1. Locate house with south orientation, +5 or - 5 degrees of due south is best. House to be elongated along the east-west axis for optimum exposure.
2. 8% to 12 % of floor area to be south facing glazing. South glazing must be vertical to prevent overheating in the summer. In general avoid the use of skylights but if used, they should be designed with much caution and thought as to thermal gain and loss.
3. Passive design houses can be direct gain, Trombe walls, mass walls, water walls or isolated gain (sunspaces or greenhouses). For the majority of designs, direct gain or isolated gain are used. Direct gain design relies on the interior mass of the house to store the solar heat.
4. Optimally insulating the house envelope is the most important issue - R20 (3.52 rsi) walls, R30 (5.29 rsi) roof, R10 (1.76 rsi) footer. Make the envelope like a thermos bottle. There is no compromise on this issue. Insulate on the exterior of mass walls. The mass walls will act as a thermal flywheel keeping the temperature of the space consistent through the day and night. Insulation must block any thermal path to the exterior. Keeping surface temperatures up (mean radiant temperature) and interior internal mass are the keys to a successful thermal environment and the proper placement of insulation is the tool for achieving this.
5. Use fixed or adjustable overhangs to block out sun completely from May 1 to July 30. Full sun should be allowed on Dec. 21. This rule will vary according to the local latitude and climate conditions.
6. Locate living areas and high activity areas on south side of house.
7. Locate closets, storage, garage and less active rooms on north side of house.
8. Locate baths, kitchen and laundry facilities near the water heater's location to minimize pipe runs.
9. Keep exterior entries away from wind. Air lock entries are always a good idea.
10. Keep infiltration to a minimum. Eliminate unwanted air entry. In very tight houses, an air to air heat exchange for ventilation is a good idea.
11. Free ventilation (operable windows) should be 6% to 7.5% of floor area. 
12. It is best to use mass floors (stone, marble, tile) only where sun strikes floor. Floors in other areas should be of a light density, such as wood or carpet.
13. In less than favorable passive solar orientation or design, use hydronic radiant floors. If optimum passive design is utilized, there is no need for a radiant floor. If radiant floors are used, solar heating of the water is ideal because of the lower temperatures required for floor heating. Insulation under the radiant floor is required.
14. Double pain windows on south exposure, on other exposures use triple pane or low-E glass especially north glass which should be kept to a minimum.
15. Keep west facing glass to a minimum to reduce summer overheating. If required for a view, use high shading coefficient glass or low-E glass (or reflective blinds).
16. To optimize passive gain, use night window insulation such as shutters or insulative curtains.
17. South exposure sunspaces (greenhouses) are solar rooms attached to the south side of the house. In Italy south facing terraces would be ideal to close in with glazing that could be opened in summer. The terrace can be closed off from the main house and opened and closed as needed. South glazing should be a maximum of 6" above the mass floor to allow optimum sun exposure to the mass floors. The floor perimeter or floor itself must be insulated as do all the columns and walls.
18. Use active solar panels for water heating. Insulate pipes and storage.
19. Without a doubt for maximum thermal comfort and cost effectiveness, the best use of the construction funds is to put it into the envelope rather than the heating system. If the envelope is designed with optimal passive solar features, the size and sophistication of the heating system can be designed to be much more economical plus the utility bills will be much less.
20. Use natural landscape to help both in controlling winds and shade for natural cooling