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Raising Part Of A House

Editor's Note: This is material of a highly risky nature. Do not consider this as "instructions"; this is for entertainment value only. If not done properly, lifting a house can lead to personal destruction as well as financial ruin. Read our Disclaimer.

I recently purchased a house in Massachusetts. It is a 40 yr old Colonial. The house settled about 2 inches in the southeast corner. The previous owners lived there for 30 years and told me that the settling had occurred prior to them moving there. I read your article on the Web Site entitled "Raising a Floor" and I found it very helpful. My question is, is raising the corner of my house 2 inches considered a large amount to raise it? Also, how long should this process take before the house is raised to level?

Thanks

John


Raising a house, or just a part of a house, is serious stuff. It may be within the grasp of a serious do-it-yourselfer, IF the proper precautions are taken. Iím not going to actually recommend that you tackle this project, that is something only you can decide. I have known people who would ask contractors for quotesÖ with the intention of only picking their brains for ideas. That is considered impolite in this business, so I canít recommend it either.

But if you do try this, then the following may help.

The Short Answer:

Raising a part of a house by 2 inches is not excessive (in my opinion). And you could do the entire lifting process is 10 minutesÖ though there would be negative consequences, primarily cracked plaster. When I was taking Building Construction Technology courses in college I heard a general rule about raising or leveling houses: 1/8 inch per day maximum to prevent excessive cracks in drywall or plaster. So you could do your lifting job over a two week span to be safe. But because of the large amount of settling there is a high likelihood that you will have some cracked or bulged plaster.

The Long Answer:

Houses typically donít weigh as much as people imagine, especially when they are built with common building materials. By that I mean conventional wood framing, asphalt roof shingles, and materials that are NOT stone, concrete or masonry. For instance, one of our project houses has concrete block walls on an absurdly shallow crawl space. We would raise up the house and excavate a proper basement, but lifting a house with concrete block walls would be impractical.

My first opportunity to raise part of a house occurred when I needed to lift up the middle of a "built-up" beam in a basement, because it had sagged in the middle. I used a 6 Ton hydraulic jack with a 4x4 wood post for jacking, and then I supported the beam in the middle with a new adjustable steel lally column. It all went smoothly.

When lifting a building one needs a thorough understanding of the structure and which walls are load bearing. But first one needs to understand house framing and be able to identify the parts of the structure. I would guess that a 40 year old house would be built with "platform" framing. I recommend that you do a little reading about house framing methods. There is also "balloon" framing and "post-and-beam" framing, both of which are quite rare for houses built after WW2.

I would also want to know why the house settled in the first place. It is quite possible that the original builders failed to compact some soil and the foundation settled soon after construction. If so, then there should not be any more settling. But if your house is built on a "problem soil" such as muck or decaying organic matter, then the problem could continue. I would bet that you will see no further settling, but you should monitor the situation. In either case, then you should be able to see cracks in the foundation that are consistent with the settling. That is, you should be able to find some cracks in the foundation wall that are tapered (larger at the top). Perhaps you can locate a pair of similar sized cracks that seem to delineate the settled portion of the house.

You must also disconnect the house from the foundation, if it's attached. Today most houses are anchored to the foundation with anchor bolts or anchor straps. The straps are just nailed to the mudsill. Anchor bolts use large nuts and washers to clamp the mudsill to the foundation. You may be able to locate these nuts in the space between the joist ends. But I have seen houses built as recently as 1975 (in Wisconsin) with no mudsills and no anchoring.

Lifting a house involves understanding some things about allowable bearing pressures. Wood can tolerate only about 625 pounds per square inch (PSI) of compression load. Concrete can handle 3,000 PSI, and steel can handle easily 30,000 PSI. These figures illustrate why it is so easy to punch a hole right through a floor or into joist when attempting to raise a house. 

What Iím saying is: the lifting force must be spread out considerably. And, the wood structure immediately above the lifting device must be monitored for crushing of the wood fibers. Crushing of wood fibers MUST be avoided.

It is also possible to punch a hole through a concrete basement floor with a hydraulic bottle jack or a lally column. I have always used one of several heavy steel plates under the hydraulic jack. I have a couple of pieces of ľ inch steel plate that I use under the jack, between the jack and the lifting column, and between the lifting column and the wood structure. I have also managed to bend these plates. I would recommend nothing thinner than ľ" steel plates for distributing loads. The ones I have are about 4" x 6", but you can use smaller plates, possibly as small as 3" x 3". You might try calling some smaller metal fabrication shops, they probably have scraps that they can sell you, or they can quickly cut some steel for you.

But BE CAREFUL with these. The biggest risk I have seen while raising houses has been the danger of a heavy steel plate falling from the top of the lifting post while I am crouched down fiddling with the jack. It takes only 600 inch-pounds of kinetic energy to deliver a fatal skull fracture. So a 10 pound object falling from 60 inches above could kill someone. This really is a "hard-hat" type of project.

