Hello all,

What a great resource this forum is!  I've gleaned some GREAT info by trolling through the forums, but haven't seen anything to QUITE match my specific application, so I thought I'd ask.

I've got a 1948 cinderblock (4") and brick (slightly less than 4") 1000 sq.ft. ranch in Denver, CO.
There's NO cavity in the wall or between the block and interior plaster, and it's pretty darned cold in winter!
Flat roof, 2x8 joists at 10" o.c., rock-wool insulated from inside, tapered bead-board system under new torchdown roof (no idea what R value we're looking at up there).

Slab-on-grade with cast-iron radiant heat in the floor
Supplemental wood heat (this winter it's primary.  Ask me about it )

We plan on putting some insulation on the OUTSIDE of the walls so we can take advantage of the masonry's thermal mass, but I've come across a few conflicting methods of applying it.  I'd like to get the biggest bang for a relatively thin layer, keep in mind, without breaking the bank.

The plan so far:
2" of faced polyiso applied to exterior bricks with construction adhesive (and possibly ramsets? - tapcons if I'm feeling masochistic)
2" XPS from 6" below grade to 2" above (to insulate slab edge, the best I can do under the circumstances)
bright white stucco over the works.

The holes in the plan:
I'm not sure whether to use an EIFS type stucco or traditional stucco.  CAN traditional stucco (which I prefer) be applied over a smooth layer of polyiso board?  Should I be furring THROUGH the 2" of foam with long screws and then applying something to attach lath to?

I've found other examples of people building an exterior frame of 2x4s (possibly 2x4 furring on edge, I suppose) fastened to the existing structure with 4" of ISO butted to the 2x4s.  The advantage I can see here is that it gives you a solid surface to attach exterior features (electric meter, etc.) & stucco lath to (as well as more room for insulation.  DOW also makes some products that come with a stucco-ready gypsum facing, but I've not seen it retail anywhere, it's made in thinner boards than I'd like, and I'm sure it's pricey.

Ideas?  Tips/tricks?  Am I on the right track or completely off-base?

Thanks, everyone, for being such a great resource,
charlie
Denver, CO

i would look into the quad-lock icf retrofit product. it's basically the icf eps insulation mechanically fastened to your existing exterior. i would assume any traditional finish/siding would go over it. seems like a pretty slick system, but not sure about the cost, and have never actually used it.

I'll be honest with you, if I had a brick house, I would try to find a way to put insulation on the inside. Foam, furring strips, and drywall would be able to fit the bill, and you wouldn't ruin your outside look. However, if you really want to go on the outside, I would try to incorporate some kind of wood. Maybe 2" foam, 2*4's on the flat, with long screws, then sheating over that. Heck, get some 1.5" used insulation cheap and cut it to fit in between the furring strips. The biggest problem I see with trying to attach stucco directly to the foam is actually securing the foam to the wall. You would have to get some big fender washers or thin metal plates to prevent just sucking the screw into the foam, then when it was loaded up with stucco, I would think the foam would slowly slide down the wall, with the screws just cutting through the foam like a knife. Construction adhesive would work, but I would be worried about moisture getting in there, and making the adhesive let go over time.

I looked up the quad-lock. Something to think about, but it looks like something one would drop serious coinage on! I signed up on their "free estimate" form, so we'll see what they've got to say. The wife and I would like to eventually build a rammed-earth, passive solar, offgrid home . . somewhere, and those ICFs seem like they would be a great alternative to building forms!

point taken regarding losing the "look" of brick. However our house has been painted several times with lead-based paint (one thankfully covered coat is a beautiful shade of pistachio), and incorporates details in textured brick which would require some serious media-blasting (and some kind of capture system to catch all the resultant lead dust) to get clean. As it is, it doesn't look a whole lot like brick from afar, and we'd put more sweat into getting the "brick equity" back than we'll make on resale! Denver has so much brick, I wonder if we even see a price difference here . . .

The issue with interior insulation is the fact that the house is SOO small (tough to explain, it's a layout thing), and we'd need to tear out the entire kitchen and the (freshly tiled) shower wall, as well as the tub, not to mention having to figure out some really interesting finishing to go around the fireplace. I thought about it, believe me!

