Insulation of attic overlap on wooden beams and on reinforced concrete slab

Welcome to "All about the Roof," where we will discuss the fundamentals of attic insulation and roofing. Today we cover an important subject: insulating the attic floor, regardless of whether it is supported by a slab of reinforced concrete or wooden beams.

Maintaining comfort and energy efficiency in your house depends heavily on insulating your attic. Choosing between concrete slab foundation and wooden beams affects the insulation technique when thinking about attic floor insulation. A more conventional foundation is offered by wooden beams, which frequently need insulating materials positioned above and between them to keep interior temperatures stable and reduce heat loss.

Conversely, attics featuring reinforced concrete slabs present distinct insulation opportunities and challenges. Despite their strength, concrete slabs conduct heat more easily than wood, so in order to effectively reduce heat transfer, insulation materials with higher resistance values are required.

It is essential to comprehend insulation principles in order to maximize energy efficiency. In addition to keeping interior spaces cozy throughout the year, proper insulation lowers energy costs by lightening the strain on heating and cooling systems.

Here at "All about the Roof," we’re committed to offering you useful guidance and insights so you can decide on your attic and roofing needs with confidence. Stay tuned as we investigate different insulation methods and materials that work well with various attic construction types to get the best possible comfort and energy savings for your house.

Wooden Beams Reinforced Concrete Slab
Insulates effectively but requires careful sealing to prevent drafts. Offers robust support and thermal mass; insulation must be carefully installed to avoid thermal bridging.

We examine the significant distinctions between insulating attic spaces over wooden beams and reinforced concrete slabs in this article from "All about the Roof." Comprehending these distinctions is imperative for homeowners seeking to enhance their homes’ energy efficiency and comfort levels. Our goal is to offer readers useful insights that will enable them to make well-informed decisions regarding their insulation projects by analyzing the particular difficulties and best insulation techniques associated with each kind of attic structure.

What heaters are suitable for the attic?

If there are no plans to use the attic space for housing, the attic overlap should be insulated. T.e. We are discussing a chilly attic with completely uninsulated slopes. Furthermore, not all materials are chosen for slopes based on whether they are already appropriate for the ceiling.

Mineral wool: without harmful dust

Thus, utilize the "stretch method" appropriately when heating the attic overlap with mineral wool. In essence, it involves first laying the isolation material in the spaces between the beams.

Subsequently, three layers of vapor barrier film are applied to a mineral wool slab or rolled insulation, totaling approximately 150 millimeters in thickness. Following that, the plywood is already at a thickness of no less than 18 millimeters.

Foam polystyrene and polystyrene: simplicity of laying

Superior polystyrene foam insulation covers the attic, with the primary benefit being the elimination of the need for a vapor barrier and the easy installation of foam to fill in all the gaps.

Superior insulation: fashion and rationality

In recent times, blow-in insulation for attic overlap has gained significant popularity.

The bleeding insulation’s primary benefit is that it creates a continuous, even layer by itself, filling in all the gaps. This eliminates the need to cut tiny, prickly insulation pieces in order to seal an opening. It also does away with joints, seams, and adjustments.

In Russia today, Ecowata and Surting Vata are the two most common types of stooped insulation used to warm cold attics.

Up to 80% of ecowata is made up of cellulose fibers, which are extracted from regular waste paper, and 20% is made up of additives like boric acid, which acts as an antiseptic, and buran, which acts as an antipyrene. The heat conductivity of this type of insulation is high.

However, ordinary mineral materials that were ground for thermal insulation did not, for some reason, pass product acceptance, and this is how blowing cotton wool is produced.

For instance, their density and fiber structure were both inadequate. And since this kind of material is compressed and packed under high pressure, transporting it to the object’s location is simple. Once there, everything is once more released.

However, the ecowatus is still the material that is utilized the most frequently. The insulation process itself looks like this: while loading the material, one person should stay close to the installation to watch over normal operation. Along with the hose, the second person ascends to the attic, cuts a cross-shaped opening in the vapor barrier (between the beams), inserts the hose into the opening, and fills the cavity with the substance.

Additionally, bulk materials that are reasonably priced are utilized to insulate the chilly attic:

What insulation parameters should you pay attention to?

