Dow Styrofoam SIS

[Tim Uhler]

I saw an ad in JLC this month with this product http://www.dow.com/PublishedLiteratu...romPage=GetDoc and was wondering if anyone had any experience with it.

Or anything to say about it, the concept, etc.

I was thinking of sending out flyers to the 3 main developments that we've built in over the last 20-25 years (before I was pushing a broom) to encourage homeowners to consider residing their homes.

I saw this ad and thought, maybe that would be a worthy upgrade considering that many of these homes have let in bracing and that's it, and 2x4 construction, so this would maybe be a decent upgrade

1) to increase wall bracing
2) efficiency of the home
3) lead to window replacement at the same time

I don't know, but we are getting slow and I'm thinking that this might be a decent avenue to approach to keep busy (enough).

Any thoughts from the building science standpoint?

[Pete Engle]

Re: Dow Styrofoam SIS

With 2x4 construction, adding an inch of foam on the outside will increase the effective R-value by about 50%. That might be a strong selling point. In general, exterior foam is a pretty good idea, and in your climate, 1" ought to work pretty well. Taped and detailed properly, and it also gives you an additional drainage plane, and that's also a good point, especially in a wet climate.

Can you sell it? Hard to tell. Foam, siding & windows is a pretty big nut for most homeowners. Everybody's slow right now because most owners either have no extra $$, or the ones that do are hanging onto it just in case.

People who are really motivated to save energy will probably want a thorough audit and testing to show them where to improve, how to do it, and how much they'll save. Telling them, "you'll save a whole lotta money" might not do it.

Maybe you can look around for an energy auditor who needs good contractors to work with.

[Tim Uhler]

Re: Dow Styrofoam SIS

With 2x4 construction, adding an inch of foam on the outside will increase the effective R-value by about 50%. That might be a strong selling point. In general, exterior foam is a pretty good idea, and in your climate, 1" ought to work pretty well. Taped and detailed properly, and it also gives you an additional drainage plane, and that's also a good point, especially in a wet climate.

Can you sell it? Hard to tell. Foam, siding & windows is a pretty big nut for most homeowners. Everybody's slow right now because most owners either have no extra $$, or the ones that do are hanging onto it just in case.

People who are really motivated to save energy will probably want a thorough audit and testing to show them where to improve, how to do it, and how much they'll save. Telling them, "you'll save a whole lotta money" might not do it.

Maybe you can look around for an energy auditor who needs good contractors to work with.

Pete,

Thanks for posting. I do appreciate it. Mostly I want to go into siding restoration (not resides according to Mark ;-)) because I think that is easier for me to go into.

Part of it is that we are slow, but when things start to pickup, likely we'll be at the front of that for a few reasons. One is that this area has a lot going for it in terms of future growth, two there isn't going to be anyone left to build and we are positioned to ride this out and we have quite a bit of land bought at good prices before the run up and we do a good job.

So in between the project we are finishing and the next one we don't have and I don't see us getting something in the next two weeks, I need to redirect a little.

I'm not expecting people to really make some major changes, but would like to be able to offer it. In addition my father is an energy guy who used to work for the city of Tacoma, worked on the energy codes and once upon a time worked with Joe Lstiburek (sp?). So he could do the energy audit.

In other words, there are lots of good reasons for me to attempt this, and for us as a home building company, this product seems like a good selling point considering we aren't adding much in the way of labor (which is offset by not installing housewrap).

I'm kind of going "stream of conscious" so this post may not make that much sense :-)

[Ted S.]

Re: Dow Styrofoam SIS

Tim,

One thing that comes to mind after reading the literature is that you may be able to offer the same or better end product with standard rigid extruded polystyrene?

These homes you built, you say they have let in bracing, they have no plywood or OSB sheathing? My point is they obviously have some lateral support whether let-in bracing or sheathing, why can't you just strip the existing siding, add rigid insulation and reside? I would think that cheaper than this product.

I have never seen this Styrofoam SIS before, looks like they have begun to finally offer a truly thermally efficient structural sheathing. I wonder how you cut it, it has a thin layer of laminate?

All in all, it looks like a good product, probably a premium cost to standard XPS, looks like it may be a full vapor barrier, something to consider when doing an exterior insulation retrofit in your climate.

[Pete Engle]

Re: Dow Styrofoam SIS

I can't find any technical info on Dow's site on the SIS. Granted, I didn't look very hard, but I'd need to know the actual shear values, fastener schedules, etc before I could really tell how "structural" it is. However, if we take their word for it that it is roughly as strong as OSB, that's not too bad.

If the houses you are targeting are 20+ years old, chances are that the let-in bracing does not meet current seismic bracing requirements. This could be an additional selling point. WA is an active seismic zone, and properly done, adding structural panels to the walls will make them substantially stronger for both earthquakes and windstorms.

