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mwpiper 04-16-2010 07:53 AM

Cutting through masonry wall
 
I have a story and a half house with the first floor exterior walls consisting of 10 inch masonry, about half brick on the outside and half terra cota tubes running horizontally on the inside and plastered over.

We are contemplating expanding the back (west side) of the house. In order to get the kitchen in earlier, I am looking at a two stage expansion: a bump out to enlarge the kitchen itself, then a bigger addition later that will absorb the bump out. Knowing the larger expansion is coming means that the bump out has to be done in such a way as to not interfere with the bigger footings, walls, et al.

The back of the house is 27 feet wide. 25 on the inside. Looking at removing 10 to 12 feet of the wall for the bump out starting at the north corner. Basically half the wall will go away. This section includes a single double hung window and the back door. (House has three doors; front, side and back. side door is main traffic door, is located right at the bottom of the stairs for emergency egress. The back door has always been almost unused so we were going to eliminate it for now. New back door comes with big extension.)

For the kitchen bump out, I wanted to cut the back wall right up to the inside of the side wall so that the inside side wall would be straight and continuous. This means that masonry wall will no longer have a corner to reinforce it. I am thinking in terms of attaching a steel plate or channel to the end of the wall, anchoring it in the brick and down the foundation wall (full basement) to stabilize the wall since about a fourth of the house will be sitting on that end. The cross beam may even end up directly on the plate.

The end game as I visualize now is a header across the back of the house above where the wall was with the second floor joists, old roof rafters and extension roof rafters attached with joist hangers (in order to maintain a flat ceiling). There will be a center column because a 25 foot span will be too hard. The steel plates at the ends of the side walls will stabilize the side walls and provide racking resistance to the house.

Q: Does this sound even slightly viable?

There will have to be some serious engineering on this but I am trying to get a feel if the very concept is doable before we get too far into designing kitchen layouts.

Rory Read 04-16-2010 12:25 PM

time & money
 
With enough time & money...

But it does sound doable.

Consider that you will most certainly need new point footings under the posts/wall ends that are going to support the new beam system. If you do the remodel in stages, try to stage things so that the inbound footing that goes in to support the stage one beam is in the right place to support the final beam after both remodels.

It's not uncommon to convert an existing interior wall to a shear wall to compensate for the loss of shear strength when the original outside corner is removed. I believe it is uncommon to use a post, which is really what your flange or channel amounts to, to provide that kind of shear strength. I suspect the post would have to be quite substantial and embedded very deep.

It is possible to engineer very short shear walls (often seen at the side of wide garage door openings). Your worst case/fall back scenario could rely on a short pony wall into the new finished space.

Regardless, you might want to engineer first, and then consider kitchen layouts after that.

Good luck.

mwpiper 04-17-2010 01:04 AM

The idea of using an interior sheer wall is interesting. the back room of the house is a country kitchen 25' x 10'. The inside wall is 10' from the back of the house and straight across with only two door openings. AND we're going to be pulling down bad plasterboard and underlying lathe and plaster as part of the remodel. It would be open for crossbracing. Then the bracing of the end of the side wall would just be to stabilize the wall rather than trying to stabilize the house.

mwpiper 04-17-2010 01:12 AM

Next problem. The bump out I am hoping for is maybe 2-4 feet. Cantilevering is probably not reasonable. Is is an acceptable practice to brace the extension on knee braces; ie, attach a ledger board to the foundation above the ground and provide diagonal supports to avoid cantilevering the joists? This would put the joists in tension rather than bending and shear. Piers would be the next option. I just can't see the justification for pouring a footing and foundation wall with yards of concrete for such a small extension.

Rory Read 04-17-2010 10:30 AM

I can't speak that. I haven't done it, so I would have to defer to an engineer to help me work through the issues and specific costs.

It does sound a bit odd, and odd can often cost more than you think. If you have a good relationship with your engineer, you could talk to him and settle on a course before he starts his clock.

(Always a good idea to talk before your architect/designer/engineer/contractor starts; they may come up with a perfectly reasonable solution that at the same time manages to be totally unsatisfactory to you. Guess who pays for the second attempt then.)

You might have to reinforce the foundation wall supporting the knee braces.

Post and pier construction is the more common alternative to full foundations, but it's not usually an option where I am with our seismic code.

As for the interior shear wall, you would strip it and sheathe it with plywood or osb using a specific nailing schedule.

Good luck,


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