Ahmet Alptekin Kasar
Founder, Managing Director
Updated: 2026-10-21
This is a product and data-sheet guide to BK45 for developers, contractors, specifiers and importers working in Hungary and the wider CEE region. It summarises what the Declaration of Performance (DoP) states, where BK45 and BD70 sit in a loft-floor build-up, how 20 m compares with the EKR limit, and how to check the DoP of a delivered batch. The full product description of both membranes is in our BD70 and BK45 article (in Hungarian). Why a vapour control layer belongs on the room side is covered in BBarrier vapour barrier and moisture (in Hungarian). What the Sd value itself means is explained in Sd value explained.
What the BK45 Declaration of Performance declares
A Declaration of Performance is the document in which the manufacturer declares the performance of a construction product. Under the 2011 Construction Products Regulation it is a DoP; under the 2024 regulation it becomes a Declaration of Performance and Conformity (DoPC). CE marking is affixed after the declaration has been issued, and only a product covered by a harmonised technical specification (or a European Technical Assessment) can carry it (European Commission).
The BK45 Declaration of Performance states:
- Reference: DOP-BBARIYER-LW-BK45/082025-01, product type BK-45.
- Intended use: "Párazáró műszaki textil membrán tetőkre és homlokzatokra", a vapour control technical textile membrane for roofs and facades.
- Manufacturer: Bilnur Plastik Tekstil San. ve Tic. A.Ş., Sincan/Ankara, Turkey (brand B-Bariyer / BBarrier). EuConX ISO Kft is named on the declaration as authorised representative.
- Harmonised standard: TS EN 13859-1:2014 and TS EN 13859-2:2014.
- AVCP: system 3. Notified bodies: TZÚS (NB 1020) and TEBAR (NB 2164).
- CE marking: shown on the declaration.
- Build: 2 product layers, 45 g/m² mass per unit area.
The figures are in the table below, side by side with the BD70 breathable membrane, because the two work in one build-up.
| Characteristic (test method) | BK45 vapour control | BD70 breathable |
|---|---|---|
| DoP number | DOP-BBARIYER-LW-BK45/082025-01 | DOP-BBARIYER-L4S-BD70/082025-01 |
| Sd value (TS EN ISO 12572) | 20 m | 0.02 m |
| EKR limit (Decree 18/2025 EM, annex) | ≥ 20 m (1.3.1.1 g)) | ≤ 0.03 m (1.5.1.1 g)) |
| Mass per unit area (EN 1849-2) | 45 g/m² | 70 g/m² |
| Resistance to water penetration | class W1 (TS EN 1928) | 259 mm H₂O (TS EN ISO 811) |
| Tensile strength MD / CMD (EN 12311-1) | 95 / 55 N/5 cm | 175 / 100 N/5 cm |
| Elongation MD / CMD | 70 / 55 % | 65 / 58 % |
| Resistance to tearing (TS EN 12310-1) | 55 N | 90 N |
| Reaction to fire (EN 13501-1) | E | E |
| Roll (EN 1848-2) | 1.6 m wide, 160 m² | 1.6 m wide, 160 m² |
| Harmonised standard | TS EN 13859-1/-2:2014 | TS EN 13859-1/-2:2014 |
Source: the two Declarations of Performance (BK45, BD70); EKR: Decree 18/2025 (VII. 31.) EM, annex (in Hungarian). The full data set is in each DoP.
Two rows are often read together when they should not be. W1 and the 259 mm water column describe liquid water; Sd describes water vapour. Grammage is mass, not vapour resistance: the lighter BK45 is a thousand times tighter than the heavier BD70. The BD70 declaration also gives Sd 0.02 m after artificial ageing (70 °C, 12 weeks).
