour barriers and colder, air conditioned parts of the house.
In some places, vapor barriers are controversial. Some people believe that in temperate, humid climates, you should leave out the vapor barrier entirely. The highest R-values per inch are provided by spray foam and rigid panel insulation. These are still only conductive thermal insulators, not radiant barriers, except in the case of rigid panels that have a reflective metal facing.

REFERENCES:
1.       http://en.wikipedia.org/wiki/Insulation (retrieved April 2, 2011)
2.       BSD-011: Thermal Control in Buildings From: http://www.buildingscience.com/documents/digests/bsd-011-thermal-control-in-buildings/ (retrieved April 2, 2011) and Your Home Technical Manual - 1.6a Insulation Overview from: http://en.wikipedia.org/wiki/Insulation (retrieved April 2, 2011)
3.       US Department of Energy - Energy Savers From: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11350 (retrieved April 2, 2011)
4.       BERC - Air tightness From: http://www.ornl.gov/sci/roofs+walls/whole_wall/airtight.html (retrieved April 2, 2011)
5.       DOE Building Technologies Program: Building Envelope From: http://www.eere.energy.gov/buildings/info/design/integratedbuilding/buildingenvelope.html (retrieved April 2, 2011) V-E Framing From: http://www.energystar.gov/ia/new_homes/features/VEFraming1-17-01.pdf (retrieved April 2, 2011)
6.       http://www.natural-building.co.uk/PDF/Pavatex/Pavatex-Walls/Pavatex_diffutherm_timberframe.PDF (retrieved April 2, 2011) Pavatex Diffutherm ETICS
7.       From: http://www.glacierbay.com/dowtest.asp (retrieved April 2, 2011) and http://www.rstud.com (retrieved April 2, 2011)
8.       Design of Low Cost Passive Cooling Systems, Think Cycle Open Collaborative Design,From: http://www.thinkcycle.org/tc-notes/note-view?topic_id=27256
9.       http://en.wikipedia.org/wiki/Installing_building_insulation (retrieved April 2, 2011)

[2] BSD-011: Thermal Control in Buildings From: http://www.buildingscience.com/documents/digests/bsd-011-thermal-control-in-buildings/ (retrieved April 2, 2011) and Your Home Technical Manual - 1.6a Insulation Overview from: http://en.wikipedia.org/wiki/Insulation (retrieved April 2, 2011)
[3] US Department of Energy - Energy Savers From: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11350 (retrieved April 2, 2011)
[4] BERC - Air tightness From: http://www.ornl.gov/sci/roofs+walls/whole_wall/airtight.html (retrieved April 2, 2011)
[5] DOE Building Technologies Program: Building Envelope From: http://www.eere.energy.gov/buildings/info/design/integratedbuilding/buildingenvelope.html (retrieved April 2, 2011) V-E Framing From: http://www.energystar.gov/ia/new_homes/features/VEFraming1-17-01.pdf (retrieved April 2, 2011)
[7] From: http://www.glacierbay.com/dowtest.asp (retrieved April 2, 2011) and http://www.rstud.com (retrieved April 2, 2011)
[8] Design of Low Cost Passive Cooling Systems, Think Cycle Open Collaborative Design,From: http://www.thinkcycle.org/tc-notes/note-view?topic_id=27256
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