Hi, I live in Quebec (Canada) (not far from Vermont). I have a well insulated and air leaks tight house. The perimeter of the house is approximately 45' X 25'. My foundations were insulated by a R4 factor with expanded polystyrene (that polystyrene was not taped between the seems, at some places it was not tight with the foundation, etc.). The sill joist was insulated with R7 fiberglass. The floor is not insulated. They estimated that I was losing 40.5 gigajoules by the basement. They recommanded to insulated the sill joist by a R 27 factor and the foundation by a R17 factor. But then, I would lose 26.5 gigajoules by the basement, a 16 gigajoules reduction. To me, it seems to underestimate the improvement. First, expanded polystyrene boards with no tape in it's seems and not tightly put with the foundation is almost like not having insulation at all, and 2.5 inches of medium density sprayed polyurethane foam (R17) is a much better product, since there is no seems anymore, it sticks very well with the foundation, etc. Am I right if I think that the Gigajoules saved should be higher than 35% (14 reduction from a 40.5)? Thank you very much for your opinions and toughts! Cheers!

The R-4 EPS is better performing than the R-7 Fiberglass

Posted By Partner24 on 15 Sep 2011 09:54 AM
Hi, I live in Quebec (Canada) (not far from Vermont). I have a well insulated and air leaks tight house. The perimeter of the house is approximately 45' X 25'. My foundations were insulated by a R4 factor with expanded polystyrene (that polystyrene was not taped between the seems, at some places it was not tight with the foundation, etc.). The sill joist was insulated with R7 fiberglass. The floor is not insulated. They estimated that I was losing 40.5 gigajoules by the basement. They recommanded to insulated the sill joist by a R 27 factor and the foundation by a R17 factor. But then, I would lose 26.5 gigajoules by the basement, a 16 gigajoules reduction. To me, it seems to underestimate the improvement. First, expanded polystyrene boards with no tape in it's seems and not tightly put with the foundation is almost like not having insulation at all, and 2.5 inches of medium density sprayed polyurethane foam (R17) is a much better product, since there is no seems anymore, it sticks very well with the foundation, etc. Am I right if I think that the Gigajoules saved should be higher than 35% (14 reduction from a 40.5)? Thank you very much for your opinions and toughts! Cheers!

Unless there are huge top & bottom ventilation gaps, the fact that it's not tight to the foundation doesn't mean it's not still working.  If the foam is on the exterior and below-grade it's working to better than R4 in winter. (R4 EPS is rated at a median temperature of 75F, but EPS will be closer to R4.5 with a median temp of 32F/0C)  It's average performance over the whole wall will only be severely degraded if there are actual gaps between adjacent sheets that are more than 10% of the total surface area.  Even if it's VERY rough you're likely to be getting at least R3.5 out of it.

To be sure R17 of spray foam will be a huge improvement over R4 of poorly applied EPS.

Whether R4 outperforms R7 fiberglass depends a lot on the actual application, density of the f.g., the air-tightness of both surfaces, the temperature of operation, etc.  Apples to apples, R7 of 1.8lbs Optima will outperform R4 EPS 2:1 on a 120F roof, assuming both are installed between rafters, with the same thermal bridging.  But an R7 econobatt stapled into a 2x4 cavity will dramatically underperform unbroken R4 EPS over sheathing under almost any conditions.  I'm not sure how that's relevant to this discussion here though.

To be sure R17 of spray foam will be a huge improvement over R4 of poorly applied EPS.

Well, that's the big question here. They think that with insulating the entire foundation with 2.5 inches of medium density polyurethane foam and the sill joist with 4.5 inches, you only have a 35% heat loss reduction from the basement, wich frankly seems low to me. What do you think about that 35% estimate?

Going from R4 to (4-17=) R21 will reduce the heat loss out of the walls by more than 35%. But at that point the heat loss out an uninsulated floor slab will probably be larger than at the walls.

See the discussions & graphs starting on page 10 of this document:

http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis

Thank you Dana. From that chart, the +/- 35% is confirmed. It's disapointing, but it makes sense.

I guess the foundations are one of the tougher ($$$) place to reduce % of heat losses significantly, unlike air leaks (caulking) and attic (fiberglass batts, blown cellulose, etc.). And from what I've seen, the total heat losses from a basement can be very significant.

Cheers!

Insulating the floor slab after the fact gets to be pretty expensive(!). But in cold climates the subsoil temperatures are much warmer than the wintertime outdoor temperatures, and even though reducing percentage of foundation heat loss is expensive, the heat loss out an insulated basement (even R4) is usually less than 25% of the heat loss from the whole building. Basements have fewer and smaller windows. Basements that have NO insulation can have quite large heat loss though. There is usually a reasonable economic return to increasing R4 to something more than R10, even R20 if done using less expensive methods:

In the parts of Quebec near Vermont, adding 2" of EPS or 1.5-2" XPS (seal the seams) and a 2x4 studwall with unfaced rock-wool batts on the interior (and no interior poly) would have about the same performance as R17 of spray foam, usually or less cost. If the inspectors demand a poly vapor barrier, put it between the rigid foam and the studs. See the analysis of case 4 and case 8 in that document. You would still need to use spray foam on the band joist & foundation sill though.

