Fire Prevention & Protection, Firefighter Training, Truck Company

Reading A Building – Wood Frame Construction

By John W. Mittendorf

Wood frame construction may be the most common type of construction in the country. Every community has these structures as they have been built since the 1700s. Virtually every portion of wood frame structures is capable of burning with rapid fire spread. Common considerations follow.

Type and Size
On your initial size-up, does this building fall into the classification of a residential or a commercial type of structure? If it is a residential, consider the following types:

  • Single story, single family dwelling;
  • Multiple story, single family dwelling;
  • Center hallway residential;
  • Garden apartment residential;
  • Any of the above with or without a basement

If it is a commercial, consider the following types:

  • Center hallway commercial;
  • Garden apartment commercial;
  • Ordinary commercial type occupancy;
  • Any of the above with or without a basement

Once you have identified the type of wood frame building, consider the approximate size of the building. As an example, is it a typical “older” single story single family dwelling, or is it a common two-story wood frame house that has a basement and the attic has been converted into an additional living area (for a total of four stories: basement, first floor, second floor, and converted attic)? Remember, the typical Queen Anne or Victorian type structures are normally referred to as homes, houses, single family dwellings, etc., but when the size is evaluated for suppression operations, they are really much larger than a house.

The age of the structure is a good indicator of the following:

  • The older the structure, the more common will be renovations, hidden spaces;
  • Sub standard construction, and other similar types of variances from the norm;
  • The older and larger the structure, the greater the possibility of the structure being divided into multiple/separate living spaces for multiple families;
  • A typical consideration that can have an effect on fireground time is the age of the roof. As most roofs are re-roofed approximately every 20-30 years, it is easy to see that a structure that is 100 years old can have a significant dead load on the roof if the old roofing materials were not removed prior to installation of each new roof.

Balloon and Platform Construction
If these structures were constructed prior to the 1940s or possibly the 1950s, they can be a prime candidate for balloon frame construction which features no fire blocking in the walls and a lack of plates at the top of vertical walls. Instead, a ledger is attached to the inside of a wall which is used to support the floor joists/ceiling joists which allows the upward extension of fire. Conversely, platform construction, used since the 1950s, employs fire blocking in the walls and a plate at the top of vertical walls. These two features will restrict the vertical extension of fire. Remember, the key to balloon frame construction is to open the walls above a fire and check for extension of fire.

Older wood frame structures (residential and some commercial) can be expected to have knob and tube wiring throughout the structure – unless the electrical has been updated. Before Romex and wiring in conduit, wires were suspended on ceramic insulators and were run through ceramic tubes when passing through walls, etc. This wiring also used the typical fuse box on the service porch. People used to put pennies behind the fuses to prolong fuse live. An excellent indicator of this wiring is:

  • Age of the structure. This was used about the same time frame as balloon frame construction.
  • Two-wire service into a structure
  • 1 x 4 stripping around the windows. This was used to hide the open space on either side of double hung windows that was used for lead weights that were attached (by a cotton cord or small chain) to the upper sliding portion of the window (this weight would simplify raising and lowering the upper portion of these windows).

    John W. Mittendorf joined the Los Angeles City (CA) Fire Department (LAFD) in 1963, rising to the rank of captain II, task force commander. In 1981, he was promoted to battalion chief and in the year following became the commander of the In-Service Training Section. In 1993, he retired from LAFD after 30 years of service. Mittendorf has been a member of the National Fire Protection Research Foundation on Engineered Lightweight Construction Technical Advisory Committee. He has provided training programs for the National Fire Academy in Emmitsburg, Maryland; the University of California at Los Angeles; and the British Fire Academy at Morton-in-Marsh, England. He is a member of the editorial advisory board of Fire Engineering and author of the books Truck Company Operations (Fire Engineering, 1998) and Facing the Promotional Interview (Fire Engineering, 2003).