How hard would it be to “raise” the roof on a 18’ X 20’ buildi

Carol Marszalek
by Carol Marszalek
We have a building on our property that was built and used as an Aviary. I want to turn it into a guest house and would like to raise the roof line to accommodate a couple of twin beds. I would like to do so without tearing down the entire structure. We have to remove the slide ding glass doors and install walls, windows, and door. Here is a picture of the building: want attempt myself, any advice would be appreciated!

  11 answers
  • GrandmasHouseDIY GrandmasHouseDIY on Jun 22, 2018

    Hi Carol, I would honestly be pretty leery in trying something like this but if I were to try it this is how I would do it. You will need to separate (cut the roof) from the walls. You could do this with a recriprocating saw run around the outside top edge and inside top edge. From there I would rent tall floor jacks and get lots of helpers. You will want to raise the roof slowly and evenly on all sides. Then you can build new walls to accommodate the new height of the roof or add to the top of your existing walls. GOOD LUCK!

  • Sharon Sharon on Jun 22, 2018

    First would be to draw plans of all the structural studs every 16" on center, headers over doors and windows with jack and king studs supporting roof and floor plates, any foundation present, and have a structural engineer check to see if that building can support a second floor. All these are building requirements to code. Then you have to check with city planning department to see if your town allows mother-in-law cottages before you start as you will need a building permit.

    You could download a CAD program to help you make your plans.

    • See 2 previous
    • Sharon Sharon on Jun 23, 2018

      Still have to have the structure to support the extra weight, and still need a building permit..... or they could make you take the whole thing down.

  • Sharon Sharon on Jun 22, 2018

    Ophs and forgot, you need two points of egress in the building, the front door, and either a back door or an egress window.

    • Carol Marszalek Carol Marszalek on Jun 23, 2018

      Thank you. Have already checked with city. Due to small size don’t need two doors, though it has two now. Foundation is good, will have to level as it was built with a center drain for washing down.

  • Mogie Mogie on Jun 22, 2018

    But there's an important structural issue you need to address first: you can't simply add a new wall ( a knee wall) on top of the existing walls. Doing that creates a "hinge" between the new and existing walls - and that's a very unstable structure.


    Instead, the walls have to be made taller from the bottom up. One way to do that is by installing new, taller wall studs alongside the existing studs. Another method is covering the existing wall and new knee wall with full-height plywood sheathing to eliminate the hinge.


    Either way, you'll need the help of a structural engineer to make it safe.

  • Paperdoll Paperdoll on Jun 23, 2018

    A guest house??? What will they do for a bathroom, etc.? I think you need to do a lot more than raise the roof to make it into a guest house.

    • See 1 previous
    • Paperdoll Paperdoll on Jun 24, 2018

      Wonderful. Have fun with your project.

  • Lisa S. Lisa S. on Jun 23, 2018

    The foundation may not hold additional height. Check you r local building codes as well.

  • Melodi Whitaker Melodi Whitaker on Jun 23, 2018

    I wonder if simply adding 2x12s all the way around th top of all of the walls would work? I‘m not sure how high you wanted to raise the roof, but that might work. If you wanted it higher, you could make frames from 2x4s with cross pieces for added strength and attach them to the top of the walls and then put the roof back on? I’m just guessing here, but it seems like that would work.

    • Carol Marszalek Carol Marszalek on Jun 24, 2018

      thats kind of what I have in mind, there doesn’t meet to be a lot of head room, but enough so youngsters can enter and exit without banging their heads to badly!

  • Emily Emily on Jun 23, 2018

    what about sewer for shower and kitchen water?

  • Carol Marszalek Carol Marszalek on Jun 24, 2018

    There is a small drainage field behind that could handle shower and kitchen run off. Honestly, they could all shower in the house, and we would only need a chemical toilet for any night time needs. It is really to provide extra sleeping space. But by making it akin to a mother in law suite we can use it for Air BNB rentals when not needed by family.

  • P P on Jul 27, 2018

    Your zoning commission may prohibit doing any or all of this work - you may not be allowed to build any higher close to the property line or be allowed to make any structural changes to existing structures at all. and a structural engineer and a gas/plumbing inspector & electrical inspector are going to be needed too. And Air BnB rentals may be prohibited in your area but the board of health also has codes you'll need to meet.

  • Cynthia H Cynthia H on May 11, 2021

    Hi! I would consider if your foundation is sufficient for the extra weight load. I would also find out about local building and zoning requirements. Good luck!