Insulation Layers: Wall Cross-Section
Insulation in a light steel wall isn't a single panel. Correct application is the result of several layers working together:
| Layer (Outside to Inside) | Material | Function |
|---|---|---|
| Exterior cladding | Siding / render / Cembrit | Weather and UV protection |
| Ventilation gap | 30 mm air gap | Moisture drainage |
| Wind barrier | Vapor-permeable membrane | Blocks outside moisture, releases water vapor outward |
| OSB panel | OSB/3 – 12 mm | Structural stiffness + wind load |
| Insulation between studs | Mineral wool – 100/150 mm | Thermal and acoustic insulation |
| Vapor barrier | PE film / kraft paper | Prevents condensation from interior moisture |
| Interior cladding | Drywall – 12.5 mm (single/double) | Interior surface + extra acoustic insulation |
The vapor barrier must always be placed on the warm side (interior face) of the insulation. Incorrect placement leads to condensation — this is the most common application error in light steel construction.
Thermal Insulation: U Values
Insulation performance is measured by the U value (W/m²K). The lower the value, the better the insulation. According to the Turkish standard TS 825, Tekirdağ is in climate zone 2, and a maximum U = 0.60 W/m²K is required for exterior walls.
| Wall System | Insulation Thickness | U Value (W/m²K) | Assessment |
|---|---|---|---|
| Light steel – mineral wool | 100 mm | 0.35 | TS 825 compliant |
| Light steel – mineral wool | 150 mm | 0.25 | Close to passive house threshold |
| Reinforced concrete – 5 cm exterior EPS | 50 mm | 0.55 | Marginally compliant |
| Reinforced concrete – 8 cm exterior EPS | 80 mm | 0.40 | Good |
A light steel wall with 150 mm mineral wool provides better thermal insulation than a reinforced concrete wall with 8 cm of EPS. Moreover, in a light steel wall the insulation material sits inside the structure itself — no separate exterior thermal cladding is needed.
The one disadvantage of light steel is the risk of a thermal bridge: steel stud profiles conduct heat far better than mineral wool, so heat can escape through these profiles. The solution is to apply an additional layer of continuous insulation on the outside, across the profile. MefSteel applies this detail as standard at critical points in every project.
Acoustic Insulation: Rw Values
Acoustic insulation is a different discipline from thermal insulation. The unit of measure is Rw (dB) — the higher the value, the greater the sound absorption. In Turkey, a minimum Rw = 45 dB is required for walls between residential units.
| Wall System | Rw (dB) | Perceived Effect |
|---|---|---|
| Single drywall + glass wool | ~42 | You can faintly hear loud sounds |
| Double drywall + rock wool (100 mm) | ~50 | Normal conversation is inaudible |
| Double drywall + rock wool (150 mm) | ~54 | Even music is barely noticeable |
| 20 cm reinforced concrete wall | ~48 | Normal conversation is very faintly audible |
With the right choices, a light steel wall shows equal or better acoustic performance than a standard reinforced concrete wall. The key point: choose rock wool (mineral wool). Glass wool retains heat well but is less effective for sound; rock wool is good for both.
Roof Insulation
The greatest heat loss and gain in a building happens through the roof — under the sun, roof surfaces can reach 70-80°C. This makes roof insulation even more critical than wall insulation.
- Pitched roof: 200 mm of mineral wool between the trusses, a breathable membrane above, a vapor barrier below
- Flat terrace roof: 80-120 mm of XPS on the poured concrete surface, with a waterproofing membrane on top
- Additional measure: reflective (aluminum) foil insulation inside the roof — reduces radiant heat in summer
Reflective foil placed on the roof reflects back most of the radiant heat arriving during the day. This single measure can lower indoor summer temperature by 3-5°C — directly affecting air conditioning costs.
Condensation and Moisture Management
The most common mistake in light steel homes is neglecting condensation management. When moisture from indoor air penetrates the insulation, it condenses on cold surfaces over time, reducing the effectiveness of the mineral wool and potentially causing rust on the steel profiles.
The three rules of proper moisture management:
- Vapor barrier: PE film or kraft paper is laid on the interior (warm) face of the insulation, with all seams taped
- Vapor-permeable membrane: a breathable membrane on the exterior face of the insulation — releases residual interior moisture outward while blocking moisture from entering
- Ventilation gap: a 30-40 mm air gap is left between the exterior cladding and the membrane; this gap drains moisture
When these three details are correctly applied, the moisture problems that would shorten the steel profile's lifespan simply don't occur. MefSteel applies all of them as standard.
Floor Insulation
In a light steel building, at least 50 mm of XPS is recommended on the ground floor (over the concrete slab). This prevents the cold that's felt underfoot, especially during winter. For upper floors with wood-joist construction, mineral wool fill is placed between the joists.
Light Steel or Reinforced Concrete? Insulation Comparison
| Criterion | Light Steel | Reinforced Concrete |
|---|---|---|
| Wall U value (good application) | 0.25 W/m²K | 0.35 W/m²K |
| Acoustic insulation (double drywall) | Rw ~52 dB | Rw ~48 dB |
| Thermal mass (heat storage) | Low | High |
| Insulation cost | Included as standard | Added separately |
| Application error risk | Medium (detail-critical) | Low |
| Heating speed | Fast (low mass) | Slow |
The one advantage that stands out for reinforced concrete is thermal mass: concrete stores heat during the day and releases it at night. This is advantageous for passive solar design. However, in continuously occupied and actively heated buildings, light steel reaches comfort faster and with less energy.
In our 120 m² MefSteel project in Tekirdağ (150 mm mineral wool + double drywall), the client who went through their first winter reported: "In my old concrete house I used to burn through 4 tanks of boiler fuel each season — here I got through it with half that." That's how tangible the difference from standard application can be.
Frequently Asked Questions
Is a light steel home cold in winter?
No — not when properly built. The perception of cold is usually caused by a thermal bridge or incorrect vapor barrier application. With 150 mm of mineral wool, the U value reaches 0.25 W/m²K; that's better than most reinforced concrete homes in Turkey.
Doesn't it get hot in summer?
Not if the roof insulation is done correctly. In summer, the main heat source is solar radiation. Reflective foil roof insulation blocks most of this radiation. The low thermal mass also lets the interior cool down quickly at night.
Will I hear my neighbors?
The combination of double drywall and rock wool provides Rw ~50-54 dB. A single-story detached light steel home has no neighbor noise issue to begin with. In multi-story buildings, a floating floor technique is applied at the floor slab.
Mineral wool or glass wool?
For sound, rock wool (mineral wool) is best; for heat, both perform well. Rock wool is superior in moisture resistance, acoustic performance and fire performance. MefSteel uses rock wool as standard in all its projects.
Can insulation be fixed afterward?
Adding insulation inside a wall after the fact is a difficult detail to correct. External EPS/rock wool cladding can be applied, but at increased cost. That's why insulation thickness needs to be chosen correctly at the design stage.