22O 



Commercial Gardening 



board is made exactly the width of the wall, plus twice the thickness of 

 the planking to be used for the concreting: in the case of a 4-in. wall and 

 1^-in. plank this will be 6J in. At one bottom corner, A, cut out a little 

 square piece the thickness of the planking, 1 in. Now if the plumb-board 

 is set up with the point B, as in figure 166, touching the line, the wider part 

 of the board will overhang the line by the correct amount, and if the posts 

 are driven in touching this edge they must all come right. When cutting 

 out the posts it must be remembered that they must be made long enough 

 to allow for the height of the wall at its highest point, plus the depth of 



the footings and 4 or 5 in. to 

 go into the ground, and about 

 6 in. extra, so that if the wall 

 is to be say 2 ft. 6 in. high, 



Fig. 165. Corner Post fixed with Stays 



B 



Fig. 166. Plumb-board 



the posts must be at least 4 ft. high, and if the ground slopes much across 

 the house, they had better be higher by the amount of the slope, so that 

 they can be used for both walls. 



This point must now be considered. A greenhouse should have a fall 

 of 6 in. in the 100 ft. This will allow the gutters and pipes to be fixed with 

 the least amount of trouble. Probably the ground will have more natural 

 slope than this. The wall is to be 2 ft. 6 in. high, so measure off that 

 height on the post which is in the lowest corner of the site. This can be 

 judged near enough by the eye. At this height nail on a small crosspiece 

 square with the post. About 6 ft. off put up another crosspiece dead level 

 with the top of the first one and in a line with the footings. Now sight 

 along the tops of these two crosspieces, and mark off on the post in the 

 farther corner of the trench where the eye strikes it. This point is level 

 with the 2-ft.-6-in. mark on the first corner post. Mark off on the farther 

 post a height of 2 ft. 6 in., as on the first, and see what the difference is 



