Tag Archives: R rating

Windows and exterior doors

Windows and doors are not only necessary for the proper functioning and livability of your home. They can add a great deal to the beauty and architectural interest of any building.

The variety available in window design, functioning and construction is huge, and largely limited only by your imagination. In some cases, you may even want to design a portion of your house around a window or group of windows.

The front entry door can make a statement about you and your house, and suggest what a visitor may find inside. An entry can be large and ornate, suggesting a palatial interior, or it can be warm and inviting, suggesting a cozy space inside.

Doors are often of glass, or partially so, and often have windows surrounding them as an integral part of the entry.

The purposes of doors and windows need to be considered ,when designing your house, and before purchase. Doors are usually chosen and placed with utility in mind, with appearance as the secondary consideration. There may be several motives for choosing and placing a window.

Interior and exterior appearance is always a factor for windows. Ventilation should be considered. Is a window placed to take advantage of a pleasing view, or do you want to watch your children in the yard? Is light a part of the equation? What about security, or safe egress, from bedrooms in an emergency?

windows

Lots of windows

Windows can open or be a non opening “picture” window or a combination. There are also bay windows, bow windows, skylights and garden windows. Picture windows may be used in garages, outbuildings, in places where they are hard to reach, or if the shape of the window is unusual. Windows that open can save some of the energy used for cooling, if placed to provide cross ventilation. A Window that opens widely enough to provide an escape route from bedrooms are required by most building codes. Removable screens should be provided to prevent insects, birds and animals from entering.

Windows that open are normally rectangular, but there are different types. A common and inexpensive type is the slider, which can be horizontal or vertical. They can be double hung, as in a vertical slider that opens from either the top or the bottom, or single hung in which only one half opens.

They can be a casement window which opens similarly to a door, awning which swings open from the bottom, or hopper which opens from the top. These three may have a crank mechanism for opening and closing, and locks which tighten them. They provide a better air seal than sliders which need to be a little loose to operate. An awning type window can afford a little better protection against the elements if inadvertently left open.

Casement window

A casement window

Material used in making the window frames is varied.

Vinyl has become quite popular in recent years. Economy, low maintenance, and low thermal conductivity are some of the reasons. Vinyl is not damaged by moisture which is an important consideration in cold climates where frost may form on the inside of the glass and later melt. Voids can be incorporated to provide thermal breaks. Expansion and contraction is minimal which can mean a window will remain easy to open in different conditions. Paint does not adhere well, so choose your original color carefully.

Wood is another popular choice, which gives more interior decorating options. The exterior should be clad with metal or vinyl to reduce maintenance. Painting or staining is possible with wood. Moisture is the bane of wood, and causes rot and mold problems. Wood will swell when damp, and may make it difficult to open windows.

Metal is seldom used anymore, except for structural reasons. The main disadvantage is its conductivity, which can create thermal bridging.

The thermal qualities of windows will vary by a wide percentage, but no matter how good, their insulating value is still pretty dismal.

It is quite expensive to achieve an R rating of over 4, and more common is a rating of less than 3.5. A double glass window sealed with an inert gas inside and with a low E coating is probably the best you will get at a reasonable payback. The low E coating is inexpensive and very worthwhile. This will give a rating of about 3.2. Compare this to a normal 2 x 6 wall, which has a rating of about 22 when properly insulated. This is a compelling argument for keeping window space to a minimum. Building codes may require that 10% of the wall space be devoted to window. Most people would want more than this. I don,t believe in spending large sums on extra window efficiency. The percentage gain on the window may be quite large, but the overall energy savings are quite small. Better options may be lined window treatments, or wide eaves to block the sun. Your motives , however, could be quite different from simply looking at the best value.

Note: R values can be confusing and are expressed differently in much of the world. Please use this link for an explanation which I hope doesn’t confuse you more.

Doors can be purchased in many styles and materials, and at costs ranging from a couple of hundred dollars up to several thousand. Most people would spend the most attention and money on a front door, and use more utilitarian doors in other locations.

A door may be mostly of glass, and as such, is similar to a window. It can have various sized and shaped openings with glass, often called lites, which may be decorative. Stained glass can give interesting effects. There can be one or more side lites, and there may be a transom window over the door, which may or may not open.

