Built-in gutters are very popular among architects. Prop-erly installed, built-in gutters can provide a lifetime of trouble-free service. However, built-in gutters expose a building to higher risk of water intrusion than any exposed type gutter. When leaks occur in built-in gutters the water is likely to intrude directly into the building.
|Figure 1-4, Built-in gutter design, page 1.17 of the “Architectural Sheet Metal Manual,” sixth edition.|
The built-in nature of hidden gutters requires exemplary attention to critical construction details such as:
- Corrosion resistant materials should be used
- All joints should be lapped, riveted and soldered
- Continuous support is recommended
- Long-lasting underlayments should be applied
- Expansion control is critical
- The front edge should be a minimum of one inch lower than the back edge
For the best built-in gutter design soldered seams are always better than using sealants. Downspouts should be located in a manner that minimizes or eliminates the need for expansion joints. Continuous cleat and drip edge are recommended along the front, while waterproof membranes should extend at least 24 inches behind wall lines in ice dam areas.
While a slope to the drain is best, many designers prefer no visible slope and SMACNA's "Architectural Sheet Metal Manual" recognizes the use of that practice by illustrating sufficiently-deep built-in gutter designs. This low-slope preference is just one of the reasons it is recommended that built-in gutters have soldered or welded seams.
The construction and installation of low-slope specifications is problematic and it is difficult for contractors to install a low-slope gutter so that no points along the gutter "hold" water. Just the variance caused by normal oil canning along the bottom profile of the gutter can counter slope that is typically measured along the gutter's upper/outer edge.
Minor "puddles" of standing water are not a problem unless the depth of the standing water exposes the gutter to damage from the expansion of freezing water. Where freezing water might be an issue a bottom profile with a 45-degree turn in the back of the profile provides additional safety if shallow puddles freeze. One should consider that minor debris accumulations can easily create "dams" along the length of a gutter and cause puddling.
The old adage-out of sight, out of mind-too often applies to built-in (hidden) gutters. If hidden gutters are specified, designers should call attention to the need for regular inspections by the owner to remove debris and to make sure that gutters and downspouts are kept clear.
Built-in gutter design and construction are covered in detail in the first chapter of the "Architectural Sheet Metal Manual."
Members may purchase the "Architectural Sheet Metal Manual," (sixth edition, 2003), at the special member price of $42 for the book, $50 for the CD-ROM and $42 for the PDF download. The IFUS price for the book is $139 and $166 for the CD-ROM and $139 for the PDF download.
Architects and engineers may purchase the publication at a discounted price of $184 for the book, $220 for the CD-ROM and $184 for the PDF download. The list price for the book is $262, $315 for the CD-ROM and $262 for the PDF download.
To order, call SMACNA's Publications Department at (703) 803-2989 or visit www.smacna.org/bookstore/.