Floor insulation using joists: materials for thermal insulation + insulation schemes

Regardless of whether there is a screed under the floor or just a filling of expanded clay, or maybe there is even damp earth under the floor, in order for the floorboards of a wooden floor to be warm, the space under the top flooring will need to be insulated.

For this, the well-known and most common method is used: insulating the floor along the joists. What logs are and what insulation is best suited for thermal insulation of wooden floors, as well as what schemes are best to implement this will be discussed in our material.

Types of floor insulation

The logs are wide bars installed on an edge and running from wall to wall parallel to each other. Plastic or metal beams can also play their role. Next, the finished floor boards are attached to them, so it is very important to lay them correctly so that over time the floor does not begin to creak or deform.

The selected insulation option is placed between and sometimes under the joists. Let's try to figure out which material for floor insulation is better to give preference to, and which should be completely abandoned.

It is not necessary for the logs to be exactly boards. Often this is an ordinary beam, adjusted to the level in one plane.The main thing is to secure them well and level them so that subsequent laying of the floor does not bring problems to the homeowner.

We will consider the most popular types of insulation materials, which are distinguished by fairly high heat saving rates.

These included:

• sawdust or sawdust mixture;
• expanded clay;
• glass wool;
• mineral wool;
• ecowool;
• penoplex;
• expanded polystyrene.

All of the listed insulation materials are quite airy, which means they will let the cold through with great reluctance. In addition, a high-quality layer of insulation can prevent the appearance of high humidity in the house, which is also important.

Option number 1 - budget sawdust

This material has the most unstable characteristics. Often, it becomes saturated with moisture, which significantly worsens its heat-protective properties.

In this case, the owner better take care of the bottom layer of waterproofing, since wet wood will begin to rot, and this can cause not only damage to the coating, but also a number of serious diseases.

Often, as a relatively inexpensive option, pellets or sawdust granules similar to pellets are used to insulate the floor. In them, sawdust is compressed and held in place by an adhesive base.

This insulation has indicators thermal conductivity will be a little better, but experts do not recommend insulating the floors of your home with such material. Its moisture resistance leaves much to be desired.

Of course, if you plan to insulate the floor in a country house or in an outbuilding, you can use sawdust, but they are completely unsuitable for insulating floors in a house. It is better not to save money, but to purchase more expensive and high-quality insulation.

According to experts, sawdust is one of the most undesirable materials for floor insulation. But the budgetary nature of the material often takes its toll. Experienced builders recommend using sawdust only when insulating the floor of outbuildings

Option No. 2 - environmentally friendly expanded clay

This material is quite in demand, due to its affordable cost, as insulation. Therefore, it is no wonder that he has the most mediocre performance.

With relative and comparatively low thermal conductivity for thermal insulation materials (within 0.1 W/m*K), it also has a number of unconditional advantages:

• this is the most environmentally friendly material of all presented in our list of insulation materials;
• it is free-flowing and therefore easy to install;
• completely fireproof, as it does not burn at all;
• does not rot;
• its granules have a high degree of strength.

But residents of the northern regions, who have expanded clay as insulation under their floorboards, often complain that it feels cold from below. And this is no wonder. Even though expanded clay is a porous material, its very base is solid, and therefore is just as prone to absorb cold as it is to give it away.

And, of course, its thermal conductivity varies greatly depending on the size of the granules. The larger the granules, the higher the level of thermal protection, and vice versa.

After insulating the floor with expanded clay, the result will not be the warmest floor. But owners often use this material, especially in southern latitudes or when constructing floors for utility rooms

Option No. 3 - affordable glass wool

Despite the fact that glass wool is a subtype of mineral wool, it is considered an unsafe material, so we will consider it separately.Its fibers are nothing more than real glass fibers. They can not only irritate the skin and damage the eyes, but also cause serious lung problems. That is why they everywhere prefer to replace it with mineral and ecowool.

The main advantages of glass wool are:

• chemical inertness, the material is dangerous only due to its physical characteristics;
• high vapor permeability;
• ease of installation. This material cuts well with scissors.

But some still haven’t given up using it. After all, its thermal conductivity parameters are more than two times lower than those of the same expanded clay (within 0.04 W/m*K).

And if a protective layer of vapor barrier is laid on top of it and the threat of damage from glass wool fibers is thereby reduced to 100% zero, why not use this material?

Glass wool is not the safest material. Some people have a severe allergic reaction to it. Therefore, nowadays they prefer to replace it with other types of cotton wool.

Option No. 4 - popular mineral wool

This is a more expensive analogue of glass wool. It has all its advantages, but at the same time, it is completely safe for health.

This is due to the fact that mineral wool fibers are smaller, softer and made not from frozen glass fibers, but from natural minerals - carbonates, that is, rocks, which are mixed with various additives.

This type of cotton wool is even more convenient, since you can take it even with your bare hands without fear. For convenience, it is available both in rolls and cut to specific sizes.

On sale you can find mineral wool of several varieties - stone, basalt and slag.But it is not 100% composed of rocks. Some part of it is occupied by processed products of the metallurgical industry

Option No. 5 - high-quality ecowool

Ecowool is an even more expensive analogue of glass and mineral wool. Its advantages mainly lie in its 100% environmental friendliness, as in the case of expanded clay and sawdust. It, like previous materials, has a low degree of thermal conductivity, but at the same time remains the only material of all that is not affected by rodents.

