ECOBROWNSTONE: The Art of Brownstone Greenovation -
Insulation and the Building Envelope: Controlling Heat Loss and Gain
Noreen Adler
Founder and President, Ecobrownstone

Noreen is Founder and President of Ecobrownstone.  She has been a resident of brownstone Brooklyn (Park Slope, Brooklyn Heights and Carroll Gardens) for over two decades and has planned, designed and managed a wide range of renovation and real estate development projects in Brooklyn and elsewhere. As a developer she is a member of the NYC Committee evaluating the LEED for Homes Guidelines for application in New York.  She also has a personal passion for sculptural relief ceramic tiles and murals which she has designed and fabricated at her studio on the Gowanus Canal. 

By Noreen Adler
Published on 05/21/2008
Save energy and lower your utility bills. Learn the basics of heat gain and loss, and how to prevent it.

The single most important thing you can do to reduce your energy consumption and costs is to ensure that you have a tight building envelope -- the building's roof, walls, windows, and doors, in other words the envelope, or separation, that controls the flow of energy between the interior and exterior of the building. Insulation and the building envelope are inseparable components in the analysis of how to control heat loss and heat gain and, consequently, save energy and create a more comfortable living environment. A “tight” building envelope refers to maximizing the integrity of the building envelope to reduce or eliminate heat loss and gain.

Brownstones are particularly prone to leaks and draughts due to the natural settling that would have taken place over the last 100 to 150 years since their construction, causing cracks and gaps to form in the building envelope. Additionally, they are replete with single-pane non-insulated windows that may be just as old, and with exterior walls that may completely lack insulation -- we discovered, for instance, that the rear exterior wall of the parlor floor of 168 Clinton St. was constructed with a 6-inch gap between the interior plaster wall and the brick, with no insulation whatsoever, even though it was apparent that the wall was not original because the lathe was metal and not wood (we know the wall dates back to the 1940s at least).

Frequently, as was the case with the lovely bay windows in our brownstone in Park Slope, there is no insulation in the wood millwork and around the windows which explained why the new replacement windows installed by the prior owner did not eliminate the persistent draughts. 

A typical brownstone which has not been insulated and maintains its original single pane windows experiences complete air replacement about 6 to 8 times per hour, compared to a well-built new home which typically boasts 1 to 2 air changes per hour – this means brownstones are heating all new air 6 to 8 times per hour! On the bright side, starting out with such a bad track record makes for very dramatic results when you institute improvements!

Building green does not have to be sexy. Insulation does not have a lot of flashy bells and whistles, but it is one of the most effective things you can do to save energy. The holistic approach, however, also takes into account indoor air quality – a warm house in the winter and a cool house in the summer is still not comfortable if it gives you headaches or otherwise makes you sick, so choose your insulation carefully.

This Article will guide you through:
The Basics of Heat Gain and Loss
The Basics of Insulation
Insulation Materials Options and Planning
Vapor Barriers
Health and Indoor Air Quality Issues and Insulation
Eliminating Leaks - Sealing Cracks and Gaps
The Role of Windows in the Building Envelope

The Basics of Heat Gain and Loss
Let's first understand how heat is transferred. It moves from warm to cold in three ways:

1. Radiation – electromagnetic waves traveling through space, such as from the sun or a radiator.

2. Convection – moving air. This is the reason for warm air leaks and cold air infiltration through cracks, seams and other gaps in the building envelope. Warm air rises upward to the attic or up the chimney and pulls in cold air through the basement or gaps in windows and doors, etc. on lower floors.

3. Conduction transfer of heat though a solid object, moving from warm to cold. Certain substances, like glass and metal, are very good heat conductors while other substances, such as cellulose, soy, hay or other materials used to make insulation, are good insulators. The degree to which a particular object resists the conduction of heat is referred to as its R-value, and the higher the R-value the better the resistance/insulation.

