Foam and insects
I am involved with two projects right now that have carpenter ant infestations – and in both cases they are in the foam. One is particularly difficult to fix as it is a flat roof with tar and gravel above and a wood T & G ceiling, making it hard to get at the nests. The owners tried for a season to deal with it themselves resulting in the colony splitting, so there are now multiple nests across the whole roof. The processional exterminators have told us it may take more than a year to eliminate the problem – during which time the damage will continue.
When this topic comes up typically the responses tend to fall into three categories. First, don’t think about it, it’s used all the time so it must be alright; Second, as long as the foam is dry they won’t move in; And third, treated foam is available.
Leaving aside the ostrich response, my experience has been that the foam doesn’t need to be moist to attract carpenter ants, they just need a nearby source of moisture for the colony. And, although treated foam may be available, no one seems to stock to use it.
As foam is now increasingly being used as an integral part of many structures, and often in a load-bearing capacity, how wise is it to use a material that is so vulnerable to pest and insect damage?
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Replies
Malcolm,
Excellent question. I don't have an answer, but it certainly sounds like a topic for a future in-depth article.
I invite GBA readers to discuss their experiences. The "ants in the rigid foam" question may resemble the "lingering odor from spray foam" question: Major problems are rare, but when the problems occur, the results can be devastating.
This link may be of interest. This project is Joseph Lstiburek (Building Science Expert) own renovation.
"The message here is obvious: keep things dry and you will not have ants. By the way, keep things dry and you won’t have a lot of other bad things as well. The dry/wet thing with ants is pretty much proving to be the case in all the ant foam infestation cases I (and others) have looked at over the years."
Short story is that the exterior of his barn/office is covered in foam and he had ants in only two places which happened to be damp/wet. Therefore one could deduce if "having water near by" was the only requirement then ants would've been found through out the dry foam as well.
http://buildingscience.com/documents/insights/bsi-056-leiningen-versus-the-ants-redux
I don't think the barn experience proves that there would have been no ants in the foam if the foam was dry. It might only mean that the ants prefer damp locations. If there were two ant colonies looking for homes, and no wet foam, they might have both moved into dry foam.
It might be better to have them nesting in foam than in structural wood ... better to have some thermal leaks than to have the building collapse. But I assume one can't count on them staying in the foam and not migrating to the wood.
This is the question I think about most. I worry that widespread use of rigid foam, combined with bad water management/flashing details that are so common, will create a backlash against "green" and specifically outsulation. I hope someone makes a fortune popularizing an easy method, perhaps using standoffs of some sort, to put up cladding over mineral wool. And the I predict (well, hope) the beautiful simplicity of vented attics becomes more common as people struggle with unvented attic/roof failures. What a mess.
Charlie,
Agree but keep in mind that research shows carpenter ants will live in dry wood but prefer damp wood so technically there's nothing keeping them from setting up shop in any stick built structure. So yes absent a preferred (i.e. moist) environment carpenter ants "may" take up residence in dry foam/wood or they may just move on.
I think that distinction is different than saying "Carpenter ants will set up residence in foam over X".
My two cents.
btw carpenter ants are actually beneficial as they prey on other pests such as termites and they have a certain sweetness when eaten. ;)
@Andrew
I have the same concern. Living in 'termite country" I'm wondering if dense mineral wool batts (ex. Roxul ComfortBoard IS) is a better alternative. Roxul has never made claims that insects won't bore into their product, but I'm not surprised since IMO their product is generally sold in climate zones which don't have termites.
Of course one can purchase foam treated with an insecticide.
What Charlie says mirrors my own experience with carpenter ants. Dampness may be a preference but doesn't seem to be a prerequisite for them to move in.
WhenI built my own house here in the PNW 20 years ago, the only foam I included was a strip on the exterior of my second floor rim joist. The nest was on a sunny south wall which as bone dry when I opened it. Unfortunately by then they had also eaten a large hole in my top plates (which were not rotten or damp) in able to move down the wall to nest next to a baseboard heater. i surrounded the foundation with insecticides but the tenacious and alarmingly intelligent colony found the one possible path out to forage by using my power lines and descending the pole on the street.
As I said in my initial question, what I find particularly worrying is that the line has blurred between the use of foam as insulation, and as part of the structure. Perhaps Martin is right and the situation is analogous to the bad spray foam question. Or perhaps there are regions, like the PNW rain forest where I live, which just make it too risky.
Chris,
Each spring the carpenter ants here send out winged scouts looking for places to establish new colonies. For several days it isn't unusual to find several hundred of them clinging on the exterior of every house. I presume that they are looking for specific conditions in which to set up new nests, and in the absence of finding them, leave most houses alone.
