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Skillion and lean-to roof design

jackofalltrades777 | Posted in Green Building Techniques on

If using SIPS (properly taped & air sealed) for a skillion and lean to roof design. What’s nice with SIPS on a skillion roof is that they would make it REALLY easy to install vs stick framing the roof to get a skillion roof. Plus the overhangs are part of the SIPS so no framing needed there either.

Are there any inherent drawbacks (not SIP related) to this type of roof design? I like the looks and the simplicity with no valleys or ridges to deal with.

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  1. Expert Member

    The only drawbacks are that the interior walls (and exterior ones if they aren't also SIPs) are sloped or differing heights, meaning the framing takes more time and materials. And depending on how deep the house is, the rooms on the high side of the pitch can end up with ceilings which may seem disproportionately high.

    Neither of these is a significant problem, and I agree Slillion or Shed roofs have a lot going for them.

  2. jackofalltrades777 | | #2

    One thing you can do in regards to interior ceiling height difference is to frame in a false ceiling/attic and create a flat ceiling area.

    1. Expert Member
      MALCOLM TAYLOR | | #4

      Yes, and this can be a useful conditioned space for storage or mechanical equipment. The high ceilings can sometimes also offer the opportunity to add a loft space.

  3. GBA Editor
    Martin Holladay | | #3

    Peter L,
    Planning for solar orientation can be tricky. If you want a good slope for roof-mounted PV panels, the short wall will be the south wall and the tall wall will be the north wall.

    That may seem odd to the occupants, though, who probably want the taller wall to have more windows (if traditional passive solar principles matter to the designer and homeowner -- a big if, admittedly).

  4. jackofalltrades777 | | #5

    Would a 2-story skillion design pose any special issues?

    If I do solar, it would be on-ground solar as I have numerous acres of land to work with.

  5. Expert Member

    No, the roof doesn't know how many floors it has underneath it. The only effect I can think of is that a trussed or stick-framing roof is a bit more involved as the height increases, so your choice of SIPs has another advantage.

  6. jackofalltrades777 | | #7

    One question I did have. When installing the glulam beams on the wall for support of the SIP roof. The glulam beams would have to be cut/planed at top in relation to the roof pitch, correct? Otherwise you are laying a flat panel on a 4:12 angled roof pitch onto a square glulam beam plane which won't work.

    Only other way it could work is if you installed the wall glulam beam lower and just below the 4:12 plane of the SIP roof angle. Which it would still require a wedge of some sort to fill the gap between the angled roof SIP and squared glulam beam.

    1. Expert Member
      MALCOLM TAYLOR | | #8


      The Glu-lam manufacturers here all will supply beams with sloped tops. I'm sure yours will too.

  7. jackofalltrades777 | | #9


    Unfortunately in my neck of the woods, the glulam company will NOT supply beams with sloped/planed tops. Foxworth Galbraith and Home Depot are the 2 main suppliers for this area and NEITHER one will supply sloped/planed glulam beam.

    1. Expert Member
      MALCOLM TAYLOR | | #10

      That's annoying. How wide are the beams? If they are 4" or less, two passes with a circular saw will work. More than that and you will have to finish the cut with a reciprocating saw.

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