Expert: Dan Griffin - 9/25/2010

Question
Hello! I am an artist and writer with no experience at all doing home improvements. I am attempting a restoration of a craftsman home built during the 30's. The basement of the three story house is built on a slope. Two sides are
in a hill. One side opens into a garage I wish to remodel and turn into a sitting room. It seems easy enough to remove or open the existing garage door, raise the floor with concrete blocks, add french doors and windows where the garage door closed. I could, I think, drop the ceiling below the garage door when it is raised. If I ever want to sell the house I could return it to its original purpose by removing the entrance doors which would be built outside the garage door. There is a recess between the exterior wall of the house and the closed garage door which is about 16 inches deep and is cement block.

My problem is adding a window to  another room in the basement, the room  has one small casement window placed in a block wall. The window is recessed. It seems I could simply knock out the blocks below the window and enlarge it lengthwise, but the wall shows cracks. I would prefer to enlarge the window to the size of a double paned window. How do I find out if the concrete blocks supporting the two floors above the window are strong enough to manage the stress of an additional opening? I can imagine knocking out the space and watching the house cave in.

I hope to convert this very primitive basement (cellar) into a small studio apartment for extra money. The basement does traverse the entire length of the house and it is divided into separate spaces. Going through a side door in the garage a small room, 12 x 10 parallels the staircase to the kitchen. At the foot of the kitchen is the pantry, if I take off the doors and finish the interior it is large enough for a utility. On the other side of the staircase is a narrow room we use for the laundry it is  12 ft x 18 ft and has the casement  window near the ceiling. Opposite the staircase, and west of the laundry is a door leading to the workshop where we have a room with an exterior door.  This room has the water heater and could be a great bathroom. The laundry room would make a nice kitchen if it had a window, and the niche accessed from the garage could handle a Murphy bed.The sitting room would be the garage.  How do I find out if the concrete blocks on the exterior wall in the laundry room are strong enough to support a large window or patio door? I have big ideas but a small budget. I spent the summer patching leaks one bucket of cement at a time. I am proud of myself. I won't be so proud if the house caves in.

Thanks, Kathryn

Answer
Kathryn, windows and doors need headers to carry the loads that are above them.  In wood framing this is usually doubled up 2x12's that rest on jack studs at each side.  In masonry construction this is done with steel lintels, concrete precast lintels, or rebar encased in concrete inside some special cement blocks.  I cannot see your esisting window.  

Basement walls hold back a lot of lateral load that is trying to push the wall over.  Cement block (CMU) walls have cells which are filled with concrete and rebar to make them strong enough to resist these loads.  It is certainly possible to make windows and doors in existing walls, but they do require careful study and execution to prevent load bearing issues.

I cannot see the situation.  You really need someone who can see the installation and verify the circumstances.  A good carpenter/builder is qualified, though a structural engineer would be ideal.  If this window wall is above the ground, it makes it much easier as there are not the lateral soil loads.  If you have to cut rebar in the block cells, you are affecting the structural integrity of the structure.

I hope this answers your question, if not don't hesitate to ask again.