Foam seems to mimic the decaying stumps they prefer in the wild, but as you say I've found them in wall cavities filled with fibreglass, often adjacent to some indoor heat source, like a fireplace or wall heater. I wonder if the seasonal swings in the moisture of exterior sheathing is enough to make them set up shop in usually dry and decay free wood structures? They sure like foam though.
I've run into the insect damage on a project because of foam. There was two infestations. One was where particle wood was put directly on the ground for a floor to the basement. The other section was the front door. A previous owner had used spray foam relgiously underneath it - top sill of basement - only one spot. The front door and all the struture around it had to be replaced. The particle wood was replaced with cement.
This particular case was interesting because the damage was limited to those two points. The foam and the particular board. I know that foam is the cure all of insulation. All should bow down to it. As with any product it has its good and bad points. Good - high rvalue and sealing. Bad - separates from wood over time (expansion/contraction), insects nest in it, cost is high, produces huge amounts of smoke during house fire killing people and is hard to find a good installer.
Not against using foam, but it has limited uses.
Does seem to be kind of a shame to build a green home and have to douse it with insecticide.
I wonder if this is a situation where residential construction best practices have not kept pace with variations in insect pressure due to climate change. A few degrees warmer and a few more high intensity rainfalls each year seem like a recipe for greater insect problems.
Another observation is that there appears to be ample focus on termites but less on carpenter ants and other winged creatures. We have spent a lot of effort kerfing metal strips into our ICF blocks to serve as termite shields. And we are even deploying a removable trim system at the base of our stucco covering so we can do inspections (and spraying). But you know what, carpenter ants are just going to walk around those barriers, or as Malcolm says fly around them. (One of our biggest nuisance problems last fall was an invasion of lady bugs, wow.)
It's not just insects that are a problem with country living though. We have some ancillary window wells that we made out TimberSIL that I had purchased some years back. The neat thing about TimberSIL is that you can stain or paint it. Unanticipated was that its sodium silicate treatment proves irresistible to porcupines!
Andrew,
Once we deal the insects let's get after the porcupines next!
"use rigid mineral wool boards" would be the logical fourth category of responses, as a couple of others have alluded to...
As far as I know, ants and termites and others will not chew through rigid mineral wool boards...and the density is too high (I think) for them to crawl through. This is just one of the reasons I prefer it over foam for our climate, CZ4, in Virginia (mixed humid...not marine).
Photo courtesy of Promethean Homes (www.prometheanhomes.com) in Virginia.
John,
I'm with you. Hopefully mineral wool manufacturers continue to expand their product lines with more high density products that can be used in load-bearing situations.
That's funny photo. it's like the rain screen furring installers showed up and started working while the flashing and insulators were on coffee break. or maybe it is all the work of one guy with ADHD?
Several years ago, when I needed new siding on my house, I re-sided the house with 2 inches of foil faced polyiso sheets with a rain screen. The bottom is covered with insect screen but I don't think it is attached very well - meaning that ants could easily get between the siding and the screen to get to the foam. I also had some moisture issues in my basement so we did something similar to a frost-protected foundation to slope water away from the basement in addition to sloping the area around the house better.
Last Spring, I did some insulation and air sealing in my attic.I found some carpenter ants crawling around but I didn't really worry about it. I see them every year. It's the South. Ants always get in your house during certain seasons. I also noticed a mouse in my attic so I put a humane mouse trap out. It did not catch the mouse, of course, but there were a good amount of ants around the food so I decided to look further. I crawled around and followed them to the back corner of my attic. When I pulled up the ancient fiberglass I saw a teeming mass of carpenter ants so many that I couldn't even estimate how many - hundreds? thousands? I don't know but it was a solid mass of ants at least 12 inches square probably larger. When I shone the light on them, they scurried around moving eggs.
I have no idea if there is wet wood in that corner of my attic. It's a pretty low slope roof and cannot physically get to that area.
I try not to use toxic materials so with my mask on I squirted bottle after bottle of boric acid and diatomaceous up in the attic. I have not seen any of my carpenter ant friends in my house this year. Nor have I returned to the site of the infestation to try to replace the insulation. I hope to do that in the spring.
What would I do differently considering that I live where carpenter ants and termites thrive?
1. Insulate with mineral wool. I love this stuff. I hate to work with it, but I love it's insulation properties and pest resistance. And instead of using foam sheets (the pink stuff) to insulate around the foundation, I would try mineral wool (I know about the compression risk) or use foil sheathed foam sheets and tape the foam edges. I don't think ants or termites are going to chew through the aluminum tape. Then I would lay down a heavy amount of boric acid at the base of the foam or apply bentonite clay (clumping kitty litter) below and all around the base of the foam. Then replace the soil - no mulch.
