Many older homes have missing fire-blocking. Fire-blocking is just what it sounds like—pretty much. The idea is that we want to “block” the spread of fire from one level to another.
Fire-blocking can be made of almost any approved material—even wood blocks if the space is such that a piece of wood will work. Sometimes it is drywall that covers the opening. Sometimes it amounts to metal rings like would be necessary around where chimney and gas appliance vents run through ceiling or floor structures. Sometimes it is spray foam insulation or rockwool insulation stuffed in cracks.
In simplest terms we are looking to minimize the flow of air and thus heat and fire from lower areas to upper areas. For example we do not want a fire in the living room to have immediate access to the roof structure through missing fire-blocking as is very common at uncapped stair wells, or around chimneys and dropped ceilings. In the following two pictures we can see missing fire-blocking around a chimney and missing fire-blocking over a stair well. Also note the missing insulation in the walls around the stairwell and in the walls that enclose the chimney.
When you are in your attic, you should never be able to look down inside a space and see the surrounding walls. You should never be able to see the top of your fireplace surround etc like in this next picture.
This missing fire-blocking also affects the energy efficiency and comfort of the home. In the winter missing fire-blocking will allow cold air to drop into the spaces and allow heat from the living space to escape. Typically the walls around these spaces will not be insulated because, if the fire-blocking was in place, the insulation would be in the attic.
Home Inspectors should always identify these by-passes for both safety and energy efficiency. Often these breaches are not located, or not visible, if the inspector cannot or does not traverse the attic--or they are hidden for some other reason.
This is a good example of how older houses can benefit from improvement, for fire safety and energy efficiency, even while possibly considered acceptable at the time of construction. It is doubtful that this would have been acceptable for a very long time, given how long it has been known how fire travels in structures. It is more likely that there was no oversight to catch it.
Charles Buell, Real Estate Inspections in Seattle
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WA State, Home Inspector Advisory Licensing Board