In the Corinthian, the girders and roof-opening are constructed on these same principles, but the girders run in from the side walls, and are supported all round on columns.
In the tetrastyle, the girders are supported at the angles by columns, an arrangement which relieves and strengthens the girders; for thus they have themselves no great span to support, and they are not loaded down by the crossbeams.
From Mau the house of the surgeon, pompeii Illustrating The Tuscan Atrium 1. Fauces9, 10. Dining rooms 2, 3. Shops13. Kitchen, a, hearth 4. Storage14. Rear Entrance 5. Atrium16. Portico 6. Chambers18. Stairs to rooms over the rear of the house 7. Tablinum20. Garden 8. Alae | From Mau house of epidius rufus at pompeii illustrating corinthian atrium |
| 1. Fauces | 9, 10. Dining rooms |
| 2, 3. Shops | 13. Kitchen, a, hearth |
| 4. Storage | 14. Rear Entrance |
| 5. Atrium | 16. Portico |
| 6. Chambers | 18. Stairs to rooms over the rear of the house |
| 7. Tablinum | 20. Garden |
| 8. Alae |
2. In the displuviate, there are beams which slope outwards, supporting the roof and throwing the rainwater off. This style is suitable chiefly in winter residences, for its roof-opening, being high up, is not an obstruction to the light of the dining rooms. It is, however, very troublesome to keep in repair, because the pipes, which are intended to hold the water that comes dripping down the walls all round, cannot take it quickly enough as it runs down from the channels, but get too full and run over, thus spoiling the woodwork and the walls of houses of this style.
| a. fauces | p. andron |
| d. tetrastyle atrium | r. peristyle |
| n. dining room | w. summer dining room |
| o. tablinum |
The testudinate is employed where the span is not great, and where large rooms are provided in upper stories.
3. In width and length, atriums are designed according to three classes. The first is laid out by dividing the length into five parts and giving three parts to the width; the second, by dividing it into three parts and assigning two parts to the width; the third, by using the width to describe a square figure with equal sides, drawing a diagonal line in this square, and giving the atrium the length of this diagonal line.
4. Their height up to the girders should be one fourth less than their width, the rest being the proportion assigned to the ceiling and the roof above the girders.