I expect that the vapor permeability is rather low, but again, I couldnt' find the data. I would take a look at your minimum winter design temperatures before using this to see if the low permeability might cause condensation. If your average winter lows aren't much below freezing, you'll probably be OK.

[Tim Uhler]

Re: Dow Styrofoam SIS

Ted,

The homes we build are fully sheathed. I was talking about the homes built during the 80's that would be part of the market I would target to over siding restoration.


Pete,

That is one thing too that I've been thinking about. We don't spend much time at all below freezing. I think the avg temp here between dec and march is down to mid 30's as an avg low.

Hopefully I'll find out pricing today.

[Dick Seibert]

Re: Dow Styrofoam SIS

Tim:

I understand what you are trying to do during the downturn in new housing but you've got several issues going on here, I don't see technical information so I'd contact them and get as much as you can, including all ES Reports. I would then go into the AHJ with the information, as I understand it you are in the same seismic zone we are, are they going to require an engineer's stamp for structural? Even though the older homes are now braced to yesterday's requirements doesn't mean that the AHJ is going to accept a job to the extent you are proposing without structural engineering.

From you pictures it appears that you build in wooded areas subject to wildfires, even in our cities foams aren't allowed on the exterior without fireproofing, when used here they require covering the foam with 5/8" Denshield or a similar gypsum fireproofing product.

The code requires an approved WRB, their literature suggests that you don't need it, I find that highly problematic.

To summarize:
1) You live in a difficult seismic area, look at engineering requirements.
2) You live in an area subjecet to wildfires, look at the fire marshal's requirements.
3) You live in about the rainiest spot in the entire world, look at waterproofing requirements.

[Tim Uhler]

Re: Dow Styrofoam SIS

Tim:

I understand what you are trying to do during the downturn in new housing but you've got several issues going on here, I don't see technical information so I'd contact them and get as much as you can, including all ES Reports. I would then go into the AHJ with the information, as I understand it you are in the same seismic zone we are, are they going to require an engineer's stamp for structural? Even though the older homes are now braced to yesterday's requirements doesn't mean that the AHJ is going to accept a job to the extent you are proposing without structural engineering.

From you pictures it appears that you build in wooded areas subject to wildfires, even in our cities foams aren't allowed on the exterior without fireproofing, when used here they require covering the foam with 5/8" Denshield or a similar gypsum fireproofing product.

The code requires an approved WRB, their literature suggests that you don't need it, I find that highly problematic.

To summarize:
1) You live in a difficult seismic area, look at engineering requirements.
2) You live in an area subjecet to wildfires, look at the fire marshal's requirements.
3) You live in about the rainiest spot in the entire world, look at waterproofing requirements.

Dick,

We don't live in an area prone to wildfires. But we do have forest. I have our PE looking into the product and over this product we'd have fiber cement in most cases.

I'm just thinking out loud on this, so I appreciate your comments.

[ThingOfBeauty]

Re: Dow Styrofoam SIS

I've been looking into this stuff. To get similar shear value as osb, you nail it 3" oc on edges and 6" in the field.
It's a layer of therm-a-cardboard with a layer of polyiso (r-max) type foam and a layer of foil facing like Rmax. I talked with the engineer who invented/developed it at Dow and he said even though the nail heads don't hit the cardboard, you use so many it holds.
The foam absorbs little water and they want you to use a special 2-7/8" tape that covers the seams and the nail holes on the edges. The other nail holes don't absorb much water.
Windows and adjoining roof flashing are taped with the Dow tape as well, at the end of the day that tape is holding out the water if you don't add a separate WRB to the whole assembly. I haven't fully bought in to this though the engineer said the tape was God's gift, apparently it has three times the adhesive as normal tape and has been tested in every way know to humankind. Will it last as long as shingled WRB material...? you pay your money, you take your chances.
SIS is more than regular foam board so I was thinking what Ted S. posted, why not just use regular foam board. You give up shear strength but save money.
The permeance is very low. But the foam raises the dew point on the inside face. They say it works out. In a warmer climate like yours it doesn't raise the alarm bells as in a colder place.
At the end of the day I would expect your re-sided houses using SIS to be stronger and warmer, and less vulnerable to water than they are now with no sheathing...whether they're as good as they could be, I'd say not quite...whether they're good enough...well, you pay your money and you take your chances.
For us, in this climate, on new work, I'm not convinced SIS is the right stuff.

[Dick Seibert]

Re: Dow Styrofoam SIS

Tim:

This is how they are doing it here. I can't believe with all those fir or pine trees in your pictures that the fire marchals will allow unprotected foam on buildings, fire people are going around the country giving lectures on the evils of foam.

[Mark Parlee]

Re: Dow Styrofoam SIS

It is a polyiso foam and ants seem to love the stuff.
Add the boracare treatment to the deal and you have a complete package

[Ted S.]