Insulation primarily addresses the heat radiation and conduction issues and will also help with convection. Sealing cracks, gaps and the like, addresses convection issues. By now it's probably obvious to you that properly controlling heat loss and gain involves paying attention to all three aspects of the heat equation; only dealing with one aspect, such as caulking windows, without giving attention to the others, such as adequately insulating your attic, will only be a band-aid with limited results, and making a radical change, like replacing y our furnace with a high-efficiency model, will only result in limited savings if your efficiently-produced heat is flowing out of your leaky windows

The Basics of Insulation
The R-value of insulation that a particular home needs depends on its location. First, evaluate what insulation you currently have in your walls, attic, basement and crawl spaces. For finished walls this is tricky but not impossible. You can start by removing outlet covers so you can see into the wall, or drill a small hole in a hidden place such as a closet, and then identity the substance and measure its thickness. Multiply the R-Value per inch in the table below corresponding to the type of insulation you have, by the number of inches you have in your application to calculate the actual R-value of the insulation currently in your walls and elsewhere.  Unfortunately the R-Value of a particular kind of insulation material produced by different manufacturers varies, so the chart shows a range of R-values to be used as a guide. 

 Type of Insulation  Material                      R-Value per inch
 loose-fill  cellulose  3.1 - 3.7
   fiberglass  2.25 - 4
   mineral wool  2.4 - 4.0
 blankets or bats  fiberglass  3.4 - 3.4
   mineral wool  3.1 - 3.4
   high density fiberglass or mineral wool  4.0
   cotton  3.7
 rigid board  expanded polysturene beadboard  3.5 - 5
   extruded polystyrene  5
   polypolyisocyannurate (foil faced)  5.4 - 7.5
   rigid fiberglass  4.2
 blown-in insulation  cellulose  3.2 - 3.7
   fiberglass  3.2 - 4.1
   mineral wool  3.4
   polyurethane foam (from petrochemicals)  5.4 - 7
   soy (open cell foam)  3.7
   soy (closed cell foam)  5
 small particle, pourable substances**  vermiculite**, perlite and polystyrene beads, foam plastics   4 or more
** Some vermiculite contains naturally occurring asbestos, so if your insulation is a type that looks  pourable then have it tested before you disturb it.  If it is vermiculite that has traces of asbestos then have it abated by a licensed asbestos abatement professional.
©Ecobrownstone 2008 All Rights Reserved.

Next determine the recommended R-Value for your house -- the Department of Energy map and chart below indicates the recommended R-value of insulation in different climate zones, and the DOE website also has a nifty zip-code finder that will help you pinpoint the R-value insulation level best suited for your home based on its location, the kind of house it is and the type of heating system in use, however the DOE notes that its recommendations are meant to be cost effective levels based on information it has on local fuel and materials costs and weather and may differ from building codes. New York City is in zone 2.

A.  R-18, R-22, and R-28 exterior wall systems can be achieved by either cavity insulation or cavity insulation with insulating sheathing.
For 2 in. x 4 in. walls, use either 3½ in. thick R-15 or 3½ in. thick R-13 fiber glass insulation with insulating sheathing.
For 2 in. x 6 in. walls, use either 5½ in. thick R-21 or 6¼ in. thick R-19 fiber glass insulation.

B.  Insulate crawl space walls only if the crawl space is dry all year, the floor above is not insulated, and all ventilation to the crawl space is blocked.
A vapor retarder (e.g., 4- or 6-mil polyethylene film) should be installed on the ground to reduce moisture migration into the crawl space.

C.  No slab edge insulation is recommended.

We will be reviewing every kind of insulation for application to our brownstone renovation at 168 Clinton St., and we will need various kinds because we’ve got some rooms where interior walls will not be taken down, one gutted room where a spray insulation is feasible, and no attic requiring specialized insulation for the roof, so check the 168 Clinton St. blog, or subscribe to an RSS feed.

Insulation Materials Options and Planning
Planning Your Insulation Upgrade

Start in the attic and the basement
. Insulating the attic prevents warm air from escaping and also substantially cuts down on the amount of solar heat gain you will experience in the summer, substantially reducing the cooling load. If the attic is accessible you can add more batts between or on top of the joints, 12 inches in the NYC climate zone, or if it's a small crawl space you can use blown-in insulation. If you have a brownstone that has no attic space because the top floor room ceilings butt up against the under-side of the roof, then consider adding rigid insulation from the top side of the roof (see Roof Insulation below). In the basement you can attach insulation to the underside of ceiling/ floor joists of the floor above.