Regarding the foundation insulation options in my climate, if one wants to insulate from the inside, there is the R value of a material, but there is other very important elements to consider. One of them is the mold creation barrier. EPS is not a vapor barrier, neither a vapor retardant. So the water vapor can condensate on the foundation, get trap there and create mold. It's even worse if there is some air gaps between the EPS and the foundation. As far as I know, you have 100 x more water vapor that comes from air than by going through not vapor retardant materials. A vapor barrier might help, but it would need to be applicated everywhere (difficult to do) and the foundation will then only be able to dry to the outside.

Since XPS is a vapor retardant, it helps for the vapor that comes through materials, but not air, so if someone install this, be sure to put it very tightly to the foundation wall.

The additional $ for medium density polyurethane foam are worth help you sleep at nights, since after 1.5 inches it is a vapor retardant and you can be sure that it stick very well to the foundation and there is no air gaps that could create mold.

Just imagine the cost of insulating with a so so material and so so applied by a hurried contractor, finish your basement, having mold, be forced to demolish your finished basement, pay for decontamination, reinsulate and refinish your basement. You would thing that the few hundred dollars saved initially would have been a very penny wise, dollar stupid decision.

If someone insulate from the outside, it is a different story. The foundation will then be nearly at room temperature and condensation risk is very very low.

Mold in the basement is still a very unknown problem for most of the population, but some say that it will be the asbestos of the 21th century and I would not be surprised by that. But that's another topic.

Cheers!

How could you get mold on a surface that isn't organic? Neither concrete nor EPS is organic, therefore there's nothing to decompose and create mold. Moisture and an organic material is necessary for mold growth. Now I guess if you're trapping a wood product between the EPS and the concrete, you could run into the situation you're discussing.

I am new in real estate business i don't understand of this wait next person i hope will be better answer.

we buy houses cash

At 2" mid-density (Type-II) EPS is a class-III vapor retarder, at 4" it's class-II vapor retarder. XPS becomes a class-II vapor retarder at 2", but is only class-III at thinner layers.

But if the foam is the condensing surface (as it is here), the issue then becomes whether it has sufficient R-value relative to the fiber in the studwall on the above grade portion to keep the studs from accumulating winter moisture in that climate, and it clearly does. Even if the condensing surface were plywood with the EPS on the exterior, 2" (R8) would be sufficient to protect the sheathing, given that the climate there is essentially cool edge of US climate zone 6:

http://www.buildingscience.com/documents/guides-and-manuals/irc-faqs/irc-faq-insulating-sheathing-vapor-retarder-requirements/

With the R4 of existing EPS on the exterior, and the ~R0.5 of concrete, the R value to the exterior of the studs with 2" of interior EPS would be about R12.5, which means even in zones 7-8 (much cooler than southern Quebec) even wood sheathing would be protected. But the ~ R3 studs stay even warmer than the center-cavity EPS, and literally NEVER fall below the dew point of the interior air.

That assembly in this location does NOT need an interior vapor retarder of any kind to protect the studs, and it has no susceptible sheathing, so keeping it vapor-open toward the inteior provides the best overall drying capacity for ground moisture wicking up from the footing, protecting both the studs and the foundation sill.

If block drying toward the interior with a low-perm foam, it raises the moisture content of the concrete, putting the foundation-sill at risk. But if you have a good sill gasket between the concrete and foundation sill that's fine. If you take the studwall approach (or any studwall resting on a slab, even a partition wall) put sill gasket as a capillary break there too.

I could bet ten of thousands of dollars that mold can grow on concrete. I'm 100% sure about that. The problem with rigid polystyrene boards, even when they are vapor retarder classified, is not the material itself. The theory is perfectly fine with the material itself. That's not where the biggest problem is. It's the application of it on the foundation. No foundation is perfectly square, so it's difficult to apply it tightly on all the foundation surface. That leaves a gap where warm air can go, (no matter what the vapor resistance classification of the material itself), condensate on the cold foundation wall, get trapped and create mold. That's one of the big issues. I would advice the people who live in cold climate to be very cautious about how it will be applied. Not all contractors and their employees are aware about that, and even if some of them are, they are often in a hurry to finish the job to go to another one and it's a long term problem that will not be visible for years (or even decades) to come. So be really careful about that if you use these materials in order to save. Be sure that no air can go between the insulation material and the foundation. That's the huge difference with polyurethane sprayed foam. Set aside the R value/inch, it's a sprayed, sticky and expanding foam material that will be evenly and tightly applied on all the surface of the foundation where it will be sprayed, so you'll have no gap between the foundation and the insulation material, so significantly less risk of condensation, long term health, legal and costs. I might sound like a polyurethane promoter, but I'm not. Another way of preventing mold is to insulate from the outside with these polystyrene boards, and I even like it better than insulating from the outside since your foundation will not be submitted to frost and it provides a drainage board to rain water. The only big problem that I see with it is cost when it is retrofitted (excavation on all the house perimeter), but if the house is new, that's a very interesting option.

