1. Wood as a building material

2. Wood as a Building Material
Sawn lumber is the most common material used to build house frames. It is relatively light for its’ strength, due to its’ structure.
Wood can be compared to a bundle of straws (tracheid cells) held together by glue (lignin)
Wood cells are produced in the roots, leaves, and under the bark (cambium)

3. Wood as a Building Material
Wood in the cambium layer grows at varying rates, depending on the season.
Springwood produced fast, and has a low density
Summerwood produced more slowly, and has a higher density.

4. Wood as a Building Material
Alternating layers of springwood and summerwood form “rings” of a tree
The orientation of the rings relative to the wood surface affects how the wood behaves
Plane-sawn (flat-grained) and Quarter-sawn (edge or vertical grained) are the two classifications

5. Wood as a Building Material
When wood dries, the rings tend to “straighten”, causing one of the most common lumber defects, “cup”
Vertical grain is more expensive than flat grain lumber, but will not cup as it dries.

6. Wood as a Building Material
The structure of the lumber also depends on the type of tree that is harvested.
Softwoods, Evergreens, Conifers, or Angiosperms have enclosed seeds
Hardwoods, Broadleaves, Deciduous, or Gymnosperms have exposed seeds

7. Wood as a Building Material
Hardwoods are not necessarily harder than Softwoods (Balsa is a hardwood, botanically speaking). But Softwoods are much more plentiful in large acreages and therefore less expensive to convert to a building material.

8. Wood as a Building Material
Softwood lumber is classified (and graded) according to use:
Boards (up to one inch thick) used for appearance, e.g. window trim and fascia – Graded based on size and type of knots, amount of wane, blue stain
Dimensions lumber ( from two to four inches thick) used for strength e.g. studs and joists – Graded based on splits, wane, shake, and knot holes.

9. Wood as a Building Material

10. Wood as a Building Material
Wood grades –
Divided into boards, dimension lumber, and timbers (based on different usages)
Grading done visually or mechanically
Boards graded for appearance
Dimension lumber graded for strength
Timbers graded for strength

11. Wood as a Building Material
Nominal vs Actual size
Lumber is sawn at a target size, and then dried and planed down to the actual size.
The difference between the Nominal (Name or what the lumber is called) and Actual size depend on the thickness of the lumber
If you measure a 2 x 4, you will find that it measures 1 ½” by 3 ½”, but a 1 x 8 measures ¾” by 7 ¼”.

12. Wood as a Building Material
Dimensions up to 1 inch nominal are – ¼” actual
Dimensions 2 to 6 inch nominal are – ½” actual
Dimensions over 6 inch nominal are – ¾” actual

13. Wood as a Building Material
Green wood is filled with water when it is harvested. The weight of the water is about equal to the weight of the wood in the tree.
Lumber is dried depending on the use and final location. Wood will eventually balance its’ moisture to the humidity in the air (about 8% m.c. in the northeast)
Construction lumber in the northeast is dried to about 19% moisture content (below 20% decay is negligible). Furniture lumber is dried to about 8% moisture content. Construction lumber loses moisture and shrinks during the first heating season.

14. Wood as a Building Material
The moisture content of the lumber is determined by:
Green weight – Oven dry weight x = % moisture content
Oven dry weight

15. Wood as a Building Material
The behavior of wood drying is similar to what happens to a sponge as it dries
From Green to fiber saturation point (approx 30% m.c.) water is lost from the cell cavity (free water) and no shrinkage occurs
From Fiber Saturation Point to Oven Dry (0% m.c.) the bound water in the cell walls is removed, and the wood shrinks

16. Wood as a Building Material
Board Foot Measure – Softwood lumber is commonly priced by the stick (individual piece) and by the board foot. Determining the cost for all of the lumber in a project can be done quickly using board foot e.g.
Price the following:
15 – 2x10s – 8.15
22 – 2x8s – or board feet at .35 bf
73 – 2x6s – 2.80

17. Wood as a Building Material
What is a board foot?
It is a measure of lumber volume, equal to the volume of a board 1” thick by 12” wide by 12” long = 144 cubic inches
The 144 cubic inches can come in many different shapes

18. Wood as a Building Material
The most common way to calculate board feet is the following:
# of pieces x width (in) x thickness (in) x Length (ft) 12
N.B - The dimensions used are the nominal dimensions
How many board feet in 17 – 2x4s 10 ft long?
17 x 2 x 4 x10 =

19. Wood as a Building Material
Sheathing- APA rates sheathing for their structural use-
Plywood – Crossbanded veneers give the material high dimensional stability and a definite strength axis. Still manufacturers suggest it be installed with a 1/8” gap at edges (“sized for spacing”)
Veneer quality on the faces is graded with a letter designation
A – No knots
B – Any knots replaced with plugs
C – Knots over ¾” plugged
D – Knots over ¾” present

20. Wood as a Building Material
OSB – Oriented Strand Board – Made from wood chips (instead of full sheets of veneer) and therefore less expensive than plywood. Can be used for same structural applications as plywood if the span rating is the same
Strands are oriented for
strength on long axis, giving
it a strength axis like plywood.
Span rating classifies the
maximum spacing for
supporting members
when used on roof/floor.

21. Wood as a Building Material
Wood Preservative Treatments- Designed to resist insect attack and fungal decay. Not designed to change wood/water relationship. If you let water lay on wood, it will absorb the water and shrink and swell.
Creosote, Pentachlorophenol, Copper Cromated Arsenate (CCA) have all been used and discarded for health concerns
ACQ – Ammoniacal Copper Quaternary is the current pressure treatment method, Most commonly with an amine carrier. Very corrosive to fasteners.

22. Wood as a Building Material
Pressure treated wood-
The treatment salts tend to corrode fasteners, thus hot-dipped galvanized, stainless steel, or plastic coated fasteners are recommended.
The treatment chemicals should be bound to the cell walls, and thus not leach out in contact with water. Avoid contacting the chemical if released by:
Cutting – wear dust mask.
Handling – wear gloves.
Burning – don’t burn in open fires.

23. Wood as a Building Material
Engineered Wood Products
To span distances ( 16’-24’) not easily handled with solid sawn lumber, or for loads too great for solid sawn, Laminated Veneer Lumber (LVL), Parallel Strand Lumber (PSL), Laminated Strand Lumber (LSL) or I joists may be used.

24. Wood as a Building Material

25. Wood as a Building Material
Nails
Smooth shank – Most common
Spiral shank – Used to increase withdrawal resistance
Annular ring shank – Used to increase withdrawal resistance, shock resistance
Galvanized – Used to resist rusting
Cement coated – Used to aid driving and increase withdrawal resistance
Stainless steel – Used to resist severe corrosion

26. Wood as a Building Material