Wall insulation can be achieved through a combination of cavity insulation and insulated sheathing. Remember, gaps in insulation lead to convection heat loss – leaks – so be sure it is installed properly with no gaps. If you are not removing interior walls you will need to have insulation blown into the walls, and special care needs to be taken to reach every nook and cranny. This can be a particular challenge, and possibly unfeasible, in brownstones and other old housing with plaster-and-lathe walls because, when the wall does not have a huge uninsulated gap as noted above, you often have essentially no gap because the lathe may simply be attached to the exterior wall furring strips, leaving no space into which insulation can be blown. See the discussion below regarding factors to consider when choosing insulation (density, loose fills may sag etc.). 

Don't be discouraged if you've got an older house that has no, or inadequate, gaps for blowing in wall insulation. Convection heat loss – leaks— usually account for the greatest amount of heat loss. Wall insulation primarily addresses radiation heat loss. Therefore, if it is not practical or is outside your budget to peel off your interior walls in order to add wall insulation, then simply removing your floor shoe molding and/or baseboard and caulking and sealing all the joints between floor and wall will reduce or eliminate leaks (convection heat loss) and make a positive difference in your energy consumption and heating bills.

Roof insulation  If the top floor of your brownstone has no attic or crawl space allowing for traditional methods of insulation then you can apply methods used to insulate cathedral ceilings. One method is to install a layer of rigid foam insulation in the ceiling, from inside the room, between the joists (this means you'll have to take down your ceiling) leaving a small air space between the foam and the roof. Another option is to use structural insulating panels (SIPs), usually composed of a foamboard core sheathed on both sides with plywood, that are applied on top of the roof over your existing roofing material. SIPs can be obtained with a nailable side so that a waterproof membrane and roofing finish materials may be nailed to it. SIPs are a good alternative because they reduce the need for structural lumber and cut down on air leaks. SIPs, by the way, are also available with drywall sheathing for use as walls and SIPs also provide sound insulation.

Other roof heat loss/gain issues: Flat roofs, typical on brownstones, act like solar collectors. Cover your roof with a reflective surface, white or metallic finish, to reduce solar heat gain.

Adding an extension to your brownstone? You're lucky in more ways than one. Starting with a clean slate enables you achieve maximum efficiency with sustainable products. If you are planning on brick to match your brownstone facing then Concrete Masonry Unit (CMU) with high fly ash content (a by-product of burning coal) are an excellent alternative to cinder blocks (which uses Portland cement, the product of an extremely energy-consuming manufacturing process) for building the structure and has good insulating value. Incorporating SIPs can cut down on the lumber you need for framing and provide insulation and sound proofing. You also have completely open walls enabling you to use spray foam insulation which is an ideal insulation because it insulate against both convective and conductive heat loss.

Don't forget the small things: only use insulated recessed lighting cans, outlets and wall switches.

Types of Insulation

Insulation comes in a variety of forms. Be sure to read the Health/Indoor Air Quality section below and avoid certain types of insulation give off harmful VOCss; it is possible to get insulation made from cotton, cellulose and fiberglass that is free from formaldehyde.

Batt and Blanket Roll Insulation is typically made from mineral fiber (fiberglass or rock wool) and is now also available in "green" substances like recycled cotton.  It is manufactured in blankets of various sizes and thicknesses. Batt insulation is typically fitted between studs, joists, and beams and should fill the wall, floor, or ceiling cavity without any gaps, voids, or compression.

Blown-in, Loose Fill Insulation is blown into wall cavities through holes and is typically made from fiberglass or cellulose, or the latest green products derived from soy and denim, and is literally blown into the walls and attic through a large hose. Blown-in insulation should completely fill the wall cavities and be an even thickness and density throughout the cavity otherwise it will sag over time and create gaps. The R-value of a particular kind of blown-in insulation will depend on how densely packed it is so follow the manufacturer's instructions.