Position: BK45 below, BD70 on top
In the heating season the air in the dwelling is warmer and carries more vapour than the air in the loft, so vapour moves up through the ceiling. The rule is tight on the warm side, open on the cold side. On a loft floor that means:
1. On the slab, below the insulation: BK45 vapour control layer, Sd 20 m. This is the warm side.
2. In the middle: ODE Starflex glass wool, 2 × 12.5 cm = 25 cm, second layer cross-laid, λD 0.039 W/(m·K).
3. On top of the insulation: BD70 breathable membrane, Sd 0.02 m. This is the cold side.
The order cannot be reversed. A vapour-tight sheet on top of the wool would trap the vapour coming up from the rooms inside the insulation, so only a breathable layer belongs on top. Whether a vapour control layer is critical on a given slab type is covered in Vapour barrier on a loft floor: needed or not.
| Role | Position | Declared Sd | EKR limit | DoP no. |
|---|---|---|---|---|
| BK45 vapour control layer | below, on the slab, warm side | 20 m | at least 20 m: meets it, exactly at the limit | DOP-BBARIYER-LW-BK45/082025-01 |
| ODE Starflex glass wool | middle, 2 × 12.5 cm = 25 cm, 2nd layer cross-laid; λD 0.039 W/(m·K) | no separate Sd requirement | manufacturer data | |
| BD70 breathable membrane | on top of the insulation, cold side | 0.02 m | at most 0.03 m: meets it | DOP-BBARIYER-L4S-BD70/082025-01 |
| Ratio | 20 / 0.02 = 1,000 | calculated |
The ratio means the bottom layer holds back vapour a thousand times more than the top layer. What little vapour still gets in can leave upwards.
The EKR limit: 20 m against 20 m
The EKR catalogue (Hungary's energy efficiency obligation scheme) asks, for loft-floor insulation, for a vapour control layer of at least Sd 20 m under the insulation, and a breathable dust cover of at most Sd 0.03 m over fibrous or blown insulation (Decree 18/2025 (VII. 31.) EM, annex, points 1.3.1.1 g) and 1.5.1.1 g), in Hungarian).
BK45 declares 20 m. The requirement reads "at least 20 m", so BK45 meets it, but exactly at the limit, with no margin. One practical step follows: we recommend checking that the DoP supplied with the delivered batch declares the same 20 m and carries the same DoP number. BD70, at 0.02 m, is below the 0.03 m upper limit.
Where the designer wants a margin on the vapour control side, the BBarrier range includes membranes with a higher declared Sd (per the manufacturer's data sheets: ALU PRO TEK 150, 50 m; MET 90, 100 m). Which membrane suits which construction is covered in our guide to choosing a vapour control membrane.
When another document quotes a different Sd
Product listings and shop data sheets sometimes quote a different Sd figure for a similarly named vapour control membrane, for example 30 m. Such a figure may refer to another product, another grade or another document. That cannot be settled from the outside, and it does not need to be.
What counts in the construction and in EKR documentation is the value declared in the Declaration of Performance of the delivered product. A DoP is identified by its number. For BK45 that is DOP-BBARIYER-LW-BK45/082025-01, which declares Sd 20 m (TS EN ISO 12572). If a quotation or data sheet shows another value, it is good practice to ask for the DoP behind it and compare it with the figure above.
How to check the DoP of a delivered batch
Checking the DoP once at design stage is not enough. We recommend matching the paperwork against the rolls when the batch arrives. Points to check:
1. Product type: BK-45 on the pack and on the DoP.
2. DoP number: DOP-BBARIYER-LW-BK45/082025-01, or the number of a newer declaration if the manufacturer has issued one; in that case, ask for the new one.
3. Sd value: 20 m, test method TS EN ISO 12572.
4. Manufacturer and representative: Bilnur Plastik Tekstil San. ve Tic. A.Ş.; authorised representative EuConX ISO Kft.
5. Harmonised standard: TS EN 13859-1:2014 and TS EN 13859-2:2014.
6. CE marking: on the product or the pack.
7. Roll size: 1.6 m wide, 160 m² (EN 1848-2).
It is good practice to photograph the label and file the DoP with the job documentation. On an EKR job, we recommend keeping the DoP with the documents for the ≥ 20 m requirement. Which documents travel with a Turkish shipment, and what to check before the trailer is sealed, is covered in our Turkey–Hungary logistics guide. For CE marking in general, see our CE marking guide.
