Stevenson-like Small Shade Box

A temperature sensor must be shaded but with good airflow to be accurate. One way to do this is with a Stevenson screen, named after its inventor Thomas Stevenson. Not finding any I liked on the web, I opted to design my own as shown here. My friend Bob Paauwe helped me refine the design and actually cut all the pieces in his wood shop.

Rather than measure all these identical pieces, we built jigs and measured the jig once. Then just use the jig to make many identical parts. I finished the box with a marine grade varnish. The finished weight is 13 pounds. It was installed as shown here on July 20, 2002. Check out my station information page for a description and graph of the resulting temperature change.


The louvers are 1/8" white tileboard cut to 1-1/2" wide strips. The ends are cut at 45 degrees while sitting on a jig that holds the face at 45 degrees from the table saw surface. This forms the compound angle where the ends meet. The length to the tips must be 13" for the outer louvers and 10-1/4" for the inside ones.

The louvers are held in place by 1-1/2" square posts. The outside and inside of the posts have 5/8" deep slots cut at 45 degrees leaving 1/4" of uncut material up the center of the post. The slots are one inch apart with the inside set staggered 1/2" from the outside set to get the alternating louver positions. 8" posts are shown but the height can be extended easily by just adding more louvers.

Four posts are used, one in the center of each side. The posts are permanently fixed to the ceiling, as shown by the screw. The floor remains removable and is how the sensor is installed. The floor has a board sticking up inside for mounting the sensor. Square screw hooks go up into the bottom of the posts and extend down through slots in the floor. Turn them 180 degrees to secure or open the floor.


The floor and ceiling are solid 3/4" x 12" x 12" wood. They have sixteen 1" ventilation holes to let air move through vertically. Three vertical "truss" triangles are also made from 3/4" material to support the roof. These are 3-1/4" high at the center except that the end ones are cut short 3/4" to allow air to escape out the "attic". The center one has a vent hole or two to allow cross-ventilation. A screw eye can be mounted in the peak of the center if you need to hang the box rather than mount it on a post.

The two sloped roof sides are 1/8" x 8" x 14" made out of white tileboard, the same material as used for the louvers. This allows about a one inch overhang. 1/8" tileboard is also used on the end caps to complete the covering with the same material. The end caps and roof are glued to the 3 trusses and then six screws secure the finished roof to the ceiling.


If all this looks like too much work, you're might be right. It took me most of two saturdays, one to cut the parts and one to assemble it all. Plus an evening for finish work. In retrospect, an older drawing of different louver support may be easier to build. It requires twice as many posts and slots, but has simpler 90 degree cuts on all louvers.

Timothy D. Witham <twitham@quiknet.com>
Last modified: Fri Aug 9 00:15:36 PDT 2002