Letters

Dampproofing vs. Waterproofing

The article "Building a Block Foundation" (5/06), by Rob Corbo, shows "dampproofing" below grade in the wall section.

In my opinion, dampproofing is the wrong material for this application; waterproofing should be indicated. I define "dampproofing" as a product used above grade in the absence of hydrostatic pressure, in applications like the outer surface of CMU backup for a brick and block cavity wall.

"Waterproofing," on the other hand, is a product used below grade in the presence of hydrostatic pressure, in applications like the foundation wall in the wall section.

Whether one uses dampproofing or waterproofing on a foundation wall, it won't keep water out for long without a drainage protection board to keep the membrane from being punctured during backfilling.

I'd like to hear Mr. Corbo's response to my suggested improvements.

Rex Garton, AIA

Hart Freeland Roberts

Brentwood, Tenn.

Author Rob Corbo responds: We simply followed the specifications presented to us in the architect's drawings. I agree that "dampproofing" is an appropriate description of the method used on this job. I keep my fingers crossed, but I usually find that parging and asphalt coating in conjunction with perimeter drainage, sump pits where needed, and surface-water controls — proper grading and ground cover, as well as gutters, leaders, and dry wells — will keep the basement walls dry. We explain the differences between waterproofing and dampproofing to the client, but bid projects per the plans. I also prefer a waterproofing membrane, for two reasons: It's a fairly straightforward process and can easily be subcontracted (whereas we can't find a sub willing to parge and coat), and the waterproofing subcontractor assumes responsibility for the basement staying dry.

More Door-Hanging Tips

Regarding the question "Do Door Jambs Need Shims?" (Q&A, 5/06), there is no need for a shim at the top hinge: The force at this point is outward, not inward. Not shimming behind the top hinge allows for a little adjustment later by tightening the 21/2-inch screw going into the stud.

We have also had good experience with foaming between the jamb and stud instead of shimming.

Charlie Weedon

Pomfret, Conn.

Sound Control

We have provided acoustical engineering on many single and multifamily home projects, and we found the article "Innovations in Sound Control" (3/06) to be one of the more comprehensive and accurate articles that we've encountered in a building-trades publication, especially regarding residential applications.

Nevertheless, we do have a few additional comments.

While an STC rating is a good guideline for the control of many types of sound sources encountered in residences, in cases where very low frequency sound is concerned (such as in home-theater applications), this descriptor is limited.

The STC rating is based on test data that extends only down to 100 hertz (Hz), whereas theater sound systems can often produce considerable sound energy down to the 30-Hz range.

A single-stud wall assembly (with some type of isolation device or proprietary sound-control sheathing) may have an STC rating comparable to a staggered-stud or double-stud assembly, but the sound-insulation performance below 100 Hz will be considerably less and is not reflected in the STC rating.

Also, there are no isolation devices that could connect any two building elements that will outperform an actual structural separation.

This probably makes intuitive sense to most readers. Staggered 2x4 studs on 6-inch plates with standard fiberglass-batt insulation will outperform any single-stud assembly of the same overall thickness, regardless of the devices involved.

Finally, the "loaded vinyl limp-mass barrier" noted in the article is indeed effective. When the material is unconstrained ("limp"), it is free to convert sound energy to mechanical energy.

Adding the limp-mass barrier in the air space of the staggered-stud assembly noted above, for example, will provide added sound insulation. Adding the mass barrier between layers of sheathing, however, will provide only a small increase in sound insulation, proportional to the mass added. (It is no longer "limp," as it is constrained between rigid sheathing.)

Thomas Schindler, PE

Charles M. Salter Associates

San Francisco

Protecting Fascia From Ice Dams

I'm a home inspector and roofing-project estimator in the western New York region, and have followed your debate on roof waterproofing membranes (Q&A, 1/06; Letters, 6/06). Over the last 20 years, I've solved all types of problems relating to ice-dam leakage.

The eaves waterproofing membrane should be folded down over the finished fascia. If the home is to have formed aluminum fascia, it can be installed first. Next, the leading edge of the membrane can be folded down onto the fascia 1 to 2 inches, then the drip edge installed.

Installing membrane on top of the drip edge or stopping it at the edge of the roof sheathing will give no protection where the fascia and the decking meet. This area is tested first and is very prone to leakage as the gutter fills with ice and water.

The membrane should also extend up the roof a minimum of 24 inches horizontally over the heated area of the home.

Rob Bommer

Buffalo, N.Y.

Concealed Splices? Proceed With Caution

I wrote to one of the companies listed in your article about electrical connectors that can be used to tap conductors and then concealed behind drywall (Q&A, 4/06). The company denied having any. Could you please clarify?

Louis Duke

Tucson, Ariz.

Editor Don Jackson responds: The electrical code is very specific about leaving access to splices in Romex, so I can understand the reluctance of a manufacturer to encourage the use of this kind of product without fully understanding your circumstances. There are two key points to keep in mind. First, you should speak with your electrical inspector before proceeding with this strategy. Second, the device in question must be listed as meeting NEC 334.40(B), which excludes its use in new construction.