Installation essentials
The declared Sd only applies in the construction if the layer is continuous. An untaped lap or an unsealed penetration lets vapour bypass the membrane. Alongside the manufacturer's installation instructions, we recommend:
- Preparation: a clean, dry, even slab without sharp debris.
- Laying: BK45 on the slab, below the wool, as a continuous layer.
- Laps: overlapped and sealed with tape, not just laid on top of each other.
- Wall junctions: turned up the wall and taped, folded into the corners.
- Penetrations: cables, pipes and the loft hatch taped all round. At the chimney, agree the detail with the chimney sweep.
- Damage: repair any tear with tape before the wool goes on.
- Wool and cover: the second 12.5 cm layer of glass wool cross-laid, BD70 breathable membrane on top.
For context, for Hungarian homeowners EuConX offers a loft-floor package with the same build-up: BK45 below, 2 × 12.5 cm cross-laid ODE Starflex glass wool and BD70 on top, including delivery and installation.
Frequently asked questions
What is the Sd value of the BBarrier BK45 vapour control layer?
20 m according to its Declaration of Performance (DOP-BBARIYER-LW-BK45/082025-01), test method TS EN ISO 12572. The membrane resists vapour like 20 m of still air.
Does BK45 meet the Hungarian EKR requirement?
Yes. The EKR catalogue asks for at least Sd 20 m under the insulation, and BK45 declares 20 m. The value sits exactly at the limit, so we recommend checking that the DoP of the delivered batch declares the same value.
Where do BK45 and BD70 go?
BK45 goes below the insulation, on the slab, on the warm side. BD70 (Sd 0.02 m) goes on top of the insulation, on the cold side. Never the other way round: a vapour-tight sheet does not belong on top of the wool.
A data sheet I saw quotes 30 m. Which value is right?
A different figure may refer to another product, grade or document. In the construction, the value declared in the DoP of the delivered product counts. The BK45 DoP (DOP-BBARIYER-LW-BK45/082025-01) declares 20 m.
How do I check the DoP of a delivered batch?
Match the product type (BK-45), DoP number, Sd value (20 m), manufacturer, harmonised standard (TS EN 13859-1/-2:2014) and CE marking on the pack against the DoP. File the DoP with the job documentation.
How big is a BK45 roll?
According to the DoP, 1.6 m wide with 160 m² of membrane (EN 1848-2). Mass per unit area is 45 g/m².
Membrane supply, DoPs and project enquiries: contact form · +36 30 485 0258 · info@euconx.com. We reply on the same working day.
Sources
1. BK45 Declaration of Performance, DOP-BBARIYER-LW-BK45/082025-01: https://euconx.com/downloads/dop/euconx-bk45-dop.pdf
2. BD70 Declaration of Performance, DOP-BBARIYER-L4S-BD70/082025-01: https://euconx.com/downloads/dop/euconx-bd70-dop.pdf
3. Decree 18/2025 (VII. 31.) EM, Annex, points 1.3.1.1 and 1.5.1.1 (Magyar Közlöny, in Hungarian): https://magyarkozlony.hu/dokumentumok/665fad784d41c3417b9f5eeeb2bab1fe61474464/letoltes
4. European Commission: CE marking and Declaration of Performance and conformity: https://single-market-economy.ec.europa.eu/sectors/construction/construction-products-regulation-cpr/ce-marking-and-declaration-performance-and-conformity_en
5. Bilnur / BBarrier: ALU PRO TEK 150 technical data sheet (downloaded 2026-10-21): https://www.bbariyer.com.tr/dosya/teknik-tablolar/aluprotek150-tds-168b19ac0993be.pdf
6. Bilnur / BBarrier: MET 90 technical data sheet (downloaded 2026-10-21): https://www.bbariyer.com.tr/dosya/teknik-tablolar/met90-tds-168b19bd3534b6.pdf
7. EuConX: BD70 and BK45 membranes (in Hungarian): https://euconx.com/resources/bd70-es-bk45-parazaro-es-paraatereszto-foliak-az-ekr-szigetelesben
8. EuConX: Sd value explained
9. EuConX: How to choose a vapour control membrane
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