Alternatives to petroleum based insulation for basements

We will be renovating our basement this winter. The current insulation is 1960s fiberboard which has soaked in humidity from the concrete and needs to be taken out. I have done quite a bit of reading and the consensus seems to be: "do not put wood directly on the concrete and put a semi-permeable foam board". The rational is that we want to break the thermal bridge and avoid condensation against the concrete that would then touch the wood and cause molds and rot. Makes sense.



Are there any alternative to the extruded foam insulation that would serve the same purpose?

I always thought papercrete would work. You could pour it in 4x8 sheets and then apply it to the walls. The R-Factor is not that high, but it would be enough to break the thermal bridge.

It probably depends...  It may be worth considering simply addressing, properly, the specific problem which you have rather than trying to create the perfect design solution. The below is pretty generic. A hit list in case you haven't considered stuff.

What is the current water problem? Is the water coming from inside or outside? Is it condensation or is groundwater getting in? Is there a problem on the walls or on the floor or both?

What is the existing wall structure? "Exterior basement walls don't have to touch the foundation wall. I don't recall if it's "kosher" to seal the basement walls with poly sheeting to stop moisture ingress; stone and concrete doesn't much care if it's wet. You can also build the exterior basement wall 3/4" short in a place convenient to carpentry, seal the outside of the exterior basement wall with poly sheet, move the wall into position 1"-2" off the foundation wall, secure it in position and seal the top gap and caulk the bottom. You have just made an impermeable moisture barrier on the outside of that wall and can insulate the wall itself anyway you choose. Rockwool doesn't degrade with moisture, although the wall s/b dry as installed.

For condensation, you just want to keep the water vapor (moist air) away from cool surfaces. For water and moisture coming through the walls or floor, you want to keep the outside soil dry and possibly trench around the perimeter and apply a sealant to the outside basement walls. To keep soil dry, you can bury a water proof membrane from the exterior wall out 3-4'; put it 12-18" under grade level and slope it away from the house; seal the seams and run it up the side of the exterior wall if you have a lot of water moving over the surface. Gutters/downspouts or a water proof swale under the eaves sloped to drain the water away from the house helps.

It's all rather detailed and nitty picky which is why I started out asking how exactly the problem manifests and considering curing just that issue. If that is possible and depending on how the basement "performed" in the time you've been there (whether it had other gross problems or whether it was mostly ok).


Regards,
Rufus

I was researching insulation for below grade applications and I think I got interested by mineral wool and/or fiberglass panels that were designed to be outside a foundation.  I either couldn't find them or couldn't verify they'd work horizontally in my "swedish skirt" insulation application so I didn't pursue them.  I can't remember if they were both an option or if just one of the two was an option.  

We used Rock Wool Comfort Board 80.
It's basalt rock made into 2x4 rigid panels and at 1.5 inches thick it gives you an R6.
It's designed for underground exterior use.
You can get through Lowes or Home Despot but you have to order a whole pallet.

Travis Johnson wrote:I always thought papercrete would work. You could pour it in 4x8 sheets and then apply it to the walls. The R-Factor is not that high, but it would be enough to break the thermal bridge.

Papercrete would not be a good choice; it acts like a sponge and will mold. Addressing the problem from the outside would be the best option, but this may not be practical. Rock wool might work on the inside.

it would be a lot more work, but I really like the idea of insulation outside the concrete that a couple of other folks have mentioned. that would move the dewpoint to the outside of the concrete and your living space and turn the foundation into a nice thermal flywheel to moderate temperatures.

I like the product Alex suggests. I would probably excavate around the exterior of the structure, underpinning at need, and slap those puppies up to a depth sufficient to accomodate the frost line. I would then seal the exterior of those with a sealant designed for the purpose, or depending on the application, salvaged impermeable materials that I would use to line the wall and wrap the insulating board. I would then drop some weeping tile around the structure, tied to a french drain at need, and backfill appropriately to prevent blockage of the weeping tile, and to fill the excavation.

-CK

When the foundation wall rises above grade, any exterior insulation must be physically protected from damage by shovels and lawn equipment. Some insulation "modules" integrate this protective layer, many don't.

Research carefully any pest problems associated with various types of exterior insulation in your area. Most building inspectors are happy to share what they know if you don't take to much of their quality time. Professional home inspector sites may offer the chance to talk with contractors in your area - your particular location matters because the bugs are different in different places. Here are a couple sites (the "nachi" site has helped me in the past. The other two I just picked off the top of the hit list):

https://www.nachi.org

https://www.homeinspectorpro.com

www.homeinspectionforum.net

In my personal experience trenching around a foundation is a simple job with few problems per se. A ton (!) of work, but quite doable manually by strong people who actually work hard. An experienced digger, working honestly, can do a lot more than we would initially expect. It may (or may not) speed things up to rent a _big_ ditchwitch to make one or two cuts all the way around and then finish by hand. A mini excavator might do the whole job (mostly), but I don't know how easy it is to "get it right" for somebody who's never operated equipment before. However, clay and rock soil may cry out for powered equipment. Balance the equipment cost against wages and decide what looks good to you. Good labor is far, far more flexible than equipment. Of course, locate the utilities, etc, prior and dig those out by hand just to be sure what's down there so you don't do something terribly embarrassing.

