GENERAL PREPARATION

Exterior trim can be applied in many different ways, depending on the design of the house and the type of siding. For wood shingles or clap­boards, use trim boards that are thicker than the siding, and apply trim to the sheathing before putting up the siding. For flat shiplap and board- and-batten sidings, apply trim boards over the siding. In general, try to use the same materials and installation methods that were used on the house originally.

Solid-wood exterior trim should be a rot — resistant species such as redwood, cedar, or hard pine and sufficiently dry to avoid shrinkage, cup­ping, and checking. For those reasons, avoid sugar pine, knotty pine, hemlock, fir, and the like. If you’ll be painting the trim, you may find it cost effective to use finger-jointed trim stock fabricated from shorter lengths of high-grade wood. Such stock is widely available and can be durable if you keep it sealed with paint. For best results, specify vertical-grain heartwood grade because it

Eaves Trim___________

Rake trim

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Fascia, soffit, and frieze boards are collectively called the eaves trim.

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Prime all faces and edges of exterior trim and siding, including the back faces. Back priming is especially important because moisture trapped between back faces and sheathing can lead to paint or sealer failure, cupping or—in extreme cases—structural rot. After cutting trim or siding, be sure to prime the cut edges as well.

resists decay, holds paint well, and is the most stable dimensionally. Caution: If this trim is allowed to absorb moisture, its finger joints may separate.

BACK-PRIMING AND PAINTING

Apply primer to all faces and edges of exterior wood (and engineered wood) siding and trim, including the back faces. Back-priming is critically important because wood will cup (edges warping up) when the sun dries out the exposed front face, while the back unexposed face retains mois­ture. The greater the moisture differential between front and back faces, the more likely the cupping.

While cutting trim or siding, keep a can of primer and a cheap brush nearby to seal the ends after every cut; unprimed end grain can absorb a lot of moisture. (It’s especially easy to forget to prime cut edges when you’re using preprimed trim.) Ideally, apply at least two top coats of acrylic latex paint after priming to seal trim and siding. If you want stained or clear-finished trim or siding, use cedar or heart redwood.

ATTACHING TRIM

As a rule, for best attachment, secure exterior trim to framing. In those rare instances where you have only sheathing to nail to, angle the nail so that it will be less likely to pull out.

Choosing attachers. Pick a nail meant for exte­riors. If you’ll be using a transparent finish, mak­ing nail heads visible, stainless-steel nails are the premier choice; though expensive, they won’t

rust. Aluminum nails won’t stain but are some­what more brittle and more likely to bend. Galvanized nails are the most popular because they’re economical, stain minimally, and grip well. Many nail types (including stainless) also come in colors matched to different wood types—cedar, redwood, and so on. Ring-shank nails hold best.

For stained exteriors, some contractors prefer galvanized finish or casing nails because their heads are smaller and less visible. Box nails are a good compromise. Their larger heads hold better than finish nails, yet their shanks are smaller than those of common nails, making box nails less likely to split wood. There are also “splitless” siding nails that come with preblunted points to minimize splits. (The blunt point smashes through wood fibers, rather than wedging them apart.)

Where trim is exposed—say, at cap trim atop a half wall—and you want maximum grip, use stainless-steel trim-head screws instead of nails.

drive nails quickly and accurately, reducing splits and eliminating errant hammer blows that mar trim. After setting the trim with finish nails, you can always can go back and hand nail with headed nails to secure the trim further. Or you can use headed siding nails in the nailer.

Подпись: Engineered Trim: A PrimerПодпись: Pneumatic nailers. Most pros use pneumatic nailers to attach exterior trim. Using a finish nailer with galvanized nails allows you to tack up trim exactly where you want it. Anyone who has spent time trying to simultaneously hold and nail a 16-ft. corner board in place while balancing on a ladder will appreciate this tool. Nailers alsoПодпись: Preassemble corner boards, soffit-and-fascia boards, and other exterior trim on the ground whenever possible. The joined pieces will be tight and square, even if the framing and sheathing behind them isn't.

