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I will be expanding a master bedroom to add a ensuite bathroom. I will be using the existing window area to make it the entry door to the bathroom, see picture below. I always thought the best would be just extend the current gable roof over the addition, matching slope and dimensions.

After removing the siding my plan was to attach rafters on each side to the existing sheathing, support one end of the ridge beam that way, and just continue the same all the way to the other end (16ft long) (similar to Option A below).

At some point, someone mentioned that it would be easier to have the roof for the addition lower than the existing roof line (I don't really know why) like some construction have gable roofs (stepped or two layers). I hope I'm making sense with my explanation.

Any suggestions? Pros and cons? Something I'm not thinking about? Any feedback and suggestions is greatly appreciated. I'm in the Midwest US where wind is something to look for during spring. Not so much snow during winter. Using 2x6 for rafters and a non load-bearing ridge beam for the roof.

Existing room to be expanded

Existing bedroom to be expanded

Option A

enter image description here

Option B

enter image description here

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  • Show us the rest of the structure. If aesthetics are important, you probably have other options. Also tell us the intended dimensions of the new space.
    – isherwood
    Jun 7 at 21:04

7 Answers 7

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Option B is really only possible when you'll change both the roof and the indoor ceiling heights. (Note the heights of the overhead doors in the photo: they indicate a change of indoor ceiling height in that building.) Thinking about proportions of the features I see in your photo, I'll estimate the existing room is 8 feet tall, window is 4 feet tall, and there's about 3 feet from floor to sill and 1 foot from window head to ceiling. In my view it's not viable to drop the level of the ceiling in the bathroom addition. The only way to do an Option B step in the roof would be to build the roof of the addition higher than the existing by building say 10 foot exterior walls or by using a raised heel truss.

Maybe it's a regional difference, but to my mind there's no such thing as a non-bearing ridge beam. I would use the term ridge board when roof and rafter weight is borne at the exterior walls and ridge beam when weight is carried both at the ridge and at the walls. The photo of Option A depicts a load bearing ridge beam, though I realize it's just a stock image and not necessarily representative of your intentions.

Have a look inside the attic and do more of whatever roof system is already in use. If it has trusses order a few more of those. You might need only two or three and in fact if there's a gable truss it could likely be relocated to the new exterior wall by replacing it with a regular truss. If the existing system is ridge board or beam, continue the pattern.

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    I agree on both your points. Lowering the roof opens a bag of worms, and I'm also confused about the plan to support a roof beam (which probably isn't even needed).
    – isherwood
    Jun 7 at 20:44
  • yeah, I meant a ridge board (at least I mentioned it won't be load bearing haha). thanks for your input it. I really had some of those thoughts at some point (height of ceilings, etc) but didn't put everything together until I saw it here.
    – Sergio A.
    Jun 7 at 21:49
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When we did something similar we did option A. So it looked original. The builder removed the wood soffit and joined to the existing beams with no problem.

Option B is often used when there is a change in ground level and an internal step. You might have a change in internal ceiling height with option b or just less insulation.

It is, at the end of the day your choice.

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  • Totally right about the internal step, which is not happening. Option A it is..
    – Sergio A.
    Jun 7 at 21:50
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I do like breaking up long roof planes, but you don't really have that option here.

Drawbacks to Plan B:

  • You'll have more fascia and soffit to deal with.
  • You'll have a jog in the transition between old and new fascia and soffit to deal with.
  • You'll have to lower wall height.
  • You'll have to lower ceiling height.

Even after all that, it won't look like your diagram. You'll only be able to drop enough that the upper fascia will essentially stack on the lower roof. It'll be like this, or even tighter:

enter image description here

That creates either an awkward soffit access issue or fascia with flashing to the lower roof. It isn't a great situation, either practically or aesthetically.

Plan A is really the only sensible option unless you're really opposed to a long ridge and are willing to deal with all that added complexity. Aligning new and old isn't difficult with some basic carpentry skills.

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  • Great picture. In my answer, the distance was about a foot.
    – JACK
    Jun 7 at 21:15
  • Thank you for your input. That image definitely looks like what I would have to deal with, which means I'll have to add an overhang to the existing roof anyways! Option B represent more little things to deal with rather than trying to extend the existing structure. Definitely not lowering the ceiling as it's pretty low already.
    – Sergio A.
    Jun 7 at 21:53
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Option B means that nobody would notice if the framing was a teensy bit off. (Either immediately or after the building settles.) Lots of folks will add a small overhang to the old roof (helps a lot with water), but that means the siding/flashing etc between the old and new is fiddly to get at.

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  • Option B adds a whole bunch of complexity and expense. It's not difficult to align new and old framing with a little care. Framing is never perfect.
    – isherwood
    Jun 7 at 20:48
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    @isherwood Respectfully disagree. Complexity-wise, it’s just a roof (notwithstanding the overhang note). Expense-wise, not sure where you’re going with that… again, it’s just a roof. Agree that framing is never perfect, but if you try to extend the ridge and it doesn’t work well, you’ll see it.
    – Aloysius Defenestrate
    Jun 7 at 23:23
  • See my answer. A second plane adds a lot of trim detail.
    – isherwood
    Jun 8 at 18:45
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Option A means measurements must be perfect or the tiny difference will show.

Matching of the old roof colour to new roof will also be difficult unless doing the whole roof. The old roof will be faded compared to the new roof even if using the same roofing material. Integrating the new to old roof is more complicated also, you do not want a straight line running down the two roofs, unless it is a steel roof.

Option B gives more choice in design of the roof, does not need to be the same type and colour can be different(a design/art statement) also till the old roof needs replacement.

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    Framing is never perfect, and it's not at all difficult to match rafter length (and therefore pitch and ridge position).
    – isherwood
    Jun 7 at 20:41
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Your "someone" was right in the fact that lowering the new roof would be easier and it would also be cheaper to do if hiring a contractor. The problem is that it would always look like an addition.

I actually worked in an area where room additions were/are pretty common. The customer I was working for lowered his roof like your Option B. A close by neighbor added a similar room but chose Option A. When all was said and done, my customer totally regretted doing it the way he did because of the lower ceiling in the new room and the addition look from the outside. Thankfully, I wasn't part of the decision making on that roof.

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    I'm not sure how B would be easier. The ceiling and walls would also have to be lower, which adds complexity. And you haven't said why your neighbor regretted the decision.
    – isherwood
    Jun 7 at 20:42
  • @isherwood In this particular case they didn't lower the existing ceiling. That was the main reason for the dissatisfaction. The "easier" part was due to the new part being added on without disrupting the living space.
    – JACK
    Jun 7 at 21:11
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I'd extend the roofline so that it doesn't forever look like an addition.

Going with a lower roof results in a few things:

  • New water/bug/critter infiltration points
  • The ceiling will be lower in the addition
  • Added labor for gutters
  • Added roofing labor due to flashing against existing wall
  • Good luck making the siding look nice
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