Insulation Method Options for a Basement
captainjman2
| Posted in Energy Efficiency and Durability on
Hello, I’m looking for some ideas on what my best options are to insulate my basement. I bought a house, took the paneling off the stud walls and would like to add some insulation. The issue being not only is the stud wall up but it has a bunch of stuff behind it already.
Ideally, I would like to avoid removing the studs and replacing them in order to add foam boards on the concrete. I was hoping to use some kind of soft insulation between the studs such as mineral wool. The basement wall is 2/3 below grade. At worst, what kind of issues would I run into by not insulating?
Thanks in advance.
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While you wait for others to chime in . . . it would be helpful to add your climate zone and your intentions with the basement space--what will be the function. Also, in case you didn't see this: Three Ways to Insulate a Basement Wall.
The basement will be drywalled with exposed ceilings. Will be an entertainment space. Zone 5b
captainjman2,
Unfortunately you can't use soft insulation in the walls.You need something that will stop the interior air coming in contact with the concrete and condensing. That basically leaves you rigid or spray foam.
As long as nothing changes, what will happen if you don't insulate is probably that things will continue much as they have until now. If you don't currently see any problems, there isn't much reason to believe they will occur down the road.
I assume given the obstacles as seen in the picture, rigid may not be the best solution. I do not currently see any issues, but I do know a warm basement would be nice for the winter.
I am loath to suggest spray foam for anything where it isn't absolutely necessary, but this does look like a situation where you might want to consider it.
Thanks for your help. I had a feeling that would be the answer.
I'm a bit hesitant to write this, but we'll see: We're designing a new build in western Colorado, zone 6b. When I talked to builders about basement insulation, they consistently told me they just frame the walls and put in fiberglass batts. I discucssed with them that this conflicted with everything I was seeing as 'best practice' or even 'required practice', but I talked to several builders and the residential construction lead with the Valley's energy conservation center and they _all_ said they'd never seen an issue, with a new build or in remodels, with just framing and insulation (no rigid foam). It's possible -even likely - some of these walls included water barriers (poly or whatever), but certainly not as a routine practice. When I calculated the dew point for our winter RH levels, it was easy to see that the typically very low humidity (like 15%) meant only the exposed parts of walls were likely to ever be at or near dew point. Any part of the wall at or near frost line would remain above dew point almost all of the time. I'm still going to use a layer of rigid foam in our build, but my conclusion was that the situation in the arid west is way different than what's typical in the NE or Canada, and that it's worth consulting local builders you trust and carefully looking at your specific situation versus the 'worst case' that IRC has to consider.
johngfc,
I agree. The answers we give to questions here on GBA have by necessity to be generic and reflect best practices. That means there are lots of regional differences or situations they don't capture.
That said, I'm always wary of solutions that rely on conditions - exterior water management, perfect air-sealing, or maintaining certain levels of indoor humidity - which may not reflect the house in a few years, or with other owners.
I also worry about the advice local builders give - especially older guys like myself. Building science and practice has changed a lot in the past decade or so. Many of us value the experience we have painfully build up, and are resistant to change the way we have always done things - without acknowledging that the reason a lot of these things worked was due to conditions - like low levels of insulation - are no longer features in current builds.
If captainjman2 was proposing using batts on the walls without finishing them it might be worth the experiment. But to gamble with a strategy that might or might not work when the consequences of failure are much higher to me doesn't make much sense.
Malcolm -
I totally agree, thus my hesitancy to post that, and why I'm going with current best practice in our build. Nonetheless, many houses in the arid west are in exceptionally favorable conditions - well drained and dry soils, no subsurface water flows, year-round low precipitation and RH. These houses very rarely experience many of the water-related issues so common on GBA. Depending on your risk tolerance and specific circumstances - and a realistic cost-benefit analysis, preferably including a quantitative analysis - sometimes it's worth listening to the old builders.
I agree that the very low average humidity levels in much of Colorado are likely to make some moisture issues less common. I have family in Aurora (outside of Denver for those who don't know the area), and the basements in their subdivision are all insulated with what I like to call "bagged batts" -- fiberglass batts that are inside a polyethylene bag-like tube. I haven't seen moisture issues with these assemblies, even though the building science info all says there SHOULD be problems. I attribute the lack of problems to the much dryer climate compared to most regions. Many on GBA are used to the Northeastern US, which gets cold and is fairly wet much of the time. Much of southern Canada has similar conditions, and out around Vancouver moisture is a way of life.
Using batts is something that MIGHT work under the right conditions. It's not as safe as rigid foam that, that WILL work under ALL conditions. It's entirely possible that you could potentially have an unsually rainy season in Colorado some year, and then have mold problems. With rigid foam, you don't have to worry about the what ifs.
Bill
Best practices are often reach goals. But avoiding worst practices like basement diapers (or "bagged batts") should be a requirement for every new project. Even if local weather and custom vary.
I do recognize that this is an ideal stance and that the current building market is even more difficult than usual (labor, supply constraints, costs), but still.