The May Practical Engineering column looked at the issue of lateral thrust in roofs — the tendency for rafters to spread apart under load. Conventionally framed roofs (see Figure 1) are often strong enough to resist this lateral thrust as long as the carpenters use enough nails or bolts where the rafter laps the attic joist (though this can be a challenge in shallow-pitched roofs). A problem with this framing detail, especially in cold climates, is that the attic insulation tends to get compressed above the wall plate. Even with ventilation chutes, the increased heat loss at the plates may contribute to ice dam troubles. So many energyconscious builders use a "raised rafter plate" detail (Figure 2) which lifts