This house is GREAT in summer as-is, but let me tellya, splitting your entire supply of winter heating fuel with an 8lb maul really puts energy efficiency into perspective! I PRAY i've got a little nest egg of seasoned wood come spring ;)

Thanks for the thoughts on foam 'n' stucco. We had planned to do the adhesive in vertical strips to help drainage (though the house has 2.5' deep eaves, so drips are pretty minimal), but i hadn't thought about the added weight causing the foam to slide & cut on the screws. Perhaps that's why stucco companies use 3/4" foam and synthetic stucco? Would vertical furring installed to frame a standard 4x8 panel allow drainage & still provide enough support for stucco lath? Is the lath SUPPORTIVE or does it just tie the layer of cement together? Essentially, can I get away with not putting sheathing over the foam? I think I need to leave the bottom of the ISO and stucco layer open per Denver code, so a supporting lower 2x4 might not be so great . . .

How much insulative value will I lose due to bridging from the furring strips and is there any way to cut those losses? Of course, ANYTHING would be an improvement. I was awoken last night when my hand brushed against the bedroom wall last night. BRRR!

Thanks for the thoughts, keep 'em comin'!

I think most solutions to your problem will involve dropping 'serious coinage', unless you can do most of the labor yourself. My previous house was constructed very similarly, but with a pitched roof. I concentrated on air sealing and upping the insulation levels in the attic, and during remodels (kitchen & bath) I was able to up the wall insulation in those spaces. Those things add up, though still not ideal. As always $$$$!

@aard: I just re-read your post and I think answered my own question re: thermal bridging. You're saying attach the foam directly to the wall (4x8 panels butted together) with adhesive and use long screws to attach the 2x4s OVER the foam, not in between panels? That way the 2x4s would be supported by the screws, which could then support sheathing and stucco. Would that allow enough support to hold up the 2x4 frame and stucco, even with 2" of screw essentially hanging in space?

furring holding up sheathing would certainly provide the "rain screen" I keep coming across. . . It would also allow me to fur 16" o.c., meaning I could buy thinner osb to sheath with, right? Then tyvek over the osb, followed by lath & stucco? Could I fur with something thinner than 2x4 in this case, just to save additional wall depth? It's already going to be interesting around the front door . . .

I do plan to buy used ISO, by the way. There are several building salvage type places in the Denver Metro Area, one of which seems to regularly stockpile used ISO in thicknesses up to 4"!

@ sammy: I certainly understand that things add up, but we'd like to keep them as cheap as feasibly possible without sacrificing quality and efficacy! We're DIY types, and we've already put considerable sweat equity into this former HUD home, so the labor will be performed by us and our friends (paid in burritos and beer). I'll probably have a pro come in to flash the windows & doors, but the rest seems simple enough for us to tackle.

One of us is a student with a part time job, the other is an arborist (hence the handle ;p). Cash needs to stretch pretty far around here, but we're not willing to sacrifice our ideals in exchange for a quick-fix. Previous owners have already cut too many corners in this house & we'd really like to break that pattern . . .

Thanks for the help & again, keep it coming!
charlie

ps- admin question: Is there any way to move this thread from the building/construction forum to the residential forum? Seems like there are more readers and responders over there. . .

Yes, that was how I was intending it. As long as you tightened all the screws to the point it was almost crushing the iso, I would not think the 2" of screw just hanging out would hurt, provided you put enough screws into each one. Being you are going to need large screws to get the length you will need, the diameter should be large enough to carry the weight. Just to be safe though, you could get some 8" or so pieces of 4*4 to go on the bottom part under each furring strip, with no foam behind them. This would still finish flush, but give you even better loading characteristics for the furring strips.

I was meaning 2*4's on the flat, so only 1.5" thick.  You could use 1*4's so only 3/4 inch thick, but considering this is a semi-load bearing situation, I would suggest against it. To save money you could use 2*3's if the 2*3's in your area are any good. I had a bad experience with a load of 2*3's that we had to cull a lot (like 1/3 or more) of but if you get to pick through them (like at a big box store) to ensure straightness, go for it.

Thanks again, aard!

I'm hoping we can get to this sooner than later, as it's been COLD in Colorado lately (yes, even for December). Can I get as far as the building paper and leave it at that stage until it warms up enough to stucco? This would annoy a couple of our neighbors, I'm sure, but it would keep us WARM for the remainder of the season!

I've been thinking about polymer stucco lately . . . A friend's father insulated his home in OK with 3" of XPS and synthetic stucco directly attached. I've heard a few horror stories about synthetic stucco without a rainscreen, but it's lighter, and thus might negate the need for furring and OSB sheathing. Am I on-track? I'm thinking I might be able to afford a pro to do finishing with what I'd save in 2x4s and OSB. . .

whaddaya think?
charlie

treeguy, I used to live in Germany until last year, and there I saw tons of retrofits of masonry buildings done the direct way you're describing (no furring strips, no sheathing).