Trench design: It's night and day easier to do the actual job when the trench is 24"+ wide; 36" is better. Try not to move the dirt. If possible mound it in a line alongside the trench but leaving 24" open at the edge of the trench for access. Now is the time to bring in better draining material, if you like, to backfill around the foundation wall.

But it's a big job, with an open trench for at least a week; if your digging method allows, you could do it in sections, but that may not be efficient if you rent equipment. The real problem I have found is 1) building entries; 2) decks; 3) concrete walkways close to the building; 4) landscaping one doesn't want to trash.

Landscaping can go either way. Tearing out what's there close to the building may yield a big plus: I have formed a strong opinion that there absolutely, no question, needs to be at least 24" clear along all exterior walls of a building. I go further and I install an impervious layer just below grade all along this area, sloped away from the building; seal it to the foundation wall if feasible. It is backfilled to slightly above grade with clean sand sloped 1/4"/ft away from the building and concrete tile is laid with tight joints from the building out 24". This gives me clear sight and access to the foundation wall and the bottom of the exterior building wall; It discourages vermin from the space near the building; it helps keep the soil next to the foundation wall dryer; it severely discourages trees from getting a start against the foundation wall; ditto any stuff enthusiastic gardeners do; it makes clearing and keeping that area clear a task easy enough that it actually gets done most of the time. If shading an exterior wall is desirable, my approach is largish shrubs planted 3'-4' from the building and/or tall frames (10+') 3' out on which spreading vines can grow. I have found that maintaining the exterior walls of a building at grade is damn important and that it's much more difficult, to the point that it doesn't get done, when one has to fight their way in to the wall along 40-50'.  You could say I have developed serious attitude. <G>  Walkable space along the exterior wall also provides for running a long hose w/out bisecting a "user area" and, less fortunately, a place to "temporarily" lean tools and place ladders...


Cheers,
Rufus

However, perfect as exterior upgrades might be, interior work might more than meet particular needs, depending. Holding interior wall framing a couple inches in from the exterior foundation wall isn't that hard to do. Installing a moisture retarding membrane on the exterior of that framing is doable with planning; sealing the top and bottom of that skinny cavity at the foundation wall is picky and detailed, but might yield good results for less upset over all.

However, I would never contract such detail work that I myself had spec'd, ever. I would employ and ignorant but smart kid who know nothing about nothing and would do what I told him, exactly. My call, my responsibility, completely. The attention to detail and the time involved would just be too much for any professional priding himself on making money - IOW, a really bad bet, that way. Professionals make their money by doing the same ol' same ol' again and again. They have to do what they know how to do, what they have developed as a "tried and true" system. They can't afford to learn new tricks, try out new methods just to please one customer. That can get _really_ expensive - I learned the hard way, more than once, I'm afraid. That's a general statement, of course, but beware and respect _their_ need to make a living in a way they can understand and control. So when using pro's, you really need to listen carefully and understand _their_ way and then decide if it will work for you; maybe a tiny tweak or two, but no more. And try in every way you possibly can to make sure the communication is accurate for all concerned. Do NOT assume - ask.

Best luck, have fun.
Rufus

I should have said earlier that we had the whole foundation excavated in the summer and an impermeable membrane installed. The contractor also put 2 in blue foam insulation below grade. I thought about adding insulation above ground, but it would not work well with the bricks.

Again, whoever is doing the work would need to know what was required to support the structure to get this done, but theoretically, if you have internal moisture problems, you could lay an internal perimeter of weeping tile draining to a sump pump, probably put down in a cavity in the middle of the basement floor reaching underneath the slab (if there is one) to handle fluctuations in ground water levels and oversaturation, draining outside, anywhere you won't mind potentially mineral-rich water.

I haven't seen anyone mention this, so I will. You really want to get rid of all the moisture you can. I am concerned by the fact that you are still having moisture issues after having already excavated the foundation and sealing it. Giving it a good place to collect easily and giving it pathways to drain there that aren't through your structural and insulative materials, I think, should be top priority, as otherwise the least you'll have to worry about is running a dehumidifier on high every time it rains or thaws.

And if you're not already doing that, I would. Excess humidity courts everything from mildew and mould to cockroach infestations. They start to die off when ambient humidity falls below 40%.

But let us know how you proceed, and good luck.

-CK

I've got a heat pump water heater in my basement that acts as a dehumidifier. of course, it also cools the air, so probably not a great idea for a living space that will be heated.

