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Rot, mold, or insects: how do we distinguish among these types of infestation & damage on or in buildings? How do we distinguish between carpenter ants and termites, how do we identify carpenter ant damage, carpenter bee damage, powder post beetle or old house borer damage and termite damage.
What building construction details increase the risk of insect damage, and how do we evaluate the extent of structural impact of existing insect damage on a building. Preventing damage by wood destroying insects (termites, carpenter ants, powder post beetles) by good design and by building maintenance is preferred to simple chemical applications around a property. When use of pesticides is required, there are some important choices.
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Here we outline major topics of concern regarding insect infestation or insect damage and we link to more in-depth diagnosis and repair information.
If we do see insects in or on the building, it's pretty easy to tell CARPENTER ANTS (stomping around boldly in view, often near water or a sink or tub drain indoors) from a TERMITES (rarely in view unless swarming, but may fall out of a disturbed mud tube).
If you want a single rule, ants have a segmented body with a very very narrow waist (below left) while termites look more wormlike in their body (below right).
Below from the left we illustrate carpenter ants, including swarming winged carpenter ants, a termite (sketch) and a carpenter bee.
Common flies such as cluster flies are illustrated separately at FLIES, REMOVE or REPEL.
The first course in recognition of types of insect activity in or on a building is often the observation of the actual damage to wood materials in the structures. That's because depending on the type of insect, season, temperature, and other conditions we won't always see the wood destroying insects themselves.
Insect Damage Photos
At below left you can see typical powder post beetle or old house borer damage to a wood joist or beam. At below right you may notice the characteristic mud tubes we associate with termite damage.
Below our photos illustrate typical carpenter ant damage (below left) and termite damage (below right).
Below our photos illustrate typical wood rot.
All wood rot is caused by wood decaying fungi, typically basidiomycetes, some assisted by certain bacteria.
Watch out: you may find wood rot and insect damage together in a structure. But they are visually distinct.
Photos Assist in Telling the Difference Between Insect Damage & Wood Rot
Wood rot (below left) tends to show breaks in the wood grain across the grain and in more or less rectangular forms.
Insect damage involves holes penetrating the wood and removal of the softer summer wood, tending to leave latewood or winter-wood behind to form walls and galleys (below right where my pen points to remaining hardwood).
Watch out: because moisture is involved in most wood destroying insect infestations (excepting drywood termites), you may find multiple sources of wood damage all together: wood rot along with termite or carpenter ant damage. (Carpenter bees prefer more dry wood and burrow right through both winter and summer wood in a board).
Question: can you tell from these photographs if this is mold or "dry rot"? Our surveyor says the beam needs to be replaced.
I have found your website most useful, and am emailing to ask your opinion (just from photos as am in the UK) with regards to suspect material on a timber beam. I appreciate you charge for consultations and I am happy to make a donation to your website if helpful.
I like in a top floor apartment in an 1850s terrace brick property in London. We had a leak in the Spring in the roof which damaged the front wall.
There are some exposed beams (although covered in plaster), part of the plaster was damaged exposing the beams and I partially painted the gap 3 months ago, a few days ago I noticed odd black stains with black looking hairs sticking out of it (see photos).
For photos on your website it looks like brown mold (but more black in colour), our surveyor is assuming it is dry rot and the beam needs to be replaced.
While it is hard for you to judge from photos, in your personal opinion what do think it is? Thanks so much for your help - J.G. 1/4/2014, London
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone.
For example, to assess the scope of damage in the building you are describing one would want to trace the location(s) and extent of leaks and to perform appropriate probing tests (STRUCTURAL DAMAGE PROBING) to assess the depth & extent of actual structural damage to the beams involved. While manual probing is usually sufficient, there are also more sophisticated tools available (WOOD STRUCTURE ASSESSMENT).
That said I offer these comments:
From your photograph there is no doubt that there has been protracted leakage as the fungal growth that I see involve mycelia or "root-hair" -like structures characteristic of wood destroying fungi on wet wood. While mold growth can appear quite rapidly, when I see extended mycelial growth along with cracked wood characteristic of brown rot fungi it is reasonable to infer that the leakage in that area has been going on for some time.
At above left we see fungal mycelia on what looks like the back-side of a fragment of drywall.
At above right we see the same mycelia on the side of what is probably a wood beam - indicated in your first photo above. We also see "cracking" in the wood characteristic of wood rot, typically caused by a wood-rotting fungus in the Basidiomycete family but possibly involving other fungal genera/species such as Stemonitis sp. that I often find in buildings.
I'd need to see the fungus under the microscope to identify it - a step that is not necessary to decide on the need for structural repair except where MERULIPORIA FUNGUS DAMAGE is involved. As that fungus is a characteristic yellow-gold, I don't see evidence of it in your photographs.
