Connecting masonry cavity foam insulation to windows and running services in CMU hollow cores
Hi.
I live just out of Melbourne in Australia. For reference, our climate zone is Cfb (temperate, without a dry season and with warm summers). Annual HDD (Farenheit, with base 65 degrees) is 2,838 degrees. Annual CDD is 450 degrees. It very rarely goes below freezing temperature.
We live in a Mid Century Modern double leaf masonry courtyard house, with exposed internal and external CMU walls throughout. For historic/aesthetic purposes, we want to maintain this and would like to improve the building’s insulation and airtightness with this significant constraint in mind. Without exception, every door and window is floor to ceiling,and a number of windows are actually full window walls coming off the two attached masonry walls at either end perpendicularly. The masonry wall in these situations usually extend past the window, in effect like a “horizontal parapet” wall, so to speak. (They also are actual parapet walls above the roof as well). The width of the CMU leaf is 4 inches with a 2 inch cavity.
My plan is to make the most of this 2 inch cavity and fully fill it with closed cell polyurethane foam to function as our insulation, vapour, and airtight membrane. We will also upgrade our windows to some form of double glazing, and will need to replace the roof and insulate it at the same time. The roof is a thin, flat (very low slope) roof.
I have some concerns / queries about the connections:
1. I don’t know how we can connect the cavity insulation to the windows. The masonry between these two elements will be a significant thermal bridge and a source of air leakage through the porous CMU. The ‘best fit’ so far is a retrofitted ‘expansion joint’ (for want of a better term) in the internal leaf at the position of the window, but filling this joint with some sort of airtight and insulated material. The R value doesn’t have to be exceptionally good; it’s only functioning as a thermal break and airtight connection. I also imagine I’ll have to also put in some wall ties to reinforce the now weakened wall (wall ties connecting the two leaves and/or wall ties bridging the gap I’ve now just made in the internal leaf. Can anyone provide advice or guidance for this plan? I’ve never seen it or heard of anyone doing it. Any better alternatives that I’ve missed?
2. Similar situation with the cavity to ceiling insulation / airtight layer connection. Because of the many parapet walls, what are my options? There is only 3-4 courses of CMU above the roofline in the parapet walls, in case the internal leaf of parapet needs to be rebuilt with a single course of insulating concrete block (or similar). Any other suggestions or advice?
3. Lastly, does anyone know if it’s possible to drill through the actual core (hollow) of the CMU block itself from above when the roof is off? There is a 1.5-2 inch wide hollow core in the blocks, but unfortunately this tapers just at the bottom of the block to almost close the hollow core off at one end. This taper is very thin (quarter to an eighth of an inch thick). If I could drill through this thin lip of concrete in all cores in a vertical stack of inner leaf, then I may be able to rewire the electrical and new data wires through this route (hopefully with conduit first to future proof somewhat) and avoid rewiring through the cavity which will eventually be filled with closed cell polyurethane foam.
Thanks very much for my long winded and multipart question. I think it needed the backstory to make sense / give it some context.
George
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Replies
The rewire and insulation retrofit INSIDE the cores of the CMU seems impractical. By the time you finish exposing and drilling enough channels for the wiring alone you'll probably expend as much labor as went into the original construction of the house.
For the insulation improvements I think your efforts should be focused on the roof and new windows. EIFS is worth investigating for the exterior walls, but the aesthetic impact of that is something that you would have to consider carefully.
George,
My first thought is that you need a bulldozer, not an insulation plan. Your house is a thermal nightmare.
However, here's what you have going for you: a very mild climate and low energy bills. So an imperfect solution might work.
Here in the U.S., we never advise anyone to fill the air space between two masonry walls (or a masonry veneer in front of a wood-framed wall). The air space serves to de-couple the two walls, reducing moisture transfer. In your climate, I'm not sure whether wind-driven rain is a problem -- but if it is, the air space in your walls should stay were it is. The insulation would then need to be installed on the interior or exterior side of your masonry wall.
Ideally, you need to demolish the masonry walls that run continuously from your indoor environment to the outdoors, as well as your parapets. If you can't do that, then you will have to do some type of cobbled-together compromise, as you suggest.
There's a saying that all politics is local, I think you could say the same about building construction expertise. GBA tends to be focussed on the relatively extreme climate of the NE US, and I think that's where Martin's alarmed 'thermal nightmare' comment is coming from. I think you can make sensible and cost-effective improvements to your building enclosure but you will need well-informed and experienced local advice to do so. Your local code officials or a nearby school of architecture might be able to point you toward a good energy consultant or at least to a contractor experienced in thermal improvements to this form of construction. That said, I'll stick my neck out and offer a few general comments.
First, I know cavity fill insulation has been common in the UK, where they certainly do have wind-driven rain, but not all fill materials are suitable for this kind of work. A good local insulation contractor should be able to advise. If this is not recommended EIFS as David suggests may be the way to go, but above all (literally!) make sure your parapet flashings are correctly installed and in good condition.
