ESB vs OSB — why ESB is the better choice

ESB and OSB do the same job — they sheathe and brace the timber structure. The difference lies in what they are made of and how they behave with the two things in a house that cannot be seen: the air you breathe and the moisture in the wall.

ELKA esb Plus is made from fresh spruce wood. It emits several times fewer volatile substances than OSB, lets water vapour through 2.5 to 4 times more easily, swells less and is equally strong in both directions. That makes it the better choice for a house that people live in. The reasons are set out below — along with where OSB nevertheless has an advantage.

Two boards for the same job

OSB (oriented strand board) is a board made of long flat strands — 100–200 mm long and 10–50 mm wide, arranged in three cross-oriented layers. The raw material is most often pine. The binder in most modern boards is an isocyanate-based adhesive, and the origin of the wood is often not stated. In building, class OSB/3 to EN 300 is used: a load-bearing board for humid conditions.

ESB (elka strong board) is a wood particle board to EN 312, class P5 — also load-bearing and also for humid conditions. It is manufactured by ELKA Holzwerke in Germany. The raw material is fresh spruce wood only — residues from the plant's own sawmill, from forests within a radius of up to 150 km, with no recycled wood. The particles are not oriented, the binder is an MUF resin without isocyanates, and the surface is sanded and light in colour.

At first glance the difference is cosmetic. In practice everything else follows from it: spruce is low in resin and pine is not; non-oriented particles give equal strength in all directions and oriented ones do not.

Indoor air

The big difference is not in formaldehyde but in volatile organic compounds (VOC) — what you notice as the smell of new OSB.

Pine is a resinous wood, rich in fatty acids. The resin gives off terpenes, which decline within weeks. The fatty acids, however, oxidise slowly, even at room temperature, into aldehydes such as hexanal — and this process goes on for a long time.

Measurements on pine OSB show emissions of 500 to 1200 µg/m²h, in individual cases over 5000. Spruce is low in resin. According to ELKA, the VOC values of esb are about 4 times lower than those of OSB, and the board is practically odourless.

With formaldehyde the picture is more even. esb Plus has an emission of ≤ 0.03 ppm — below the WHO guideline value of 0.06 ppm and three times lower than the 0.1 ppm limit for class E1. Modern OSB with isocyanate-based adhesives also declares ≤ 0.03 ppm. Old and cheap OSB with formaldehyde-based binders is a separate matter — for those the value has to be checked in the manufacturer's declaration.

That leaves the binder. In finished OSB it is cured and bound, but isocyanates are a problem during manufacture and during recycling. ESB is free of isocyanates.

esb Plus is certified with the Blue Angel (RAL-UZ 76), is listed in the Sentinel Haus register and is QNG-ready — three independent confirmations of low emissions in living spaces.

Moisture in the wall and the roof

ESB lets water vapour through 2.5 to 4 times more easily than OSB. The vapour diffusion resistance factor µ of esb Plus is 80 when dry and 40 when wet, while for a typical OSB/3 it is 200 and 150.

For a 15 mm board this means an Sd of 1.2 m dry and 0.6 m wet for ESB, against 3.0 m and 2.25 m for OSB. It also matters that with ESB the value halves when the board becomes damp: the damper the construction, the more easily it dries out.

Where this helps depends on the position of the board. As external sheathing on a timber frame wall or as roof sheathing under wood fibre insulation, the board has to let the vapour out. There, OSB with an Sd of around 3 m holds the moisture in the construction, while ESB lets it out 2.5 times more easily.

As internal sheathing, ESB allows the construction to dry towards the room as well in summer. Whether a vapour barrier is also needed on the inside is decided by a calculation for the specific wall or roof. The joints between the boards are taped with tape for both ESB and OSB.

Two more differences matter on site:

Swelling. After 24 hours in water esb Plus swells in thickness by 10–11%, while for OSB/3 the standard allows up to 15%. Less swelling means more even joints if the board gets wet during construction.
Roof sarking. esb with tongue and groove is recognised as a sarking board under the rules of the German roofers' association (ZVDH) — it protects against rain and remains vapour-permeable.

Strength and handling on site

ESB is equally strong in both directions; OSB is not. The bending strength of esb Plus is 14–18 N/mm² depending on thickness, whichever way round the board is laid. For OSB/3 it is 16–22 N/mm² along the major axis and only 8–11 N/mm² across it.

Lengthways OSB is stronger; crossways it is almost half as strong. On site this means that OSB has to be installed in the right direction, and offcuts cannot be turned round. With ESB there is no wrong direction and there is less waste.

The tensile strength perpendicular to the board — how firmly the particles are bonded through the thickness — is 0.40–0.45 N/mm² for esb Plus against 0.29–0.34 N/mm² for OSB/3, that is, about 40% higher. It determines whether the board delaminates under load and moisture.

The surface of ESB is sanded, light and uniform. It can be painted or varnished and left exposed — on ceilings, furniture, shop fittings. OSB is rough and mottled and is usually covered. In reaction to fire the two boards are in the same class: D-s2,d0.

