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Combustibles Too Close To Chimney Or Fireplace

So, you have just been told you have combustibles in contact with your chimney or fireplace. Now what?

During an inspection or estimate, someone mentioned to you that you have combustible material (studs, framing, plywood, even sheet rock) either too close or in actual contact with your masonry fireplace and/or chimney.

These brings up many questions:

  • How much clearance is required?
  • How did this happen?
  • Is it a problem?
  • Am I required to do anything about it?
  • What can I do about it?

How much clearance is required?

Current building codes call for four inches of clearance on the back wall of the fireplace (because this is where the fire is hottest) and two inches of clearance on the fireplace side walls and the smoke chamber walls. Interior chimneys (built inside the home) require two inch clearance while exterior chimneys (built outside the home) require one inch clearance to combustibles.

How did it happen?

The answer to this can be two-fold. In many cases, your fireplace and chimney was built before the building codes existed or before building codes recognized the need for clearance. In Virginia, this generally means before 1973 but that date is not absolute as some cities and counties required clearance to chimneys and fireplaces before that time. In other cases, the people who built the fireplace/chimney and the house ignored the requirements to provide adequate clearance to combustibles. This certainly was common in the first few years after clearance requirements went into effect but unfortunately we still see this from time to time in current construction.

 

Is it a problem?

Well, it certainly can be. Inadequate clearance to combustibles is cited in many fire reports, and ultimately that is the reason building codes were updated to include clearance requirements. But what about the millions of homes that were built without clearance to combustibles, they aren’t all burning down are they?, you might ask. No, they aren’t, at least not most of them. So what’s the big deal? The big deal is this – combustibles in contact with your fireplace or chimney may cause a fire and it is hard to predict when that will be. In most fire reports we see, the cause of the fire is multi-factored with lack of adequate clearance being one of several factors that led to the fire.

Some of those other factors include:

  • Other construction defects
    Defects such as inadequate wall thickness around the fireplace or smoke chamber. Fireplace and smoke chamber walls are required to be eight inches thick, which generally means two courses of brick. If the mason skimped on brick and only used one course of brick and there is no clearance, that is a significant problem.
  • Pre-existing damage
    If the chimney has damage such as soft or open mortar joints, cracked flue liners, loose bricks, etc and improper clearance this would represent a problem as well. Pre-existing damage may be the result of age and normal deterioration or some sudden occurrence event like a chimney fire or lightning strike.
  • Unlined chimney flue
    A chimney built without a flue liner and with improper clearances poses a great hazard. Current thinking is that unlined chimneys are unsafe to use.
  • Long duration fires
    Masonry fireplaces can absorb a lot of heat but will ultimately transfer that heat through the walls. In a typical “entertainment oriented” fire of two to four hours the structure doesn’t get hot enough to ignite combustibles. But if the fire is kept going for long periods or multiple days the heat will transfer through the masonry and ignition of nearby combustibles is possible. Long duration fires often occur during power outages where the fireplace is the only source of heat.
  • Time
    Combustibles like wood dry out when exposed to heat, even low levels of heat over long periods can lower the ignition temperature of nearby combustibles, especially if they are in contact with the heat producing appliance or device. This is known as pyrolysis and is the cause of many fires, especially around appliances that run for long periods like wood-stoves or heating systems. With pyrolysis, the ignition temperature of the combustibles is gradually lowered (over many years) until spontaneous ignition takes place. For this reason, you shouldn’t assume that because you haven’t had a problem in fifty years that you won’t have a problem. The likelihood of a problem actually goes up over time due to pyrolysis.
  • Chimney Fire During a chimney fire, the temperature in the chimney can exceed 2000 degrees. This can be enough to ignite combustibles adjacent to the chimney.

Am I required to do anything about it?

This is another great question with uncertain answers. If your fireplace/chimney was built before the building codes required clearance then your system should be “grandfathered” and you are (probably) not legally required to make corrections. Since this question involves many considerations such as the age of your home, laws and ordinances that were in effect at the time of construction, etc it is beyond the expertise of your chimney service professional to make this decision for you. Another question is “Should I do anything about it?” Even if you aren’t legally required to make changes to the system it may still be advisable to do so. After all, the codes were changed due to a known fire risk. Consider all the factors noted above and weigh that with your own personal tolerance for risk.

What can I do about it?

There are a couple options for repair. One option is to have a carpenter/framer remove the combustibles that are in contact with the fireplace or chimney, and move them back to achieve the recommended clearance. Another option is the installation of some type of zero-clearance liner system, which might be a liner for just the chimney or a liner for the fireplace and chimney. Some inserts are approved for installation in chimneys without clearance. Liners are a good option when there may be concealed combustibles in contact with the fireplace or chimney, as the concealed areas are harder to evaluate, access and repair.

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