A valley is where two adjacent faces of the roof meet in a downward slope. Valleys carry the largest volume of water out of all the surfaces on your roof. An open valley is where the tiles are cut back to allow a space in between the tiles for water and debris to flow through (in theory). A closed valley is where tiles are cut to fit closely together in the valley to keep out debris and allow water to filter through the tiles and run through the flashing under the tiles.
Some roofers opt to cut tiles back in older style valleys as compared to fixing the valley properly with new moisture barrier and high flow flashings. Cutting the tiles back is faster and less expensive but does not perform well in the long term. We highly recommend having closed valleys for the following reasons:
- Open valleys fill with debris easily despite claims it will wash through. Leaves, moss clumps and twigs get stuck and create dams inside the valley – which lead to leaks
- Tiles fall out of place in an open valley causing debris dams and expose the roofing underlayment to damage
- Measures to hold tiles in place in open valleys (gluing tiles) often fail
- Other measures to hold tiles in place for an open valley (over ran battens or extenders) lead to more debris dams
- Closed valleys keep leaves out of the valley for longer periods and can easily be cleaned off topically
- Closed valleys hold tiles in place as tiles from each side support each one another and don’t slide out of place
- Closed valleys must be kept clean under the tiles to avoid leaks
- Closed valleys need to be constructed with high flow flashings to work efficiently
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Valley flashing is meant to carry the water and therefore it should not be nailed through except where another section over laps the section below which is nailed. But there should never be an exposed nail penetration in a valley even if its sealed. The two last tiles in the valley will slide out of place if they are not touching the tiles on the adjacent side of the valley. The two different sides hold each other together tight in place so that your valley tiles don’t slide off your roof. When an open valley is used these two sides are now not touching so the tiles will slip out of position if they are not nailed or glued to an adjacent tile that properly set on a batten (see our section on Tile roofs explained for more info). We already discussed why not to nail these tiles through the drain flashing, so gluing or the use of a batten extender is the only option. Tiles are held in place on your roof with wood or plastic strips called battens. These battens are not supposed to be ran into the valleys as they will cause debris blockages – even though some manufacturers detail this as an acceptable installation technique we see nothing but problems when this is done. Some tile manufactures say its ok to use a batten extender (piece of plastic that is nailed to the batten outside of the valley and that runs into the valley to hold the tiles in place) but these also cause debris backups in the valleys. Debris will naturally back up in valleys as well, but batten extenders and running battens into a valley will speed up the blockage process in the valley.
The fact is, these manufactures deal primarily with new installations over new tar paper and so leaks are not showing up for at least 15 years or so as the moisture barrier (tar paper in most cases) will keep out a leak for some time. By the time a leak shows up after a new roof is installed the roof no longer has a warranty in most cases. Yes, the tiles themselves have a lifetime warranty but not the labor or functionality of the roof, just the actual concrete tile is all that is warrantied from the manufacturer. What is different between what we do and what a manufacturer does is that they sell products to roofers who install new roofs and so they rarely receive feedback about leaks because a leak won’t happen for around 15 years or so give or take. We on the other hand only do repairs, so we diagnose, solve, and remedy these issues on a daily basis…that is all we do, 100% of the time. In some specific cases, batten extenders are needed (steep roofs only as the tiles need to stay in place in the valley).
Since battens/batten extenders in valleys can lead to debris blockages the only other option is to glue to tiles in place to the adjacent tile to the side which is set on a batten. What is the downside of this? Sealant (caulking for tiles) does not last forever. Tile roof sealants or most any caulking for that matter is often sold with a 25-50 year guarantee. But here we are following up resealing all these places the original roofer used these sealants because they are failing after only 15 years. The fact is, in our climate it gets really hot in the summer and cold in the winter. This wreaks havoc on seals. If it’s 110 degrees outside the concrete tiles are 160 degrees. So, the tile that is now caulked in the open valley to hold it in place now slips out of place as the caulking fails. Is this a problem? Well yes, for two reasons. One is that it now creates a dam in your valley where any debris now backs up behind the slipped tile and will clog your valley once again leading to a leak as the water runs out of the flashing and onto the moisture barrier. The second problem it creates when the tile slides out of place is that it over exposes the tiles. This means that as the tile slides out of place, it no longer has the proper under lap of the tile above it creating a situation where water will get in and under the tiles to the moisture barrier also eventually leading to a leak. Moisture barrier, tar paper, felt paper (all the same thing) is not supposed to get wet on a regular basis (see our section on “busting the tar paper myth” for more info).