Sprayed or Injected Foam Products are typically injected or sprayed into cavities where they expand to the desired thickness. Spray foam insulations are excellent because they make a continuous air tight barrier and a sealed thermal envelope and, as such, address both convection and conduction heat loss. Typically spray foam insulation is either open cell or closed cellOpen cell foam insulation is soft, like packing material molded around an object, and is "open" because the cell walls, meaning the walls around the air bubbles created when the foam expands upon installation, are broken.  Closed cell foam is rigid (degree varies between manufacturers) because the cell walls are not broken, has a higher R-value per square inch than open cell foam and provides some structural support to the building.  Both stop airflow and heat transfer but open cell foam allows some vapor penetration (so use of a vapor barrier is necessary) and should not be used in exterior applications or below ground.  However, being more dense means that closed cell foam is more expensive per square inch of R-value than open cell foam. 

Research these carefully, however, because traditionally foams were/are made from petrochemiclas and contain toxic chemicals that emit VOCs and may contain CFCs and HCFCs in the propellant. Biobase is a green alternative. It is made from soy bean oil (an annually renewable resource, grown in US), is inert and antimicrobial (will not support mold growth or be food source for insects). It is sprayed in as tiny particles that expand to 100x their original size so it's easier for these tiny particles to make it into nooks and crannies and fill every void when expanded. Spray-in insulation also reduces noise pollution. Biobase also claims to maintain structural integrity (will not sag to allow for air leaks).

Rigid Insulation is typically made from polystyrene, polyurethane, or polyisocyanurate foam, which is expanded or formed into large sheets. Rigid insulation can be used to provide a continuous thermal barrier in basements, crawlspaces, and on exterior walls, and can be used in conjunction with blown-in or batt insulation.

Vapor Barriers
Wet insulation does not insulate. Make sure there is a vapor barrier in place. A vapor barrier is a layer of moisture resistant material between the inside of the house and the insulation. The principle behind a vapor barrier is simple: Warm air holds more moisture than cold air, and warm air is always on the move, so as the warm air moves toward the cold space it cools and sheds moisture along the way. If it sheds its moisture inside your insulation then your insulation will get soggy, no longer provide insulation value, and possibly lead to mold buildup and rotting of structural members. The vapor barrier shields your insulation from moisture. Vapor barriers can be made out of many types of materials and come with a “vapor permeance value” called aperm rating" which should be no higher than “1”. There are several materials used as vapor barriers including plastic sheeting, foil sheeting and treated papers. You can purchase batt, blanket and rigid insulation with a vapor barrier already attached. A simple rule to apply so that you don’t install it backwards is that if you are looking at the insulation from the heated space (from inside the room) you should see the vapor barrier, but if you are looking at it from the other side such as from the attic, you should NOT see the vapor barrier.

Attic. If you are adding extra insulation on top of existing insulation in your attic then purchase insulation without the vapor barrier or peel off the barrier (make a slit down the middle with a knife and pull it away) because you don’t need or want a vapor barrier between layers of insulation. Insulation without a vapor barrier should be less expensive than with a vapor barrier. Install the added layer perpendicular to the first layer. If you have designed your attic to be well ventilated, however, with roof and soffit vents so that the attic has a continuous current of air flowing through it which can evacuate moisture that is shed from the warm air cooling in the insulation, then a vapor barrier in the attic is not crucial.

Walls. Ideally the inside cavity between your interior and exterior walls should be completely sealed, so applying this principle it is extremely important that a vapor barrier be used, and installed correctly (with the barrier toward the inside of the house, between the heated area and the insulation) to prevent moisture from building up inside the wall cavity which could lead to mold and rot. One technique is to insert unfaced insulation in the cavities between the studs and then attach a continuous layer of a vapor barrier material, like 6-mil (1 mil + 1/1000 of an inch) plastic sheeting, to the studs overlapping all the seams.

Ceilings with no attic or crawl space, like cathedral ceilings or Brownstone attics that have had the attics roofs raised just enough to make adequate ceiling heights but not enough to also allow for a crawl space for thick insulation (in NYC often due to limits placed by the Landmark’s Preservation Commission) should apply a vapor barrier in the manner described for walls: insert unfaced insulation in the cavities between the studs and then attach a continuous layer of a vapor barrier material, like plastic sheeting, to the studs overlapping all the seams.