"Dry rot" does not really mean that rot occurred with no moisture present, so use of the term can be misleading.
What we cannot assess from your photographs is the depth and extent of rot and thus the actual need for replacement of the structural members. Especially in older buildings where the depth of rot into large structural members is shallow, for example an inch or less in a 8x12 beam, generally experts will fix the leak and leave the beam in service.
Depending on the structure type, and with the caveat that I am not a structural engineer nor do I have the benefit of onsite view and exploration of your particular building, I caution that there can be special cases where structural repair could be more urgent. For example, if the ends of wood beams set into a masonry structural wall are deteriorated, and particularly where angular fire cuts were made in the wood beam ends, should the beam end become rot deteriorated there could be a risk of structural collapse.
In sum, from the very limited visual access seen just in your photos, but noting the apparent age of leakage and evidence of wood rot, a more thorough investigation is needed to determine if structural repair is needed at all (other than leak repairs), and attention needs to be given to the collapse risk points and structural connections in the building.
Beware of the "OPM" problem - a consultant who spends other people's money to reduce his or her own risk beyond that justified by the actual site conditions.
Beware of the opposite concern - a consultant whose work is superficial and inadequate and who fails to adequately identify and assess actual risk of serious structural damage or hazards.
Many thanks for your detailed and quick reply, it is immensely helpful and really appreciated. We have our original structural surveyor (from when we bought the property) returning next week but I note your comments re OPM...as his instinctive reaction from just looking at the photo was that it needs replacing with a steel beam. We will get some more expert assessments on site so we can have a full view of what to do. I will keep you informed of our progress, - J.G. 1/4/2014
The case you have described, of water intrusion detected at one end of a large wood timber in an older London home, is perhaps a perfect test case for Probett's approach to wood timber strength assessment described in the citation I include below. Before tearing out an existing structural wood beam for replacement with a steel I-beam as your surveyor (in my opinion a bit too glibly) recommended, it would make sense to explore further the condition of the beam and its connections.
As my earlier email explained, in a large wood timber, a modest depth of surface rot damage may not be at all enough to merit timber replacement. As Mr. Probett's equipment and a knowledgable user are probably not available in London, you may be reduced to a more traditional but still reasonable timber assessment approach that includes
- removal of enough finish materials to form a confident opinion of the location(s) and extent(s) of and history of leakage that affected the beam in question .
- a visual inspection to find water or rot damaged wood
- mechanical probing to explore the depth of that damage
- a thoughtful assessment of extent of timber damage and thus compromise of its strength compared with the design loads involved
- careful attention in particular to points of connection, as for example in the case you have provided, the detected leak is at one end of a large beam; even if the overall beam is un-damaged, a failure at the connection point could be catastrophic.
- an interior inspection of the building finished-surfaces for evidence of leakage or movement (stains, cracked, dislocated drywall or plaster, wall-floor separation, etc)
- an exterior inspection of the building to identify its leak points and leak history, with an eye to identifying other areas where there may be un-discovered leakage, rot, and structural damage that need to be investigated.
My concern in writing this follow-up note is to be sure to point out that on a building built in the 1850's there will certainly have been leaks through its lifetime; depending on leak location, duration, severity, building materials, inteiror finishing, building occupancy, building maintenance level and similar variables, such leaks can go un-recognized for a long time, possibly allowing damage to be significant. On the other hand, and where my comments began, superficial damage is likely not to justify costly repairs.
Because this case is a fit application for methods he is developing, I have referred Paul Probett to our public discussion at http://inspectapedia.com/structure/Structural_Damage_Probing.php
If you agree I'd like to also send him a copy of our correspondence. See
Daniel this is incredibly helpful, it is really good to get an understanding of all the various things to consider and from an unbiased source, it seems clear that each situation is different to the last and there is no 'boiler plate' solution that should be instantly applied.
While I have no expert knowledge of any of this, my instinct was that every scenario should be considered before the most invasive option of a steel beam, particularly from the structural reason that we are in an old property which has a tendency to move or expand a bit (unfortunately a curse of Islington in London all being built on clay) and hence the sheer weight of a steel beam might present its own problems on a house designed for timber and bricks, however as you rightly mentioned - surveyors, in the uk at least, want to present the best option to cover their personal liability regardless of cost
I certainly come with the view that whatever is necessary should be done (as the consequences of not doing so could be fatal) but the right solution should be found Please feel free to pass on our correspondence to Mr Probett - J.G. 1/5/2014
How do We Determine the Difference Between Carpenter Ant Damage, Carpenter Bee Damage, Powder Post Beetle Damage & Termite Damage in Buildings? Comparison photos:
For this discussion please also review the example photographs we provide above showing all of these insect types and what their damaged wood looks like. Also see the individual articles for each insect or topic. Carpenter ants, carpenter bees, termites, even powder post beetles or old house borers all provide visible indications of insect activity such as entry or exit holes, mud tubes, or the presence of the insects themselves.
