Aluminum capping: how to stop painting your window trim forever

A neighbor in Ephrata wrote on Nextdoor that we had replaced their windows and "wrapped the outside wood with aluminum" and done a wonderful job. Most people reading that had no idea what the second part meant. This is the explanation.

The problem it solves

Every house built before about 1990 has painted wood on the outside: window frames and sills, door casings, the fascia board the gutters hang on, the rake boards up the gable, porch beams and posts. Paint on wood outdoors lasts five to eight years in Pennsylvania. Then it peels, water gets into the wood, the bottom corners of the window frames go soft, and you either paint again or watch it rot.

Most homeowners paint again. By the third or fourth time, the wood under the paint has started to go anyway, and the painting gets harder because there is less sound wood to paint.

What capping is

Aluminum capping, also called trim wrap or trim coil, takes thin flat aluminum stock, 24 inches wide on a roll, in a baked-on color, and bends it on a metal brake to the exact profile of each piece of wood trim. The bent pieces are fitted over the existing wood, fastened with color-matched trim nails or hidden fasteners, and the seams are sealed where water could get in.

The wood stays. It is still doing its structural job, holding the window, carrying the gutter. The aluminum takes the weather. From the street, the house looks freshly painted. It never needs paint again. The rot stops, because the wood is dry.

What gets wrapped

• Window frames: the brick mold or exterior casing on each window, and the sill
• Door casings and the brick mold around entry doors
• Fascia boards along the eaves, behind the gutters
• Rake boards up the gable ends
• Porch beams, headers and the trim on columns
• Garage door casings
• Soffits, where they are wood, usually replaced with vented aluminum soffit panels at the same time

On a brick house, which is most of Ephrata, Lancaster and Lebanon, the wrapped trim is the only wood on the exterior. The house becomes zero-maintenance outside.

How it is done right

There is a right way and a fast way, and the difference shows up in about three years.

The wood has to be dry and sound. Wrapping wet or rotted wood seals the moisture in and the wood keeps rotting under the aluminum. Soft spots are cut out and replaced first. If the whole fascia is gone, it is replaced with new wood before the wrap.

The bends have to fit. Each piece is measured and bent to the profile of that trim. A window with a sill and a brick mold is four or five separate bent pieces. A loose wrap that flaps in wind or has gaps at the corners lets water behind it.

Water has to run out, not in. Seams lap the right way, top over bottom, so water runs down and off. The tops of pieces are sealed; the bottoms are left open so anything that does get in can drain. The sill piece has a drip edge.

Fasteners are hidden or color-matched. Trim nails in a matching color, set in the folds where possible, and sealed.

A sloppy wrap, the kind you see with wavy fascia, visible silver nail heads and caulk at every corner, is worse than paint. A good one is invisible and permanent.

What it costs

Compare that with painting the trim on a two-story house, which is $2,000 to $4,000 every six or seven years if you hire it out and a long weekend on a ladder if you do not. The wrap pays for itself at the second skipped paint job.

When to do it

The best time is when the windows are being replaced. The new window goes in, the frame around it is wrapped, and the whole opening is done and sealed at once. It is also natural to do the fascia when the gutters are being replaced, because the gutters come off anyway, and to do the rakes and soffits when a roof is replaced, because the staging is up.

It is also a fine stand-alone job. A lot of brick-house owners call just for the trim, because it is the only thing on the outside they are still painting.

Colors

Trim coil comes in about thirty colors: white, almond, clay, tan, several greys and browns, black, and a few greens and reds. White is the most common because most trim is white. Matching an existing window color, say a bronze or a tan on newer windows, is straightforward.

What it does not do

Capping does not add insulation; it is cosmetic and protective. It does not fix a window that is rotted through, which needs replacing. And it does not look right on historic wood trim with heavy profiles and carved details. On a Victorian in Lititz with decorative brackets, paint is still the honest answer for the decorative parts, though the plain fascia and rakes can be wrapped.

The combination that makes the most sense

On a typical 1960s to 1980s house around here, the exterior job that changes the most for the money is: replacement windows, trim wrap on every window and door, new fascia wrap with new seamless gutters, and vented aluminum soffit. After that, the only paint on the house is the front door, and only if you want it to be a color.

If you want to know what it would cost on your house, I will come out and count the windows. The estimate is free.