Letís do some engineering here: Take a 3.5" wide wood beam (i.e. 4x6 or 4x8) with a 3" wide by 4" long steel plate at the top of a column. There would be 12 square inches of bearing area. Each square inch can tolerate about 625 pounds of force. That amounts to 7,500 pounds that you can safely lift using such a plate to spread the load.

(The goal here is to get as much bearing area as possible while keeping the steel plate weight to a minimumÖ to reduce the risk of a falling object. You could also drill two small holes in each plate so you can screw them securely in place on the bottom of the big wood beam.)

Iíd bet that the corner of your house weighs less than that. You didnít mention the size of the area that needs raising. Letís say it was 10í by 10í. That would be 100 square feet, but since we are raising a triangle-shaped area, we are only lifting half of that. Assuming a dead load of 30 pounds per square foot (standard load for a bedroom or living room), that would be 1500 pounds to lift. But that is just the first floor. If there is a second floor, double that number. And then the roof weight must be added in. I would guess 20 pounds per square foot would be the design load in your area. You could use 30 to be safer. That would be another 1500 pounds to add to the total load calculation. So a 10í by 10í corner might weigh about 4500 pounds. Thatís not much, really. A 6 Ton bottle jack could do the trick, but Iíd recommend buying a 12 Ton jack, it wonít cost much more.

Then you need to know just where to lift. You need to basically replicate the support of the foundation wall. So you need to lift in a long strip along the ends of the floor joists, just a few inches inside the basement wall. And you cannot simply raise one floor joist at a time. So youíll need a long beam to support all the joist-ends that need raising. I would recommend at least a 4x6, but a 4x8 sounds better. You can use a "built-up" beam made from two or three 2x8ís (or larger) nailed together.

This beam will have to be supported by a lally column at each end. And youíll need a third lally column to put on top of the bottle jack. To hold the beam close to the joists (while I am re-positioning columns and such) I have used rafter ties. It can be quite a juggling act to hold the beam up in the air and also two supporting columns.

Once the beam is in position and pushed up against the joists with the lally columns, you can use the jack/column rig to lift each end of the beam a little bit at a time.

Raising a house can be a lot of fun, but it might be best to spread the fun out over a few days or weeks. Besides, the house will appreciate it. Raising a section of a house by an inch or two will create a tremendous noise as the wood framing moves and rubs together. These noises can be nerve-wracking, so do a little at a time. Expect to hear snaps, crackles, and pops for hours, even days, after each lifting session. I would also recommend a good helper to hold and tighten the lally columns while you raise the beam.

When we bought lally columns, there was a choice of capacities. The lighter-duty column was rated at "one elephant" and the heavier-duty columns were rated at "four elephants". We bought several of each type, but I was most impressed with the "four elephant" type. They had much heavier steel plates for the column ends. The light-duty columns had such thin end plates that they always bent into a cup shape. Also, the heavy-duty columns never showed a tendency to bow. Columns usually fail by buckling. This mode of failure will first appear as a slight bowing in the column. For this reason I strongly recommend that you buy three of the heaviest-duty columns you can get (within reasonÖ I think the heavy duty columns we bought were rated around 14,000 pounds at full height).

Measuring:

You will also need a good-quality level, at least 4 feet long. I understand that "box-beam" type of levels are generally the best. You can get a premium 4 foot Stabila brand of level for about $70. Youíll be the envy of your neighbors. You can also use a small laser level. The price of laser levels has dropped substantially over the past few years. You can use it to determine the exact amount of settling, and then to make a mark on the foundation walls (or some other structure that doesnít get raised) from which you can measure up to the floor structure as it is raised.

Filling:

When all the raising is done, you will need to install shims (such as strips of pressure treated plywood) between the mudsill and the foundation. Donít stick your fingers in there, if the house falls itíll really hurt! Use a prybar to position things. Since you should have a tapered shape to fill, you will need a variety of thicknesses of plywood or other hard wood materials. Any wood next to concrete must be pressure treated or preservative treated, to prevent rot. I would caulk all the small holes between the filler pieces, to reduce cold air infiltration and bug infestations. Some people use mortar to fill this gap, and it may look better from the outside if the filler area is visible. If you use any cement-based product, it needs to be packed in tightly, and you really should wait 7 to 28 days to apply load to it.

I usually raise houses a small amount more required for a level floor (maybe 1/16 inch), so the shims do not have to be jammed in so tightly. Besides, the filler material may compress or settle slightly. And donít be disappointed if you do not get the house totally level. The floor joists may have taken a "set" or permanent curvature over time.

This is a very serious project, and if you tackle this I recommend that you take your time, and maybe do some more research (but I donít know of any articles or books on raising houses).

Bruce W. Maki, Editor.

 

 

 

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Compiled March 5, 2001