Selling the Correct Size Gutters is Critical

MCS Influencer Mark Standifer explains how to handle the situation when gutters proposed are too small to properly perform. 

This month’s submittal is coming to you from a blind, somewhere in Central Texas. The feral hogs have been taking a beating this month. We donate these animals to the local Hunter’s feed the Hungry program in this county. While we (the gentlemen I hunt with) get a discount for the processing of these animals, all the processing comes out of our own pockets. Current score, 19 feral hogs, 2 deer, 0 turkeys. 

Now for this month’s topic, selling gutters and downspouts. I’ve never had this problem. This seems more of a residential roofing situation than a commercial situation. The commercial roof projects I’ve been involved in, and the handful of residential roofs have had the gutter and downspouts included in the design.   

The problems I run into, are that the gutter is too small and/or there are not enough downspouts to properly control the run-off.  What is a small gutter? I’m glad you asked.  A small gutter does not provide enough of a cross-sectional area to properly control the run-off of rain water. When I got in this business, this issue of a properly sized gutter was handled by the design architect. The architect would use drainage calculations generated by the design firm or an engineer, to determine the size of the gutter, and the size and number of the downspouts. Drainage calculations use the roof slope, the roof area(s) to be drained, and a specific rainfall event for the geographic area, to provide a cross-sectional area for the gutter. These calculations can be used to design a typical box gutter or half-round gutter.   

As an example, as determined by the calcs, the cross-sectional area should be 30 square inches. With this information the architect could design a 6” x 5” gutter, or a 6” x 6” gutter.  Should the calcs determine 24 square inches will suffice, 6” x 4” or 5” x 5” gutters might possibly be designed.  It should be noted that these drainage calculations are easy to use.  I’m an Aggie and I can use them.  I’ve provided these calcs for pre-construction meetings and with submittals.   

Recent experiences lead me to think that no one is providing these calculations anymore. I have seen  roofs with gutters that will not provide control of roof run-off.  This is where my problem starts. Let’s say, I’ve done the drainage calculations for a specific roof, that we have a contract for. The calculations indicate the current design of the gutter is too small to work properly. So now I have priced a gutter, in a size, that will work and I’m trying to get the funds/money to cover the additional materials needed.   Since we have a shear and brake, our additional cost is for the additional flat stock only. Labor cost for fabrication and installation should not have changed. Should be an easy sale. With gutter and downspout rollformers you are limited to the size(s) you can provide you customer, not so with a shear and brake. 

When you submit this information to the general contractor, architect and owner, you should be prepared for a push back. Since you are not an engineer, your math will be called into question. Okay I’m not an engineer, big deal, the calculations are easy. You will also be questioned as to why you did not provide a properly sized gutter on bid day. The answer to this question is “I bid what was shown, just like my competitors.” 

If you’re a good salesperson, you might get a pat on the back and the additional money. If you’re a good salesperson you just might also get a no sale.  Should you get a no sale for whatever the reason, you need to protect yourself immediately. Send registered letters to all the involved parties. Explain in great detail, your position for requesting the larger gutter. Include your design calculations, this is the how and why. Express your concern for them using the designed gutter. Let the parties know that you will be furnishing and installing the gutter, in the size and shape, as shown in the design drawings; but you will assume no liability for the design of the gutter, or its ability to properly handle the roof run-off. Consult your company attorney for the legally correct verbiage.    

Be prepared for the phone to ring, at the first big rainfall.  

I’ve installed half round gutters and round downspouts on more than one roof in my career. While these types of architectural features look nice, it is my opinion they rarely work as well as a “box” shaped gutter. Too many times, I have seen rainwater coming over the edge of a half round gutter, that was just not large enough.  

Chain downspouts. There is no doubt, they look cool, and if the largest rainfall was 1” an hour they might just work as designed.  A 4-6” rainfall an hour, and you have a drop tube with water rushing out of it, like a busted pipe. 

Updated score, 2 more feral hogs, on this fine rainy morning. 

Mark Standifer is currently semi-retired and consulting for metal roofing, walls and sheet metal shops. See his full bio here.