One of the most popular questions asked when considering a new eavestrough system is which size is appropriate for my home.
The most common size today is 5 inch wide. This will take care of most all residential applications with just a few exceptions.
1. These would include a very large shingle or roof overhang that causes the water to shoot over the top of the eavestrough. This is usually only seen on a clay tile roof where the bottom row of stone tile hangs way out past the fascia.
2. A large roof area flows into a short length of eavestrough. Usually this is in an inside valley area where the flow of water is concentrated.
Six inch eavestrough can handle a higher volume of water because it is not only wider but also deeper. This is good for water flow but does not fit well on homes that have a regular 6 inch wide fascia. The 6 inch eavestrough ends up hanging off the fascia as it is angled down to the downspout and can look unsightly.
Larger 6 inch eavestroughs are generally reserved for commercial applications which normally have at least a 8 inch wide fascia board.
The above picture of a Toronto Home shows an example of a large roof area/valley flowing into a 6 inch eavestrough. 6 inch was used here to help ensure that there will be no water bypassing the eavestrough. Its extra challenging to contain all the water in a area like this because of the speed the water shoots off the inside valley. Because we almost always use leafguard this adds to the challenge. The extra wide eavestrough here helps give more surface area to the leafguard allowing the water to drain faster. Even with the larger eavestrough proper valley splash guards must be used to prevent overflows. Another trick, is to drill slightly larger holes in the T-Rex to allow for better drainage.
The biggest mistake in the book is to install 6 inch eavestrough but not use at least a large 3×4 downpipe. Using a 3×3 downpipe on a eavestrough this size is a waste of capacity.
A properly sloped 5 inch eavestrough with the same large 3×4 pipes installed will drain the exact same amount of water as a 6 inch eavestrough.
The advantage of using a 6 inch eavestrough is that the downpipe size can be upgraded to a 4×5 inch downpipe which will really make sense with such a big eavestrough. However most people will not like the look of these huge commercial downpipes on their home.
In summary 6 inch is generally only required for commercial purposes where the size is proportionate and the downpipes can be upgraded to 4″x5″ without looking out of place.