Second, I think you need to worry less about thermal bridging - in your mild climate it should be a marginal problem. Though I may be misunderstanding what you are describing with your 'horizontal parapet', if your cavity walls are formed anything like they are in the UK there will be a gap at window and door jambs between inner and outer wythes with a vertical moisture barrier sandwiched between, this would be covered by the jamb itself. It doesn't provide much of a thermal break but it will probably be enough. I wouldn't advise messing with the structural connection between the wythes without very specific engineering advice.
Third, I wouldn't recommend trying to drill through the hollow block for your electrical runs. I suspect your best option will be to to cut a conduit chase into the surface of the block and then to refinish the whole wall with plaster. Modernism failure #1 - believing the world never changes and you'll never need a construction cavity to run service updates.
James,
Good advice. Consulting local experts always makes sense.
If the "...2,838 degrees. Annual CDD is 450 degrees..." is accurate, Melbourne's climate is like a very temperate version of US climate 3B (more temperate due to the modest cooling degree-days.)
If it were a cavity wall, 2" of R4/inch or higher foam in the masonry cavity it would meet or exceed IRC 2012 insulation standards for mass wall construction.
But it's not. Being a native 'merican dialect speaker, I had to look up "double leaf", which in the UK & some commonwealth countries refers to a double-wythe masonry wall with no cavity, just two abutting (but not strongly tied) single wythe walls. My understanding is that 2" cavity referenced here is isn't a masonry wall cavity, it's the open core depth of the 4" CMU. This small graphic illustrates the UK definitions of differing masonry wall types:
http://www.roymech.co.uk/images/masonry_23.gif
If it is in fact a 2" cavity wall and not a butted-up double-leaf, filling the cavity with 2" of slow-rise 1.5-2lb polyurethane foam would be just fine from a moisture point of view in Melbourne's dry climate, and would provide fairly good thermal performance. If it's simply filling the cores of the CMU with foam it's going to be better than it was, but perhaps not worth the expense. Filling the cores with perlite and spending the difference on rooftop solar (with battery to prevent backfeeding power to the grid, if your provider is as miserly on feed in tariffs as most Australian electric companies are) would probably be more worthwhile.
Thanks so much for the rapid answers.
David - just to clarify, I would be insulating the 2 inch cavity that runs continuously between the two leafs or wythes, not the CMU core itself. As for the rewiring down the hollow core of the inner masonry, I only considered it as we will have access at the top of each wall, and the drilling would only be required for a tiny proportion of each CMU block (1/4 to 1/8 inch out of the block height of 8 inches). Granted, I have no idea if drilling from such a height (10"6'), even if just breaking through this thin bottom section of concrete in each hollow core, is even possible (too long, not enough drill bit extension, hard to keep it straight from way on high, drill control etc). Sometimes there's quite easy ways to achieve something that appears on the surface to appear difficult, so I thought I'd ask. May be not in this case.
Martin - I appreciate that from a thermal performance point of view the house is a nightmare. There are many things I'd like to do to the house but taking a bulldozer to it isn't one of them. I would take a bulldozer to anyone's plans to detail walls and windows like this in a new build in 2015 , but for the standards in the mid sixties in a mild climate, I think they did an OK job, with good sized eaves, and almost exclusive equator facing glazing. It was also designed by well regarded Australian architects and is a good example of their style, which I would like to preserve for local historic reasons. Regardless, it is what it is now, and I'm trying hard to come up with the best possible solutions. In essence, I'm fishing for guidance or details about the 'cobbled up compromises' you mentioned.
From a water management perspective I thought that as long as the closed cell polyurethane was applied with good workmanship and attention to chemical quality/ratios, this would be an acceptable barrier to bulk water and vapour making its way from the outer leaf to the inner? I'd say we have some wind driven rain, but I've no idea how to quantify it or determine if it's going to be a problem. I don't think we would have the wild winters possibly seen in the northwest of the US or the UK. I'm aware of the many terrible outcomes in the UK when cavity insulation that didn't stop water ingress was used with significant water damage the end result. I was hoping closed cell would solve this issue.
James - very pragmatic advice. I wouldn't do anything without going through local professionals (architects, engineers, etc) in design and build, but given the uniqueness of my detailing, I'm casting the net wide (asking in international forums), and GBA has been the best resource by far in my quest to date. I guess I'm after previous similar solutions if they exist, or at least a 'proof of concept' before deciding if it will work in our area and with our regulations.
I see what you mean about the magnitude of the thermal bridge between cavity and window. I will get an energy assessment done to try to roughly quantify the losses in each component. This thermal bridge may fall on to the wrong side of the cost-benefit ratio. I'm not sure I fully understand your comment about a gap next to and covered up by the window jamb. Do you mean the two inch cavity gap between the two walls, or a smaller gap between the indoor and outdoor portion of the inner wall. If there already is a vapour barrier breaking the internal wall at this point, that would be good enough for me, as you suggest.
