Lifting Up a Sagging Floor – DIY

Cost, Time, and Skills:

This job took two people one afternoon. We got muddy because we were in a dirt crawlspace doing just that, crawling. We used 18,000-pound screw jacks, 4×4 lumber, a circular saw, power drill/driver, and cement blocks. Total cost was less than $200, while a pro would charge $500-$1000.

The Story:

This past Saturday, my brother had me over to help move some of his furniture during the annual rearranging of the tv room. The photo below shows what we saw when we moved the couch away from the wall.

Look for the 1 inch gap between the floor and the base board

Apparently, it’s been that way since they bought their 90-year-old bungalow and it’s been nagging at my brother ever since. You may have similar areas in your home. You probably feel the same way my brother did: “it’s not THAT big a deal and it’ll cost at least $1000 to repair, so let’s buy diapers and food and gas with our money instead.” Well, it isn’t THAT big a deal now, but it could develop into a whole host of problems down the line, especially if the sagging is caused by a larger issue.

Three 18000 lb screw jacks and solid concrete blocks for support

The truth is, it will cost you upwards of a thousand dollars to hire professionals to do anything to your foundation or the under-structure of your home. Just plan on that. Plus, it’s hard to find the right people to do this work, because it requires on-site problem solving and a certain amount of risk assessment (don’t hire anyone that seems kind of stupid). I know this. We paid to have some work done on our sill plate last summer and it hurt the wallet. A lot. However, watching the crew work on my house let me know that I could certainly do that work myself the next time the need arose.

We ripped the 2×10′s in half to make four 4 ft joists

As a homeowner with an eye for and interest in how things work, I’ve learned an extremely important thing: my house is actually really simply built and nothing in here is all that complex. The trouble is knowing what to do and what tools to buy. If you aren’t good at figuring stuff out on your own, hire someone. . . once. While they’re working, ask them questions about the process and about what they’re doing. Assess whether you think you can do it yourself. I learned most of my skills out of necessity (it’s a cash flow thing) and by watching professionals.

As with many old houses, my brother’s has a tiny crawl space door. I’m large so that makes me unhappy.

For this job, as with any job, we first needed to figure out what the root problem was. The sagging floor was the symptom, and somewhere under the house there had to be a cause. Well, after doing the navy SEAL crawl up under the house, we found that the joists that were supporting that floor were not actually attached to the sill plate any longer, as seen in the photograph below. This is an obvious problem, considering the fact that the sill plate is the first line of support above the foundation wall. You can see that the joist had dropped about an inch below the sill, explaining the inch the floors had sunk.

The joist had slipped about an inch from the sill

In order to lift this section of flooring back up an inch, we needed to purchase a few screw jacks, which can be purchased at your local big box hardware store for about $30 per jack. The ones in the photos above are actually not the ones we ended up using. We had to buy shorter ones. But hey, what’s a home improvement project without at least two trips to the store?

Moving around under old houses can be tricky. My brother’s crawlspace opens up quite a bit once you’re inside. It used to be a dry cellar for storing produce during the summer, with a trap door in the kitchen.

As you can see in that last photo, my brother’s crawl space is rather spacious in spots. Unluckily for us, the spot we were working wasn’t one of the spacious ones. Here he is squeezing through the little trap door. Note the coveralls. I’d recommend covering yourself when working under the house. It’s nasty and there are spiders and junk.

A gift my brother and I both possess: flashing a goofy smile at a moment’s notice.

Here’s where we were working. The 2″x8″ joists you see in the photo (the boards running from left to right above my brother for the lay men) are the ones we would be supporting. We decided that we wanted to sister a new 2″x10″ board up against the existing joists and support the new joists. We chose this method because of the small amount of old termite damage we saw in some of the old joists. What we did was lay the new board flush with the floor boards and with the old joist. We then fastened the two boards together with 3 inch wood screws.

The crawlspace was really tight in the area we were working. Luckily, it was pretty dry. The vapor barrier and outside drainage had done their job well.

Below, you can see my brother prepping one of the new joists by partially driving the screws into the wood. This is surprisingly difficult to do when holding a twenty pound joist and a drill above your head while lying on your back.

I used to balk at the drills and power tools that come with a light. Not any more. That little light came in very handy.

With the mud and the muck, I didn’t get any photos of the next step or two. In the photo below, you see the final product. You can see how the new joists are attached and, if you look towards the background, how they overhang the old joists so the support beam is only pushing on the new joists.

Here’s the completed job. The new joists are attached to the old joists and are supported by the 4×4′s and screw jacks.

