251. Openings in Walls

The location of all door and window openings in brick walls should be carefully considered, not only as regards convenience, but also as to their effect on the strength of the wall. The combined width of the openings in any bearing wall should not much exceed one-fourth of the length of the wall, and as far as possible the openings in the different stories should be over each other. Especially avoid placing a window either under a pier or directly over a narrow mullion, as at a or b, Fig. 149. If windows must be used in these positions, steel beams should be placed over the windows a and c, as a stone lintel or brick arch would be quite sure to crack from the combined effects of the load and the settlement of the joints in the brickwork on either side of the window.

All openings in exterior walls should either have relieving arches or cast iron or steel beams behind the stone cap or face arches. Ordinary relieving arches (see Section 265) are commonly used where the width of the opening is less than 6 feel, and steel beams for greater widths. In bearing walls, where the top of the openings come within 12 inches of the bottom of the floor joist, it is hardly safe to use relieving arches, unless the floor loads are very light.

251 Openings in Walls 100161

Fig. 148.

For door openings in unplastered brick partitions cast iron lintels may be used to good advantage, as they give a smooth, level soffit to the opening and show only a narrow strip of metal on the face of the wall.

252. Joining New Walls to Old

When a new wall is to be joined to an old one, at right angles, a groove should be cut in the old wall similar to that shown in Fig. 118 for the new wall to fit into and to allow of its settling independently. A cheaper method, and one more commonly used in light work, is to nail a scantling, or 2x4, to the wall of the old building, so that it will come in the centre of the new wall, as shown in Fig. 150. A similar method can be used for jointing the ends of an old and new wall. New work should never be toothed to old work unless the new work is laid in cement.

253. Thickness of Walls

There is no practical rule by which it is possible to calculate the necessary thickness of brick walls, as the resistance to crushing, which is the only direct strain, is usually only a minor consideration.

We must therefore rely principally upon experience in determining the thickness of walls for any given building, unless the construction of the building is controlled by municipal or State regulations.

In nearly all of the larger cities of the country the minimum thickness of the walls is prescribed by law or ordinance, and as these requirements are generally ample they are usually adhered to by architects when designing brick buildings.

Table IX. gives a comparison of the thickness of walls required for mercantile buildings in the representative cities of the different sections of the United States, and affords about as good a guide as any to the young architect. Walls for dwellings are generally permitted to be 4 inches less than the thicknesses given in the table.

253 Thickness of Walls 100162

Fig. 149.

253 Thickness of Walls 100163

Fig. 150

Table IX.-Thickness Of Walls In Inches For Warehouses, Etc

Height of Building.

Stories.

1st

2d

3d

4th

5th

6th

7th

8th

9th

10

11th

12th

Two Stories.

Boston . . .

16

12

...

...

...

...

...

...

...

...

...

...

New York .

12

12

...

...

...

...

...

...

...

...

...

......

Chicago . .

12

12

...

...

...

...

...

...

...

...

...

...

Minneapolis

12

12

...

...

...

...

...

...

...

...

...

...

Memphis. .

18

13

...

...

...

...

...

...

...

...

...

...

Denver . .

13

'3

...

...

...

...

...

...

...

...

...

...

Three Stories.

Boston . . .

20

16

16

...

...

...

...

...

...

....

...

...

New York .

16

16

12

...

....

...

...

...

...

...

...

...

Chicago . .

16

12

12

...

...

...

...

...

...

...

...

...

Minneapolis

16

12

12

...

...

...

...

...

...

...

...

...

Memphis .

22

18

13

...

...

...

...

...

...

...

...

...

Denver. . .

17

'3

13

...

...

...

...

...

...

...

...

...

Four Stories.

Boston .. .

20

16

16

16

...

...

...

...

...

...

...

...

New York .

16

16

16

12

...

...

...

...

...

...

...

...

Chicago .'.

20

16

16

12

...

...

...

...

...

...

...

...

Minneapolis

16

16

12

12

...

...

...

...

...

...

...

...

Memphis. .

27

22

18

13

...

...

...

...

...

...

...

...

Denver. . .

21

'7

13

13

...

...

...

...

...

...

...

...

Five Stories.

Boston . . .

20

20

20

20

16

...

...

...

...

...

...

...

New York .

20

16

16

16

16

...

...

...

...

...

...

...

Chicago ..

20

20

16

16

16

...

...

...

...

...

...

...

Minneapolis

20

16

16

12

12

...

...

...

...

...

...

...

Memphis. .

31

27

22

18

13

...

...