In terms of chasing and plastering, that is the most obvious and straightforward solution to the rewiring, but I'm doing everything I can to avoid covering up the CMU walls for historic/aesthetic reasons. I'm trying to have my cake and eat it too, which may not be possible!
Dana - sorry for the confusion. It's definitely a cavity masonry wall with a two inch cavity, not a solid wall. I'm sure you're right about the proper terminology; it's just that these terms are used loosely by many people and I've fallen into that trap; apologies.
The energy production side of the two sided energy requirement/production coin is by far and away the optimistic side of my predicament. Picking the lowest hanging fruit from both sides will get us as close as this particular house can to neutral energy balance. With the rate of advancement in PV panels and battery storage, this side's fruit just keeps getting lower and lower.
A 2" cavity filled with foam with a 4" CMU on the interior side has fairly good thermal performance, with a significant thermal mass component to those benefits.
In your climate you really don't need a vapor barrier (ever), but you do need a capillary break between the interior leaf and exterior leaf to keep the interior paint or other finishes from failing or growing mold due water wicking in from from the exterior after rain/dew events. The cavity in a cavity wall provides that capillary break, but closed cell foam will do almost as well as a capillary break. Some non-expanding injection foams would not be nearly as good, nor would open cell foam. The hollow cores of the CMU are themselves offer some capillary break, but it's easily defeated by the webs of the CMU in wetter climates /seasons.
Australia has some of the lowest installed costs for small scale rooftop solar in the world (it's about half the cost of the US average which is still pretty high for a complicated set of reasons), and some of the highest retail electricity prices in the world. Even without the battery a ~3-4kw array is usually cost effective for most homes, using a smart control to energize the heating element in a hot water heater to keep from donating power to the utility for 0-8 cents/kwh, avoiding the 30-35cents/kwh full-retail charge from the utility for that energy. With the crashing price of battery technology it's cost effective for many Australians to quit the grid entirely right now, and that will only become more true with every passing day.
George, this would be a standard cavity wall jamb detail from the period in the UK, possibly similar to what you have. The inner leaf is returned to close the cavity against a vertical strip of bituminous felt (called a damp proof course) which projects into a kerf in the window or door jamb. Whether this layout was reflected in AU practice at the time I do not know, it's just a guess that it was. Dana, cavity wall is the standard UK description of this arrangement which was standard since about the 1940's. The inner and outer masonry components of the wall are known as leaves, wythes is a US term unknown there, the leafs are commonly of different materials eg lightweight insulating block interior, brick exterior. By the time I left the UK in 1991 the standard cavity had grown to 3" to allow for 2" of insulation board while maintaining a 1" drainage plane against the exterior leaf. I have no idea what standard practice is there now.
George,
Sometimes my humor is a little dry. My "bulldozer" comment was intended as a tongue-in-cheek description of my own emotions rather than intended as advice. My next sentence (acknowledging that you live in a mild climate) explained why my emotional impulse was irrelevant.
Good luck!
How about blown-in EPS beads ?
Hi Dana
Again thanks for your input. Tbe capillary break rather than a vapour barrier per se makes complete sense, as does the choice of slow rise closed cell to achieve this. I'm glad I'm on a similar page with my thinking with regard to this. I also completely agree and am excited by PV in Australia. I haven't paid too much attention to the specific details, as only when we sort out the building envelope will we know what our energy requirements will be, and can then commission a system accordingly, with a view to expanding panels / batteries as they become more economically feasible in the hopefully near future. The future looks bright though (pun not intended).
James, this is great information for me. Maybe assumed knowledge for others, but I had no idea that the DPC ran vertically at the internal leaf return as per your picture. With a little luck this detail will already be there in my house, at least where doors and windows are parallel to their adjoining walls. I think I'd have to be really lucky if they are also installed somehow within the inner leaf itself, where the boundary between indoor and outdoor is (where the windows attach perpendicular to the 'horizontal parapet' wall). The lack of thermal break is not a deal breaker (pardon the pun); it was more wanting a continuous air and water management solution, which this should be. Again, many thanks for this information and new line of enquiry for me.
George.
Martin - bulldozer comment not taken literally at all and certainly no offence taken! Your advice, along with everyone elses, is very much appreciated, dry humour and all.
Pascal: The blown-in EPS beads (with water-activated adhesives) has become a standard cavity wall fill in the UK, but is considerably lower-R and less of a capillary break than polyurethane, nor does it create an air barrier. It's use in the (much wetter) UK is to deal with rising-damp on the interior leaf of the cavity wall, retaining at least a modest drying path through the not-air-tight cavity fill. Rock wool is also sometimes used in the UK, but it's more air retardent and even higher-wicking.
George: Just in case you're not yet aware of these Australian renewables information resource sites:
Small scale PV specific:
http://onestepoffthegrid.com.au/
Policy blog:
http://reneweconomy.com.au/
Dana - great websites; I wasn't aware of them, thanks. I love having go-to resources of high quality to cut to the chase, a bit like Green Building Advisor. I'll be using these r sources more and more over the coming months, for sure.
- George