More Building a Net-Positive House
In October, 2021, Connecticut-based builderBen Bogie的BPC Green Builders开辟了一个trailblazing project in the Hudson River Valley (climate zone 5). A collaboration withTrillium Architects, the 5000-sq.-ft. net-positive house is Japanese-inspired in design and building science–focused in construction. Keepingupfront carbon emissionsto a minimum is a prime objective. The project minimizes the use of virgin foam insulation, reduces concrete where feasible, is engineered to avoid the need for steel, and optimizes materials made of recycled content. GBA is following the build and sharing key construction details along the way. (SeeEpisode 1的a 10-part video series covering this high-performance build.)
The first detail of note is the way they handled the capillary break at the 12-in. by 24-in. cast-in-place monolithic concrete footings, which include two horizontal rebars and 5/8-in.-diameter vertical rebar every 24 in. (substantially more rebar than most footings). Because the footings sit directly on soil and will wick water, it is critical to create a capillary break to prevent moisture from traveling into the foundation walls and potentially moving into the interior environment; this capillary action is the reason moisture accumulates on the backside of insulated foundation walls—a situation that can lead to high humidity, mold growth, and musty smells.
毛细管休息是通过Tremco’s Tuff-n-Drifluid-applied waterproofing membrane at the top of the footings. After the footings are poured, they are allowed to set for a few days before work on the foundation walls begins. It is during this short break that a waterproofing subcontracting company (the same company that will waterproof the foundation walls) arrives to spray the membrane on the stripped footings. Ben says it’s fast and cost-effective. It took an hour-and-a-half to cover all footings. He also says it works well in an assembly with so much rebar. The alternative peel-and-stick membrane method would require a lot of cutting to get it around all the rebar penetrations—a significant increase in labor costs and, arguably, a less effective measure, given the disruption of continuity that cutting the membrane creates.
“When looking at a high-performance building, we want to control all the energy flows throughout,” Ben summarizes, “and one of them is the passage of water vapor and water, so we start at the lowest point in the assembly. We start controlling the forces there. The capillary break is the first step. If you leave that unaddressed, there is a pathway for water to get up through the foundation wall, which can affect the indoor environment.”
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Kiley Jacques is senior editor at Green Building Advisor. Illustration by Patrick Welsh.Photo by Brian McAward.
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18条评论
Many soils in the country require a keyway on top of the footing. You can create a “V” or square channel after the footing is smooth-out. This groove allows the wall concrete to set and form a mechanical connection on a cold joint, and prevent the wall from sliding across the footer with high horizontal/lateral forces, especially if you are building on expansive soils or on the side of a hill or mountain.... Required or not, I think it’s always a good idea.
Hi Armando,
Ben intentionally omits that feature in favor of this method, which doesn't require it.
Armando,
I always saw the key-way and rebar as either/or connections which both serve the same purpose countering shear forces at the joint. Rebar has the added advantage of also allowing the structure to act monolithically against vertical and horizontal forces.
Would not a water proofing Concrete Sealer, of which there are many, sprayed from a common garden sprayer be cheaper, easier, and just as effective. ?
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The sealer should be compatible with the forms. Some sealers will eat forms with foam in them. Water based sealers are required for foam based forms.
当我听到“密封剂”一词时，我通常会将其视为用于裸露的装饰混凝土中的那些。就像您说的那样，它们通常是从花园喷雾器上使用的。这些类型的涂料旨在提供一些保护侵害液体染色，并在其表面上促进串珠的意义上提供一定程度的“防水”。它们实际上并不防水，也不能抵抗水蒸气或高静水压力的运动，这是我们需要的两件事，以使该细节有效。
Ben, I don't mean to be argumentative as I'm really trying to determine why a "sealer" can't be used since it is so much cheaper and easier. I'm working on that "effective". I agree that the sealer's are not water proof but they do resist water substantially unless the water sits on the sealer for lengthy periods. For use as a capillary break on the footer, or on top of the stem wall, I can't see that there would be "high hydrostatic pressure" as what we're preventing is, what I imagine to be, a very slight pressure, if any, that of the rise of water due to capillary action, which is due to molecular bonds, not hydrostatic pressure. Is that not true ? I don't know what the permeance of sealers is but it seems to me that they would not have to have an exceptionally low permeability in order to prevent most water vapor transmission and be effective as a capillary break. I'd appreciate enlightenment.