...

...

...

...

...

Denver . .

21

21

17

17

13

...

...

...

...

...

...

...

Six Stories.

Boston.. . .

24

20

20

20

20

16

...

...

...

...

...

...

New York .

24

20

20

20

16

16

...

...

...

...

...

...

Chicago . .

20

20

20

16

16

16

...

...

...

...

...

...

Minneapolis

20

20

16

16

16

12

...

...

...

...

...

...

Memphis . .

36

31

27

22

18

13

...

...

...

...

...

...

Denver . . .

26

21

21

17

17

13

...

...

...

...

...

...

Seven Stories.

Boston . . .

24

20

20

20

20

20

16

...

...

...

...

...

New York .

28

24

24

20

20

16

16

...

...

...

...

...

Chicago . .

20

20

20

20

16

16

16

...

...

...

...

...

Minneapolis

20

20

20

16

16

16

12

...

...

...

...

...

Memphis . .

40

36

31

27

22

18

13

...

...

...

...

...

Denver . . .

26

21

21

21

17

17

'7

...

...

...

...

...

Eight Stories.

Boston . . .

28

24

20

20

20

20

20

16

...

...

...

...

New York .

32

?8

24

24

20

20

16

16

...

...

...

...

Chicago . .

24

24

20

20

20

16

16

16

...

...

...

...

Minneapolis

24

20

20

20

16

16

16

12

...

...

...

...

Memphis . .

45

40

36

31

27

22

18

'3

...

...

...

...

Denver . . .

30

20

21

21

21

17

17

17

...

...

...

...

Nine Stories.

Boston . . .

28

24

24

20

20

20

20

20

16

...

...

...

New York .

32

32

28

24

24

20

20

16

16

...

...

...

Chicago . .

24

24

24

20

20

20

16

16

16

...

...

...

Minneapolis

24

24

20

20

20

16

16

16

12

...

...

...

Memphis . .

49

45

40

36

31

27

22

18

13

...

...

...

Denver . . .

30

26

26

21

21

21

17

17

17

...

...

...

Ten Stories.

Boston . . .

28

28

24

24

20

20

20

20

20

16

...

...

New York .

36

32

32

28

24

24

20

20

16

16

...

...

Chicago . .

28

28

24

24

24

20

20

20

16

16

...

...

Minneapolis

24

24

24

20

20

20

16

16

16

12

...

...

Memphis. .

54

49

45

40

36

31

27

224

18

13

...

...

Denver. . .

30

30

26

26

21

21

21

17

'7

17

....

...

In compiling this table the top of the second floor was taken at 19 feet above the sidewalk, and the height of the other stories at 13 feet 4 inches, including the thickness of the floor, as the New York and Boston laws give the height of the walls in feet instead of in stories. When the height of stories exceeds these measurements the thickness of the walls in some cases will have to be increased.

The maximum height of stories permitted by the Chicago ordinance with these thicknesses of walls is 18 feet in first story, 15 feet in second story, 13 feet 6 inches in the third and 12 feet in the stories above.

Although there is a great difference in the thicknesses given in the table, more indeed than there should be, yet a general rule might be deduced from the table, for mercantile buildings over four stories in height, which would be somewhat as follows:

For brick equal to those used in Boston or Chicago make the thickness of the three upper stories 16 inches, of the next three below 20 inches, the next three 24 inches and the next three 28 inches. For a poorer quality of material make only the two upper stories 16 inches thick, the next three 20 inches and so on down.

In buildings less than five stories in height the top story may be 12 inches in thickness.

For the walls of dwellings, 13 inches and 9 inches may be used for two-story buildings; for three-story buildings the walls should be 13 inches thick the entire height above the basement, and for four-story buildings 17 inches in first story and 13 inches the entire height above.

In determining the thickness of walls the following general principles should be recognized :

First. That walls of warehouses and mercantile buildings should be heavier than those used for living or office purposes.

Second. That high stories and clear spans exceeding 25 feet require thicker walls.

Third. That the length of the wall is a source of weakness, and that the thickness should be increased 4 inches for every 25 feet over 100 or 125 feet in length. (In New York the thicknesses in the table must be increased for buildings exceeding 105 feet in depth. In the Western cities the tables are compiled for warehouses 125 feet in depth, as that is the usual depth of lots in those cities.)

Fourth. That walls containing over 33 per cent, of openings should be increased in thickness.

Fifth. Partition walls may be 4 inches less in thickness than the outside walls if not over 60 feet long, but no partition to be less than 8 inches thick.