Floors: Typically floors do not have vapor barriers because sub-flooring made of plywood or other sheeting materials usually are manufactured with some kind of waterproof substance that acts as a vapor barrier, however if you have a crawl space under your house or extension – typical in brownstones – put a vapor barrier in place on the ground under the house, such as a layer of 6-mil plastic laid directly on the dirt floor. Check back to our 168 Clinton St. blog to see how we deal with the sagging ground level floor of our extension where it seems the joists may have rotted.

Health and Indoor Air Quality Issues and Insulation
Many conventional insulation materials off-gas VOC’s, toxic chemicals like formaldehyde and HCFCs that affect health or the ozone, or are made from petrochemicals.  See our Article Indoor Air Quality -- Identifying Sources and Making Renovation Choices that Eliminate Contamination.  There are new products on the market for loose fill, blown-in and blanket and batt insulation that are made from sustainable or renewable sources such as cellulose, recycled cotton and soy, are not derived from petrochemicals and that do not off-gas VOCs, even new fiberglass products that do not contain formaldehyde are available, so there really is no reason to have to settle for an unhealthy or otherwise environmentally challenged product.  The Green Home Guide has prepared The Green Buyers Guide to Insulation which is a helpful summary of insulation products, and comparative pros and cons including health issues. 

Eliminating Leaks: Sealing Cracks and Gaps
If cracks or gaps are present in the building envelope then warm air leaks out and cold air can infiltrate into the space. Leaks can add 10% to your energy costs and are a major cause of heating energy waste in brownstones.

Below is a Department of Energy breakdown of where most leaks occur in a home.

Sources of Air Leaks in Your Home:
 1 Dropped ceiling  7 Door frames
 2 Recessed light  8  Chimney flashing
 3 Attic or crawl space entrance  9 Window frames
 4 Sill plates  10 Electrical outlets and switches
 5 Water and furnace flues  11 Plumbing and utility access
 6 All ducts  

You can find leaks by holding a lit incense/smoke stick around windows, doors, electrical outlet and switch boxes, plumbing stacks and spots where pipes enter the walls, ceiling fixtures, vent holes air conditioning or exhaust vents, and other areas where it seems there might be a seam. Leaks will be obvious as the smoke will flatten and move with the breeze. To increase the effectiveness turn on all exhaust fans which will have the effect of pulling air in through any cracks – kind of like a mini blower door test. The most accurate results can be obtained from a full scale blower door test.

You can seal leaks by caulking or inserting expanding foam (for cracks larger than ¼-inch) or cotton wool around things that don't move (outlet and air conditioner covers and window frames, plumbing chases and attic hatchway for example), or by weatherstripping things that do move (like windows and doors).   See our Article  Window, Skylight and Door Basics -- Increasing Energy Efficiency for a specific discussion of window-related issues.

Caulking compounds vary in strength and properties. Caulk is a substance that can emit VOCs and luckily there are many caulk options available that do not adversely affect indoor air quality. See our Artricle Indoor Air Quality -- Identifying Sources and Making Renovation Choices that Eliminate Contamination for an in-depth review of air qality considerations.

The Department of Energy has prepared the following useful guide to caulks:

