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Melting EPS Foam with EIFS Synthetic Stucco

airfix | Posted in General Questions on

Our EIFS synthetic stucco has been loosing its flatness.  See the attached pictures.  It has now happened 2 summers in a row.  the same thing happened last year and the the subcontractor fixed it has his expense thinking it was an application defect.

This year it has happened again in the same spot.  My General and Sub contractor are telling me the sun is being reflected off the 2 windows (shown in the second picture) and concentrating the sun enough that the EPS is melting.  It seems plausible considering you can see a flat spot between the two deformed areas which I assume is where the header is.

Our EIFS is one of the Masterwall systems and I think IIRC we have 4.5″ of EPS foam.

Have you heard of this before?
Any suggested solutions?
Can you get foam with a higher melting point?
I thought about putting shutters on the outside of those windows to stop the suns reflection but that will change the look of that wall but clearly better than damaged EIFS.

I’m going to put a thermal camera on the area this afternoon to see what kind of temperatures we are getting.

Thanks for the help.


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  1. GBA Editor
    Kiley Jacques | | #1

    Hi Steve,

    I wonder if you can tell readers about the rest of the assembly? It could be a water management problem--although it would likely show up elsewhere too, unless that corner is more susceptible for some reason. Whatever the case, knowing the other layers would be helpful. Also, read through this Q&A thread to get a fuller sense of the issues related to EIFS.

  2. Expert Member
    Akos | | #2

    Windows melting vinyl siding happens often enough. Low-e windows especially if they are slightly concave from the gas fill can easily concentrate enough sun over a darker surface to melt the EPS underneath.

    You can replace the glass with units that have less reflective coating, add shading or shutters. Replacing the EPS with rigid mineral wool can also work but you could still damage the surface coating from the heat eventually. Best is to fix the source of the heat.

  3. airfix | | #3

    Kiley, The assembly as I can remember it, from inside to outside is:

    1) sheetrock
    2) 2x6 stud cavity with BIBS blown in fluffy insulation.
    3) OSB
    4) Masterwall paint on water barrier barrier
    5) Masterwall adhesive per the EIFS system
    6) 4.5 inches of EPS. I forget the density but it was a required by Masterwall.
    7) Masterwall Eifs finish coating.

    I'm in climate zone 6b I think. New construction that finished this time last year. I spent a lot of time researching the EIFS systems and I have a certificate from Masterwall that states my installation is per their requirements.

    Akos, good info. I'm surprised it gets hot enough. EPS apparently melts above 200C?

    I'm about to go look at the temperature readings in a minute.

    Shutters might be the easiest option. I'm not sure what the glass ratings are but I'll look them up. I'm worried that replacing the glass still may not fix the issue.


    1. Expert Member
      Akos | | #6

      EPS is nowhere near 200C. One data sheet I found puts the melting point at 180F.

      Seems to be a common enough problem:

  4. thegiz | | #4

    Amateur opinion but couldn’t you make an additional layer or a thicker coat of finishing that can protect the eps? Sounds like your finishing coat is not strong enough to protect the eps in this particular setup

    1. Expert Member
      BILL WICHERS | | #5

      Presumably. A rainscreen gap would also help with cooling, especially if it was vented at both the bottom and the top. Convection currents through a rainscreen gap will do a lot to limit the temperatures of whatever is "behind" the gap.


      1. creativedestruction | | #7

        A rainscreen gap would also unfortunately negate much of the insulation value of the EIFS. Instead, most (all?) installations these days are water-managed with drainage grooves troweled on to the substrate. EIFS coatings are applied directly to the EPS.

        1. jason_v | | #31

          This is an absurd comment.

  5. thegiz | | #8

    Just out of curiosity how does it negate much of the insulation value? How thick is the final coating?With 4.5 inches of eps you could toss the extra r value of coating and not have your wall melt

    1. creativedestruction | | #9

      EIFS is a system. The coatings have to be applied directly to the EPS foam, so any rainscreen air gap for ventilation would have to be behind the EPS. If air flow is happening behind the EPS, then heat exchange is also happening at a rate faster than would occur with only the troweled drainage grooves. How much loss in performance depends on how much air flow.

