Insulating masonry wall
I’m looking to build an efficient home in Zone 6 with a focus on durability and sustainability, while keeping comfort in the back of my mind. Yes, concrete (I’m looking into fly ash) is a hot topic but the durability and comfort are hard to beat, and as a bonus, I love the look of board-formed concrete. Unfortunately, there is not too much information on exposed concrete walls: insulation, waterproofing, etc.
Insulation
While looking at the Thermomass system, I came across Rockwool CONROCK. I’ve read a bit on Thermomass but have found very little on CONROCK. Does anyone have any experience or thoughts on the difference between these two? I know Thermomass offers XPS, but I’d like to steer clear of that. Also, I assume polyiso would be a poor choice due to concrete and moisture? Or would it dry fast enough to limit degradation?
I like the board-formed look on both the interior and exterior walls. However, I will be framing and finishing (Drywall) part of the exterior walls. Is it even worth throwing insulating between the studs? That brings me to…since this is a zone 6, I will be purchasing quality, triple-pane windows and lift-and-slide doors; is it worth adding more than 4″ of insulation to the concrete walls?
Waterproofing
Is there a product that you recommend for an exposed concrete finish? Can I use this with concrete additives? Since the home will be in a cold climate, I assume drying to the exterior would be ideal? How would that effect detailing the sandwiched EPS (If I go that route), or even the CONROCK?
General
Since I am going after the board-formed look, and this is a highly-skilled trade, I want to limit mistakes. I know some wall systems mention a minimum of 2.5″ of concrete per wythe, but I want this done right. For board-formed, what would you say the minimum wall thickness should be? I’ve seen helix micro rebar and it looks interesting; would that affect the look of the board-formed concrete? Not sure if I can reduce the width of the wall by using Helix.
It’s easy to rack up a pretty thick wall, so I am trying to keep it as slim as possible, but I want to do it “responsibly”. The rear of the home faces south so I will be adding vast amount of windows/doors (Floor to ceiling, with proper shading/overhangs) to capture the light, energy and views. Therefore, maybe the wall thickness does not matter so much.
Hopefully I can become a bit more knowledgeable before speaking to industry experts and contractors. Thanks in advance for all of your help.
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Replies
User...481.
Houses that use a core of foam generally end up with very thick walls, and some tricky detailing where they meet openings or other materials. Probably the most well-known recent example is this house by Peter Zumthor: https://www.dezeen.com/2018/10/29/peter-zumthor-secular-retreat-living-architecture-villa-devon/?li_source=LI&li_medium=rhs_block_1
Much easier is a hybrid approach where the concrete walls alternate between being exposed on the inside or exterior, and the insulation moves accordingly:
http://www.truckeecustomhomes.com/wp-content/uploads/2010/09/Exploiting-the.pdf
That would be my preference if I as building a house and wanted exposed concrete as a finish.
Whatever system you choose, the amount of foam needs to be determined by energy modelling. It's really not that useful to give a rule-of-thumb amount when the rest of the assemblies, and area of glazing, etc. aren't known.
There are very good exterior and interior concrete sealants available at Big Box stores. Stay away from the solvent-based ones (especially Xylene). At some point they will need re-applying, and that becomes very difficult in a occupied house when they contain high VOCs.
Good luck with your build.