They would use thick sheets of EPS foam on the exterior of the masonry, 4 inches thick or more, and drive a long screw through the foam into the masonry. There would be a wide plastic fender type washer on the screw to hold the foam in place. Then they would apply stucco directly to the foam. I saw them use STO quite often, which is a polymer modified stucco, but I also saw them use lime stucco (maybe they modified that too?). Beautiful results.

just as an fyi, adding that extra thickness on the outside of your windows, you will probably lose some light, too.  It may not be your primary concern, but I would expect that your house may get a little less natural light when you're done.

@Jelly: You've got me looking again . . . I think my main concern with lime-based stucco over thicker insulation is weight and the ability of the foam to support that much of what is essentially cement. I'd feel pretty confident with polymer stucco, but have heard stories about rotting without some type of rainscreen. In this climate, and with our 21" eaves, I'm not super worried about WATER infiltration, but I'd still like to be careful.

@JL: Natural light is sort of a concern, but not a problem with this house. It's one of the things we first fell in love with here. Big 12-pane window in the livingroom, good almost-celerestory windows in the south bedroom and an open plan keep things light, while those eaves do a decent imitation of passive-solar in the summer, keeping it diffuse but still light.

treeguy, I would think polymer stucco would be the way to go - the rotting you've heard of is when polymer modified stucco is not properly installed on *wood framing and sheathing*, not on CMU or masonry. Besides, you've probably got a rainscreen behind the existing brick. Do you see weep-holes at the bottom?

No weep holes here. This house is pretty ol' skool in its construction. No cavity, no metal ties. Three courses of 3" thick (?) block on the inside followed by a tie course of bricks. The exterior of the wall is all brick. The thickness of the wall is equal to the length of a single standard brick, just to give you an idea. So there's not an issue of water getting trapped up against polyiso, EPS or XPS using polymer stucco without a rainscreen? I suppose the polystyrenes are approved for use below grade, so what's a little moisture behind polymer stucco gonna do?

The new polymers are such that they should repel water from the outside, but should release it again if it does get in. In other words they do "breathe" a little bit. They're used all the time on EPS ICF forms.

Take a look around the Building Science website. It may take a little digging, but there are documents there that I think you will find very helpful and will address a lot of these issues specific to your climate.

What an amazing resource! I geeked-out for two hours after reading your post!

I'm still digging, and a bit confused at this point, but I think most of my questions have been answered. Essentially, I believe our wall qualifies as "non moisture sensitive" and is, to the contrary, a "moisture reservoir," moderating differences in RH on either side and not being sensitive to moisture content unlike wood or steel framing. Adding XPS or EPS will not seal up the assembly to the point it will trap moisture (though it wouldn't matter because the masonry would still dry to the interior, right (the only barrier inside is the plaster and some latex paint)? I gather, actually, that I need to avoid installing anything that might qualify as a "vapor barrier," since I'll have a moisture reservoir on the exterior AND in the wall assembly, since we're using stucco. For drainage, it may be as simple as using two layers of 30# building paper, shingle-lapped, OVER 2-3" of foam, with stucco over the paper, to provide a drainage plane and path (Flashed at ground level and left open) behind the stucco. Still not real sure as to the ability of XPS or EPS to hold up a layer of traditional stucco, but it appears to be a non-issue in most of the "wall assembly" articles I've read, as they recommend finishing directly over foam in a couple of situations. It seems like furring is usually used to provide active air ventilation in moist climates, and in our case wouldn't do much more than add a moisture-sensitive piece to the wall (OSB and/or flashing).

Thanks for allowing me to think "out-loud" (on page?) in this post. Please feel free to point out flaws in my thinking. I may be an over-aggressive DIY'er, but I'm an over-cautious designer, especially when I'm in unfamiliar territory!

Thanks again,
charlie

Building Science is amazing isn't it? Good that you're doing lots of research. And yes, it's very important that you don't use something like a vinyl wall covering on your interior walls with a moisture reservoir construction method like masonry.

I'm a DIY'er myself (kind of a rabid one!), so I'm not an expert. But I've seen a lot of these retrofits performed in central Europe. Big thick sheets of EPS foam are dirt cheap there.

The foam isn't really holding up the stucco by itself, rather the long screws and big plastic washers which hold the foam in place are supporting any extra weight. I don't think you can just use construction adhesive by itself to apply the foam. If you use construction adhesive, it's really just there to hold the foam still while you drive the screws.

