A popular feature of many homes built over the last few years is a dome. The dome can be a distinctive feature in a home. The high vaulting can certainly add drama to any room. The lantern which tops many domes can bring light into dark, inner-rooms. But the main reason for considering a dome is cost.
A dome has very little steel and therefore is a relatively inexpensive way of getting a roof. There is some tradeoff with the beefed up steel necessary for the walls which support a dome, but even so, there is no need for the many boveda I-beams necessary for a more conventional roof. The columns which support a dome must be constructed of stronger material, for example, the rebar will need to support the extra forces that the dome will present but even considering this aspect it is still less expensive to build the dome than a standard boveda roof.
Domes can cover small spaces or larger ones. When used above smaller spaces the dome can be a stand-alone feature. When the vaulting covers larger areas, then the dome may need to be reinforced with reinforced concrete beams poured in place on the perimeter of the dome.
In either event, the brick work cannot stand alone. There needs to be a layer of cement plastered over the brick work in order to give it some degree of stability. Until the first liquid cement treatment is mopped in place the dome is actually very weak and won’t support the weight of a man. It is only after the second coat of jal and cement is poured over the outside that the dome begins to take on strength. In this regard, the brick work is nothing more than a form which is used to support the actual strength of the dome. But since the brick work is the part which is seen from inside the house it must be built very carefully.
The actual construction of the dome can only be done by a skilled mason. Not more than a meter of free-flying brick can be laid in one day. There is no form or jig employed, only skill. The dome is started in the corners of the room. As the dome is completed it moves out the side walls and at the same time closes in to the center of the space. If the calculations of the mason are correct then the dome will have evenly space bricks right up to the center with the last four bricks completing the dome in the exact center.
If the dome is to have a lantern, then the brick work stops at the outer limits of the lantern, which is built after the reinforcing has dried. It is sometimes better to have the lantern welded then set in place by the mason. You can also buy prefabricated lanterns. The advantage of the welded version is that you can usually get larger windows.
Domes do have a tendency to leak so extra care should be taken with sealing them. This is especially true about the juncture of the lantern and the dome. These two parts must be built at separate times and therefore a separation exists by design. Any separation on a roof will allow water in. The typical solution to this problem is to place a rather wide bead of cement around the base of the lantern. You may also opt for a seal with the famous Fester products. As time goes on this may be a necessary adjustment anyway.
Another common problem with domes is condensation on the inside of the lantern. One solution is to vent the lower part of the windows so that water can’t come in while allowing the window to “breathe”. This isn’t foolproof but it does reduce condensation to a manageable level.