We never recommend that you insulate your attic floor with the priciest heat-absorbing materials. But take note that any well-known company that produces materials for this purpose for a longer period of time will pay more attention to quality, altering the volumetric weight of the materials, refining its products, and raising the coefficients of thermal insulation. And already, something is being discussed here.

If not, you should always be mindful of the insulation parameters that are crucial for a wooden overlap but insignificant for concrete, and vice versa.

Parameter No. 1. Bio resistance

It has to do with the fact that bugs and other animals cannot start in a heater like this, which frequently stays open. This is particularly true for mice, who prefer to live in warm, dry attics that are, most importantly, empty.

Water resistance is a crucial prerequisite for attic insulation. Moisture or raindrops falling into it by accident shouldn’t cause it to deteriorate.

Glass wool is one of the most enduring insulation materials.

Parameter number 2. Thermal conductivity

The ability to retain thermal insulation qualities for an extended period of time is one of the primary requirements for attic flooring insulation.

When purchasing a heater, keep in mind this fascinating detail: contemporary producers of heat-insulating materials consistently list three coefficients of thermal conductivity of the material in the technical characteristic: dry state, temperature of 10 ° and 25 °, and humidity of category A and B.

Given that the attic’s typical climate is dry and 10 degrees, you should examine the heat conductivity coefficient in these conditions. You will require a SNiP table in order to calculate heat in greater detail and accuracy.

We now observe such a time. When selecting a heater, you’ll most likely be told to consider insulation as having a lower degree of thermal conductivity. However, this really only makes sense for attics in residential buildings, as excessively thick materials cannot be laid between rafters when the roof slopes must be warmed. As a result, materials with a small thickness and the greatest heat conductivity are required in this situation.

However, you can cut costs because the insulation’s thickness alone isn’t important for the attic overlap. Simply use a thicker, more affordable insulation that nevertheless has a high heat conductivity. The height of the insulation itself serves as compensation for all of you.

Parameter number 3. Weight

Every insulation has a unique volumetric mass based on its chemical makeup. Thus, materials like glass, basalt, and any other inorganic or organic compound are most frequently used as the foundation for fibers. The heat-insulating material itself becomes either light or heavy depending on its type. Furthermore, the exact elasticity of the fibers—that is, the amount of elasticity between the overlapped beams—ensures the shape of all these materials.

Keep in mind that heavy heaters’ stiffer fibers help them maintain their shape better. This parameter equates foamed heaters, or hard stone wools, to the best stability for attic overlap insulation. However, there’s a catch: the mineral wool insulation that was placed in between the ceiling beams pressed tightly and readily into the wood, causing voids to form and the bridges to become cold. To seal all the gaps, you will therefore need to use a spray can in addition.

But there will only be benefits if we use foam materials to warm up the attic overlap on the reinforced concrete slab. Not to mention that using light insulation is only a huge bonus because the attic’s concrete overlap already weighs a lot and puts a significant strain on the house’s walls and foundation.

In contrast to concrete overlap, attics have a relatively low load capacity. Thus, in this sense, the insulation’s weight is also not the final factor. After all, there are already a lot of variations: the standard weight for a cubic meter of thermal insulation is 350, but it can also weigh 11 kg.

Basalt wool is one of the harshest heating materials.

Parameter No. 4. Moisture resistance

Rainwater or roof leaks that unintentionally get into the insulation shouldn’t cause it to begin to rot. It is not good if, within six months of installation, newly installed insulation starts to smell musty.

Thus, foam or polystyrene foam—which have nearly zero hydrophobicity—is frequently used to insulate the attic overlap on concrete and wooden beams.

Parameter number 5. Environmental friendliness

Another thing to consider is that, even though maybe nobody walks through an attic like this, the insulation in the attic should not be able to detect any strong or poisonous odors.

It all comes down to ventilation: air will eventually pick up the insulation molecules and carry them into residential buildings, which poses a risk to the safety of the occupants. Select a heater that complies with hygienic requirements as a result.

Parameter number 6. Preservation of the form

The chosen insulation’s stability is a further crucial factor. Accordingly, specific laboratory testing revealed that heat loss via the matte heat insulator or the spaces between the plates can eventually approach 40%. And this is true even though, if the material stayed dry, it might not have changed its thermal conductivity in any way during that time.

