Answers to the Coastal Construction Quiz

December 19, 2007

Adjaye MIR entry for 9th WardIn last week’s post, I challenged readers’ knowledge about coastal construction, and what basic, easy design decisions can be made to radically improve the latest designs promoted by Brad Pitt for the 9th Ward in New Orleans. (Incidentally, you could take advantage of them, too.) Here are the answers.

1. A ‘hip’ shaped roof, as opposed to a gable, a shed, etc. Hipped roofs resist wind damage better than any other common shape, because they approach the geometry of the best wind-resistant-roof shape, a dome. See Bernoulli’s Principle. Gable ends need to be braced specially, which requires more care and more materials. They are also subject to corner tearoff.

2. Steel. Although wood construction is capable of handling heavy loads, in order to remain stiff for a 4’+ overhang as shown in some of the designs, the supporting beam will be so deep, and so heavy, that a more structurally efficient design would use steel. Multiply this expectation across Greater America, as role model designs are imagined to be multiplied, and you have a high consumption of a high-energy material, rather than the handy renewable carbon sink that wood construction is. Now I like steel fine – but I want it used sparingly and effectively in engineered connectors like those manufactured by Simpson and USP.

3. Cross-ventilation. One of the designs shows a bunch of open windows, and that’s good, except that casements (that’s the kind of window that opens like your refrigerator door) aren’t as effective against breezes from every direction as the good-old-double-hung. Crack your double-hung at the top and bottom, put a serious fan in one of them to start the flow, and you’ve just cooled your swelteringly humid house by 6 sensible degrees, according to studies.

Adjaye MIR entry for 9th Ward 4. Although it’s certainly possible to construct decks and ‘flat’ roofs over interior space – when it comes to building for general homeownership, it’s not a kind idea. Remember that these people are going to be working long hours to put ends together – respect their precious free time, and don’t spend it on education and maintenance about uncommon waterproofing materials. The sun at 30d north latitude – that’s the same as Cairo, Egypt, folks, except it doesn’t rain nearly as much there (NO: 64+ inches/year) – is murder on waterproofing stuff. Keep the roof shape as an umbrella, and try not to poke holes in it.

Concordia design entry

My favorite design is Concordia’s.It has a hipped roof, no deck-over-interior space, serious window and wall shading, porches big enough to inhabit the shaded space they produce, and all the corners look like they’ll accommodate adequate tie-downs. Put double-hung windows (to ventilate hot air out the top) instead of those fixed panes for cross-ventilation, and if I had a spare $150,000 looking for a good cause, I’d consider sponsoring that one. (Now, if they can get the Habitat for Humanity mechanism working on those, they might actually get some people into houses before next Christmas.)