This discussion comes from a post on doityourself.com. I occasionally browse around there and drop in my 2 cents on various home improvement projects, but this one I ran across dealt with a screen enclosure. Specifically, an under truss lanai screen enclosure.
Despite the name of the website this wasn’t a ‘Do It Yourself’ (DIY) project. Rather the poster had hired a contractor to screen in his under roof lanai and was a bit concerned with the how the contractor did the work!
We just installed a screen for our lanai/patio. After the contractor finished the work, we noticed that he didn’t put any uprights between concrete posts. The opening between concrete posts is around 15.5 foot wide and a little less 8 foot high. There is a 16-inch kick plate on the bottom.
The concern is that such large spaces of screen, without a supporting member would be put too much pressure on the screen end effect its durability.
We are located in central Florida, and worried about the durability of the screen, since this looks like a rather large opening without support in the middle, but he assured us that this won’t cause any issues. He also insisted that his quote was based on this set up, and if we want to add additional uprights now, he will charge additional $400.
The lack of members does make for a slightly better view, but it does put more pressure on the screen.
When it comes to these under truss lanai’s there’s not much regulation in terms of building codes. Few (nearly none) locale’s require them to be permitted and engineered… if they did need to be permitted and engineered the cost for them would be outlandish. So there is no code compliance issue with the current screen frame.
Practically speaking the 15.5’ opening x 8’ high is not small. That said, it is not large either. All of the types of screen out there can handle that size of span when they are in original condition (new). Of course, as screen ages it deteriorates and gets weaker. To put it in perspective, new Phifer 18/14 will hold up to a power washer, but at about 3 years a power washer will shred it. In my opinion with an opening of this size, I’d expect the screen to fall within its standard life expectancy, but on the low end. While I have no idea what type of screen mesh was used, let’s just assume Phifer 18/14 screen is in place here. That mesh usually lasts 7-9 years on a pool enclosure, and a bit longer than that on an underroof application where it gets limited sun and wind exposure. I’d say it’s a safe bet that this screen will last 7 years before it shows any tears as a result of deterioration and its size.
Optimally a polyester screen such as Ultra screen which is 3x stronger than Phifer and deteriorates much less rapidly would be used. But that material does costs a bit more and isn’t ‘necessary’ for this size.
Specifications & The Outcome for Your Project
One of things I mention quite frequently on this site, and why I started it, is the need for consumers to understand and specify what they want. In this case the consumer may have wanted an additional support to get a little bit more life out of the screen. The contractor however has to sell this service, and for many consumers, the bottom line number is the only thing they hear. The contractors to know that and in order to stay in business water down the deliverable. Fortunately, on a project like this, the lack of specification it didn’t really matter too much but on larger projects, even a simple screen enclosure, it can really turn into a pickle.
For example, what if the span of screen were 30’ wide and 8’ high (as opposed to the current 15’ x 8’)? In that case the fiber glass screens will catch too much wind pressure to hold any longer than a few years. A polyester screen should be used to get a worthwhile life span. However, when selling a product in which the bottom line number is the only thing most consumers look at (until the project is done), fiberglass screen is ordinarily used. For that reason, it is not uncommon for contractors to use a fiberglass screen in spans this large. When I was an aluminum contractor I’d even have commercial clients (general contractors, home builders) on spans as large as 40’ x 9’ and use artisan screen (the lowest grade of screen mesh). Can’t image that lasted much more than a few months.