Proud Green Home at Serenbe Construction Update: Installing the Footings

WEEK 2: Construction is underway at the Proud Green Home at Serenbe, and the concrete footings have been poured! Next up…concrete stem walls, which happens tomorrow! After that, we’re pouring the slab-on-grade.

Though we considered many good strategies to control heat, moisture and air, here is the foundation detail we are using.

Proud Green Home Construction Update Foundation Slab On Grade

Here are some photos of the preparation of the concrete footing.

Proud Green Home Construction Update Foundation Footing

The excavation crew started by staking the location of the footing. Then, they dug. As you can see in this photo, they had to dig deeper in some areas to allow for the stepped footing that was designed to accommodate for a sloping site.

Before they poured the footings, they put down a 6 millimeter thick polyethylene vapor barrier to prevent ground moisture from working its way up the foundation walls and in the home. Then, they installed the steel reinforcement to help strengthen the footings. The vapor barrier is also referred to as a “capillary break”.

Keeping moisture out is the biggest durability issue to address during construction. As we continue to follow the construction of this house, we will show how we’ve addressed this issue around the entire exterior shell of the home (a.k.a. the building envelope or enclosure).

Proud Green Home Construction Update Foundation Footing 6 mill poly Capillary Break

Proud Green Home Construction Update Footing Capillary Break and Re-Bar 6

Proud Green Home Construction Update Footing Capillary Break

Following the checklists…

We are certifying this house as EarthCraft House, ENERGY STAR New Homes (Version 3.0), EPA Indoor Air Plus & EPA WaterSense programs. For each of the first three programs, we are meeting a requirements to provide a capillary break with the 6 mil poly. We will also be installing the drainage tile outside of the footing, which is also a requirement. Note in the detail above that we are using a relatively new product called E-Z Flow, an all-in-one drain tile and aggregate product that makes installation easy. More on this to follow.

 

-written by Chris Laumer-Giddens

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5 Responses so far.

  1. Milan Jurich says:

    Chris,
    Nice clear details on the above drawing. Impressive. Question for you. I’m looking to utilize the 1 1/2″ Zip R sheathing as well. In your plan, it mates up with rigid fiberglass insulation board and it works as the brick veneer starts at the Zip and fiberglass board point. How would you treat the transition if you were working with 1 1/2″ Zip R sheathing and wanted to maintain R10 basement wall insulation (XPS, for example) which is 2′ thick and the exterior base cladding at the transition is a 42″ synthetic stone water table. The 1/2″ thickness difference would look a bit off at the flashing by the transition, right? Would you recommend using 2″ of XPS mostly along the exterior with a transition to a band of 1 1/2″ XPS at the point where it mates up to the 1 1/2″ Zip R sheathing to keep the cladding in the same plane? Or would you just relocate the 2″ XPS insulation to the interior of the basement. Least favorite option is to apply 1 1/2″ of XPS at the exterior of the foundation as I’d be losing R2.5 or 25% of the R value. Thoughts? Climate is zone 5 (cold) in central OH.

    Keep up the blog … enjoy reading your articles.

  2. Hi, Milan. I enjoy your questions as well. Thank you.

    I like to keep the insulation on the outside of the foundation so the cold doesn’t have a chance to make contact with the walls.

    Assuming you haven’t already poured the foundation, have you thought about stepping in the foundation 1/2″ so that the frame wall overhangs the foundation? This will also only work structurally if you have 2×6 (or greater) exterior walls. This will allow you to keep the R-Panel and 2″ rigid insulation flush.

    On the other hand, I just ran a quick calculation for a 2,400 s.f. basement in Central, Ohio, and determined that the impact 1.5″ of XPS vs 2″ of XPS amounts to about 800-900 btu/h decrease in total heating load (at 1% design condition). It’s not significant enough to call for an increase in the heating equipment capacity, nor will it likely ever be noticeable. Unless you have another reason for wanting to use 2″ of XPS, I would recommend using the 1.5″ XPS. The added cost to go with 2″ XPS won’t just be in the material, but also the labor of dealing with the transition. Considering the small impact the extra 1/2″ has, I don’t know that worth sweating over.

