Covering a roof's lower beams with acoustic panelling may help to thermally insulate the room, but it does little for the room's style or character. Faux ceiling beams (also known as coffered ceiling beams) may be just the ticket if you want to add a little old-world charm to a space but don't want to rip out the ceiling and insulation. Building and mounting the beams requires a few speciality tools and an above-average level of skill, but it is fairly simple once you have the process down.
Purchase the straightest and most flaw-free pieces of 1/2-inch-thick lumber that you can find. Get lumber that is 1/2-inch wider than the beams you desire. Use your table saw to shave 1/4 inch off either side of your lumber to ensure that the sides are perfectly straight. Run a belt sander or planer over one side of your lumber to remove any bending or waviness.
Use either an angle-cutting attachment on your table saw or a router with a side guide and bevelling bit to cut a 45-degree bevel along both sides of the entire length of your lumber. Run a piece of 300-grit sandpaper along the sharp edge of your bevels to remove any imperfections in the edge.
Lay one of your bevelled lengths on a table with the bevelled edges facing up; this will form the bottom of your beam. Apply a very thin bead of construction adhesive to one of the bottom's bevels, and fit another bevelled piece to form one side. Clamp the two together with a number of 90-degree angle clamps and allow the glue to set up. Repeat this procedure on the other side to create a hollow, U-shaped beam.
Run a piece of 80-grit sandpaper over the corners of your beam to smooth and blend it. You could also use a belt sander or hand-held orbital sander to remove more of the corner to create an exterior bevel. Do not remove more than 1/8 inch of material from the corner, or you'll compromise the beam's structural integrity.
Use a finger to press a small amount of stainable wood filler into the seams between your bottom and sides. Allow the filler to dry and sand the seams smooth with 180-grit sandpaper. Next, sand the entire beam with 300-grit sandpaper. You may wish to use a planer or a belt sander to remove any waviness from the bottom or sides.
Make a number of reference marks along two opposite edges of your ceiling, and another set of marks along the middle. Connect them with a chalk snap string to mark the ceiling. The resulting lines represent your beam centre lines, and determine the spacing between the beams. Beam spacing is equal to the distance between your centre lines minus the outside width of the beam. Measure the length of your reference lines from wall to wall.
Cut the beam to the measured reference line length with a table saw or circular saw. Sand the cut edge with 300-grit sandpaper, and stain the beam to the desired shade. Coat it with polyurethane and allow it to dry.
To mount the beams to your ceiling, cut a length of 1-inch-thick lumber lengthwise to the exact width of the distance between the U-shaped beams' sides. Mount this piece of lumber (called the "nailer") to your ceiling centred along the reference lines, securing it with construction adhesive and screws driven through the roof studs. Have an assistant help you raise the beam in place so that the open end of the "U" slips over the nailer. Secure the beam to the mounting strip by driving 1-inch-long finishing nails through the tops of its side and into the nailer. Hide the nail heads with a small dab of wood stain or flat black paint.