Rigid foam interior or exterior of basement?
I live in zone 5 and am planning to start the concrete work next month. Right now I am at or just over budget without factoring in any rigid foam insulation for the basement.
I think I will go with 2″ of XPS under my concrete basement slab. XPS seems to do better in humid conditions (absorb less water, and maintain better R-Value when wet). I know XPS off gasses that reduce the R-Value over time – but I feel comfortable using it over EPS. According to Owens (not sure about DOW) they are claiming to no longer use the bad HFC blowing agent. In my location, there is no local supplier for Type II EPS. They only sell Type I locally. I am looking into finding a Type-II EPS retailer, but so far nobody in a 2 hour radius has it available. Possibly special order *BUT* it would have to be shipped from 100 miles away, while DOW Blue is sold locally and Owens Foamular is sold 70 miles away.
Anywho, if I have the option to get EPS Type II, I am wanting to know if I should use it OR XPS for my foundation walls. This is a walkout basement, meaning 1 wall is completely below grade, 1 wall is half and half, 1 wall is completely exposed, and the other wall is conveniently below grade because the Garage is on that side, so it has dirt beneath it but also less exposure to elements since it is also the garage stem wall.
After deciding between EPS Type II (if available) or XPS, I would like to get an opinion if I am shooting myself in the foot if I decide to *not* install it on the exterior, but instead install it on the interior a few years after the house is built to save on funds. I understand using it on the inside if retrofitting, but if I have the walls completely uncovered on the outside, is it wise to just pony up the extra funds now and install the rigid foam on the exterior three (or 4th garage garage wall)?
Thank you. I appreciate the past help on deciding how & what to use for rigid foam on above grade walls…I didn’t give the basement enough thought before.
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Replies
Nicholas,
From a performance standpoint, either XPS or dense EPS (that is, EPS rated for burial by the EPS manufacturer) will perform well to insulate under a slab or on the exterior of your basement.
To read about the advantages and disadvantages of two different options -- interior basement wall insulation or exterior basement wall insulation -- see this article: How to Insulate a Basement Wall.
I'm not sure about code enforcement in your area, but in Climate Zone 5, basement wall insulation is required, not optional. Leaving any walls uninsulated (whether above-grade walls or below-grade walls) is an example of builder error, and in most jurisdictions it is illegal. So my advice is: you can install basement wall insulation on the interior or the exterior, but you have to install it somewhere. Omitting it is not an option.
According to the local EPS supplier, type I is the 'best bang for the buck' and they only suggested type II in cases of it being driven on or under a slab. So apparently they think Type I is find for foundation walls but I do not like the idea of it being able to take in moisture so easily compared to type II or XPS.
I know our building code in this area is not the latest...so that may be a reason I don't see any builders hurrying to put in rigid foam for basements.
Nicholas,
Everybody's appetite for risk is different. If I were installing EPS on the exterior of a foundation wall, I would go to the trouble of ordering Type II EPS. On the interior, I would use either Type I or Type II.
For more information, see EPS Compressive Strength.
Martin, I was looking at an article that discussed how to detail the exposed foam that is above grade on exterior of foundation walls. It looked like there was a quote in there from you.
First I would like to know if there is any article on here that discusses how to fasten this rigid EPS or XPS to the foundation wall?
Secondly I am wanting to cover the foam that is exposed, and maybe even below grade if it adds benefit. I would like to use a product that is fairly affordable rather than say a complete stucco or brick veneer. I am limited on siding options because I do not want to drill through the foam and into my concrete walls to anchor the siding/hardie board.
Do you have any recommendation on how to detail the rigid foam?
Thanks
Nicholas: make sure you look into reclaimed XPS or EPS. Even after shipping 150 miles,it was way cheaper than new.
Nicholas,
Q. "Is any article on here that discusses how to fasten this rigid EPS or XPS to the foundation wall?"
A. Yes. It's the same article I linked to previously. Here is the link again: How to Insulate a Basement Wall. The article discusses your options for fastening rigid foam to a foundation wall for both options -- exterior insulation and interior insulation.
Sorry I missed clicking that link last time.
The R15 'requirement' for zone 5 must not be a 'requirement' here either by a.) ignorance or b.) not having the most updated code perhaps?
I was only planning on 2" of EPS or XPS on the exterior. 3" to achieve R15 will be troublesome because it means I need to buy 2 layers to achieve 3". I know it will be back-filled on some of the sides but the side it is not covered at all, I would like to fasten without any of the anchors you mention. Is adhesive just not a good option on the exterior side?
I am not really going to be hurting for the lost space in the basement if I install foam only on the interior, but I figured it would be better to insulate the outside walls.
Nicholas,
I strongly urge you to at least meet minimum code requirements. How you fasten the foam on the exterior depends in part on your choice of material to protect the above-grade portion of the insulation.
The moisture uptake of EPS when submerged is primarily into it's interstitial spaces of the macroscopic beads, and even when soaked the R-value hit is about 15%, but that performance is restored when the tide goes out. It dries as quickly as it takes on water.
As XPS ages, releasing it's blowing agent it also takes a 15% hit after a few decades, but that performance hit is permanent.
Owens Corning still uses HFC blowing agents for XPS, (the predominant component of which is still HFC134a) and have not moved over to HFO1234_ _ blowing agents with low to very-low global warming potential. The " The "70% less Global Warming Potential than the blowing agents used before our blowing agent conversion in 2009." claim means that instead of having 200x more climate damage than EPS, they're "only" 60x more damaging. That's 6000% more climate damage than EPS.
