Letter Re: Earthquake Resistant Residential Architecture

Hello James:
Attached is an e-mail I sent to my daughter.  Her boyfriend is from Honduras and she dreams of doing missionary work there.  I thought it may be of interest to some of your readership.  I left out a great deal of information on building site selection (her boyfriend already owns five acres) and foundations.  There seems to be differences in opinion regarding firmly anchored and sand-bed isolation between footings and walls.  Most of my information was gleaned from the book Technical Principles of Building for Safety (Building for Safety Series) by Coburn.

Dear X.:
I did a little bit of reading this weekend regarding safe house construction in earthquake and hurricane prone regions.  I thought of you since you might be spending significant amounts of time in that part of the world.  Some sobering pictures of what an earthquake can do to masonry structures (Italy) 

Key points for concrete block construction (very common in Honduras):
1. Don’t build the house out of masonry, use wood which is lightweight, strong and flexible…..but if you cannot…..
2. Single story construction (probably the single most important thing)
3. Use thick blocks (at least 8″ across).  Use good blocks (should ring when blocks are struck with hammer or another block, mortar should be mixed on-site, in small batches by somebody who knows his business.
4. Simple rectangular outline.  Long, skinny houses shake to pieces while those that are closer to square in outline stay together
5. Small rooms.  No room larger than 15′ by 15′ (5 meters by 5 meters)  (probably #2 in importance….especially for bedrooms)
6. Use concrete block for interior partition walls to tie exterior walls together.  See note below about corners.
7. Door and window openings small, minimal number and evenly spaced around the building.  It is advantageous to have the tops of the windows and doors at the same elevation (see note on ring-beams)
8. No window or door openings in walls within 3′ (one meter) of an outside wall or inside partition wall
9. The strength is in the corners (see points 4,5 and 7).  Reinforce the corners with steel wire, mesh or rod laid horizontally in mortar as the walls are built.
10. Build with two ring-beams.  One even with the tops (lintels) of the doors and windows, one along the very top of the wall.  Ring-beams can be cast of concrete/steel rod or constructed of wood.  This is a picture of a structure with FIVE wooden ring-beams
11. Use a light-weight roof that is well tied together (plywood sheathing is recommended) but steel is OK.  See picture from line above.
12. Roof should be relatively steep, 30-to-40 degrees is recommended.  Flatter roofs can act like airplane wings and lift off more easily in high winds.
13. Roofs should not extend more than 24″ past wall
14. Hip roofs tend to be most resistant to blowing off.  House with five ring-beams is also a hip roof house.
15. Put the bed in the middle of the room.
16. A decent article about how to make an existing house safer