Carpenter ant damaged wood will show cleanly excavated wood passages - the frass is brought outside of the area of excavation. And seasonally you'll find carpenter ants or carpenter ant bodies.
Details are at CARPENTER ANTS
Carpenter bee damaged wood will be on the exterior of the building, typically well above ground, in wood trim, siding, decks, etc.
You will observe 5/16" to 1/2" diameter round holes, usually penetrating the edges of boards and when the bees are active you'll find coarse fresh sawdust below the working opening.
Details are at CARPENTER BEES
Probing you will find powdery sawdust and damaged wood just below this skin.
For this reason, strategic probing is important to assess the depth of damage to the wood and thus to the wood structure.
When powder post beetles are active you may see light dusting of fine wood powder around some of these holes as well as on surfaces below.
Details are at POWDER POST BEETLESAlso see COMPARE TERMITE DAMAGE to POWDER POST BEETLE
Termite damaged wood typically will include the presence of visible mud tubes and mud-like substance inside the excavated wood galleys.
It's rare to see an active termite unless you disturb (break apart) a mud tube while it's in use - in that case you'll see pale termites fall out. You will see termites if they are swarming however. (Watch out for "winged ants" that are not).
Details are at TERMITES
Wood rot itself does not produce insect entry/exit holes nor mud tubes, but of course both wood rot and insect damage are often found together and may even be found within the same wood member or board.
So not all mold causes wood rot, but basically all wood rot in homes is thanks to one or more mold genera/species. (With some help from bacteria).
Details are at
How do We Evaluate the Extent of Insect or Rot Damage on or in Wood Structures? Structural Damage Assessment Procedure
The general approach to repairing damage from wood destroying insects involves these steps:
The Point of View of the Termite Inspector May Affect the Strategy as Well as The Cost to Cure an Active Insect Problem
Watch out: Many of the large number of expert sources available on the detection and prevention of building damage from wood destroying insects (see References, related articles) have been written from the viewpoint of academics or by pest control and related industry associations.
These experts offer valuable information about insect pests, often from the pest control operator's viewpoint.
Our own point of view is that of very experienced building inspectors, diagnosticians, and repair contractors.
Taking this more broad view of the topic adds two benefits: an improved ability to detect insect infestation by knowing where to look (as do experienced pest inspectors) and additional options that may reduce the ultimate cost of building insect damage repair or insect damage prevention.
Example of WDI Inspection Report Concluding Treatment of Active Infestation was Not Feasible
During a building inspection for a home buyer in Hyde Park, NY the pest control inspector (from a local pest control operator or PCO) observed termite infestation in the first floor structure of a home. He also observed that a private water well was located just a few feet from the foundation wall. This pest control operator issued a "WDI Termite Report" report that concluded:
Needless to say, the home seller, buyer, realtor, were all quite upset with this result. What was less obvious was the thinking of the PCO which went as follows:
In other words, as the adage [with some rewording] goes:
But wait! Let's go back to the original adage:
I [DF] was asked for a "second opinion" about the un-solvable termite problem at this Hyde Park home. I am no smarter than the PCO inspector, and I saw the same things he did.
But I also noticed and confirmed by some probing and poking into the area of damage that the actual termite infestation had entered up one narrow area of the foundation wall and entered the wood floor structure beneath a leaky toilet in a first floor bathroom. The entire area of infestation was less than ten square feet of material. That suggested an alternative five-step solution to the active termite problem, a "carpentry approach" and perhaps for that reason, one that the PCO had not considered.
5-Step Termite Damage Repairs Without Requirement for Chemical Treatment
The building owner hired a contractor who cured the termite infestation by the following steps:
Following these repairs the building owner hired the same PCO to perform a follow-up inspection. All of the investigation, repair, and PCO report documentation was provided to the home buyer and buyer's lender. The result was a "clear" or no infestation found report, permitting the home sale to proceed.
Continue reading at CARPENTER ANTS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: can you identify the type of insect that appears to have infested this wood seen in our attic?
What kind of pest do you think makes this? - MJS 10/24/2012
I can't say, MJS, but what is quite apparent from your photograph is that what appears to be insect activity, perhaps from a type of borer beetle, occurred before the tree was harvested and cut into lumber.
You can see that the flat sawn and planed surface of the wood has left cross-sectional slices of exposed, sawdust-filled voids in the wood. To me the damage looks like a type of wood boring beetle, powder post beetle or old house borer, but that's uncertain.
We publish your photo here to invite other readers to comment, and I'll also review our text library for some comparison images of similar wood damage.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
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