There is no more water infiltration. However, there could still be condensation on the concrete from humidity in the air and from what I read that is why the semi-permeability of the foam boards is desirable, plus it is not sensitive to moisture.

how about cork? I don't know much about its permeability. I do know that it's pretty expensive, but also  real nice to look at.

I don't know of an insulation that is non petroleum, low embodied energy, and mold/moisture resistant for below grade.

Pick your priorities and move forward.

Paper crete won't work, but aircrete would-be just to give you another choice.  It it's probably the cheapest, but it is labor intensive.  

Alex Klohe wrote:We used Rock Wool Comfort Board 80.
It's basalt rock made into 2x4 rigid panels and at 1.5 inches thick it gives you an R6.
It's designed for underground exterior use.
You can get through Lowes or Home Despot but you have to order a whole pallet.

We buy the spun rock wool by the bale, but I remember our local Lowe’s selling the rigid foam as individual sheets. I could be wrong but I don’t think so.

The stuff is definitely in stock. We’re in New England, if that’s different than the quoted poster, it may explain it! Or it maybe we’re buying a different brand?

Also, if you’re a vet, with a little proof lowes will give you a discount. You have to sign up for the mylowes thing, but it saves us $ every time we go!

> rock wool

Three years ago I bought batts of  it off the shelf from Home Depot - near Chicago. YMMV

> could still be condensation
But that is speculatioin. Would it be possible for you to postpone basement build out for a year? That will let you see what happens "as-is". Direct hard data means a lot more than a list of possibilities. If that is possible.

There are a couple of things you might learn. One is whether your pipes in that space will "weep". Another is whether you get moisture through the floor. Another is where your walls, floor, pipes and anything else in the basement hang viz the dew point.  Humidity gauges are not costly. Put one down there with a thermometer and keep records like Jen is doing at the Abbey. If you feel dedicated to the tune of about $50, get an IR thermometer gun and keep readings from the walls and floors, as well. That would be _very_ interesting. Record the outside temperature and the soil temperature at 6", 24", 36" and any deeper you're willing to go. Done once a day over a year, this will provide what you need to _really_ design and control your HVAC, whether it consists of a floor fan with a wet towl, a' la Dale Hodgins,  and a wood stove or some modern tech miracle. Records of the actual environment are solid gold when it comes to figuring out your needs. Take pictures of any problems.

In our basements just north of  Chicago, tempmeratures stay about 10-20 degrees cooler than outside (they warm up slowly in a heat spell, but drop back down if the temps stay below 80F.). That means when humdity rises above about 70%, the basement starts to get a little clammy and above 80%, any cold water pipes w/out insulation will weep. If I don't mind the basement getting warm, I can get rid of the clamminess by opening the exterior door and runnng a big fan. Even though it's humid, when the temps go up and there is ventilation, the condensation goes away. The walls and floors remain dry regardless (that is, they do since we got rid of the surface water that was flooding the soil outside of the foundation walls when it rained) unless the humdity rises over 95%.

What I'm saying: Good information helps greatly to address the real existing problems appropriately w/out spending on things that aren't an issue. Living with the basic structure exposed for a year after you have made the MAJOR upgrade applying exterior insulation, makes  that info readily available. It may be that simply ventilating the basement a certain amount will eliminate all moisture issues.

However, that uninsulated part of the wall above grade is probably going to be an issue if your winters get below 25F. regularly. Again, being able to observe the foundation wall directly will make a lot easier to know what's going on.


Regards,
Rufus

Thanks everybody for all the input, it will take me a bit to digest the different options.

“There is no more water infiltration. However, there could still be condensation on the concrete from humidity in the air and from what I read that is why the semi-permeability of the foam boards is desirable, plus it is not sensitive to moisture.”

A couple thoughts-
You started the thread saying you wanted to break the thermal bridge, but you only need to do that above grade, where the bricks are on the outside. You already accomplished it below grade with the blue board. Sort of. The semi permeability of the foam boards is NOT desirable (a BS sales pitch) as it lowers the R value. True, they are not sensitive to moisture, but moisture is a thermal bridge, exactly what you DON’T want. It does help, better than none, and the best things you did were the barrier (I assume bituthane) and drainage.
Now, about drainage and where water is coming from. How high is the water table? What’s under the floor? Assuming the floor is concrete, a LOT of moisture can come up through the floor, then condense on the colder walls. It can also wick up the walls if there’s no capillary break between wall and slab. So all your efforts on the walls will not negate floor moisture infiltration. It may be necessary to add a vapor barrier over the floor, and tie that in to a vapor barrier on the inside of the walls. Now you have a dry environment and can insulate with anything you choose.

I assume you have read the little trick to check out floor moisture: Tape a 12"x12" or larger piece of clear poly, on all 4 edges, down to the floor and observe. If the floor gets wet (changes color) or you get water droplets under it, you have enough moisture coming up to think about addressing it...