As a result, the material’s ability to maintain its size and shape over time is crucial. Such gaps won’t matter for the attic’s concrete overlap because, unlike the attic overlap, here the overlap is sufficiently thermally insulating.

The issue, though, is that parameters like form or stability are missing from technical data for contemporary heat insulators.

Parameter number 7. Fire safety

Finally, the attic insulation needs to fulfill all fire safety regulations. Consider the well-known Ecowata, which is manufactured from more than just regular waste paper and newspaper fragments. Everything appears to be very easy and clever, so why don’t you also cut the paper smaller and avoid dozing off in the attic? Is it going to get worse? After all, when air molecules become trapped between tiny elements, as occurs in animal wool, the looseness principle is also at play here.

Let’s say that while this method’s insulation qualities won’t get any worse, unplanned fires are typically caused by old, dry paper and wood. For this reason, modern cellulose heaters must be treated with specific chemicals to prevent fire.

It is crucial that insulation has both an attenuation and does not burn when discussing the combustibility of materials. Just keep in mind that everything burns in the center of fire, along with iron and concrete, but the insulation shouldn’t catch fire if the spark lands on the attic overlap. This is the main topic.

The actual attic insulation cake should resemble this:

Vapor barrier questions: how, on which side and is it necessary?

Steam permeability is a critical factor in the insulation of concrete and wood roofing. Therefore, as construction contractors like to say, "cotton wool" and "foam" can be applied to all heaters made today that come in the form of plates and rolls.

We cover a range of thermal insulation materials, such as "cotton," stone wool, mineral wool, and glass wool, as well as organic and mineral fibers. The process of hardening plastic mass with a distinct chemical origin yields all these materials. Additionally, the coefficient of thermal conductivity for each of these materials is roughly the same at 0.04.

These materials are all made of entangled fibers. They don’t create any sealed pores, so water vapor can pass right through them and out again. Consequently, vapor permeable materials are used in all cotton heaters. The reason their heaters are hydrophobicated—that is, the water molecule from water vapor is prevented from penetrating and soaking the insulation—and why their fibers are additionally coated in a unique water-repellent material during production. She can only cling to its surface, and it turns into drops and rolls down when a certain amount of mass builds up. As it happens, hydrophobized cotton heater is not a material that is permeable to wet vapor.

Therefore, scientists from around the world still cannot come to an unequivocal conclusion: the vapor permeability of construction heaters is good or bad. Let"s just say that if you equip the attic overlap on wooden beams, it is better for you to put vapor -permeable materials on it so that wooden rafters that take moisture from the lower living rooms (and water vapors always rise up), they could freely send it to the insulation. And from the insulation they will easily come out – enough only through ventilation is enough. But in terms of insulation of the floor, there is no particular difference in concrete. But there is such a moment: when using vapor -permeable heater, it is important that the ventilation of such an attic is organized according to all the rules, and a separate ventilation system will not interfere.

It should be noted that foam insulation is composed entirely of air, hence it lacks fibers. Like a kitchen sponge, all foam insulation is made of a cellular structure with closed bubbles. As a result, these heat insulators can be non-permeable or vapor permeable. In extrusion foam polystyrene, for instance, water vapor is passed between balls, but extrusion foam polystyrene is no longer foam.

It’s interesting to note that you can use two types of insulation simultaneously to make up for each other’s shortcomings. Nonetheless, less vapor-permeable thermal insulation material needs to be placed in front of more vapor-permeable insulation. In other words, cotton wool came after polystyrene foam. On the other hand, if the opposite occurs, the material with lower vapor permeability will start to rot and become a certain steam barrier for another material, leaving nowhere for moisture to enter.

How to insulate concrete overlap of the attic

In order to warm the attic overlap made of concrete, thermal insulation needs to be installed in two or three layers, with the floor between each lower layer’s joints. Furthermore, it is crucial that the entire surface be leveled with no more than 5 millimeter bumps anywhere; this can be easily accomplished with the aid of contemporary aligning mixtures.

They are perfect for serving as the extruded polystyrene foam plate’s thermal insulation in concrete attic ceilings. Vapor barriers are not necessary for them, but if you place foam—which isn’t extruded polystyrene foam—you will obviously need them.