The first layer of polymer modified stucco goes straight on the foam, then a fiberglass fabric mesh is applied to that layer when still wet. Then a second coat of polymer modified stucco (which can be tinted) is applied. Both layers are thinner than a traditional stucco, so with just two layers the whole thing is pretty light. The polymers also make it elastomeric, which prevents cracking if the expansion and contraction rates of the foam and polymer stucco are different.

Now if you do use layers of building paper and traditional stucco, then you're going to have to add a diamond mesh metal lath before the "scratch coat" which is the first of three layers (which can total an inch in thickness). The paper is there as a "bond break" between the foam and the stucco, mostly to prevent cracks.

You might try doing some searches in the ICF segment of this forum. I know a lot of those guys finish their ICF forms with direct applied methods. Of course there are those ICF installers on the other side who don't do it that way. But do enough research as it takes to make an informed decision.

A little more reading with a clearer head, and finding an article about stucco and block construction in Florida leads me to believe I don't need to worry so much about drainage planes. With a reservoir method of dealing with moisture, it's only required that drying time is higher than wetting time. It wasn't an issue in Florida, so it sure as hell isn't an issue here. Polymer-modified or -based systems appeared to be immaterial to the amount of moisture penetration, and if XPS(or EPS, I'm now thinking my choice will depend on what's cheaper at the time of purchase) is moisture-insensitive, it won't matter if it gets a little damp, since it will have more time to dry than it did to get wet. Sound right? I suppose the bond break will also provide a little bit of screen effect, to keep moisture from being too deep in the insulation.

Am i correct in thinking that my building paper in this case should be effectively permeable, as in kraft paper? Should I avoid Tyvek? I'm really wanting as vapor-permeable a wall assembly as possible without allowing active airflow, correct?

charlie

Yes it needs to be vapor-permeable. A *vapor barrier* is what you want to avoid. I would think asphalt impregnated building felt would be best under stucco. If it's traditional portland based 3 part non-polymer stucco then you'll definitely need it.

Hey Jelly,

What's the reasoning for using asphalt-impregnated felt? I came across one article describing the two-layer paper method as a rainscreen (the layer adjacent to the stucco crinkles up during application, acting as a spacer against the second layer).

Okay, this brings up what may be a stupid question: When an article refers to "building paper," what exactly are they referring to? Is Tyvek considered a "housewrap" as opposed to "building paper?" I've not come across felt in any of the building science articles yet, but 30# roofing felt was mentioned by a builder I spoke to offhand when we were working in his elms.

The more I look, the more I lean toward polymer stucco, mainly for peace-of-mind in not worrying that my insulation will pull off the wall while I'm not looking. Traditional 3-coat seems easier to apply, but the thickness will also make finishing around my front door that much more difficult. I've so-far found one fastener, somewhat akin to a drywall anchor, designed for attaching foam to masonry. Am I doomed to stripping 20% of my drill holes using tapcons or are these things a good option? If I put felt over the fasteners, am I going to get the necessary supporting bond to the fasteners or do I need to fasten THROUGH the paper?

I'm slightly worried about the vapor barrier issue with the foam itself. 2" of xps is .55perms, which puts it pretty low on the scale. Not quite to the point it's a "barrier" but low enough to make it a class II "retarder." Is that going to be enough permeability to let the brick dry somewhat to the outside? Do I need to worry, since the vapor will be similarly retarded (nyuck, nyuck) moving from the outside-in as it is moving inside-out?

Sorry for all the greenhorn questions. I'm more comfortable hanging from a rope 50' off the ground than I am with a hammer in my hand. Not afraid to tackle it, just gunshy!

Still thinking aloud,
charlie

ps- eps is still an option, though the price seems pretty comparable, with XPS offering noticeably better R-value per inch.

Asphalt impregnated felt goes by many names - building felt, or tar paper - the black 30# roofing felt your guy mentioned, same thing.

No problem with lots of questions. But we're wading into some territory where I can't really steer you with total confidence. My experience in this type of retrofit is with polymer modified stucco directly applied to foam, without any layers of building paper or lath.

So I can't really say whether you can use Kraft paper under traditional 3-part stucco - I'm no expert so maybe it's fine. I've just never seen it done. My initial thought is that since stucco is porous, that it could hold moisture against the Kraft paper, causing either mold or deterioration, but I don't know that to be fact. There is an exterior finish portion of this forum. You may try posting a new thread over there asking for help with stucco.

Don't forget you're going to need lath with traditional 3-part stucco. The screws would need to penetrate all layers of lath, building paper, foam, and into the brick. The washer will stay on the outside of the lath.