How to pour a foundation for a wooden house if it is old: description and video

It is often necessary to make repairs or completely replace a sagging foundation for a wooden house. Of course, such work cannot be carried out independently in a multi-story concrete house, but if the house is wooden (log house, frame), then such a replacement (laying the foundation under the house) can be done with your own hands.

Replacement of the foundation is done with the same depth as the old one, it can be done even more. But in no case should the depth be less.

Typically, the reasons for the destruction of part of the foundation or its subsidence are: changes in the groundwater level, storm water flows, thawing after severe frosts and soil heaving in shallow foundations. This article will tell you how to lay the foundation for an old house with your own hands. First, you need to inspect the foundation of the house and mark where its parts are subsiding.

Installation (summary) on a concrete foundation

To replace the foundation, it is necessary to raise the entire structure of the house to a height sufficient to carry out the work. This important operation can be performed using jacks. Their number depends on the size of the house, but it can be calculated that to lift a one-story, two-room wooden building at each corner, it is enough to place 2-3 jacks, with a force of 5 tons each.

Before carrying out this work, stock up on wooden or iron stands. Raise 1 corner with a jack by 1.6-2.1 cm and place a beam. Carry out the same operation sequentially with all corners (along the perimeter of the building). To prevent the walls of the house from sagging, it is necessary to place several pads under the lower crowns. Consistently repeating the work, they raise the house to the desired height.

There is no need to rush: attempting to lift the building to a height of more than 2.4 cm at a time will lead to cracks on the walls, distortion or complete destruction of the structure of the building.

To further guarantee safety, supports are placed at every 6-7 mm of rise. If the jacks fail, the work will simply be delayed while they are replaced, but nothing will happen to the house.

Diagram of the construction of a new foundation for a house.

The jacks themselves are installed on a strong part of the foundation, but not on damaged areas or on the top of the walls.

So, the house is raised to the required height. We begin the construction of support platforms at the corners of the building - we cast concrete columns equal in height to the future foundation.

A frame is welded from reinforcement with a caliber of 10-12 mm around the perimeter of the house, formwork is installed from wooden boards and concrete is poured to a height slightly less than the building is raised. This is done to make it possible to waterproof the new foundation. The operation is performed by applying several layers of roofing felt to the base. After this, the building is carefully lowered onto the new foundation.

Selection of building materials

Another factor influencing the choice of foundation type is the type of construction. Here we proceed from what material was chosen for the walls of the building, this changes the weight of the entire structure and increases the pressure on the ground. Accordingly, it is necessary to increase the support area.

And building materials have different linear dimensions. Log and frame walls of the house can be supported by support pillars, but brick walls need a solid tape.

The design features of the house also limit our choice.

It can be difficult to imagine a country house without a basement, the main storage area for food supplies for the winter. Columnar and pile foundations are not adapted for the construction of a more or less good underground. The best choice in this case is a strip foundation. But, if you don’t need a basement, then of course you can limit yourself to a columnar foundation. Moreover, it is much cheaper.

After the “theoretical” part of the work, they move on to the practical. The construction of all types of foundations consists of the same work in a certain sequence. But the complexity of their implementation, the amount of material and labor costs are different for each type of foundation.

Therefore, the price of the foundation can also differ significantly. Despite this, the opportunity to do the foundation construction work with your own hands is always very attractive.

Replacing the log foundation of a house

If the house stands on so-called chairs - wooden stilts, then over time the log begins to rot due to the action of groundwater. Such a damaged base must be urgently replaced. Instead of rotten logs, new ones are installed or stone, concrete or brick pillars are erected and the distance between them is filled with cement mortar. The new foundation has a laying depth equal to the height of the old foundation of the house.

Work begins with dismantling part of the building's base and freeing the chair from various elements of the house: floor boards and joists.

Scheme of hanging the foundation for a house.

Install a temporary support at a distance of 0.5-1.1 m from the rotted log on both sides of the chair under the lower crown of the house.

Using a jack, they lift all the walls in turn to free it from the holding spikes. Temporary supports are placed under the crown and wedged out. The old chair is taken out and replaced with a new one with a length equal to the size of the old log plus the depth of its shrinkage. The wall of the house is lowered so that the tenon of the new chair fits exactly into the grooves of the crown. When performing this work, the following problems are possible:

cracking of wall plaster;
distortion of doorways and window frames.

To avoid these troubles, it is advisable to replace the wooden chair with a concrete or stone column.

In order to lay the foundation for a house, the following operations are carried out:

the old destroyed base is divided into parts of 1.5-2 m;
in the marked places they dig holes, remove damaged parts of the old foundation and strengthen the walls;
A new house foundation is being built on this site.

First, work is carried out on weakened areas of the foundation of the house. A layer of crushed stone (10-12 cm high) is poured into the dug trenches and compacted. Then a frame of reinforcement is laid there and the formwork is filled with concrete. If the house is built on a shallow foundation, then after leveling the new foundation and waterproofing it, it is necessary to arrange drainage and make a blind area.

To protect the house from deformation (soil heaving during severe frosts), the foundation is covered with thermal insulation. This is done with a layer of straw, sawdust, expanded clay, slag wool or foam polystyrene. For the same purposes, you can use a hot water pipe manifold laid next to the foundation. The resulting concrete columns are coated several times with bitumen mastic and wrapped in several layers of waterproofing material. The work is completed by completely filling all trenches with soil.

Replacing the foundation under a garden house

Question:

Good afternoon Please advise on the issue - we need to lay the foundation for the existing garden house (5*7 meters). It consists of a one-story veranda and a room with a second floor. There is a lot of water on the site in the spring + groundwater nearby (there is a well on the site). The house stood on a columnar foundation - but because... Because of the water, everything was wandering, then they turned out and he moved off them. Now they have calculated the pouring of the foundation - with the house being raised by 30 cm - and they said that the height of the foundation will be 45 cm - 20 cm deep. Those. the house will be raised on supports - they will make formwork and pour the foundation, along with these supports - and the house will be on the foundation right away. Is this option reliable or is it necessary to do it differently?

Irina, Novosibirsk.

Answer:

Hello, Irina from Novosibirsk!

In the gardening partnership where I work now, almost all the owners face the same problems. Lousy, moisture-saturated soil with very high standing water. The houses gradually sag and are periodically raised either by pouring concrete or laying down concrete blocks. Using jacks.

That is, they do approximately the same as your builders plan.

I also plan similar events at the house where I work. But somewhat modified.

Namely, between the pillars of the foundation supports, dig a trench as deep as a spade bayonet, pour a layer of sand just below the surface of the soil. Then make a reinforced screed (reinforce with welded mesh cards).

And this screed will be about 80 centimeters wide, of which 20 centimeters will be under the lower crown of the house, and 60 centimeters will protrude beyond its limits and serve as a blind area, which does not exist now.

And then place 0.2*0.2*0.4 meter concrete blocks on this screed under the lower crown.

This will increase the support area under the house. This will redistribute the load from the weight of the house and the subsidence of the house will be less than if it were simply by laying blocks.

The fact that you will fill the foundation with concrete instead of blocks will somewhat reduce the cost of repairs. But the area of support and it wouldn’t hurt you to do it as we plan.

You can consult with your builders. Because their idea to deepen the foundation by 20 centimeters may not lead to the desired result. In winter, the water under this foundation will freeze and, with its plantar and tangential lateral buoyancy forces, will push the foundation along with the house.

In terms of material consumption, my version and yours are approximately equal.

But this is my opinion and it may not coincide with the opinion of your builders.

And it will be interesting in three or four years to compare the results of your version and ours. I think mine is more reliable.

Good luck!