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The grillage foundation – installation tips

The grillage foundation with metal frame, its advantages and main characteristics, installation tips.

What is grillage foundation? You could hear the definition before because of its wide popularity among the country construction life. Grillage foundation is a kind of pile foundation which is characterized by the presence of reinforced concrete foundation beams or grillage. This raft foundation is laid on top of foundation piles and located at a height of 6-8 inches above the ground.

Features of grillage foundation

The grillage connects the whole foundation into the one structure and thereby contributes to a uniform distribution of the weight of the house and all the piles. Most often this foundation is arranged as a monolithic reinforced concrete structure. The strength for it is provided by the metal frame (steel grillage foundation).

Types of grillage foundations

Grillage foundationGrillage foundation designs are divided into different types according to the type of the used piles:

  • screw piles,
  • precast files,
  • hanging piles
  • bored piles.

Advantages and disadvantages of the grillage foundation

The advantages of grillage foundation:

  • it requires less time and materials for its installation;
  • it reduces the heat-evoke of the house with the help of the foundation as it isn’t applied into the frozen soil;
  • it reduces the level of the house vibration (it is very actual if the house is built near highways).

Disadvantages of the grillage foundation:

  • the need for the construction of piles at a sufficiently great depth;
  • space under the grillage has to be filled and warmed.

The appropriateness of the grillage foundation

Steel grillage foundationThe foundation of this type is advisable to construct for buildings of light construction materials (timber, concrete blocks, concrete, etc.) on fragile soils. In other words, the grillage foundation should be selected in case if:

  • there is a desire to save up to 30% on the construction of the foundation;
  • soil characteristics and conditions of their occurrence in the area (high water table, heaving soils, large depth of freezing) do not allow to build the other type of foundation;
  • the load of the future house is expected to be relatively small.

Installation tips & getails

  1. Piles

Screw piles foundationThe wells are drilled for the piles around the perimeter of the future foundation of the house. The depth of such wells should be 2 feet larger than the depth of the usual soil freezing in the region. The depth and diameter of the holes for the piles are calculated depending on the characteristics of the soil and most often their depth is in the range of 4 inches and the diameter is about 8 inches.

The height of the frame should that so the upper ends of the valve to be displayed above the flooded piles for the connection with the frame of the future grillage. It is necessary for the reliable connection of the grillage and the piles. The elements of the frame are connected to each other with a soft steel wire knitting. After the mounting the piles are poured concrete. The concrete is previously prepared in a concrete mixer using quartz sand and gravel. After the pouring the piles are left for a month for the final setting of the concrete and the acquisition of sufficient strength.

  1. Grillage

The grillage can be made from prefabricated precast concrete elements or in the form of a monolithic belt. The second option is preferable as the solid monolithic grillage is much more reliable.

In order to produce the monolithic reinforced concrete grillage first it’s necessary to produce and install the formwork. It can be made of edging boards in the form of rectangular troughs and must be set so that you get a gap of about 6-8 inches between the lower part of the future grillage and the ground. The height of it is usually about 1 foot and the width should be equal to the minimum wall thickness of the future house.

Inside the casing you should set a framework of reinforcement connections using binding wire. Such frameworks can be configured as one or two rows of valves connected by crossed rods or as laying nets in which the two rows are connected by means of specially curved clamps. The lower number of fittings must be placed on a pedestal height of about 25-3o mm, allowing its complete immersion inside the concrete when pouring. The minimum distance from the frame to the side walls of the formwork should be the same. Concreting of pile capThe reinforcement is connected with the same binding wire with releases of reinforcing piles. Using the cement mixer prepare the required amount of concrete and pour it into the formwork in a continuous cycle. In the process of pouring the concrete you must watch its dense stacking attentively in order not to get the unfilled cavities. For better shrinkage of concrete you may use a vibrator or a conventional bayonet spade.

After the fully filling of the grillage the surface of the foundation is leveled and left util the full drying off the concrete. If the weather is very hot and very sunny the surface of the grillage should be periodically moisten. After the drying of the concrete the formwork can be removed. Now your grillage foundation is ready.

We hope this article helped you to get the necessary information on the grillage foundation.


The main Types of foundations for houses and their features and disadvantages.

Types of pile Foundations in Building Construction.

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