What do we gain by insulating a foundation and which materials should we use?

Building insulation vs construction law

In recent decades we have experienced a rapid growth of construction technologies. Builders, architects and legislators have focused on issues such as energy efficiency and the possibility to ensure maximum thermal comfort in buildings. Answers to the question about how to properly insulate a foundation or what parameters should be met by foundation insulating materials can be found, for example, in:

• Polish Standards,
• the Regulation of the Minister of Infrastructure of 12 April 2002 on technical conditions to be met by buildings and their location,
• the Construction Law.

What do the regulations say? According to § 317 of the above-mentioned Regulation, all building elements that are in contact with the ground should be protected with a layer of insulating materials. Annex 2 to the Regulation includes specific guidelines on thermal performance parameters, including the allowable values of heat transfer coefficient and the ground heat transfer coefficient (U_c). Since 31 December 2020, the maximum U_c value for floors over enclosed underfloor spaces is 0.25 W/(m² ·K) to 0.3 W/(m² ·K).

What do we gain by properly insulating the foundations?

Thermal insulation and waterproofing of the foundations from the outside or from the inside is very important. A properly protected foundation is a support for the walls and roof. If it is solid, the likelihood of cracks is minimised and money does not have to be spent on expensive repairs. Thermal insulation of the lower building sections reduces the risk of thermal bridges and prevents the loss of valuable heat through the areas directly adjoining the ground.

A properly selected waterproofing material protects concrete and masonry structures for years. Carefully insulated foundations effectively resist moisture and reduce the risk of mould and help moderate the amount of humidity in the air in the rooms.

How to insulate house foundations: practical guidance

There are various methods of insulating foundations and foundation walls. In modern construction, it is the architects who ensure that the structures fully comply with the continuously changing energy efficiency regulations. In addition, designers have expertise on the latest commercially available materials for insulating the foundations of a house with or without a basement, or of a public building.

The design of the building and insulation should be entrusted to a specialist. An architect will choose the best solution, and will take into consideration many factors, such as:

• stability and moisture of the ground,
• size of the building,
• the climate zone where the building is located.

To give an example, if you plan to build a house on clay ground that is unstable and is penetrable by water, you should use special insulation for the foundation walls. Attention should be paid to the thermal performance of the insulating material and to its resistance to water and frost. Materials should be selected by a skilled person in order to avoid any future problems with leaks and expensive repairs to the waterproofing membrane.

Insulating a foundation from the inside and outside: a review of materials

Which materials to use for insulating a house with and without a basement? In Poland, the following materials are used for insulating foundations:

• polystyrene (EPS),
• extruded polystyrene (XPS),
• polyurethane PIR foams in the form of ready-made boards,
• PUR foams,
• mineral materials: foam glass (also called cellular glass),
• anti-moisture foundation membranes, tar boards, and bituminous mastics.

The selection of insulating material should be left to the designer, whether we make a new building or insulate an existing facility.

Insulating the foundations with thermal insulation boards

Thermal insulation boards made of PIR foams grow in popularity on the market of insulating materials. These are boards that have a high compressive strength and resistance to the absorption of water, and are safe for humans. They can be used for insulating foundation walls as well as floors in rooms that are particularly exposed to moisture. They prove to be good in single- and multi-family houses and in public buildings.

An example of energy-efficient thermal insulation boards are the EUROPIR® boards, which are used for internal and external insulation. The main advantages of such materials include:

• the availability of sheets in various sizes,
• low heat transfer coefficient,
• light weight,
• resistance to fungi, putrefactive bacteria and construction chemicals,
• high insulating parameters after additional treatment.

The high quality of EUROPIR® boards is also proved by the fact that they are rated A+ in terms of indoor air quality. These materials are adjusted to the standards of ecological and passive construction.

Insulating foundation walls with Styrofoam

Styrofoam has long been used for insulating base courses and foundation walls. What are the main advantages of polystyrene and extruded polystyrene? They protect the structure very well against moisture and low temperatures. The XPS and EPS boards perfectly attenuate sounds, are lightweight, ecological, mould-resistant, and easy to install. How to insulate a foundation with Styrofoam? Just glue it to the vertical wall, protect with a foil, and cover with soil.

However, Styrofoam has some disadvantages that we should know about before we buy it. It is a plastic that gets damaged when exposed to certain chemicals. Improperly protected Styrofoam boards can deform or fall off.

Insulating foundations with foam glass

Foam (cellular) glass is a novelty in the thermal insulation sector. It is used, for example, for insulating buildings with and without a basement. A characteristic feature of this insulator is its resistance to deformations and high loads. Foam glass does not absorb moisture, is inflammable and safe for the environment.

The designers of energy-efficient and passive solutions are eager to use glass horizontal insulation for houses without a basement and buildings having a non-standard form. A glass insulator, presently used in construction, has the form of a thick gravel or commercially available boards. However, blocks and sheets made of foam glass are still quite expensive and, in consequence, building foundations are more often insulated with PIR foams, extruded polystyrene, or Styrofoam.

Summary

A tight and strong foundation ensures thermal comfort and lower cost of heating for many years. If the structure has no thermal bridges, the heat remains inside the rooms and the moisture is kept at a constant level. If you plan to build a house, a public building or a structure for investment, pay attention to energy-efficient technologies and modern insulation. Choose insulating materials that prevent the loss of energy while doing no harm to the environment.