Furthermore, you can create a cement-sand screed up to 4 centimeters thick and apply two layers of drywall sheets if you need to walk later on such an overlap. Just make sure to create a walking path from the masonry mesh for that kind of screed. To prevent cement milk from leaking between the plates, make sure to use tape to seal the joints between the polystyrene foam slabs.

Insulating the attic ceiling is acceptable almost anytime during the house’s construction as well as during the manufacturing process. Naturally, the attic is already considerably better insulated over the overlap before you move into your new home.

More information about the actual procedure:

How to insulate wooden overlap of the attic

Thus, installing a heat-insulating layer within the attic ceiling design and installing insulation on top of it are the two primary techniques for insulating the attic floor. If the attic is cold and not used for residential purposes, add a covering over the insulation and construct a complete floor. However, make sure to leave the running ramps—separate pathways from rarefied flooring—over the whole attic; this is essential for roof maintenance.

Install a vapor barrier in the shape of a trough over the insulation to shield it from the water vapor that enters from the lower living areas. Vapor barriers are not required in situations where the insulation was installed with good resistance, such as foam or extruded polystyrene foam. However, you should install a serious vapor barrier layer in an attic with a particularly humid regime, like the one above the kitchen or sauna.

When the vapor barrier only sags in between the beams, another technique is to stretch it. This method’s drawback is that it results in inadequately tight insulation inserted between the beams.

Furthermore, this option is completely inappropriate if the ceiling is also composed of ready-made companies, as these gaps quickly turn into "cold bridges." Thus, a more common method in Russia is to lay the insulation first, cover it with a vapor barrier, and then finish the flooring afterwards.

Thus, the entire insulation process looks like this:

  • Step 1. Between the beams with the help of a construction stapler, vapor barrier is fixed.
  • Step 2. Next, mineral wool slabs are cut so that their width is, respectively, a pitch of beams.
  • Step 3. These plates are neatly inserted between the beams.
  • Step 4. For a while, until the ceiling is ready below so that the insulation does not fall between the beams, it is supported by draft bars or a strong thread stretched specifically for this.
  • Step 5. Next, the diffuse membrane is quickly mounted on top of the insulation – so that steam through it easily goes outside, and the drops do not penetrate inside from the slopes inside.

However, we also observe that the final step is a moment like this. The natural ventilation of convection flows of air, which readily penetrate through holes and auditory windows, will cause thermal insulation in the cold attic to dry out, according to many experts, negating the need for diffuse membranes or windproof films.

Insulating your attic is essential to keeping your house cozy and energy-efficient. Whether your attic floor is supported by a reinforced concrete slab or wooden beams, the insulation method you select will have a big impact on how comfortable it is overall and how much your energy bills will be.

The insulation process for attics with wooden beams entails placing insulation between the beams. By establishing a thermal barrier, you can keep your house warmer in the summer and stop heat loss in the winter. For this kind of attic, fiberglass batts, cellulose, or spray foam are typical insulation materials. As gaps or compression can lower insulation efficiency, proper installation is essential to guaranteeing effectiveness.

Attics constructed above a reinforced concrete slab, however, call for a different strategy. In this case, the slab itself is usually covered directly with insulation. This technique aids in moisture control, soundproofing, and thermal resistance in addition to other benefits. Materials with good adhesion to concrete surfaces and high insulation value, like spray foam or rigid foam boards, are frequently utilized.

Appropriate ventilation is crucial to preventing moisture buildup and ensuring the longevity of your insulation, regardless of the type of attic. Sufficient ventilation aids in controlling temperature fluctuations and lowers the possibility of mold or mildew growing. Efficient ventilation systems, like ridge and soffit vents, when combined with insulation can increase energy efficiency and extend the life of your roof and attic structure.

It is advisable to speak with an expert to determine the best insulation options for your attic and to determine your specific needs before starting any insulation project. In addition to improving the comfort of your house, investing in high-quality insulation and making sure it is installed correctly can result in significant energy savings over time.

Video on the topic

Insulation of the attic ceiling (insulation of the attic)

Vapor barrier and insulation of the attic overlap of the frame house in Finland .

Insulation of attic overlap on wooden beams

Attic floors


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Denis Shcherbakov

Professional roofer with 20 years of experience. I know everything about the installation, repair and maintenance of various types of roofs. I will be happy to share my knowledge and experience with you.

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