Its important advantage is that if mice and rats make not only burrows, but also entire nests in glass wool, mineral wool and polystyrene foam, then they do not touch ecowool, since it causes a severe allergic reaction and dehydration in them.

Oddly enough, more than 80% of ecowool consists of recycled waste paper, that is, it is a product of recycled cellulose. In addition, it contains harmless antiseptics - boric acid and fire-resistant impregnation based on borax

Option No. 6 - high-strength penoplex

Penoplex is foamed polystyrene foam. In other words, it is a frozen foam mass made from molten polyethylene granules. In some ways it vaguely resembles foam rubber, only frozen and hardened.

In terms of its thermal conductivity qualities, it is ahead of all the above types of cotton wool. The thermal conductivity coefficient of penoplex varies within 0.03 W/m*K.

He has:

• low water absorption rates;
• high strength indicators;
• low density.

Its only disadvantage, and not in all cases, is poor vapor permeability. But if the room is equipped with good ventilation, this is not critical.

You can read more about thermal insulation with penoplex Here.

Penoplex is in no way inferior to foam plastic in its energy-saving qualities. But at the same time it is much easier to work with it. And that’s why it costs significantly more

Option No. 7 - popular polystyrene foam

Its performance is no worse than that of penoplex. The only difference between it and the previous material is that it is not a foamed layer of frozen plastic, but a layer made from compressed granules of airborne polystyrene.

If you look closely, you will see that the material consists of small balls. In a piece of regular polystyrene foam they will be larger in size - up to 5 mm in diameter; in extruded polystyrene foam, on the contrary, they will be smaller - up to 0.1 mm.

But this does not in any way affect the advantages of the material, which are one-to-one similar to those described for penoplex. The only difference is that the foam will be more difficult to cut, and after the work done to lay it, there will always be mountains of debris between the lags that become electrified, which is why it is not so easy to remove them.

It is also worth noting that polystyrene foam will have to be cut strictly to size between the logs with a small overlap of 1-2 mm, otherwise the gaps remaining between the board and the insulation will negate all thermal insulation. That is why cotton wool is most often used to insulate floors.

The balls that make up polystyrene foam boards are literally filled with air. It’s enough to take a slab of insulation in your hands to feel that this material is capable of warming like a dry and airy layer of down.

Popular floor insulation schemes

In practice, most often, two schemes for insulating the floor of the basement/lower floor are used.The first is the most reinforced, when the insulation is present both under the joists and between them. Such thermal insulation, as described in the first case, is used only in northern latitudes, where the ground freezes quite noticeably in winter.

But most often, on the first floor of a building, logs are mounted on top of the screed, and in some cases, on top of well-planned soil.

Let's look at both examples suitable for the basement floor, and then we'll talk about insulating the floors of the upper rooms.

The diagram provides options for floor insulation for the lower floors. The DSP layer can be simplified, which is what most owners prefer to do

Reinforced thermal insulation option

According to this scheme, first, even before installing the logs, it is necessary to level the soil and insulate it with the bottom layer.

As insulation for the first layer, builders can choose:

• expanded clay concrete;
• planned layer of expanded clay;
• extruded polystyrene foam;
• a hard and denser type of penoplex.

Logs are already installed on top of it, after which the space between them is also carefully filled with insulation. This time it can be the same penoplex or one of the varieties of cotton wool.

In this case, people often resort to double waterproofing - one is laid between the upper and lower layers of insulation, the other is placed on top of the upper one, on which the counter-battens for ventilation and, directly, the floorboards will be attached.

In this option, penoplex was chosen as the bottom layer of insulation. The material of the top layer does not have to be identical to the bottom

Conventional insulation scheme

Everything is clear here. The logs are mounted directly on top of the leveled ground surface or, in the case of a screed, on it.

Next, a layer of insulation is laid on them. On top of the insulation is a layer of vapor barrier, which, as a rule, is an ordinary thick polyethylene film. Then thin counter-battens are nailed on top of the joists (some may neglect them), after which the final flooring is laid.

If you need to insulate the floor on the upper floors, then you will have to act a little differently. Here, a layer of vapor barrier is first laid on the ceiling material - the same film, then only the logs are installed.

Often in this case, builders lay a kind of subfloor on top of the ground - the basis for the insulation. This is what it will look like on the diagram

When insulating the floor with mineral wool or ecowool, a lower layer of vapor barrier must be present. This is especially true for the second and all subsequent floors.

The space between the joists is sealed with insulation, after which everything is covered again with film. Counter battens are screwed onto the joists with a screwdriver, onto which the finished floor is laid.

We also recommend reading the article where we described in detail how to implement it in practice insulation of wooden floors.

Conclusions and useful video on the topic

You can visually familiarize yourself with the process of floor insulation using joists from this video:

It can be seen that the process of floor insulation using joists is not as costly and labor-intensive as it seems at first glance. The choice of insulation is always at the discretion of the owner. In addition to sawdust and expanded clay, any of the listed materials will be optimal. With the exception, perhaps, of polystyrene foam, the cutting of which will require a lot of tinkering.

Do you have a different opinion about floor insulation? Please share it with people who are encountering this issue for the first time.Leave your comments in the communication block located below the article.