Once the new joists were up, we found locations where the concrete blocks could sit flat on the ground so the pressure wouldn’t cause them to crack. After they were in place, we hoisted up the 4″x6″x8′ beam so that it crossed all four of the new joists, sliding the screw jacks underneath. With the beam resting nicely on the jacks, we slowly turned the red handles until the beam was in contact with two of the joists. Then we kept turning until it was in contact with all four of the joists (the lower two lifted up to be in line with the higher two). By yelling through the floor to my brother’s wife, we were able to coordinate our slow turning of the screw jacks until the crack between the floor and the base board was gone.

Here’s the final product. Total, this  job cost my brother $150-$200, where a pro would easily have charged $800-$1000. I’ll admit, this is probably not the job for a first time do-it-yourselfer, but folks with a little experience and confidence can easily repair the sagging floors in their homes.

Look for the 1-inch gap between the floor and baseboard. It’s not there any more.

The before and after is below. If you’ve got questions or comments, leave them below or contact us at Also, feel free to leave us a comment on our facebook page Thanks for reading. -Robby

Before and After

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16 Responses to Lifting Up a Sagging Floor – DIY

  1. Gail says:

    I am so impressed with your knowledge and skills. Who’dathunkit?????

  2. Wow, nice post! Plenty of pictures to get the idea across, thanks!

  3. Steve Linnegar says:

    Thanks to “The Bennetts”. I have a log burner and stone hearth and there is an emerging gap between the architrave and the boards, and worse, the chimney attachment to the top of the burner has nearly popped out because of the quarter inch drop. I am in Australia, so my screw jacks are about three times the price, but I will be tackling my problem in the same manner this weekend. Thanks heaps.

  4. Grant Joyce says:

    So the floor jacks stay permanently under the house from that point on then? My wife and I are looking at buying an old house and sagging floors is one thing I’ve noticed on the edge of the ground floor rooms.

    • The Bennetts says:

      I’ve got jacks under every room of my house. Most of them were there when we bought the place. When old wooden homes were built, the floors were not supported as much as they should have been for 100+ years of use. I guess they just didn’t expect the house to hang around that long.

  5. Tony says:

    I’m about to start a similar project… but I read you should dig a hole and put cement on it to build a strong footing rather than using a cap concrete block… Wouldnt your cement blocks sink over time due to the weight of the house pushing down?

    • Robert says:

      I agree it is probably better to dig the hole and pour cement if you’re lifting the house a lot or if you’re only using a single jack. I think we’re fine since we used multiple jacks and we were really just redistributing the weight.

      If they sink, we can go back and tighten them up, or pour a pad like you suggested. Thanks for reading.

  6. Jenny says:

    Thanks for helping us save a pile of cash!

  7. Pingback: So. . The House isn’t Always Level | Old House Crazy

  8. Pingback: Fixing a Sagging Floor : Blog

  9. Jerry & Jean Beetem says:

    will jacking up the sagging floor in our crawl space fix the sagging roof problem, its all in the same area of the house. thanks Jean

    • Robert says:

      It might. I’d suggest looking at the joists under your floor and then get into the attic and check the roof structure, looking for sagging or other abnormalities. If the floor is sagging, bit there is no noticeable snagging in the roof, it could just be the floor. If unsure, have a pro come out and inspect it and give you pointers. You may pay a few hundred bucks on the inspection, but they might convince you that you can do the job yourself. Good luck.

  10. Jin Stone says:

    The screw jacks used shown in your pictures seem a different brand product, not the Akron ones shown in your second image — I bought the Akron screw jack, it won’t turn higher due the screw base will turn also. What is the brand of the screw jack you finally used?

    • Robert says:

      I googled Akron screw jacks and what I found seems very similar to the Tapco brand jacks shown in these photos. I think that either brand will work, so long as you purchase the correct height. During one of our trips to the hardware store, they only had one size, so be sure to measure the height of your space and buy jacks that fit within that range. I can’t say for sure, but I think your jacks are too short for your space.

      • Jin Stone says:

        Maybe the early made was with turning bar insert through a hole as shown in your image. I bought the adjustable floor jack 2 ft 10 – 4 ft 7 height, multiple pieces to assemble. And I also looked at the shorter ones, not like what you showed here. Tapco brand is sold in Home Depot, very similar to Akron brand which is sold in Lowes, but they do not look like the ones shown in your images.
        I googled and found Ellis brand heavy duty steel shore jacks look more like it. But they are out of stock for the size I want.

      • Jin Stone says:

        Both Tapco and Akron should have designed with a notch-lock mechanism between the screw plate and the inner pipe that stops the screw plate turning when the screw is turned.

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