About to build a coastal home in zone 2B and would like to be off the grid as much as possible & be hurricane resistant.
kennethmsmith
| Posted in Energy Efficiency and Durability on
We have never done a new-build and never had to deal with hurricane potential. We want to start with the most off the grid build possible for our area (Corpus Christi, TX). This will be a retirement property for us so we do need to consider budget. What are the most cost effective ways to be energy efficient while also being able to withstand high wind & flood potential?
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Replies
Ken,
Being off the grid is like being pregnant. Either you are or you aren't.
Anybody interested in building an off-grid house is advised to find an off-grid rental and live in it for a month or two. If you think you're ready for the 19th century you won't have much of a learning curve, but for the other 99.7% of the population it's an eye-opening primer on home-energy management.
In Corpus Christi living off grid will mean living without air conditioning, which is quite an adjustment, given the high summertime dew points in that area. Even if the indoor temperatures can stay under 85F, the humidity can be pretty intense.
Sensible cooling can be managed by the house design, using high thermal mass construction and minimal window area (especially west facing windows) and exterior shades/shutters on what windows you have. Think "adobe", but with some insulation.
Even 2" of continuous EPS shell embedded in high-mass wall provides more than enough insulation, and a SCIP approach (essentially wire-reinforced concrete over an EPS core eg: http://ecotechbuildersinc.com/product.html ) works pretty well, and can be cost-effectively finished with stucco on the exterior, and plaster or decorative clay finishes on the interior. the more thermal mass you can put inside the EPS, the better the house will perform, so integrating stone & concrete into the interior elements are GOOD thing. Cement based rammed-earth approaches to high-mass walls also work well in that climate.
The mid-summer outdoor mean temp in Corpus Christi is about 85F, with average nightly lows in the ~80F range, so there is some potential for managing the temperature of the thermal mass inside the house with night time ventilation strategies during cooler summer weeks, but you'd have to be able to ride out the heat waves with minimal ventilation and keeping the windows shuttered from the exterior, which could take some getting used to.
Ken,
If you are worried about flooding, keep your main floor as high above grade as possible. Your lower story can consist of a garage or car-port with no finish materials and break-away walls. Of course, if this is a retirement home, you'll have to get used to climbing stairs. If you don't like stairs, don't build in a flood zone.
If you are worried about hurricanes, you should probably build with insulated concrete forms (ICFs).
And, as Dana pointed out, if you want to include an air conditioner, you'll need to be grid-connected.
ICFs are more insulation than you need (they start at R16, and then only a few vendors have them- most start at R20) and the thermal mass too isolated from the conditioned space to do much good regarding peak sensible cooling loads, which is why the SCIP option is probably the better option here.
SCIP construction where the interior-side shot-crete becomes the scratch coat for hard plaster or clay finish and the exterior shot-crete is the scratch coat for stucco is also very flood-tolerant- more so than most ICF solutions.
The Hi'ilani Eco House is an off-grid SCIP house (including a SCIP roof) in Hawaii that has been widely reviewed:
http://inhabitat.com/studio-rmas-hiilani-ecohouse-is-americas-first-carbon-neutral-concrete-structure-and-its-volcano-adjacent/hiilani-ecohouse-1/?extend=1
http://www.hiilaniecohouse.com/blog/?cat=5
By building the roof out of SCIP too the whole thing can be designed as a reinforced concrete monocoque, with HUGE resistance against hurricane force winds compared to other roof options, and having a mass-roof also helps enormously in managing solar gains.
If taking a poured concrete approach, insulating on the exterior only is the right way, and R10 is plenty. A high-mass wall with exterior R10 would outperform a 2x6 wall with R20 cavity insulation (~R14 "whole-wall" after thermal bridging) in that climate.
But it's not just a technology for hot climates in hurricane zones:
http://www.oregonlive.com/front-porch/index.ssf/2013/07/to_save_the_trees_vancouver_ho.html
In a region with lots of in-ground swimming pool contractors there has to be a surplus of equipment and talent for spraying concrete. If you keep the design simple and don't go hog-wild on luxuries you can probably build R8-R12 SCIP homes for well under $150/foot of living space (especially since you won't have central air conditioning & heating), even if it costs 3-4x that much for custom engineered drop-dead gorgeous architectural marvel builds using SCIP in Hawaii. It'll be more expensive than CMU (but it'll be 10x as hurricane resistant) and cheaper than ICF.