2. Cover soffit holes with metal screening material so insects cannot crawl through. I don't know why I didn't think of that at the time.
3. Fill the the screening material at the base of my rain screen with ridge vent material so the screen can't be compressed and so easily bypassed by insects.
4. Trim trees around the house so they don't form a carpenter ant highway into my house. That's how I think the ants made their entrance.
Carpenter ants are an impressive pest.
Another pest-proof insulation option that was available for a very short time was foamglas. Sadly I was just informed by the manufacturer that they are no longer selling it for residential use, only commercial and industrial.
For Malcolm, regarding the photo: it's funny to think of Daniel Ernst (Promethean Homes) hiring a "furring strip installer"...or a flashing or exterior insulation or siding installer for that matter. The workflow process is set up for a 2-person crew to complete the entire installation starting from the bottom, working their way up.
John,
I was being facetious. It's just something I've never seen done. I am sure they must have their own reasons for why they install that way, but it does seem as though it makes things a lot more difficult having to work through all the layers at each level. Installing, flashing and sealing the insulation and WRB are so much easier without the furring in place. In any event, what really matters is the end product, not the process, and that looks great.
I am surprised they don't seem to have made any allowance for the cavity to vent or drain at the bottom. This makes the rain screen much less effective and wouldn't pass our code.
On a similar topic - the insecticide exterminators use to stop ants will dissolve foam board. Twice I have removed siding, where the homeowners had brought in exterminators to deal with ants, to find voids where the insecticide had been applied. In both cases small holes had been drilled through the wood siding, insecticide injected, then the holes sealed with a dab of caulk.
We have termites here in Sonoma Cty, but have only observed them where wood is damp. We've assumed that termites cannot bore through aluminum tape or the foil of foil-faced polyiso, so we taped the bottom and top of every sheet of rigid insulation we've attached. I've also been meticulous with taping any little holes or rips that invariably happen. I'd prefer to do tape and then have a metal plate that the foam sat on, it would add another layer of protection and make me feel fine about spraying orange oil up there every year. Curious, has anyone seen the little buggers boring through foil?
I often keep my ears open in case I come across an entomologist. I have been wanting to ask one for some time to what depth carpenter ants and termites will live in the ground. 12" deep? 24?" 4'? The only place we use foam on our projects, typically, is EPS under our slabs. Here, on Vancouver Island, we typically do not have full basements. We will have shallow foundations on footings, backfilled to the top with a slab-on-grade inside as the main floor. I am wondering to what depth we should be concerned about bugs tunnelling "under" our footings, and working their way back up to the underside of the slab, and tunnelling around in the EPS layer? I share the concern Malcolm expressed, as on our Passivhaus projects we are beginning to see architects and engineers approve higher density EPS for structural load-bearing applications, and I too wonder if we are looking for trouble down the road.
On almost any reno we do with rigid foam on the exterior of a foundation, or on an exterior wall near grade, we find an absolute ant farm. They love the stuff, and make incredible patterns to pull apart and view! So, we have completely switched (when we have our say on specifications and assembly design) to only using Roxul Comfortboard IS for exterior insulation detailing. It can be a pain for much of the detailing around windows and doors, and for ensuring that all of your rain screen stays completely co-planar for exterior cladding, but we have learned some tricks over the years to make life easier. Not only does it appear to be totally bug-resistant, but even better is the fact that it is extremely vapour permeable (+/- 30 perms per inch), meaning that assemblies will dry much better than their exterior foam counterparts. Especially important on super-insulated designs, and here in the Pacific Northwest.
Burke,
I've never seen ants tunnel under footings and up into sub-slab foam (doesn't mean they don't though). I suspect that, like rats, they don't randomly tunnel unless there is some indication the work will pay off. If that's true we might find them quite quite far below grade in exterior foam, but not perhaps in foam placed at the same depth that didn't extend up to grade. All this is speculation from another Vancouver Island carpenter ant victim.
I suspect you're probably right. Since I haven't yet had to pull up a slab that had foam underneath it, I haven't had any anecdotal evidence to go on, in terms of what kind of critters, if any, were found in it. But, promising to hear that you haven't seen anything tunnelling in sub-slab or footing foam. Whereabouts are you located on the island? What company? I work for Pheasant Hill Homes, in case you ever come across a chance to cross paths!
Burke,
I'm out past Sooke in Shirley, right next to French Beach park. I'm self-employed and do most of my work between here and Victoria.
Cheers, Malcolm