Choosing Floor Joists

Posted September 18, 2008

Floor joists are used to frame the floor of most buildings and there are a variety of materials that have different impacts on the environment.  The joists used to frame the floor of a house fall into three general categories 1) dimensional lumber, 2) I-joists and 3) open web trusses.

From an environmental standpoint, dimensional lumber should not even be considered, as it requires the cutting down of the largest old growth trees to get lumber large enough.  The other problems with dimensional lumber is that you are limited to just over 15 feet of span for 2×12, which is the largest commonly available lumber.

The second choice is I-joists, which are made by having two pieces of wood, typically 2×3, connected by a piece of plywood or Oriented Strand Board (OSB) creating a beam shaped like the letter I when viewed from the end.  There are some I-joists where the top and bottom members are also made of laminated lumber.  This results in 60% less timber being used vs and equivalent piece of dimensional lumber.  The I-joists are commonly available with up to 16″ depth, and are manufactured with different widths of lumber for the top and bottom pieces.  With the heaviest I-joists spaced at 12″ centers, the longest span is about 32 feet.  An advantage of I-joists is that they can be cut to length on-site and many have pre-punched holes for running electrical and plumbing lines.  Holes can be cut for ductwork, but you must follow the guidelines  from the manufacturer for placement of the holes.

I my opinion the best choice for floor framing is the open web trusses which consist of a top and bottom plate which is joined by web that forms a series of triangles.  The top and bottom boards are usually 2×3 or 2×4 lumber that is finger jointed together to form the long spans and the web can be either wood or steel.  The trusses can be manufactured with depths up to 24″ for spans up to 40 feet.  The biggest advantage of the open web trusses is that there is an open space in order to run all electrical, plumbing and ductwork with ease.  The disadvantage of the open web trusses is that they are much more limited in the ability to be trimmed on site with typically only about 2-3 inches on each end being trimable, so the measurements must be fairly exact when they are ordered.

Both the I-joists and the open web trusses, being engineered products will result in a quieter floor, as you don’t have the warping and twisting found in dimensional lumber.

In my home I used the open web trusses and found them very easy to work with.  They are much lighter than dimensional lumber and having all the open webs made it much easier to route wires and pipes without having to worry about drilling holes.  Care must be taken when installing them as they have a top and a bottom and so must be oriented in the correct manner.  All the trusses also have to be aligned in the same direction, or the webs will not be in alignment and can cause problems when installing ductwork.  By using the open web trusses, I was able to avoid installing any bulkheads.  These normally would have been needed with dimensional lumber or I-joists for the installation of ductwork.  Without any bulkheads I was able to avoid any drops in the ceiling height.

Posted under Materials

Metal Roofing

Posted September 16, 2008

For an environmentally friendly building, metal roofing is one of the better choices.  One of the main reasons is that at the end of it’s lifespan, which is considerably longer than asphalt shinges, metal roofing can be easily recycled, keeping it out of the waste stream.  Asphalt shingles, on the other hand cannot be recycled and end up in the landfill when they are removed after their comparably shorter lifespan.  The roofing on a typical house would have to be replaced after 20-30 years with asphalt shingles, whereas with a metal roof, there are many that are 75-100 years old and most will last a minimum of 50 years if they are not damaged by wind.  Another advantage is that metal roofing is available in a number of light colours that will reflect the light and reduce the cooling load on the house.  Metal roofing is also recommended if you intend to collect rainwater for household use, as it will not leach chemicals and lose granules as asphalt shingle will.  Metal roofing also has the highest fire rating available for a roofing material and can reduce the chance of fire from flying embers, such as from a forest fire.

The most common types of metal roofing are corrugated steel sheets, standing seam and roofing tiles.  The least expensive is corrugated steel roofing.  It comes in sheets that run vertically from the peak of the roof to the fascia and are overlapped and screwed down.  Standing seam roofing also runs vertically from the peak of the roof, but the sheets of metal clip together to form a tight seal and the metal is held down with concealed clips.  Standing seam can be made of different metals including steel, aluminum or copper.  Metal tiles, which can be formed to appear more like a shingle, tile or shake roof, are made of smaller sheets of metal that are made with interlocking connectors.  The metal tiles are the most expensive of the metal roofing materials as they are often made of aluminum.

The sheet steel roofing can be protected with a galvanized coating covered with a coloured polymer, or with a zinc/aluminum coating, also often covered with a coloured polymer.  The two types of coatings are not compatible and should not be used in contact, as it may result in premature corrosion of the metal.  There are also some metal roofing materials that are coated with a special coating that reflects most of the heat from the sun.

If you are interested in installing the roofing yourself, the choice is between corrugated sheets or some metal tiles.  Standing Seam roofing requires specialized equipment and is only recommended to be installed by trained contractor.  You can install metal roofing yourself but you must take more precautions than with asphalt shingles, as the metal roofing materials are usually much more slick and present a slipping hazard.  Falling off a roof is not a fun experience.  The corrugated steel sheets can be quite large and can be difficult to handle, this is not a project for one person.

Posted under Materials