 Caulking Compound  Recommended Uses  Cleanup  Shrinkage Adhesion   Notes
 Household Silicone  Joints between bath and kitchen fixtures and tile,  metal joints such as gutters.   Dry cloth immediately or mineral spirits.  Little or none.  Good to excellent.  Flexible:  cured silicone stretches up to 3x its width and compresses to one-half the width.
 Construction Silicone  Seals disimilar building materilas like wood to stone, metal flashing to brick, and will adhere to painted surfaces.   Dry cloth immediately or mineral spirits.  Little or none  Good to excellent.  Flexible (stretches and compresses).
 Polyurethane, expandable spray foam  Expands when curing; good for larger cracks indoors or outdoors. Use in nonfriction areas, as rubber becomes dry and powdery over time.  Solvent such as lacquer thinner, if immediate.  None.  Good to excellent.  Expands a lot to fit large, irregular gaps.  Flexible. Can be used at varyng temperaturers. Must be painted for exterior use.  Manufacturing process produces greenhouse gases.
 Water-based foam sealant  Around window and door frames in new construction (will not overexpand and bend new windows); smaller cracks.  Water.  None; expands only 25%.  Good to excellent.  Takes 24 hours to cure and must be exposed to air. Cures to soft consistency. Production does not produce greenhouse gases.
 Butyl rubber  Seals most dissimilar materials (glass, metal, plastic, wood, and concrete.) Seals around windows and flashing, bonds loose shingles.  Mineral spirits.  From 5% to 30%.  Good.  Durable 10 or more years; resilient, not brittle. Can be painted after one week curing. Variable shrinkage; may require two applications. Does not adhere well to painted surfaces. Toxic; follow label precautions.
 Latex  Seals joints around tub and shower. Fills cracks in tile, plaster, glass, and plastic; fills nail holes.  Water.  From 5% to 10%.  Good to excellent.  Easy to use. Seams can be trimmed or smoothed with moist finger or tool. Water resistant when dry. Can be sanded and painted. Less elastic than above materials. Varied durability, 2–10 years. Will not adhere to metal. Little flexibility once cured. Needs to be painted when used on exteriors.
 Oil or resin-based  Seals exterior seams and joints on building materials.  Mineral spirits.  From 10% to 20%.  Good.  Readily available. Least expensive of the four types. Rope and tube form available. Oils dry out and become brittle, material may fall out. Low durability, 1–4 years. Poor adhesion to porous surfaces like masonry. Should be painted. Can be toxic (check label). Limited temperature range.

Caulking can be tricky. Read and follow the instructions on the compound cartridge, and follow these tips:

  • Clean all areas to be caulked or you may not get good adhesion. This means remove any old caulk and paint, and make sure the area is dry so you won't seal in moisture.  The best time to apply caulk is during dry weather when the outdoor temperature is above 45°F (7.2°C) and the humidity level is low to prevent cracks from swelling with moisture.
  • Apply caulk to all joints in a window frame and the joint between the frame and the wall.
  • Hold the gun at a consistent, forty-five degree angle to enable the caulk to get deep into the crack. You know you've got the right angle when the caulk is immediately forced into the crack as it comes out of the tube.
  • Caulk in one straight continuous stream, if possible. Avoid stops and starts.
  • Send caulk to the bottom of an opening to avoid bubbles.
  • Make sure the caulk sticks to both sides of a crack or seam.
  • Release the trigger before pulling the gun away to avoid applying too much caulking compound. A caulking gun with an automatic release makes this much easier.
  • If caulk oozes out of a crack, use a putty knife to push it back in.
  • Don't be stingy. If the caulk shrinks, reapply it to form a smooth bead that will seal the crack completely.

Weatherstripping comes in many forms, such as felt, open-cell foam, vinyl and metal, and each has a specified purpose. The Department of Energy has compiled the following information about different types of weatherstripping and their characteristics.