Double doors are a possible choice, and are commonly used for a patio entry, as well as for a front entrance. There are several different styles.

Sliding glass doors are popular for the patio or deck, and can open from either side, or both sides. It is possible to have blinds built in between the glass panels on sealed double glass doors. Maintaining a sliding door free from air leaks is more difficult than with other types.

When ordering doors, you must specify left or right swing and in or out opening. An in swing is not as easy to make secure, and their use is uncommon in exterior doors. All exterior doors should have a deadbolt lock, and if there is glass within reach, it should be keyed from both sides.

Material besides glass for exterior doors include, wood, metal and fiberglass.

An unusual front door

An unusual front door

Wood can be one of several species, and can be finished in different ways. There are craftsmen who make hand carved wooden doors to order, which can be beautiful and distinctive. One way your front entry can really make a statement.

Metal doors for residential use usually have a wooden frame, and are composed of a sandwich of wood and an insulating material between two sheets of steel. They require painting for protection against moisture. These are likely the most economical door.

Fiberglass doors may be superior for energy efficiency and maintenance, but are more costly in most cases.

A door like a window, is not great as far as insulating values are concerned. Keeping them well sealed requires regular maintenance. Storm doors may be a help, but the jury is still out on their insulating value. I think they have value beyond simple energy efficiency, such as reducing freeze ups and as a screen door if so equipped.

Careful window and door selections can greatly add to the appeal of your home and its eventual evaluation.

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Insulation, air barriers and moisture barriers

Insulation in your house is like your winter coat.

Insulation against winter

Bundled warmly

Insulation is a blanket around the house that slows the loss of heat to the outdoors. Alternately, it slows the penetration of heat from the outdoors to your living space. It is easy to see how insulation adds to your indoor comfort, and reduces the energy cost to heat or cool your home.

Your winter coat is not very effective if the wind blows through it. It needs a layer of wind resistant material to be effective. The insulation in your house is similar. It is not very effective if air is allowed to freely circulate in and out of the house. The importance of sealing your home against air infiltration can not be over emphasized, if you are concerned with comfort and energy costs.

A coat or any clothing is not very effective against the cold if it becomes wet. The same is true for insulation. As well as reducing the effectiveness of the insulation, moisture encourages the growth of mold and rot within wall and attic cavities. Once moisture has entered the wall cavity it is reluctant to leave, so it is important that even tiny holes in the moisture barrier be sealed.

Do you remember your science from school? In my case I can barely remember school, it was so long ago. Anyway, we know that heat always moves towards cold (or the absence of heat), and that there will be a greater (faster) transfer of energy when the temperature differential is higher. If there is a science teacher out there, please correct me, if I have not explained this properly. The other pertinent fact is that warmer air rises. This means that the warmest air in your house is at the ceiling, and that this is where the greatest heat transfer can occur. In cooling season, the attic space of your house is going to be warmer than the outside ambient temperatures, no matter how effective the ventilation.

It follows that, added insulation in your attic will effect the largest energy savings.

Insulation for cooling

Poor insulation makes a
hot house in summer

It is also the easiest and least expensive area to increase insulation. There are no doors, and usually no windows, to reduce the overall effectiveness of the insulation. There is a lot of space to add insulation, with the possible exception of the area near the eaves of a gable roof. The use of rafter trusses with heels can alleviate this problem.

It is difficult to get an overall high insulation value in the walls because of windows and doors. No matter how much you spend on windows, you are not going to get an R value much above 4 with 3 being about the norm. Doors are not much better, and need constant maintenance to prevent air leaks. Windows and doors will probably make up from 10% to 20% of your wall area, and in some designs much more. Windows can be an attractive design feature, but can be costly in more ways than one.

There are several types of insulation available.

Fiberglass or mineral wool insulation is commonly available as batts. They are used in wall cavities for ease of installation, and because they are not subject to settling. Each type has about the same insulating value at just over R3 per inch. In other words, A 2 x 4 wall can be insulated to about R12 using this method. A 2 x 6 wall will be about R20. Batts are also often used in ceilings as well, but in my opinion loose fill insulation is the more effective for this application, with less likelihood of gaps. If it is still available in your area, do not use the type that has a kraft paper facing. It only serves to reduce fire resistance and hide gaps that may occur.

