GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Cedar-Shingle Siding and Vertical-Grain Trim

centercarpentry | Posted in General Questions on

I am laying out cedar siding and trim on a replacement job. I am using Benjamin Obdyke rain screen, Michigan PreStain prefinished white cedar shingles, and vertical grain red cedar primed and painted 1-by stock for trim. My siding reveal target is 4-3/4″ and my window and door casing is 1×6. The water table changes elevation, the house is out of level about 5 inches from opposite corners, the doors are at slightly different heights, and the windows (many same sizes and locations) are installed with more than 2 inches of vertical variance in some cases. I am struggling to lay out the siding courses in a way that meets trim tops and bottoms without having to notch shingles and cut them short around the openings. There are so many lines to try to meet. The worst case scenario is when a trim edge falls directly in the middle of where a course would be, and this is happening within two courses of the top of my higher water table. Even if I give myself 1/2″ play in the siding course height tolerance I need 1-1/2″ play in the trim width to make this drastic adjustment (that includes cheating the water table down like an inch as well). I guess my question is, is 1-1/2″ variance too much on 5-1/2″ wide trim? Which evil is worse- drastically varying trim widths or with siding courses that don’t meet the trim lines?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Michael Maines | | #1

    Aaron, in general, only carpenters care about siding courses hitting the tops and bottoms of exterior casing. It's still good practice but in many cases, especially on existing buildings, you simply can't make everything work. I've done a lot of shingling, on Nantucket and the Maine coast, and worked out some rules. Here they are, in order of importance:

    1. Finish with a full course at the top of the eave wall, where it meets the frieze or soffit.
    2. Hit the tops of as many windows and doors as you can on the primary facade(s), without varying your coursing more than about 1/4".
    3. Hit the tops of as many windows and doors as you can on secondary facades. (Don't worry when you can't hit the tops--it doesn't affect performance and only a few carpenters will ever notice.)
    4. Hit somewhere on the window sill extension on the primary facade. It doesn't have to be exactly at the bottom of the sill extension; in fact I prefer the coursing to hit the top of the sill extension. Middle is ok too.
    5. Hit the sill extensions on secondary facades.
    6. Try to avoid courses less than about 1 1/2" tall under sill extensions, mainly because the shingles tend to break.

    Varying the height of your casing is much more noticeable than not having perfect coursing. Don't vary the height unless you want to for stylistic reasons between windows, doors and overhead doors.

    Of course others will disagree with some or all of my rules, but I've found them to be a good guide.

    1. centercarpentry | | #4

      Thanks for your input. I think what you've detailed makes pretty good sense. The bottom line is that I would have to use some crazy casing alterations and a larger siding tolerance than I'm comfortable with to make everything meet.

      EDIT: I'm wondering what you think about the water table. My plan is to install it level from the lowest point so that I have a good level base to start with. This will result in the water table hanging significantly lower than the sheathing in some areas, and also in ripping a scribe(ish) in the water table lower edge to give it some clearance off of an invasive patio on the higher corner of the house.

      Actually, another question, as you have lots of experience: I'm not settled on corner trim and water table intersection. Do you usually butt the corner trim into the top of the water table or do you butt the water table into the sides of the corner trim? Seems like running corner trim first would be much easier, and would replicate an interior trim situation with, say, door casing and baseboard.

      1. Expert Member
        Michael Maines | | #6

        The water table should be parallel to the windows and other major elements. If you install it level but windows and doors are not level, the water table will look crooked. When renovating old homes, parallel is usually more important than level, inside or out. (There are exceptions.)

        The corner board can run long and the water table butt into it, but in most cases the water table is meant to evoke classical architecture and should run continuously, with the corner boards sitting on top. This is easier when you have a separate cap on the water table. With pared-down designs you might skip the cap.

  2. gusfhb | | #2

    I wonder if varying the size of the trim around the windows and doors might look better than irregular shingle reveals around windows.

    1. centercarpentry | | #3

      I think maybe specifically for identical windows next to each other it might be worth adjusting the trim so the siding frames them exactly the same.

  3. Expert Member
    Michael Maines | | #5


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |