To find the correct skylight dome for your unit, you will want to gather specific dimensions. A common assumption is that you ought to compare the outside, or flange to flange dimension of the originally installed dome. While that is helpful, many originally used domes could have varying flange widths while our replacements have a 2″ flange. To properly compare, you should take the hole dimension on top of the roof (or the “dome only” dimension from the original dome) and compare that to our dome dimension.