Home>Discussions>EXTERIORS>does gutter length figure into calculations?
10 posts / 0 new
Millicent Lewis
does gutter length figure into calculations?
Millicent Lewis

I have a problem with a gutter on one side of my house. I've used your calculator (thanks!) and have 2363 sf of rainwater to deal with. The problem is that there are two sections of roof that meet. An 18' section of gutter along one edge feeds into a 3' section that is at right angles to it, and this 3' section takes the brunt of it all. I don't see any calculation that takes into account the length of the gutter runs.
What should I do?
Thanks!

dj1

Questions:

Are there down spouts in the 18' section? in the 3' section?

I understand from what you said that the 18' feeds into the 3', so in a normal downpour, can the 3' section handle the water from the 18' section or does it overflow?

A. Spruce

If it is possible, I'd install a downspout on the 18' length. Not only will this help overall, it's going to take the burden off the 3' section and restrictive corner to handle all the water collected. If you can't install a second downspout, then I'd oversize the gutter and definitely oversize the downspout.

When installing downspouts, I prefer to use formed elbows over notched because you get a full dimension downspout that is less prone to clogging. If you do use a notched style, make sure that the internal dimension of the downspout is minimally restricted.

What is a notched style, you might be wondering, this is where a notch is cut out and then the downspout is bent to form the elbow. The problem is that the uphill side of the notch tucks into the downhill side of the notch when the elbow is formed, creating a restriction. This is the most common type of downspout on tract homes and seamless gutter installers, the reason is that it's cheap. The problem is when the installer is careless and restricts the downspout because they didn't notch enough out and simply don't care to do it right.

Millicent Lewis
Re: does gutter length figure into calculations?
Millicent Lewis
dj1 wrote:

Questions:

Are there down spouts in the 18' section? in the 3' section?

I understand from what you said that the 18' feeds into the 3', so in a normal downpour, can the 3' section handle the water from the 18' section or does it overflow?

Yes, the 18' feeds into the 3', so the only downspout in the 18' is the feeder to the 3'. It's a really awkward area to access, so we have not been the best about cleaning them out, but aside from that, I don't think the 3' handles it. (Which is why we are going to have to repair a wall in the down bedroom.)

Millicent Lewis
Re: does gutter length figure into calculations?
Millicent Lewis
A. Spruce wrote:

If it is possible, I'd install a downspout on the 18' length. Not only will this help overall, it's going to take the burden off the 3' section and restrictive corner to handle all the water collected. If you can't install a second downspout, then I'd oversize the gutter and definitely oversize the downspout.

When installing downspouts, I prefer to use formed elbows over notched because you get a full dimension downspout that is less prone to clogging. If you do use a notched style, make sure that the internal dimension of the downspout is minimally restricted.

What is a notched style, you might be wondering, this is where a notch is cut out and then the downspout is bent to form the elbow. The problem is that the uphill side of the notch tucks into the downhill side of the notch when the elbow is formed, creating a restriction. This is the most common type of downspout on tract homes and seamless gutter installers, the reason is that it's cheap. The problem is when the installer is careless and restricts the downspout because they didn't notch enough out and simply don't care to do it right.

Thanks for that information! I have been mulling over each of your suggestions.
I haven't seen oversized downspouts in all my internet searches, and wonder how easy they will be to find. I think there is only one specialty gutter store in my area that will sell to contractors and homeowners, alike.
If we add a downspout to the 18' section, it will have to bend a couple of times, so my next question is, is there a maximum number of bends?
Thanks!

A. Spruce

The more bends, the slower water will flow through it, a relatively minute issues, but in a torrential downpour, something that could make a difference, and the more likely for clogs. Sometimes multiple bends can't be helped so having the downspout in lieu of no downspout at all, it's better to have it.

As for where to buy larger diameter DS materials, that is hard to say, with the advent of goliath chains such as Evil Orange and Lowes, a lot of better supply houses have vanished. There are still a few out there, so look around and ask around. I'd start with a large roofing contractor who is more likely to be using specialty suppliers and not a big box retailer. You may need to look at commercial gutter suppliers or adapt other types of plumbing to your needs, such as using a 4" ABS pipe with sweeping elbows. Where your biggest issue will come is transitioning a typical residential gutter to a larger DS, you may have to have a special scupper made to make the transition.

The standard DS is roughly 2"x3", this varies slightly depending on where you get the DS material. There is a plastic DS that is approximately 3"x4", which will probably be the easiest for DIY, you'll still have a transition issues to deal with, but at least the DS material can be purchased from any big box retailer.

What is a scupper? This is the transition from the gutter channel to the DS tube. Typically it is either 2" round or slightly less than 2x3 rectangular sleeve. It will do no good to increase your DS tube size without also increasing the size of the scupper. Depending on what you do, you may need to have a scupper custom made, any HVAC shop that does their own metal fabrication would be able to make you a scupper.

dj1

Also:

1. Choose your DS locations carefully and make sure the gutter is sloped correctly.

2. Make sure the gutters and DSs remain clear of debris, leaves and branches.

Mastercarpentry
Re: does gutter length figure into calculations?
Mastercarpentry

The 2X3 ds's are usually referrred to as 3"; the larger 3x4 ones are called 4", and those should always be used because they are far less prone to clogging. The pre-formed elbows should always be used for the same reasons.
Ones which turn perpendicular to the gutter are called "A" elbows; those which turn parallel to the gutter are "B" elbows or "sidesweeps". Downspout comes in 10' lengths. Get 4" pre-formed outlets and a tube of "gutter-seal" too. That sealer works best for gutters, even better than silicone. You don't often find it outside the usual trade channels.

If you go to the sales counter of a supplier and use the proper 'trade lingo' they will almost always presume you're in the business and sell to you. When they ask the billing name say "Just make this one cash." If they ask if you want to set up an account say you'll do that next time, you're in a big hurry today ;) The correct approach can often produce near-miracles :cool:

Phil

Millicent Lewis
Re: does gutter length figure into calculations?
Millicent Lewis

I'm wondering about the roofing paper that got cut and was otherwise damaged during all this. Should we try to insert new roofing paper under the shingles and over the soffit when we get it put in? All we need is less than one foot wide by 18' long. (As I understand it, because this is a porch roof we don't need the ice and water barrier, right?)

I've tried attaching photos for you to see but it won't accept my photos no matter which format I try to use. And I think we've tried every one of them!

A. Spruce

You have to use a photo host, such as photobucket. Upload your images there, then link them here using the image attachment icon in the middle of the tool bar under the smilie face.

If you've got a composition/asphalt shingle roof, you're not going to get new paper very far up because the starter row of shingle should be nailed within 4" of the roof edge. If you've got exposed roof deck, getting some new pieces of roofing felt under there wouldn't hurt. You can hold it in place with a touch of roofing tar, if you get the tube kind, you can dab a little where you want it and not get it all over yourself in the process.