 Weatherstripping  Uses  Pros  Cons
 Tension seal:
Self-stick plastic (vinyl) folded along length in a V-shape or a springy bronze strip (also copper, aluminum, and stainless steel) shaped to bridge a gap. The shape of the material creates a seal by pressing against the sides of a crack to block drafts.
 Inside the track of a double-hung or sliding window, top and sides of door.  Durable. Invisible when in place. Very effective. Vinyl is fairly easy to install. Look of bronze works well for older homes.  Surfaces must be flat and smooth for vinyl. Can be difficult to install, as corners must be snug. Bronze must be nailed in place (every three inches or so) so as not to bend or wrinkle. Can increase resistance in opening/closing doors or windows. Self-adhesive vinyl available. Some manufacturers include extra strip for door striker plate.
Plain or reinforced with a flexible metal strip; sold in rolls. Must be stapled, glued, or tacked into place. Seals best if staples are parallel to length of the strip.
 Around a door or window (reinforced felt); fitted into a door jamb so the door presses against it.  Easy to install, inexpensive.  Low durability; least effective preventing airflow. Do not use where exposed to moisture or where there is friction or abrasion. All-wool felt is more durable and more expensive. Very visible.
 Reinforced foam:
Closed-cell foam attached to wood or metal strips.
 Door or window stops; bottom or top of window sash; bottom of door.  Closed-cell foam an effective sealer; scored well in wind tests. Rigid.  Can be difficult to install; must be sawed, nailed, and painted. Very visible. Manufacturing process produces greenhouse gas emissions.
Nonporous, closed-cell foam, open-cell foam, or EDPM (Ethylene Propylene Diene Monomer) rubber.
 Top and bottom of window sash; door frames; attic hatches and inoperable windows. Good for blocking corners and irregular cracks.  Extremely easy to install. Works well when compressed. Inexpensive. Can be reinforced with staples.  Durability varies with material used, but not especially high for all; use where little wear is expected; visible.
 Rolled or reinforced vinyl:
Pliable or rigid strip gasket (attached to wood or metal strips.)
 Door or window stops; top or bottom of window sash; bottom of a door (rigid strip only).  Easy installation. Low to moderate cost. Self-adhesive on pliable vinyl may not adhere to metal; some types of rigid strip gaskets provide slot holes to adjust height, increasing durability. Comes in varying colors to help with visibility.  Visible.
 Door sweep:
Aluminum or stainless steel with brush of plastic, vinyl, sponge, or felt.
Bottom of interior side of in-swinging door; bottom of exterior side of exterior-swinging door.  Relatively easy to install; many types are adjustable for uneven threshold. Automatically retracting seeps also available, which reduce drag on carpet and increase durability.  Visible. Can drag on carpet. Automatic sweeps are more expensive and can require a small pause once door is unlatched before retracting.
Works similarly to refrigerator gaskets.
 Top and sides of doors, double-hung and sliding window channels.  Very effective air sealer.  
 Tubular rubber and vinyl:
Vinyl or sponge rubber tubes with a flange along length to staple or tack into place. Door or window presses against them to form a seal.
 Around a door.  Effective air barrier.  Self-stick versions challenging to install.
 Reinforced silicone:
Tubular gasket attached to a metal strip that resembles reinforced tubular vinyl
 On a doorjamb or a window stop.  Seals well.  Installation can be tricky. Hacksaw required to cut metal; butting corners pose a challenge.
 Door shoe:
Aluminum face attachment with vinyl C-shaped insert to protect under the door.
 To seal space beneath door.  On the exterior, product sheds rain. Durable. Can be used with uneven opening. Some door shoes have replaceable vinyl inserts.  Fairly expensive; installation moderately difficult. Door bottom planning possibly required.
 Bulb threshold:
Vinyl and aluminum
 Door thresholds  Combination threshold and weatherstrip; available in different heights.  Wears from foot traffic; relatively expensive.
 "Frost-brake" threshold: Aluminum or other metal on exterior, wood on interior, with door-bottom seam and vinyl threshold replacement.
 To seal beneath a door.  The use of different materials means less cold transfer. Effective.  Moderately difficult to install, involves threshold replacement.
 Fin seal:
Pile weatherstrip with plastic Mylar fin centered in pile.
 For aluminum sliding windows and sliding glass doors.  Very durable.  Can be difficult to install.
 Interlocking metal channels:
Enables sash to engage one another when closed
 Around door perimeters.  Exceptional weather seal.  Very difficult to install as alignment is critical. To be installed by a professional only.

The Role of Windows in the Building Envelope
Windows, being part of the building envelope, can contribute up to 30% of heat loss and gain because they can pose a triple threat -- heat moves through a window assembly by conduction through the glass, convection/leakage through gaps and cracks in the framing and assembly and joint with the wall, and by radiation by pulling heat from warm room-temperature objects including people – that’s why when you stand next a window you feel cold in the winter and warmer in the summer (heat moves to the colder space, so in the summer that would be you and the room you are occupying, and in the winter that would be away from you and the room you are in to the outdoors). But remember, replacing the windows themselves is not enough if you don’t also ensure adequate insulation around them by following the insulation and sealing guidelines we set out above. See our Article Window, Skylight and Door Basics -- Increasing Energy Efficiency for a in-depth look at window efficiency. 

Useful Links
Department of Energy - Energy Savers Tips – Insulation

The USGBCs “The Green Buyers Guide to Insulation

The Rocky Mountain Institute Home Energy Brief #1 - Building Envelope, is an excellent source of detailed information on heat loss and gain issues including how to find and fill cracks, and how and where to install insulation.

US Green Building Council’s article 3 Easy-to-Install Green Insulation Options.