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The Great Window Debate: Pocket Sill Vs Sloped Sill Window – Which is Best?


Replacing your windows does not have to be a stressful experience for you. In fact, there are plenty of benefits when it comes to replacing your windows, such as improved energy efficiency, lower utility bills and a better overall look and feel to your home. While replacing your windows is quite a sizable home improvement, the more informed you are about the different types of window replacements available, the less stressful and more enjoyable the process will be (trust us!). There are many things to consider when replacing your windows, but in this quick guide, we will be focusing on the differences between a pocket sill and sloped sill window, and which is best. It is one of the great window debates! If anything has remained consistent in the design of windows throughout the years, it is the two types of sill offered by different manufacturers. However, there are a few key differences between a sloped and pocket sill (some more nuanced than others), which we will be looking at in this article. But first … what is a sill?

What is a Sill?

A sill refers to the bottom section of your window. It is where all the dust, dirt, debris (and yes, bugs!) build up over time. Now we know what a sill is, let us look at drainage. 

Understanding Drainage 

When deciding what window sill will work best for you, one of the most important things to consider is its drainage pathway away from the window. In a pocket sill window, its design relies on a series of weep pathways to remove accumulated moisture from the window frame. Weep pathways, however, have a high failure rate as they generally become blocked by dirt, debris and other sediments. When weep pathways become blocked, the water has no place to drain, forcing the water inwards into the home. It is important to note leaks in pocket sill designs are the exception and not the rule, and many pocket sill designs do a good job of draining moisture out of a window sill as intended. 

When it comes to sloped sills and drainage, as the name of the window suggests, slope sills tilt down and outwards and offer unobstructed drainage, so there is no risk of water leaking into your home. When replacing windows, Windows on Washington use the Starmark Evo double hung windows because it offers a one-piece solid slope, which improves drainage and eliminates the need for weep holes (which tend to clog and freeze).

Sloped Vs Pocket Sill – What is the Difference? 

Pocket sill windows are made to surround the bottom edge of the window sash when the window is shut. The benefit of such a design is that in many cases, your home will have better air infiltration and also more glass to your window. The disadvantage, as we have discussed, is that the sill looks and acts like a window gutter, which can in time cause major structural issues as it begins to fill up with dirt and debris.

On the other hand, sloped sill windows are designed with a sill that eliminates any build-up of dirt and debris whenever it rains. Its main advantage is that there is very little maintenance required and much less chance of any structural damage to your window frame over time, making it a very durable sill.  

Who Wins? Pocket Sill or Sloped Sill? 

When determining which is better – a pocket sill or sloped sill – it will depend on who you ask. Pocket sill enthusiasts will say pocket sills are better because they minimize problems with viewable glass, are possibly stronger because they shut into a fully supported pocket and provide better air sealing when the window shuts into a pocket that has weather-stripping layers. 

At Windows on Washington, however, we are bigger supporters of sloped sill windows and the above points are only accurate when comparing pocket sill windows to poorly designed sloped sill windows. The newer designs of sloped sill windows almost always outperform the majority of pocket sill windows.

So who wins? In our books, it will always be the sloped window sill. If you still have questions about which sill is best, get in touch with us today. We are more than happy to discuss in further detail why we recommend a sloped window sill. 

Replacement Windows Buyer's Guide

Topics: Replacement Windows