Re: Dow Styrofoam SIS

I think I'd need to get my hands on a sheet of this stuff before I had any really definite comments. But anyway, from the general description I can tell you this:

I was never a fan of polyiso in moist areas. That would concern me as it is more absorptive than both EPS and XPS. Even through paper faced polyiso was use in roofs probably since I was born, it still concerns me. Also, rigid insulation forms oxidation and when that happens is very hard to adhere membranes too, we had a terrible problem trying to use XPS as an air barrier several years ago, no peel and sticks would stick- now I don't consider any details that rely on tapes or membranes sticking to foam.

The fact that the WRB (the foam) and the sheathing (which is laminated to it) align and are not stagger as would be the case with plywood and conventional rigid insulation concerns me also. You loose that natural break through the wall, if the tap fails the water has a direct line into the wall.

I can't be understanding this product fully through, per TOB above:

"I talked with the engineer who invented/developed it at Dow and he said even though the nail heads don't hit the cardboard, you use so many it holds."

How can that meet seismic codes if the nail heads don't sit flush on the panel?

[ThingOfBeauty]

Re: Dow Styrofoam SIS

I think I'd need to get my hands on a sheet of this stuff before I had any really definite comments. But anyway, from the general description I can tell you this:

I was never a fan of polyiso in moist areas. That would concern me as it is more absorptive than both EPS and XPS. Even through paper faced polyiso was use in roofs probably since I was born, it still concerns me. Also, rigid insulation forms oxidation and when that happens is very hard to adhere membranes too, we had a terrible problem trying to use XPS as an air barrier several years ago, no peel and sticks would stick- now I don't consider any details that rely on tapes or membranes sticking to foam.

The fact that the WRB (the foam) and the sheathing (which is laminated to it) align and are not stagger as would be the case with plywood and conventional rigid insulation concerns me also. You loose that natural break through the wall, if the tap fails the water has a direct line into the wall.

I can't be understanding this product fully through, per TOB above:

"I talked with the engineer who invented/developed it at Dow and he said even though the nail heads don't hit the cardboard, you use so many it holds."

How can that meet seismic codes if the nail heads don't sit flush on the panel?

Ted, I'm with you on most of this. Let me just start out saying that if you're interested in the product the Dow reps seem to be responsive and the people at HQ are very knowledgeable. So, you can actually get the REAL information from them, if you are interested in SIS.

To address a few of the things you brought up (all of which were questions for me too, and here I'm just repeating what I was told, take it with a grain of salt as it's basically the Dow company line being repeated without much checking):

Polyiso/water: they say the foam is closed-cell and very water resistant, they wouldn't tell me what the blowing agent is but I specifcally mentioned all the nail holes in the foil facer as a possible issue and they said it really isn't.
Facing stickiness: Ted, that's interesting! hadn't heard that before. So plain XPS won't hold adhesive for long?!?!?! So much for Dow's XPS window install details! ...however, SIS does have a foil facing which (based on short term experience with R-max) should be a lot better with stickiness.

Sheathing/foam joint alignment: hmmm, believe in the situation we're contemplating here there is no sheathing to begin with, and two layers weren't on the table anyway...guess you might be right, but if you have water leaking through the foam joints aren't you kind of hosed even if there's sheathing behind?

Nail heads: that was my first question. Well Dow has enough money to do good testing on shake tables and all that. I would consider re-nailing after an earthquake (!) but it seems to me nailing 3" OC with the nails not quite hitting may actually have about the same strength as 6" OC with the heads snug. Long term--doesn't feel right. 'Course we don't have earthquakes here anyway. Parenthetically, in the 1/2" product there's about 3/8" of foam, you can probably set a lot of nailers to blow right through the foam and snug the nail up, or very close anyway.

OK infomercial over, I'm still thinking I would hold off for new construction, but in the situation posted above it makes a certain amount of sense.

[Dancing Dan]

Re: Dow Styrofoam SIS

There's a piece on SIS and some other new sheathing products in the latest FH - just got it in the mail today.

[Ted S.]

Re: Dow Styrofoam SIS

TOB: I'm going to have to read up more on this product, it sure appears very progressive in the descriptions above. Take anything I say with a grain of salt right now because I have not used it.

As for the "facing stickyness" of XPS, when the air barrier code came out in 2001 here in MA, the Board of Building Regulations and a number of architects from the Boston Society of Architects developed designs to meet these codes, the most common was XPS over a vapor impermeable peel and stick which is still in use to day.

However we had more designs, one of which that depended on XPS only, with no air/vapor/water barrier behind it so we tried to seal and stick to the XPS. That did not work out to well, I am attaching a pdf of it. Perhaps due to the oxidation of longer exposure to UV's in a commercial construction duration - I don't know. All I can say it that I will no longer rely on adhesion to foam unless it is an foam air sealant. I'd be interested in others comments on sticking rubberized flashings to foam.

This product may be different as it looks like there is a foil film? Maybe that will stick better.