Loose fill insulation is either of fiberglass, rock wool or cellulose. Vermiculite was once widely used, but is not popular today, because of possible asbestos contamination. Loose fill insulation is easily installed in open attics by blowing it in. Insulation suppliers will usually supply the equipment for this at a low rental fee, or possibly even for free. Contractors specializing in this type of insulation, and with truck mounted blowers can be hired, if you do  not want to get itchy. Truss members can add difficulty, but are not a serious complication. Application may not be possible in some types of roof. Fiberglass has an an R value of about 2.2 per inch, while rock wool and cellulose are at about 3.1. Cellulose may have the advantage of providing some air barrier qualities. Cellulose insulation is a environmentally friendly product in that it is usually made from recycled newspaper that has been treated with a fire retardant and rodent and insect repellents.

Foamed in place, or spray applied insulation comes in three types, wet spray cellulose, open cell polyurethane, and closed cell polyurethane. R values per inch are respectively 3 to 3.7, 3.6 and 5.5 to 6. The polyurethanes can act as air barriers, and the closed cell type is also a moisture retarder. These are not a do it yourself application, and can be more costly. Polyurethane foam insulation is excellent for providing extra insulation in narrow cavities. They are effective for difficult to insulate areas such rim joists. Available in aerosol cans and formulated for specific uses, foam insulation is excellent for sealing around windows, doors, and other wall perforations.

The more common type of rigid board insulation is polystyrene (often called Styrofoam which is actually a brand name). Other less common types are rigid fiberglass, or rigid mineral fiber insulation. Polyisocyanurate (WHEW, say you can pronounce that and be honest) is a foil faced board. Expanded polystyrene has an R rating of 3.6 to 4.4 per inch while the higher density extruded type is 4.5 to 5. The polyiso sheet is R10.8 for a 1.5 inch thick sheet or R7.2 for 1 inch.

Board insulation can be used as sheathing, and under siding on walls. It is effective at breaking thermal bridges, occurring in house framing with cavity insulation. Self adhesive aerogel insulation strips can be applied to the framing under the drywall to reduce thermal bridging, as well. I am not sure how easy this is to find, as it is a relatively new product. A 2 x 6 stud has an R value of about 7 which is not too terrible. Framing will have to be braced, if using rigid insulation for sheathing. It does not provide the same protection against racking, as plywood or OSB. All insulation must be carefully installed to prevent gaps or compression.

For an air barrier on the exterior walls, a house wrap is applied under the siding. This is material that will allow moisture to escape outward, but prevent air and moisture from penetrating inward. It has replaced tar paper for this application, and is required by code in many jurisdictions. I cannot attest to it’s effectiveness, but demonstrations I have seen are pretty convincing. It must be meticulously sealed with special tape, and caulking at all joints and penetrations. My thinking is that the fasteners used should be somehow sealed over, as well, with tape or caulking, but how would you do that when you apply siding. I would appreciate some input on this. Always lap an upper application over the lower one.

To protect the insulation, a moisture barrier must be applied on the interior side,and also sealed well at joints, openings and penetrations.

It also acts as a barrier against air infiltration. A 6 mil poly sheet is required by most codes. A mil is a unit of length equal to one thousandth (10-3) of an inch (0.0254 millimeter).

Pay special attention to sealing electrical outlet boxes and plumbing penetrations. Electrical penetrations are a serious source of air infiltration. Don’t forget to caulk where wires go through wall plates. Plumbing penetrations occur in areas where humidity is higher, and as a result can be a serious source of moisture penetration. Keep all plumbing to interior walls if possible. Even then sealing is important to prevent condensation from forming on cold water pipes, and creating a pleasant environment for mold growth. Don’t forget the ceiling penetrations for plumbing vents.

I am not very concerned with fastener penetration in the interior. Primer sealer and paint over drywall, provide an extra layer of protection against moisture.

Careful consideration to insulation, air barriers and moisture barrier will pay excellent dividends in comfort and energy savings.

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