EPS is in fact vapor retardent, even without facers, and sealing the seams/edges with 1-part foam or mastic would prevent convection loops. At 1" (R4), EPS is between 2 and 6 perms, depending on density. At 2" that becomes ~1-3 perms, and at 4", ~0.5-1.5 perms, again all dependent on density, not facers. (Even low-density Type-I EPS is ~1.5 perms max @ 4".)

It's pretty standard to seal the foundation sill & band joist to the rigid-foam & top late of the studwall all in one shot.

But if you prefer a closed cell spray foam solution, R8 (half the volume of your proposed R17) at would be more than enough to allow the rest of the R to be done as an unfaced fiber insulated studwall. R13 batts in a studwall with very few or no window & door openings delivers about R11 with thermal bridging calculated in, so you'd be adding a true R19 rather than R17.

At R8 most closed cell foam will be about 1 US perm, but with Icynene MD-R-200 it would be a bit over 2 perms. At R17 that foam is still a bit over 1 perm, but other 2lb closed cell foams would be ~0.5 perms, maybe a bit less. Ideally it would be more than 1-perm on the interior to allow the foundation to dry toward the interior. Above grade it has plenty of capacity to dry toward the exterior, so if air-tight even 5 perms of openess to the interior would not create a buildup of moisture in the concrete.

On new construction it's easier (and sometimes cheaper) to insulate the foundation using insulating concrete forms (ICFs). These are usually made of type-II or denser EPS, and since the concrete is poured between the EPS layers there are no air-gap concerned. The minimum R-value for ICF is about R16, but R20s are pretty common, and more than enough R for a foundation wall in southern Quebec. The cost per R of EPS as rigid-board is usually about $1.00/R per square meter- a bit more when done as ICF (but not 1.5x as much.) The $/R for closed cell foam tends to be about $1.70/R per square meter which gets to be quite expensive.

I agree that mold can grow on concrete, but it's not the concrete that is supporting mold growth. It definitely needs something organic. This is from Wiki:

"Like all fungi, molds derive energy not through photosynthesis but from the organic matter in which they live. Typically, molds secrete hydrolytic enzymes, mainly from the hyphal tips. These enzymes degrade complex biopolymers such as starch, cellulose and lignin into simpler substances which can be absorbed by the hyphae. In this way, molds play a major role in causing decomposition of organic material, enabling the recycling of nutrients throughout ecosystems."

Now if you have dusty, dirty concrete walls that have moisture issues, mold might take to that. Also, efflorescence is common among moisture prone concrete. That white substance looks a lot like mold.

Dana, well it might be less obvious that you think. I agree that by sealing the bottom and the top of polystyrene boards, it can reduce the convection looping and condensation risk significantly. But I wonder if people in the construction and inspection industry are aware of that. Not so sure about that, at least not here in Canada.

Jeepster, as for mold on concrete, I can assure you that it can live very well on it...and deeper than I could have tought! Whatever what Wikipedia write, I can assure you that toxic molds can live between a expanded polystyrene board and concrete...and in the end it will live in the concrete and it might get into the air of the home enough for an expert to say "Well, your basement has to go back to Go, then decontaminate it, then reinsulate it properly, then test if everything is fine, then finish your basement, then after some time test once again to be sure that the source of mold is gone".

Can you imagine the cost of that?!

I cannot say how much it is important to insulate your basement with proper material and in a proper way. If people in the green industry do not realize that enough, then mold might give them a significant obstacle to their ecological dreams for a very long time (but the mold remediation industry will be very happy and grateful).

I'll repeat it once again for people who live in a cold climate like me (I don't know about other types of climate, so I'll stick with what I know):

- If you find expanded polystyrene on a foundation in a cold climate, be careful. Before buying a house that has that, be sure to test further for mold before buying. If it has extruded polystyrene, a thermographic analysis might be enough just to be sure that you don't have that convection loop problem that can create mold. I write "might" because it is a guess, but mold experts veterans could put more light to that. 

- If you plan to finish your basement and insulate from the inside, closed cell polyurethane foam (with enough thickness) is the best solution to sleep the better at nights. If you want to save few $ with other materials, be very careful about the details of it's application on your foundations.

- If you build a new home, consider to insulate your foundations from the outside while your at it. It has many advantages over the inside option. A good basement insulation is dollars wisely and carefuly invested over the short, mid and long terms. You're second bathroom can wait.

Regarding the foundation drying issue that Dana has raised, I agree. Part of the solution is to have an enough part of your foundations walls over the soil grade. Here where I live, they say 6 inches minimum, but I don't know that particular part of the science enough. Anyway, my foundations are above soil enough and do not have a significant contact with water both from rain and groundwater, so it is not an issue.

Rule number one with basement insulation: don't be penny wise, dollar stupid.
Rule number two with basement insulation: don't forget rule number one.

Cheers!