Q: I have exposed 8-inch beams throughout the house and no attic. Is there some kind of attractive insulation I can put between the beams, not more than 4 inches thick, that will give me the maximum amount of insulation with the least thickness?

A: We don’t know of any insulation that you can just tack up between the beams and have it look like anything but what it is — cobbled together. But with a few more steps, we do have a good solution to give you much-needed insulation and an attractive ceiling.

Your description of 8-inch beams and no attic tells us that your house is probably one of the post-World War II homes built with beams for rafters, 2-by-6 tongue-and-groove Douglas fir for sheeting, and probably a built-up tar-and-gravel roof. The roof has probably been replaced with asphalt shingles, but the substrate remains the same.

Acres of these homes were built all over the San Francisco East Bay. An example is the Palma Ceia subdivision in Hayward, where street after street of semi-flat-top homes have covered the landscape since the 1950s.

To say these homes lack energy efficiency is an understatement. We’re sure you cook in the summer and freeze in the winter. Insulating the ceiling will provide some relief.

There’s no way we know of to economically get the R-38 ceiling insulation suggested for modern homes. But we can get you R-13. We recommend that you create bays between the beams to install batt insulation, then cover the newly insulated ceiling with drywall for a finished look. Here’s how to go about it.

In this type of construction, beams are usually set every 4 feet, or 48 inches on center. There is no batt insulation that we know of that is this wide. Also, if you try to cover a 4-foot span with wallboard, it will bow. The solution is to create a series of 2-foot-wide bays to accept the insulation and to provide proper support for the drywall.

Install 2-by-4 blocking between the beams every 2 feet. Two-by-fours are 3 1/2 inches wide. Adding 1/2 inch of drywall reduces the reveal of the 8-inch beam to 4 inches — enough to form an attractive pattern on the ceiling.

Start at the wall and nail a block between the beams. Measure 23 1/4 inches from the outside edge of the block and make a mark. Nail the next block on the mark between the beams. Measure 24 inches from the outside edge of the block you’ve just nailed and install the next block. Repeat the process until you reach the ridge. This pattern will ensure that the edge of an 8-foot length of drywall will get full purchase on a block.

Make sure to nail a block to the beam between each cross block to form a square. These act as a nailing strip so the drywall can be fastened to the ceiling on all edges.

With the blocking in place, install the insulation between the beams. Use a faced insulation and place the vapor barrier toward the living area. If you want to go green, environmentally friendly insulation made from blue denim is available. For more information on this product, check out links.sfgate.com/ZRR.

Next, install the drywall. Trim 8-foot sheets of drywall to fit between the beams. Use drywall screws to secure the drywall to the framing. Place screws every 6 inches on the edge and every 8 inches in the field. If you framed the blocking correctly, the edge of the drywall should cover only half of the last block. If it doesn’t, just sister another block to the existing one so the edge of the drywall is fully supported. Tape, texture and paint the drywall and you’re done.

We suggest you consider using a decorative molding where the wallboard and beams meet rather than trying to tape that small gap. Molding also eliminates the chance that a crack will develop where the beam meets the rock.


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