      Joe estimates 5% loss in R value for an 1/8" gap:

      1. airfix | | #11

        Jason S,

        Thanks for replying to these comments. I was going to reply with similar information. Eifs is a system not to be messed with. I just can't see a rain screen gap being feasible.

    2. Expert Member
      Deleted | | #17


  6. thegiz | | #10

    I was thinking it was just a retrofit, the rain gap would be in front and also work as a veneer, I guess it doesn’t work that way. I wonder how real stucco would perform, although that wouldn’t be green it wouldn’t change the look of the wall.

  7. airfix | | #12

    I measured the surface temperature yesterday afternoon in an obscured sunlight. It was 125°F.

    The sun was obscured by a thin layer of clouds so I can see in direct sunlight the temperatures bring much higher.

    We did the EIFS system in this location because it was on the back of the house as a lower cost option than using the Boral siding (with poliso foam and rain screen gap) we used everywhere else.

    The only solution I can think of (except putting shutters on our windows) is to replace that surface with siding. I'll have to find out the melting temperature of polyiso foam, which I'm sure will be higher than eps.

    I wonder if this will be covered by home insurance?

    So much for our cost savings.


  8. Aaron_P2 | | #13

    I think I had a similar thought to Hammer of building a shading wall out of the same material as your soffits. This likely would want to be independent from the EIFS so there aren't penetrations voiding the warranty. (see blue option)I think this would look nice, but another option without shutters would be to put a louvered solar shade above the windows. (see green option) It would require figuring out the right size based on time of day/year for worst case. (could be as simple testing with a piece of cardboard, but could also be done digitally).

    1. airfix | | #14

      Those are good options. I had been thinking of the 'eyebrow' shades.

      The shade wall is an interesting idea. I'd want to avoid blocking sunlight from coming into the kitchen windows though and it would need to be far enough away to allow the window to open.

      I had thought about using vegetation (large tree) but I don't think I can get it high enough to shade the summer sun.

      I need to do some more thinking about it.


  9. jackofalltrades777 | | #15

    What kind of windows are those and what is the SHGC of them?

    I have synthetic stucco (StuccoMax) on my house wall and the temps get up to 140F+ in direct sunlight and never had any melting issues with the EPS.

    1. airfix | | #18

      Those are Windsor Pinnacle series with a Dual Low E coating. Per their quote they are U 0.3, SHGC 0.23, and VT .51

  10. thegiz | | #16

    Not sure if what Im reading is true but would a lighter color actually make a difference? Looks like a dark grey, I read this online, I don't know if this is true for all energy savings:

    "While installing items that shade your home such as awnings, or planting trees will also help keep your energy costs down, painting your home a light color can definitely make a difference. Studies show that white paint gains up to 35 percent less heat than darker colored walls, which could add up to a pretty significant savings throughout the year."

    1. airfix | | #19


      Yes I am aware that a lighter colored house would definitely help in the summer months. However the inside of the house doesn't get terribly hot for more than a few weeks a year (we're at 7000ft elevation). The house was designed for the heating months which dark walls should help with.

      Either way the color was not really chosen because of it's thermal absorbtion properties more to do with the style of house and color scheme me and the wife were looking for.


  11. airfix | | #20

    Well I had a cloud less day yesterday with air temperatures not that high only up to about 75F. We have days above 80F here. It's amazing how hot the EIFS is getting. 211F was the highest I measured at around 6pm.

    See the thermal images.

  12. airfix | | #21

    Does anybody have experience with this product:

    It seems the Low E windows are exacerbating the problem. If I put a coating on the windows to reduce their reflectiveness I'm then bringing all that heat into the house which is what I was trying to avoid with the LowE coatings.

    Shading or eyebrows seems like the best way forward but I can't really see a good aesthetic solution.


    1. Expert Member
      BILL WICHERS | | #22

      I don't think you can put a non-reflective coating on the window that will cancel out the Low-E coating. The Low-E coatings work by selectively passing or reflecting certain wavelengths of light. A new coating in front of the Low-E coating isn't going to change that.

      I can offer you an alternative though... If you think the reflection from the window is the problem, trying angling the window in the wall just a little bit -- just enough to move the reflection to somewhere else where it won't be a problem (if possible). If there is a good distance between the window and the trouble spot, it will take only a very small angle change on the window to move the reflection a good distance. This way you can potentially solve your problem with the reflection without messing up the appearance of your house.


