Pitch for gutters?
I live in climate zone 4A in Virginia. Plenty of rain, but not usually much snow. Ranch house with roof of 5/12 pitch, 48 feet long, with a small gable extending out over a porch at one end.
I’m reading a lot of different recommendations for the pitch (slope) of gutters on fascia – anywhere from 1/8″ per foot, to 1/4″ per 10 feet, or to completely level.
I rarely see gutters with any noticeable slope towards the downspouts. But an extremely common problem that I see in my area is gutters sagging along the fascia, with standing pools of water for long periods of time. When you see flocks of starlings collecting in a gutter to drink and take baths several days after a rain, then you know you’re also breeding mosquitoes!
So when we have seamless aluminum gutters installed, how much slope (pitch) would you recommend?
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Replies
The roof of our recently purchased condo was designed ...without much thought. It violates every design principle that Martin has ever even considered as an ex-roofer. And the problems are compounded by poor gutters. I will give you my take.
a) I agree with you, too many gutters seem to have not enough slope. 1/4" in 10 feet seems minimum, 1/2" in 10' seems more reasonable, combined with general rule of every gutter sloping toward the nearest downspout, and no more than 30' between downspouts.
b) Consider bigger gutters.
c) If you've got valleys that get a lot of water, consider deflectors to keep water from just flowing over the gutters.
d) Don't forget the kick-out flashing if you have a gutter meeting a wall.
e) Gutter spikes always loosen. I'd choose another fastener. Loose spikes also lead to sagging gutters and all the attendant problems of standing water/low areas.
Debra,
This is one of those construction questions where the answer depends on where you live. Some places slope their gutters, some don't. Perhaps surprisingly, considering the amount of rain we get here in the PNW, most installations here don't include a slope. The thinking behind this it twofold:
-Straight gutters look better.
- Sloping the gutters creates a different relationship between the drip edge on the roof above and the gutter below. If the gutters start tucked up under the overhanging drip edge or shingles and there is a steep slope, the gap at the downspout might be several inches. This can lead to water getting behind the gutters.
The downside of flat gutters can be, as you say, standing water. My experience is that standing water is almost invariably the result of debris, and affects sloped and flat getters in a fairly similar way.
Whatever way you choose to proceed, Andrew has given you some very good advice to consider.
Debra,
Andrew and Malcolm both have useful advice on this issue.
1. Short lengths of gutter are easier to slope, so consider a plan with more frequent downspouts.
2. In some climates -- ones with lots of snow and ice -- the best approach is to design your roof without any gutters. If you go this route, you'll need wide roof overhangs, and you might also want to consider a so-called "underground gutter." Here are links to relevant articles:
Ground Gutters
An Underground Roof
Fixing Those Drainage Problems, 30 Years Later
GBA Encyclopedia: Inground Gutters
GBA Detail: Underground Water Barrier Retrofit
FHB: Inground gutters keep basements dry
I appreciate everyone's suggestions. Thank you! We generally only have 1-2 snowstorms each winter with more than 6" of snow. Usually only 1-2", which melts quickly.