To Cap or Not To Cap?

To Cap or Not To Cap?
The term capping, or wrapping, refers to the aluminum or vinyl cladding sometimes applied over the exterior trim around a window or door.

This material is most often pre-finished aluminum in the Chicago area, though vinyl is occasionally used.  It comes in coil form and is known in the industry as ‘coil stock’ or ‘trim coil’.  It’s typically formed, or bent, on site with a portable sheet metal brake. Often sold as an “upgrade” to a building’s exterior, it’s touted by some salesmen as being low or no maintenance.

So why the debate on whether or not to cap?  After all, it sounds good and is commonly done, so there must be some benefit to it, right?

Not so fast.  Let’s examine some of the common reasons homeowners choose to cap their windows (or maybe what they’re led to believe by some window salesmen).

CLAIM:  Capping, combined with a clad wood or vinyl window creates a maintenance free installation.

FACT:  We already debunked the maintenance free myth about windows in our  ‘Why We Don’t Install Vinyl Windows’ post.  Now let’s do the same for capping.

The Marvin clad windows and doors we offer are coated with a special finish called Kynar.  This finish is incredibly durable, carrying a 20 year warranty.  We’ve installed clad Marvin units over a decade ago that still look as good today as when they were new.   By contrast, the finish on cheap aluminum coil stock is just durable enough that it generally looks good for 5 years or less before it shows signs of fading, chalking and weathering, at which point it often must be replaced or painted to restore its finish (does that sound maintenance free?).

Finding a particular trim coil color that’s an exact match to the cladding on a window can sometimes be a challenge when off brand and vinyl windows are used.  The solution here is to identify whether the window manufacturer offers coil stock in the same color palette & finish  to match the window line.  If matching trim coil is available, it’s often at premium upcharge over off the shelf coil stock found at many building supply houses & home centers.  This premium tempts many installers into using the cheaper product, resulting in poor color matching, premature fading, etc.

CLAIM:  Old, damaged wood can be easily concealed by capping, creating a like new appearance.

FACT: The above claim is true, but (and you knew it was coming), there’s a catch. The catch is, deteriorated material should never be left around a window or even worse, covered with anything – capping included.  The reason is that the decay process is not halted simply by overlaying wood with another layer of material. The term “out of sight out of mind” applies here.  Covering rotten or decayed wood keeps the decay or rot out of sight, creating the illusion that the problem is solved, when it may actually be systematically progressing. Just as a dentist would never put a cap or a crown over a cavity, rotten wood should never be covered, but rather removed to stem the decay.

CLAIM:  Capping protects wood trim from the elements – particularly moisture.

FACT:  Capping can and often does trap moisture behind it, leading to decay that’s not visible. If the capping is done improperly (and it often is), capping can direct water behind itself and keep it there, not allowing the moisture to drain.

The reality is that wood is a pretty durable product, assuming it can dry out after it gets wet.  As long as it has air circulating around it and a bit of sun to draw moisture out of it, it performs very predictably.  The problems with wood generally arise when some or all of the following precautions are disregarded:

1.     Not sealing all 6 sides of the lumber: Front, back, edges and ends all need to be primed and/or painted to minimize moisture absorption, shed water, & resist decay.

2.     Installing untreated lumber or a species of lumber that’s not rot resistant in direct contact with soil or masonry. Soil and masonry contain large amounts of moisture – especially after a rain.  They’re essentially reservoirs; butting lumber directly to them is a recipe for failure, as moisture will migrate into the lumber & remain there.

3.     Not creating positive drainage.  If one were to examine the exterior sills of windows & doors on old houses, they would likely discover carpenters and builders back then knew a thing or two about managing moisture.  It’s almost a certainty that those sills would have a pitch away from the building, permitting gravity to do its thing and positive drainage to occur. The laws of gravity haven’t changed, yet many newer wood exterior elements aren’t being installed with positive pitch, leading to many a failed installation.

4.     Not installing flashing over window and door heads or other elements that project beyond the siding.  Sounds simple, but it’s remarkable how many window and door installations are out there that are missing flashing at the tops of the units.  A lack of flashing permits water to enter behind the window or door unit, often running down the wall and rotting much of what it comes in contact with, especially where it pools.

5.     Not permitting moisture to escape. If you’ve ever seen an aluminum storm window, perhaps you’ve noticed the little holes at the bottom of the frame.  These are weep holes and permit moisture that may get behind the window to drain while also permitting a path for a small amount of air to enter the space between the storm and primary window, encouraging evaporation.  This is a sound practice, yet is often overlooked during the installation of many exterior elements- storm windows and capping included.   If you’re like us and can’t get enough of good building practices, have a look at a rain screen detail, which is the above type of exterior moisture management on a large scale.

So is all capping bad?  Of course not.  Done properly by a competent installer using good quality products and with attention to detail, it can be an option for some installations. We’ll be shooting & uploading a video in the not too distant future of a skilled carpenter demonstrating proper capping techniques, so check back to see it.

I qualified the above statement by saying “some installations” because there are instances where capping can detract from a building’s appearance, such as when it’s applied over ornate, multi-dimensional trim. These instances should not be overlooked, as covering ornate trim with flat capping really is a shame. The look of the building is changed, with the depth & shadow lines of the trim replaced by a homogeneous swath of coil stock that’s usually flat in profile. This look may be fine on a modern building, but all too often vintage buildings with wonderfully detailed window trim suffer this indignity. A better option in these instances is to forgo the capping & simply maintain the trim, which if done properly doesn’t usually require much of an effort.

The building industry has rushed to bring us one “maintenance free” product after another when in reality all that’s often required is some knowledge of proper methods & materials, as well as the commitment on the part of consumers not to be hornswaggled by those selling such products. If you really detest having to paint windows, consider using a good quality clad wood window, such as the Marvin Ultimate series mentioned above. These units will allow you to put off painting them for at least 20 years & in the scheme of things, having to paint the trim around your windows is a small job compared to painting the rest of the components of the windows themselves.

CWDS does offer capping for some projects, but our first preference is to use a good quality material such as western red cedar, cypress, or an engineered wood product for exterior trim. When installed & finished properly, these materials will generally require similar or less maintenance over the long run than capping, and often have a lower installed cost. In addition, we can mill solid lumber into almost any shape, creating or recreating traditional profiles – something capping simply can’t compete with.

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