  3. Milan Jurich says:

    Chris,
    That’s good to hear! We’ve planned mainly 2×4 construction with the Zip R-6.6 product as zone 5 (central OH) requires min R-5 to stay out of trouble in terms of condensation within the wall cavities. 2×6 would have required R-7.5 and I’d need to then go with exterior rigid at a greater thickness. The Zip R should provide a good enough thermal break and an exterior air sealing plane. We’ll still cover it all with the Obdyke’s Hydrogap to ensure an added safety layer to the Zip tape and also simplify the flashing around the windows (outies). Bib cellulose within the wall cavities at a high density as well.

    I’m absolutely amazed at how you easily calculated those values … re-assuring to know. I was debating interior rigid in the basement to get to the 2″, but for now, I’ll stick with the 1.5″ product at the exterior to mate up with the 1.5″ Zip R sheathing above it. Spec calls for 2″ of sub-slab XPS or EPS Type IX. Would a small amount around the basement slab perimeter make sense as well? Like 1″ to frame the floor?

    I know you and Allison like mini-splits. In our central OH zone 5 climate, I’m considering an air source heat pump coupled with a natural gas furnace … It’s Carrier’s new Infinity Greenspeed product with the variable-speed compressor. I’m thinking although the overall load may be smaller with a tight home at 3400 sq. ft., the extra cost for the modulating product would be a better choice to improve overall comfort and humidity control.

    Thanks again for your response … looking forward to your blog!

  4. Hi, Milan,

    Re: HydroGap – I’ve had this come up on a recent project where applying the HydroGap over the ZIP System was recommended. It turned out to not be the “belts-and-suspenders” that some thought. In fact, Huber Engineered Woods (ZIP System) frowned upon it because it was unnecessary, and negates some of the functions of it’s product. The other thing to consider with HydroGap is that when used with lap siding, the little nubs actually compress to the point of being ineffective. This eliminates the rain screen potential.

    Benjamin Obdyke’s HomeSlicker is a very good rain screen product that maintains the necessary gap for breathing and moisture management. Here’s a video from our Mike Guertin and our friends at GBA about both the HomeSlicker and one other (possibly less costly) option for rain screen, and some of the critical detailing that goes in to installing it.
    http://www.greenbuildingadvisor.com/vented-rain-screen-siding-assemblies

    RE: BASEMENT INSULATION – If your basement slab is more than 2 feet below grade, slab insulation is negligible. Basement walls (and the band joist on top of them) are the critical areas, and is where you should concentrate your efforts. That’s where the most heat loss and infiltration (band joist) is going to happen in the basement.

    I am familiar with the Greenspeed and several other VRF/inverter compressor models for other manufacturers, and while the verdict is still out because they’re new to the VRF world, I’m a big fan. The technology has been tested for more than 30 years, so I’m confident that it will do the job well. Many of the homeowners I’ve worked with want gas for back up, or because they don’t like heat pump heat. The later is because they’ve not lived in a well-built (aka high performance) home. You feel the heat much more effectively from a heat pump in these homes. You can size the VRF heat pumps to handle the heating load down to very low temperatures, even below 0. The ducted mini- and multi-splits also give better zoning capabilities and control, though the single upright VRF systems are far superior with a zoned duct system than conventional systems. This is why I’m confident that conventional technology will be replaced by VRF.

    One more thing. With low load homes, you will have some zones down below 5,000 btu/h, and the lowest capacity on the Greenspeed 15,000 btu/h. The low end of a mini-split indoor unit is 3,800 (universally). This can be an issue if the lowest load zone is the only one calling. It will have a tough time removing moisture (albeit a relatively small amount). It’s not often talked about that equipment in high performance homes can short cycle just as much as standard homes, for this very reason. Mini-splits still make the most sense, unless all of your zones are minimum around the low-end of the capacity range of the single upright systems. Make sense?

    Thanks again, Milan!

  5. LukeS says:

    I am researching wrapping the footings and am really confused about if water does get in through a rip or something how will it get out? The exterior foundation wall has damp proofing and insulation so that will not breath and the interior of the foundation wall is covered with poly. It could breath through the slab but what if you put rigid foam under the slab as I plan.