      1. airfix | | #25

        That's a good suggestion Zephyr7 thank you. The angles of adjustment as you mention will be small. It would mean a lot of really difficult work though. I'd have to expose both window flanges thus requiring re-application of the EIFS on the window wall as well as the damaged wall.

        I'd also have to pull up my sheetrock from inside to shim the windows at an angle.

        Good input though. Thanks.

  13. thegiz | | #23

    As another thought you mentioned you could get a tree but are worried about how fast it would grow. What does the landscape look like. I'm not sure what climate zone you are in but there are trees that grow several feet a year. You might be able to get some 8-12 footers in there without spending too much and they grow several feet per year. Here are some examples, again don't know your climate zone and how trees grow there. Might take a year or so to get to the height you want but you could use shutters or shades temporarily while they grow and then remove them later for the look you want. Probably be the greenest solution to plant trees and with right choice could improve landscape.

    1. Expert Member
      BILL WICHERS | | #24

      Maybe we've finally found a useful application for kudzu -- that stuff grows like crazy! ;-)

      I like the tree idea, but it might be tricky to get that positioned so that it works throughout the day. An arbor or pergola with a vine on it might work a little better.


  14. airfix | | #26

    Regarding another coating on the outside of the window I appreciate that input and how it probably won't work because of how LowE coatings are done.

    I actually like the idea of putting an external screen on the windows (like an external bug screen). One that I can remove during the winter months and install during the summer months:

    These guys make a solar screen that can clip onto the outside of your windows. If I get a dark color screen it will absorb rather than reflect the light.

    Also I heard from Masterwall. They do a type of EIFS using Polyiso. Maybe I'll use the screens and then replace that wall with their Polyiso system:

    Polyiso seems to have a melting point above 300F.

    I might do a combination of both the polyiso EIFS and the screens.

    Due to the tightness of my back yard I don't have the space to put up big trees but I do agree this would be the slickest solution (if it were possible).


    1. thegiz | | #28

      There are trees that are very narrow and shoot straight up. Several can be planted in a row to create a natural hedge shade, I have used them in a tight yard more for privacy than shade. Of course most can be pruned to be narrow. Like a juniper skyrocket is about 2-3ft wide and shoots up to 20feet.

    2. Expert Member
      KOHTA UENO | | #29

      Reading this thread, the exterior screens were the first thing that sprang to mind. If the problem is fundamentally the reflection of the window (and concentration of sunlight) onto the wall, an exterior shading screen would tend to 'diffuse' this reflection. They are a very common, off-the-shelf solution in cooling/solar gain dominated climates. For instance, in Phoenix, the utility offers a rebate for adding them to windows.

  15. Expert Member
    BILL WICHERS | | #27

    Steve, you could try a diffuser on the window to prevent a direct reflection. Think something that is like hammered class, or a frosty-type look. The downside is that you won't be able to see out the window clearly anymore. A diffuser will act to break up the reflected light so that there is no concentrated, direct reflection. You could potentially build a storm window out of hammered glass and only put it in when needed, similar to a screen.

    If you use a screen, you can easily calculated how much energy it will block. Find the open aperature of the screen (usually given as a percentage). If it's 80% open, then it will pass only 64% of the energy compared to the window alone. Why 64%? Because the reflection has to pass through the screen TWICE, so you take 80% of 80%, giving 64% remaining. If you need more than that, look at "shade cloth" at a greenhouse supply place. Shade cloth is commonly used on greenhouses to reduce light levels when and where needed.


  16. Expert Member
    Akos | | #30

    Your problem stems from the low SHGC of your windows. With these coatings, any heat that is not going through the window into your house gets reflected which is causing the issues.

    There are low-e coatings with much higher SHGC, swapping the glass for one one these along with a higher temperature foam under the EIFS should fix your problems.

    Fixing the EIFS is not cheap as you have do re-do a good section of that wall, I think a simpler alternative is to mount a wood trellis over the affected section.

    I would go with a more modern look to match the house, a horizontal slatted design with the same wood and stain as your soffits should look great.

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