Aside from the tiles sliding out of place and causing overexposure and or damming, another reason not to do an open valley is that even if the tiles do stay in place and are regularly sealed an open valley will fill with debris much faster than a closed valley. For homes with no trees around (150ft or more away), debris is not as much of an issue, however, moss clumps can also clog up these open valleys. So, for homes that have trees within 150ft of the home that are OR ONE DAY may be taller than the roof line we suggest against an open valley. Open valleys are like an open rain gutter, they will fill up with debris which can lead to a water dam and a roof leak. With a closed valley the debris sits on top of the tiles while the water filters through to the flashing which then carries the water out as designed. The leaves that sit on top of the valley can be easily blown off as is needed which will be far less often than they would be with an open valley.
When and open valley fills with leaves it makes a dam and water then backs up behind the tiles again and runs out of the flashing sideways onto the tar paper (moisture barrier) and we all know what happens next…it rots away and you have a roof leak. So, the next question is, well why can’t we seal the tiles so the water can’t get under them sideways? Roof types other than tile are composed of a rather thin material (asphalt / composition, EPDM, Rubber, or Standing seam metal roofs etc.). This means that for these roofs the roof material is sealed to the valley flashing and yes, they have an open valley on these roof types because the material is thin and can be easily sealed to the flashing eliminating any backflow under the roof material. An open valley on a thin material roof requires little and simple maintenance and small debris flows easily in most cases through the valleys. With concrete tile, the tiles are made of a thicker material, and when cut at a 45-degree angle to match a valley with two adjacent sides meeting the tiles are often 1.5″ thick + or – at these cuts. In addition, courses of tile are not sealed together as they are other roof types, instead with tile roofs the tiles are laid on top of each other and interlocked side to side with drain channels on each side that carry water as well. Since concrete tiles have such a large thickness to them, when they meet in a valley, they cannot be sealed to the valley flashing unless mortar is used. Regular tar will not work as it will not seal a hole that large. The downside to using mortar is that it has a tendency to crack and these pieces will fall into the valley and clog it up causing leaks. In addition, the use of mortar makes repairs/maintenance very difficult as the tiles are now cemented in place and if a tile gets broken for any reason in any area of the roof that drains water to the valley water will then flow under the tiles and to the valley damaging the area under the valley. When the valley is mortared, getting in there with mortared tiles is not a fun task and also one that many roofers won’t want to take on.
Now onto closed valleys and why they are better (if the proper flashing is used):
- Tiles fit tightly together from either side and hold each other in place eliminating the need for batten extenders (which can clog valleys) and eliminating the eventual slippage of tiles leading to over exposure.
- Valleys are kept cleaner for longer because any debris sits on top of the tiles and can easily be blown off as compared to open valleys which fill with leaves very fast.
In order for a closed valley to work properly the flashing must be kept clean, and the reality is all things in life need maintenance. A closed valley with the proper flashing will require far less maintenance than an open valley. The proper flashing is a 5 rib, which makes six drain channels. And more importantly, the ribs need to be 3/4″ tall so as to create sufficient lift for the tiles to create a space for water and debris to flow through the valley more freely. Flashings with smaller ribs and or less drain channels will require more frequent cleanings. No valley is made with ribs larger than 3/4″ because any larger will not fit the profiles and match up correctly with the rest of the tiles on the roof as the tiles transition to the valley. As a matter of fact, the 3/4″ rib is actually a bit too tall and in order to make the valleys blend with the rest of the tiles, taper wedges should be used on the battens to gradually grade the tile transition to the valley. This is actually a technique we developed and we have not seen anyone else use it. Because the 3/4″ rib is more difficult to transition, a lot of roofers use a 1/4 or 3/8″ rib. The downside to a smaller rib is that it does not hold the tiles up enough to create enough space for debris to flow through. An alternative that some roofers do to increase the flow rate through the underside of the tiles is to hammer out the lugs (rear support of the tile designed to add strength to the tile and used to allow the tile to hook onto battens) for the tiles that are in the valley. We do not believe this is a good approach as it weakens the tiles and simply installing the proper 3/4” ribbed valley accomplishes the same thing in a far more efficient manner that maintains the integral strength of the tiles. what We have many customers who come to us after having their roof repaired by another company only 5 years earlier with roof leaks because a smaller rib valley was used and it clogged up very fast. So, for that reason we use the 3/4″ rib six channel valley flashings when we update valleys for our customers. We also recommend to all our clients to have us out to check on the roof every 7 to 10 years.