Q–I would like to keep my energy costs to a minimum in my new home. Do you think it would be worthwhile to have my builder install a whole-house wrap air barrier? Does it have other advantages besides energy savings? Are there any special tricks to the installation?
A–I have used the house wrap products on all of my jobs. They are an extremely important feature, which is often left out of new homes. Not only does the house wrap save you money on heating and cooling, but it also will protect the structure of the house in the event of water infiltration.
The idea of wrapping houses is not new. Many of the older homes that I rehabilitated early in my construction career had been wrapped with tar paper, which functioned primarily as a water barrier on wood frame houses. It probably helped to limit the amount of air that infiltrated as well. For some reason, this use of tar paper was abandoned by many builders after World War II.
The modern house wraps are actually air retarders. Air infiltration can be a huge drain on utility costs. Air leaks into and out of houses in between gaps that are usually found where exterior walls sit on foundations and wooden subfloors. Air can also leak where sheets of plywood or wall sheathing abut one another. An average house has between 70 and 200 square inches of air leaks.
The air infiltration products do not block the flow of air entirely. To do so would be a big mistake. Water vapor from the inside of your house needs to be able to escape outdoors because if it’s trapped, moisture-related rot problems can result.
The air infiltration products resemble some modern fabrics: They repel liquid water but allow water vapor to pass freely. All houses that are framed with lumber need this protection. Brick veneer is not waterproof. Wood, vinyl, and aluminum siding can develop leaks. Construction details around doors and windows are sometimes sub-standard. The whole-house wrap products, when installed properly, create a very effective waterproof skin. Water that gets behind the exterior finish material of the house then flows down the wrap and exits just below the top of the foundation or slab.
Installation of whole-house wraps require attention to detail. Just like with the old tar paper wraps, start from the bottom and let subsequent pieces overlap the lower ones. All seams must be sealed with a special adhesive tape sold by the manufacturer.
The wrap needs to be in place before doors and windows are installed. In fact, it should be installed prior to the placement of the second top wall plate that sits immediately below the roof rafters. By sandwiching the wrap between the double top wall plate, you virtually eliminate the entry of any soffit downdrafts behind the house wrap. Be sure the house wrap extends at least one inch over the top of the foundation.
Some house wrap products can hide the location of wall studs. If you use such a product, be sure to align the outer wall stud markings on the house wrap with the studs. If this is too much trouble, consider using a translucent house wrap. In either case, the bricklayers and siding installers will thank you.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352. Questions will be answered only in the column.
For a list of manufacturers of whole-house wraps, comparative performance data, and other tips on installing house wraps, send $2 and your name and address to Tim Carter at the above address. Ask for Builder Bulletin No. 132.
You can obtain a free order form for a wide variety of individual job bid sheets and other available Builder Bulletins by sending a business-size, stamped, self-addressed envelope to the same address.
Ask the Contractor can also be accessed via the Internet at http://www.chicago.tribune.com/homes/articles/askcon.
