Shielding effects on housing in neighborhoods

In this study, shielding is referred to as the effect upwind and/or downwind structures have on the wind loads of an instrumented model. Because of shielding, a home in a neighborhood of like sized homes or a home surrounded by a fence would feel the effects of the wind less than a home in an open field. Numerous tests were conducted in a wind tunnel study undertaken at Texas Tech University on a single model, with 98 total pressure taps, of a low rise building surrounded by like sized homes at differing arrangements. Tests were also conducted with a representative, 35% porosity fence at varying distances upwind of the instrumented model. Point pressures were integrated to give uplift and drag forces on the models. The aim was to obtain a better understanding of shielding and the parameters of significant influence in a domestic scale neighborhood. The results of this study have produced these conclusions:

1. The wind tunnel results for the isolated home agreed with codified values of ASCE7-02 and AS 1170.2 and with values found by the studies of Holmes and Best.
2. The addition of an adjacent row changes the overall drag (-5%) and uplift (+10%) forces very little.
3. Shielding is provided by a single row of like sized homes upwind up to 16 times the eaves height (Sx/h = 16) of the instrumented model.
4. When spaced at a distance of 4 times the eaves height, shielding remains when multiple rows are added upwind. When considering the mean values, shielding appears unaffected after two rows. When looking at the pseudo-steady values, however, there appears to be a decrease in shielding due to the reattachment of the separation bubble after 3 rows.
5. Maximum shielding is provided when the wind attacks normal to a wall. When rows are added upwind and downwind of the instrumented model, funneling occurs and larger forces were recorded on the instrumented model for wind directions other than normal to a wall for a regular array of elements.
6. At close spacing, 4 times the eaves height, the homes and fence provide the same shielding. As the spacing is increased, the fence provides greater shielding. This effect is more evident in the configuration with the additional row downwind.
7. When comparing the results from the wind tunnel to those of the Australian and American wind load codes, the current standards are conservative.