The "Zero Ozone Depletion Potential " claim should really read, "We are not in violation of the Montreal Accord, so you can't take us to court to declare our goods contraband, barring sales." Zero ozone depletion blowing agents is not a special green feature they should be commended for- it's a legal requirement that must be met to sell it in most developed countries. (Good for them- they're not actually criminals !! :-) )
Install 2-3" of Type-II EPS under the slab, and put 2" of EPS between the slab edges and the foundation wall. You can then hit R15 whole-wall R performance using 1.5" of EPS or 1" of foil-faced polyiso trapped to the foundation wall by a 2x4 studwall insulated with unfaced (or kraft faced, but not foil faced) R13-R15 batts. At R5+ for the foam you have sufficient dew point margin a the above grade portion of the foundation to avoid condensation issues at the fiber/foam boundary in climate zone 5 using only latex-painted wallboard as the interior side vapor retarder. If you put the studs 24" o.c. and don't have a lot of window/door framing, with cheap Type-I R6 EPS and cheap R13s you'll have a framing fraction low enough to hit R17+ whole-wall performance. At 16' o.c. spacing you'd be at R15+, certainly within code.
If you can't find local sources, you may have a big enough order to rationalize a shipment of used-once, surplus or factory-seconds goods from Nationwide Foam (http://nationwidefoam.com/ ) or Green Insulation Group (http://www.greeninsulationgroup.com/ ). The discounts below virgin stock goods is large (50-75% off!) , so it comes down to the shipping cost, and what they have in stock. Nationwide has multiple distribution depots in various parts of the country, Green Insulation Group is (SFAIK) a New England only type of operation- not sure if they'd ship to zone 5B, but Nationwide will.
Dana, so you are suggesting to use foam on t he interior of the wall. Can you explain what you mean by "2" of EPS between the slab edges and foundation wall." ? My understanding is the footings will be poured first, and then the foundation walls and then the slab. I am not sure if the footing is 4" tall for the floor to set in that, or if the 4" of slab will be butting up against the foundation wall. That must be what you mean, but having 2" of foam as a perimeter all around the slab seems odd and I don't know if I like the idea of that foam 'gap'?
Closer to the build. Going to go with EPS on the outside if i can get type II - otherwise the XPS will be used on my exterior walls and for the slab perimeter. I did want to ask about two things. 1.) Should I just use foam for the parts of the wall in contact with soil, and leave the daylight/walkout parts uninsulated?
and 2.) if I were to insulate the rim joist on the outside with 2" foam...would insulating the inside down the road(sandwiching it) cause moisture problems?
1) The benefit of insulation is even more on the exposed parts. Below grade the soil provides a little insulation in the winter, but above grade the outside of the wall sees the cold air directly.
2) As long as you have a good capillary break at between the top of the foundation and the wood, I see no problem with insulation on both sides.
A note of experience with exterior-applied XPS foam- Back in 1987 I built a home in New Hampshire- climate zone 5, and based on the common wisdom of the time, insulated my foundation on the exterior with XPS foam- 2 layers of 1 1/2" each. Discovered one New Year's Day That the South wall of my kitchen was disintegrating. It had been nearly eaten, consumed, by a sequence of termites and carpenter ants. Yup- they found their way in through the darkness of space between the XPS and the concrete foundation. I will never apply exterior foam on the foundation in contact with the soil again......Creating an unseen highway for the critters to move in and FEAST-on my house.
Thanks James, way to scare me away from foam and alleviate the confusion altogether! :)
Copper Z-flashing over the top of the foam and behind the WRB along with a copper clad plastic (or sheet metal) capillary break between the concrete and foundation sill goes a long way toward discouraging ants & termites.
The 1980s practices did not usually have capillary breaks at both the footing and between the foundation & sill, which leads to higher moisture content in the foundation sill (even if it had a foamy or fiberglass sill gasket). A capillary break at the footing as well as under the foundation sill reduces the humidity in the basement, and keeps direct wicking into the foundation sill well controlled.
Keeping the wood drier and putting some metal between the ground-contact foam and any wood helps quite a bit. Copper is a good choice since the leaching copper is toxic to most wood-boring insects, particularly (but not exclusively) termites.
http://www.h-b.com/index.php?main_page=product_info&products_id=182
http://www.h-b.com/images/submittal/18MITEOUTTERM.pdf
Applying a cemeticious finish material like Quikrete Foam Coating on the foam over it's entire length (not just above grade) would reduce insect penetration & tunneling in the foam too. Put the waterproofing on the concrete rather than the foam.
Dana, are you suggesting something besides the standard foam roll between the top of the concrete foundation and the PT 2x8?
Not too worried about using foam on the inside with the only drawback being how to insulate the stair landing where it makes a turn, because it goes all the way to the concrete wall to meet the rise/run code, and having a 2x4 framed out wall would make the stairs have to be moved at least 4 if not 5" back, messing up the floor plan.
IT is truly unfortunate that PWF, (pressure treated wood) basements are not considered. The greenhouse gas emissions due to making the cement make concrete foundations FAR from GREEN! A PWF basement will cost less than just the concrete and can easily be insulated with mineral wool bats between the studs. A typical 2x8, 16"OC +3/4" plywood insulated with Mineral wool comes in at r25+ and the total thickness is 8 1/2". No concrete is needed for footings with PWF as well drained gravel is all that's needed. Before you dismiss PWF, there are over a million in North America, none has termite problems & they come with a 75 year guarantee.
Jerry, Who guarantees the basement for 75 years?
Malcolm,
I've copied a bit of text from one of the web pages of Chelsa Lumber, a material supplier.
"We’re the area’s leader in wood basements.
Check out our big inventory of .60 pressure-treated materials. Choose from kiln-dried, grade-stamped, and foundation-stamped wood – all guaranteed for 75 years, and with a projected lifespan of 150 years or more. "
duplicate post removed.
I suppose the PT 2x8 Sill Plate will be just fine with a foam roll between it and the foundation, then...if people are using PT for basement walls?