Подпись: Just as engineered lumber revolutionized structural materials, there's now an engineered trim rated for exteriors. Many such trim products are perfectly straight, flat, and factory primed on all six sides. If you're accustomed to working with wood, engineered trim requires getting used to, and the jury is still out on its long-term stability and durability, especially that of the hardboards. Here's an overview of types: ► Laminated veneer lumber (LVL) is made from thin wood veneers glued so the grain runs in the same direction, faced on one side with a medium-density overlay (MDO) of resin-impregnated paper. LVL trim is available in 1-in. and Ш-in. (5/4) thicknesses; in standard widths from 4 in. to 12 in., in 2-in. increments; and in standard lengths of 16 ft. and 20 ft. It's easy to cut, drill, nail, and handle, and its MDO face paints wonderfully. However, LVL is expensive. Clear Lam® is one well- known brand. ► Hardboard, fiberboard, or wood-fiber composite is fashioned from wood chips steamed, pressed, and glued. There are many brands in this category, including TrimCraft®, MiraTEC®, PrimeTrim®, ChoiceTrim®, and ProTrim®, and product features vary greatly. Composites tend to be available in 1-in. and UA-in. thicknesses, in standard widths of 4 in. to 12 in., and in 16-ft. standard lengths. Some are primed on all sides, some not; some have MDO-like paper facing, some not—so check with your distributor. Hardboard sidings have had widespread problems with moisture retention, swelling, and degradation, so hardboard-trim makers have worked hard to improve their products. That noted, however, take pains to prime all sides and the cut edges. Drive corrosion-resistant nails just flush to the trim surface; nails driven deeper may need caulk to keep out moisture. Last, gap butt joints ‘A in. to allow expansion; then caulk and paint the trim ASAP. ► Fiber-cement trim is wood fiber mixed with Portland cement and sand, and it's virtually indestructible. Few people would mistake it for wood, but it's rot, insect, and fire resistant; strong; lightweight; and very stable. HardiTrim® is available in thicknesses from Ум in. to 1 in.; in widths of 4 in., 6 in., 8 in., and 12 in.; and in lengths of 10 ft. and 12 ft. Nail it with galvanized nails; cut it with a carbide- tipped blade, always wearing goggles and a dust mask.

Nailing schedules. To face-nail nominal 1-in. trim (actual thickness, % in.), use 8d box nails spaced every 16 in. Nail both edges of the trim board to prevent cupping, placing nails no closer than h in. to the edge. If the trim goes over sid­ing, say, at corners, use 8d to 10d box nails. To draw board edges to each other, use 6d nails spaced every 12 in., and drive them in a slight angle. If you’ll be painting the trim, also caulk this joint or glue it using an exterior urethane glue, such as Gorilla Glue®.

image275"Подпись: EXTERIORПодпись: Join trim boards on the ground, especially in these situations: The joints are complex, the heights are daunting, the house framing is out of square, and/or the boards are long and unwieldy. To do this most easily, place the trim stock on sawhorses to shape, assemble, and prime it. The resulting joined pieces will be a little heavier to raise than single pieces, but the assembly will be straight and crisp, even if the framing isn't. Use an exterior glue such as Gorilla Glue and 6d galvanized box nails to draw the boards tight. ► TIP 2. If your trim run is longer than individual boards, join the boards with bevel joints, which won't show wood shrinkage as obviously as butt joints. When using beveled joints on vertical boards—say, corner boards—make the top bevel slant down, away from the building, so water can't collect. Last, stagger trim joints by at least 32 in. so they'll be less obvious. rior Trim tips

About nail heads. Taking the time to line up nail heads makes the job look neater. For example, when nailing up jamb casing, use a combination square to align nail pairs. If you’re putting up a long piece of trim that runs perpendicular to studs, snap chalklines onto the building paper beforehand so that you’ll know stud positions for nailing. If the trim will be painted, take the time to set the nail heads slightly below the surface, using a flathead punch. Then use exterior wood filler to fill the holes. If you don’t set the heads slightly, they may later protrude as the wood shrinks, compromising the paint membrane and admitting water. On larger jobs, carpenters are usually expected to set nail heads. Painters fill and paint them.

EAVES TRIM

Because eaves trim is often complex and can impact framing, roofing, ventilation, and the house’s aesthetic integrity, draw a cross-section of it as early as possible.

There is no single correct way to construct the eaves, but the boxed eaves on the facing page are a good place to start. First, a fascia board that overhangs a soffit by % in. to in. enables you to hide rafter irregularities—rafters are rarely per­fectly straight or cut equally long. Second, that overhang accommodates a rabbeted fascia-soffit joint, which protects the outer soffit edge, even if the wood shrinks slightly. Third, if you rabbet out the back edge of a frieze board or build it out using blocks, the frieze will conceal the top edge of the siding. A built-out frieze also creates an inconspicuous space to install an eave vent.

Ventilation channels at eaves allow air to flow up under the roof and exit at ridge or gable-end vents. This airflow is beneficial because it lowers
attic temperatures and helps remove excess mois­ture from the house, thus mitigating mold, ice dams, and a host of other problems. To keep insects out, soffits need screening. In a wide sof­fit, there’s plenty of room for screened vents in the middle. In a narrower soffit, you may need to leave a M-inch space at the front of the soffit or at its back, hidden behind a built-out frieze board.

If the house has exposed rafter tails rather than soffits, cut down the blocking between rafters so air can flow over the top. Again, staple fine mesh screen or corrugated vent strips behind ventilation passages to keep insects out.

Updated: 15 ноября, 2015 — 3:41 пп