Wednesday, April 18, 2012
Most back yard pergolas are in the 8-12' range of dimensions. In most cases, if you create a span of anything more than 14' then you may need to add another post to the design to prevent the beam from sagging. Remember that the posts and beams are supporting the rooftop rafters and slats so you need to make sure you don't create something that will not bear that weight over time. Unless you are a professional contractor or experienced carpenter, it is always best to consult with a local lumberyard or home improvement center to get advice on such topics. For instance, the material type you choose could be the final determination on potential for sagging.
There are also many great DIY forums online where you can post questions and get answers from professionals and experienced deck and pergola builders. The point is - all of this advice is free! Once you've gathered the information you can get out some graph paper and start drawing out your own pergola plans complete with dimensions that are specific to your design needs.
If you are wary of starting off your own drawings, you can always grab a set of free pergola plans and just adapt those to match what you want to build.