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I read an article, I believe it was one from Building Sciences, that it's hydrostatic pressure that drives the water through the footing and the cold joint with the foundation wall. I see this as one of the things that can't be done after the foundation is poured and the consequences of failure are extremely difficult and expensive to fix. It's cheap insurance.
我真的不认为用花园喷雾器涂抹的密封剂比Tremco Tuff N Dri或Henry CM100便宜得多，但这只是我的看法。这不是我选择省钱的地方。我宁愿将其从柜台上拿出，或内置橱柜或装饰装置。
艾伦（Allan），我同意地下水的静水压力将使水通过混凝土驱动。但是，正如我所看到的，这是一个单独的问题。如果可以缓解静水压力（烟膜，砾石或其他），可以使水自由地向下排水，从而在页脚旁边自由排水到排水系统，那么静水压力就不是问题。这使我们回到了页脚和坐在上面的基础墙之间的单独问题。由于消除了静水压力的问题，我们只需要阻止页脚中水分的毛细管作用，从而升入基础墙。这需要一条狭窄的材料带，就像适当材料的基础壁的厚度一样宽。我的问题是：从花园喷雾器上喷洒的常见廉价混凝土密封剂是否有效？在上面的文章中，用防护装备，泵，喷嘴和承包商明显高于带有混凝土密封剂的花园喷雾器，肯定会在上面的文章中使用材料的劳动力和成本。我可以将其放在卡车的后部，倒入后，只需要几分钟即可跳出并喷洒所有必要的区域。似乎我的问题归结为混凝土密封剂提供毛细管断裂的有效性问题。
When I look at the picture in the article I wonder why he is spraying the entire top of the footer, as the only area that requires a capillary break is the narrow strip on which the foundation wall sits. To me, it seems the picture represents a waste of time, labor, and materials. Spraying the entire top of the footer doesn't seem to achieve anything, though it does look neat. If a concrete sealer is effective, then it's got to be quicker, more convenient, cheaper and easier.
Ted,
一个潜在的问题是,大多数我网上的密封材料e used have to be applied to cured concrete. I have used Cure&Seal, but I suspect it is designed to provide surface protection, while still allowing moisture to move through it. Maybe something like Drylok would work?
I agree with you that it makes little sense to do the whole top of the footings.
//m.etiketa4.com/article/capillary-breaks-above-footings
我认为您正在低估静水压力。尽管流动横跨一个狭窄的区域，因此“总”压力不大，而且体积很低 - PSI可能很重要。
Scott,
我认为泰德（Ted）不忽略静水压力的力量，他说那不是毛细管中断的目的。这是通过不同的机制 - 毛细作用来阻止水进入混凝土杆壁的原因。
As per that link, when I contacted Henry about Blue Seal as a footing capillary break they responded with this:
"Thanks for your interest in Blueseal, yes you can use Blueseal in that application. Let us know if you have any other questions.
Christopher Benoit | Product Support Rep | HENRY COMPANY | 336 Cold Stream Road, Kimberton, PA 19442 | P 800.486.1278 |http://www.henry.com"
"If a concrete sealer is effective, then it's got to be quicker, more convenient, cheaper and easier."
I'm not convinced it's as effective and I'm not willing to take the chance that it is, but that's just my opinion and decision on where to spend. Of course, YMMV. There are many areas of a build that could be cheaper. Like spray foam insulation. We could just stuff fiberglass bats in the rim joists to save money, but again, I will decide not to and use spray foam in the rim joists. Everyone could use fiberboard sheathing as well because it's cheaper.
除了这里概述的文章，总有其他方法和通常更便宜的方法来做事。我感谢阅读它们，然后决定我想做什么。我也感谢成员像您一样发表评论和询问，TED。
Wasteful and expensive: my choices would be to concrete sealer or MasterSeal 583 Formerly Super Thoroseal.
绿色建筑解决方案通常是环境影响，成本和可用性之间的折衷方案。虽然我欣赏液体涂抹膜的有效性，但阅读SDS表使我停下来。它主要是石油产品，显然是毒性很大的。有毒性较小吗？没有那么多碳含量的液体应用膜？
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