ESB vs OSB in figures

Property	ELKA esb Plus	Typical OSB/3
Raw material	fresh spruce from forests within 150 km of the plant, no recycled wood	mainly pine, long strands; origin often not stated
Binder	MUF resin, no isocyanates	most often isocyanate-based adhesives
Standard and class	EN 312, P5	EN 300, OSB/3
Formaldehyde	≤ 0.03 ppm	≤ 0.03 ppm with isocyanate-based adhesives; up to 0.1 ppm for class E1
Volatile organic compounds	about 4 times lower than OSB (ELKA data)	500–1200 µg/m²h for pine
µ, dry / wet	80 / 40	200 / 150
Sd at 15 mm, dry / wet	1.2 m / 0.6 m	3.0 m / 2.25 m
Thickness swelling, 24 h	10–11%	up to 15%
Bending strength	14–18 N/mm² in both directions	16–22 N/mm² along the major axis, 8–11 across it
Tension perpendicular to the board	0.40–0.45 N/mm²	0.29–0.34 N/mm²
Thermal conductivity	0.12 W/mK	0.13 W/mK
Reaction to fire	D-s2,d0	D-s2,d0
Surface	sanded, light, can be left exposed	rough, mottled
Emissions certificates	Blue Angel, Sentinel Haus, QNG-ready	vary by manufacturer

The values for esb Plus are from ELKA Holzwerke for thicknesses of 12–25 mm. The values for OSB/3 are from the EGGER OSB 3 technical data sheet and are typical for the class; they may differ for other manufacturers.

Which board when

ESB is the right choice when:

the board faces the living space — internal sheathing of walls, ceilings and floors, especially in bedrooms and children's rooms;
the wall or the roof is open to diffusion, with wood fibre insulation;
the board is roof sheathing or external sheathing on a timber frame wall and has to let the vapour out;
the surface is left exposed;
the building is being certified or the client insists on proven low emissions.

OSB does the job when:

the board spans in one direction and maximum bending strength along its length is needed;
the structure is temporary — formwork, site hoarding, packaging;
the building is unheated and nobody lives in it — a store, a shelter, a workshop.

In a residential building with natural insulation OSB is a compromise: you choose breathable insulation and then close it in with a board that holds back the vapour and smells.

Is OSB harmful, does it contain formaldehyde, and what is the alternative

These are the questions most often asked about OSB boards. The answers use the figures from the table above and the data for ELKA esb Plus and ELKA VITA.

Is OSB harmful?

It depends on the board. Modern OSB/3 bonded with isocyanate-based adhesives declares a formaldehyde emission of ≤ 0.03 ppm — below the 0.1 ppm limit for class E1 and below the WHO guideline value of 0.06 ppm. With pine OSB the bigger issue is volatile organic compounds (VOC): measurements show 500 to 1200 µg/m²h, and the smell of a new board comes from them. For old and cheap boards with formaldehyde-based binders the value has to be checked in the manufacturer’s declaration.

Is there formaldehyde-free OSB?

Most modern OSB is bonded with isocyanate-based adhesives rather than a formaldehyde resin and declares an emission of ≤ 0.03 ppm. ELKA esb Plus is not “formaldehyde-free” in the literal sense: its binder is an MUF (melamine-urea-formaldehyde) resin, but the emission is likewise ≤ 0.03 ppm and the board contains no isocyanates. For either board, what counts is the declared value in ppm.

What is the alternative to OSB?

For the same job — sheathing timber frame walls, roof decking and floors — the alternative is ESB: a wood particle board to EN 312, class P5, load-bearing and for humid conditions. ELKA esb Plus is made of spruce, with tongue and groove, in a 2580 × 675 mm format and thicknesses of 12, 15, 18, 22, 25, 30 mm. For exposed walls and ceilings there is also the ELKA VITA three-layer solid wood board, 19 mm.

Is OSB vapour-permeable?

Less so than ESB. A typical OSB/3 has a vapour diffusion resistance factor µ of 200 when dry and 150 when wet; for a 15 mm board that is an Sd of 3.0 m and 2.25 m. ELKA esb Plus has µ 80 and 40, i.e. an Sd of 1.2 m and 0.6 m at the same thickness.

How much does an ESB board cost?

ELKA esb Plus costs from €13.13 to €31.03 per m² incl. VAT, depending on the thickness (12–30 mm). One 2580 × 675 mm board covers 1.7415 m².

ELKA esb Plus: thicknesses and prices

Thickness	€/m² incl. VAT	Per board incl. VAT	Weight per board, approx.	Boards per pack
12 mm	€13.13	€22.86	14 kg	75
15 mm	€14.28	€24.87	17 kg	60
18 mm	€16.10	€28.03	21 kg	49
22 mm	€21.43	€37.32	25 kg	40
25 mm	€27.34	€47.61	29 kg	36
30 mm	€31.03	€54.04	34 kg	30

Prices for end customers including VAT, for a 2580 × 675 mm tongue and groove board. Work out the quantity for a wall or a roof in the calculator; all prices are in the price list.

The conclusion

OSB became established because it is strong and affordable. ESB does the same without you paying for it with the air in the house and with moisture in the construction: spruce instead of pine, no isocyanates, more open to vapour, less swelling and equal strength in both directions. For a timber house with wood fibre insulation it is the logical continuation of the choice you have already made.

MODOPAN offers ELKA esb Plus in thicknesses from 12 to 30 mm, format 2580 × 675 mm with tongue and groove. Prices are in the price list, VAT included.