Coastal considerations
Looking to build a small, age-in-place cottage down in Rhode Island. It’s across the street from a bay and faces west. I’m thinking the west side will have a good ammt of windows and will be the gable end. Solar opportunities on the south facing side.
It gets really windy there, so I’m wondering what type of insulation scheme we should persue. Or if the wind factor changes your approach at all. I’m also wondering if we should build on piers.
If there are any green builder architects in RI coastal work you can recommend, it would be appreciated.
We’re just starting the site work now. Trying to figure out the allowable footprint, septic and well setbacks with the engineers. I’d like to have a general vision before talking to the architects..
Thanks, Steve
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Replies
Stephen,
If you are worried about wind, you should clearly pay attention to airtightness. Set an airtightness goal and put that goal in your specifications. Make sure that the contractors understand, and verify airtightness with a blower door.
When it comes to insulation, there are many approaches that can work. It's wise to exceed minimum code requirements for R-values.
If you expect to have lots of west-facing windows, make sure that the west glazing has a low solar heat gain coefficient (SHGC). Your south-facing windows, on the other hand, should have a high SHGC (and an adequate roof overhang).
Thanks Martin. What type of framing and insulation would you recommend for a cape style on the coast? 2x4 advanced framing with exterior polyiso? Outtie or innie windows?
Stephen,
You need to choose a wall construction method that fits your budget and is familiar to your contractor. As long as you achieve a high R-value, address thermal bridging, and pay attention to air tightness, there are many approaches that can work: double-stud walls, 2x6 walls with exterior rigid foam, 2x6 walls with exterior mineral wool, SIPs, or ICFs.
Attention to workmanship is more important that the wall construction type you choose.
"If you expect to have lots of west-facing windows, make sure that the west glazing has a low solar heat gain coefficient (SHGC)."
+1!
Better yet- think very carefully about just how much window you really need to take in the view from your easy-chair. It's (unfortunately) all too easy to build a 1000' house with a 5 ton cooling load if you load up the west side with glass, since it's difficult to shade the west side from the low late afternoon sun, and the solar gain from the windows starts coming on strong just as the daily outdoor temperatures are peaking. DO consider exterior roll down shades on the west windows as part of the overall thermal design.
A mass-wall approach using exterior insulation-only (not ICF) can help manage the high-gain PM hours, which would then keep the place warmer after the sun sets and the cool breezes come on strong. Code min would be R13 continuous insulation on the outside of a poured concrete or cinder-block/CMU wall. If the house is going to have a full basement or a crawlspace, doing the foundation as ICF with the exterior EPS continuous with the exterior insulation of the above grade wall for minimal thermal bridging can make sense. Then a couple inches of EPS under the basement floor (or rat-slab) continuous with the interior-side EPS of makes it easier to keep the sub-grade space (and any goods stored there) mold-free.
Building on piers may make sense if you're low enough in elevation that storm surges would flood a crawlspace or basement, but it otherwise just complicates the air-sealing and thermal issues.
If going timber-framed, an ICF foundation with 2x4 framing (16" o.c., not necessarily AF) + 2.5-3" (whatever thickness makes it roughly even with the ICF's EPS) of exterior foam brings you up to a better than code condition for R-value, (>R20 whole-wall, even with the thermal bridging of the framing factored in.) There are multiple vendors of reclaimed roofing foam in southern New England (eg: http://providence.craigslist.org/mat/3667200869.html , http://www.insulationdepot.com/ ) and it typically goes for ~1/4-1/3 the cost of virgin-stock, making it a relatively inexpensive way to go higher-R (cheaper than high density batts or half-pound spray foam.)
But timber framed doesn't have quite the same heat buffering aspects of a mass-wall, which may be important for maintaining summer-PM comfort if you're designing for sweeping bay views. A deep porch roof on the bay side would help considerably, if you can handle not having the full sky view as well, but it's almost impossible to build an awning-shade deep enough to deal with the west side (which would be susceptible to wind damage too.)
You said the bay is across the street. Will the home be elevated? How far above sea-level is the site?
Dana's suggestion of a porch on the west side can solve many issues - shading, street-side privacy, traditional look, sheltered entry, outdoor living space. It really depends on the specifics of the site, and the view lines.
For design ideas, we did a lot of driving, biking, and boating (camera in hand) in neighboring communities of RI's "East Bay". Plenty examples of excellence, and even more design mistakes to be avoided! And some great architects and builders.
Piers vs foundation is a flood/storm engineering question. A foundation is usually more practical, even on the water.
Great stuff guys. I'll look into how high above sea level it sits.
Stephen,
We have been dealing with similar issues - design and regulatory - in RI. Not sure about etiquette of moving discussions off-line, but I would be happy to chat with you; my email is Curtis R Betts at gmail.
best,
Curtis