Does the rug match the drapes?
I’m in the process of making decisions for our new build. We live in West Virginia (zone 4). My last project was in Wyoming 12 years ago. This milder climate is a blessing, but technology, efficiencies, and internet sharing have overwhelmed me with the possibilities. Like everyone, I am weighing cost verses long term savings. We are on a tight budget, but I still would like the smartest/greenest home possible.
Right now, we are planning a 1400′ slab on grade with hydronic radiant in the floor. I’m thinking 2×4 walls with bats and continuous external insulation outside of OSB. And then closed cell foam at the roof. Does it make sense to have the thermal break on the walls, but not the roof? Thanks in advance for any advice or direction.
GBA Detail Library
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GBA contains quite a few articles of building the "pretty good house." I think there are lots of options for making a home efficient without busting the bank, but you have to keep building science requirements in mind. For example, you can install any thickness of rigid foam (or none at all) on your sheathing in Zone 4A, but you must install at least R-5 on a 2x4 wall and R-7.5 on a 2x6 wall in Zone 5A. (I'm assuming you are in one of these zones.) Similarly, you can install radiant heat, but a conventional forced air or ductless mini split will likely be more cost effective (assuming you insulate your slab.
Closed cell foam at the roof is expensive. It's cheaper and higher performance to install 3" of rigid polyiso above the roof deck and R25 -R28 batts under the roof deck, even with the cost-adder of a nailer deck above the foam through-screwed to the structural roof deck on which to attach the shingles. It's cheaper still if you use reclaimed or factory-seconds foam:
While IRC 2015 code-min for zone 4 is R13 + R5 continuous insulation, it's cheaper to go with 2" of reclaimed or factory seconds foam than a code-min solution with virgin stock material. At 2" the wall thickness is the same as a 2x6 wall, and would be pretty much co-planar with the R10 slab edge insulation. Metal Z-flashing at the transition from wall-foam to slab-edge foam would be a good idea in termite risk areas. Reclaimed 2.5" roofing EPS would be a cheap way to do the R10 slab edge foam too, in which case you might as well bump the wall foam to 2.5". Don't use polyiso below grade, since it can become saturated when in contact with soil, but EPS is fine, even though most contractors prefer 2" XPS. XPS is blown with high environmental HFC blowing agents, and as they dissipate over a few decades R10 XPS drops to the R8.5 range. With EPS the R-value is stable over time, and it's blown with low-impact hydrocarbons (usually pentane.)
Loose fill insulation on the attic floor is less $/R and less heat loss/R (less area). With scissor trusses if you want a higher ceiling.
Look into a frost protected shallow foundation.
First of all, can you tell us your name?
In-floor hydronic heat is expensive -- and you probably still want an air conditioner. So why not consider ductless or ducted minisplits from the start?
More information here: All About Radiant Floors.
A 1-zone hydronic slab is pretty cheap radiation and a pretty simple system, not a bad way to go if you're using a condensing natural gas boiler or a condensing water heater for heat.
A 76,000 BTU/hr condensing tank type water heater like HTP's Phoenix Light Duty or a small Polaris has more than sufficient burner to handle both loads simultaneous for a better than code 1400' house, and an isolating plate type heat exchanger and a couple of pumps (only one of which has to be suitable for potable water) can come in pretty cheap and should be good for 20 years or more.
Given WV's 90%+ coal fired grid-source a condensing gas solution has substantially lower carbon emissions than a mini-split heating solution. That won't always be the case, but within the lifecycle of a boiler or mini-split it's pretty much a given.
Hydronic heat doesn't fit well with this climate zone the way it might in WI. Zone 4 has four seasons almost three months each. In spring and fall, many times I like to turn on the heat just for an hour to take the chill off. Afternoons become glorious and all windows get opened. Temps remain great until late evening, but the heat stays off because we like to sleep in cooler temps.
You just can't turn off a warm floor, so this is useful for the three winter months only. Summer in the SE requires AC to control humidity as well as heat, which would require a whole different system.
I endorse the mini split solution. I am using the ducted option. I also highly recommend separating the design pro from the installation contractor—this provides confidence in the outcome. Isaac Savage at HVACDesignPros.com has been both affordable and incredibly responsive in my experience.
If hydronic heated slabs can be managed well with the diurnal load swings in US climate zone zone 4B Arizona (and they can), there's no reason they can't be managed well in WV.
But unlike AZ (where most of the time the latent loads are usually negative), you can't easily use the slab for cooling.
Depending on where the load calculations fall the place can probably be cooled with a single 3/4-1.5 ton ductless head. At which point one might look at the up-charge for a heat pump version to have some options, but in West Virginia that's a lot LESS green than heating with condensing natural gas. See:
(Unfortunately the links to the EPA's Clean Power Plan targets & projections no longer work, but can surely be found in an archive site if you really want to see them.)