Rufus

That works, as long as you do it in several areas and during different times of the year. To me it’s faster and simpler to just assume there’s no vapor barrier in an old house and poly the whole floor. Doesn’t cost much or take long. You also eliminate any radon gas concerns.

> poly the whole floor...

That can be best. But involves work and detailing. Both in putting the poly down _and_ in integrating it with all other construction, floor and wall systems. Some weighing of options, with good info, may be in order provided the data can be had w/out too much cost.

> radon...
I strongly believe it's best to get solid info on the local radon history, risk, before reaching any decisions or making any plans.  Talk with local know-it-alls, building departments, university extensions (if near), contractors, possibly state authorities. There is some serious planning, detailing and work when radon is actually a risk. Also, rules about it. Not something to address as an aside. Too potentially expensive in many ways.

Find out what's there. Then  do what you need to. Again, it must be integrated with other building systems, especially HVAC.


Regards,
Rufus

Very cheap ($20ish) to test for radon without the need to consult local ‘authorities’ who really know nothing about your specific floor/sub grade. People get very worked up about it, when in fact it’s common accepted (by code) procedure to block it with well sealed 10 mil poly. Yes, it’s better to do it during construction, but unless someone has high levels and proof of below-slab pressurization (which IS a serious matter and requires professional help) it isn’t a huge issue. With the time you spend to consult with locals you could have already installed the poly and cured any potential moisture issues as well.

Judith

> [radon - easy DIY; local authority no help]

That is not my take. Except in very sparsely built areas, local authorities and also regional ones, can have knowledge of radon problems, based on history in that area, that any owner should make a point to seek out. Testing oneself is something I would always do - but in the case of something as nasty as radon, getting as much info as possible is warranted.

I am not saying go drop $thousand$ into "professional" services. I am saying this is something a responsible person needs to take seriously and address with full due diligence. It's not that much cost in time/money in view of the potential risks.

If there are any red flags, deciding on what measures, if any, are needed requires some serious research unless you happen to be connected with that particular work area already.  Radon is like CO - it harms people badly w/out any indication at the time it's happening. As I understand, it can happen over a long period before bad health problems occur and people take notice.

It's true that, fortunately, it's not that common. But it's common _enough_. An old unsealed building with radon coming up from the ground may not hurt anybody, because of the "ventilation" which disperses the gas quickly. Seal up that same building and what was a non-issue can become deadly.


Regards,
Rufus

I wasn’t suggesting that local authorities are no help, just that regardless of what they may or, more likely, may not know about your specific house is still no substitute for testing. An area (ie- Colorado) may be known for radon being common. Another area may not. But it shows up everywhere more or less. My house may have it, your house across the street may not. But consulting experts won’t tell me which of our houses has it. They will suggest testing, which we already knew.
And I don’t mean to minimize the dangers of it. I agree it should be taken very seriously. It’s the second leading cause of lung cancer (though WAY smaller numbers) after smoking.

Hi Julie

Yes, for sure nobody can say anything meaningful about a particular building w/out data on that particular site.

But. The local people should know if radon has a record anywhere in their territory in the past 40 years or more, since bureaucracy took up residence. If so, that is an important red flag. At the regional level there may be maps of "risky" areas.

A red flag indicates the need for serious testing. We can check for those flags at minimal cost.

The following is not directed at you Julie, or anybody specific.
So: (even if I preach to the choir - as I hope I do)

I flog doing serious research to encourage people to respect something with risk of BAD consequences and maybe get motivated to _really_ check it out. But, even so, In my personal experience the fabric of "book learning", even by smart  well motivated people, almost always has big holes not noticed until a problem comes up. DIY is basically OnJobTraining - w/out any instructor. Over and over again I have seen people misinterpret, simply not see, forget, wish away, change/substitute unacceptably, rush and begin next phase w/out respecting set-up times... The list goes on and on and on and I have seen this and more real time, close up and personal, on job sites and in simple personal projects. It's the norm, not the exception.

That being my experience, in certain high risk cases I try to push the idea that it's smart and right to talk with people who have a _lot_ of experience and, usually, real knowledge and, often, smarts; this almost always means that person is professionally involved. We need to do this even if they are of abhorrent political persuasion or remind one of their righteous father or older brother or something. Even if they are government. My own experience has been that 90% of these people are decent and try to do their job well and _like_ to help people. I have found that 99% plus are people we can work with if we don't enter the room with an attitude drawn, aimed and cocked...

When screwups or missteps result in pain and anguish and money lost, well OK, lesson learned. But if there is risk of serious permanent damage or death to people, please slow down and take advantage of the due diligence resources we in the "1st World" are fortunate enough to have available for minimal  cost.

The life you save may be your own or somebody your really love.


Rufus