WISA Spruce Plywood

What WISA spruce plywood is

WISA is UPM’s plywood brand, made in Finland, and the spruce range is its construction board. It is spruce all the way through rather than a spruce face over something cheaper, and it is made to a consistent standard, which is the main thing separating it from the general run of building plywood.

That consistency is worth more on site than it sounds. Sheets are the thickness they say they are and they lie flat, so when you are laying a deck and every board has to meet the next one along a rafter, the joints land where you expect them. A pack of cheaper board that varies by a millimetre or two between sheets costs you time on every joint and shows as a ridge under a floor finish.

It is a structural panel rather than a furniture one. The face is sound and flat but plain, with the open grain and occasional knot you would expect from spruce, and it is meant to be covered by whatever goes on top of it.

WISA spruce plywood size

We hold 18 mm WISA Spruce plywood in the standard 2440×1220 mm sheet, FSC certified and bonded to EN 314-2 Class 3. It is the thickness that covers most roof and wall work at normal rafter and stud spacings, and it is the one people come back for once they have handled it against a hardwood board.

It is a sanded board with a sound face, but it is a construction grade rather than a furniture one, so expect the occasional small knot and a colour that shifts a little from sheet to sheet. If any of it is going to be seen, prime the face before painting: open softwood grain takes paint unevenly and the first coat sinks in further in some places than others, which shows as patchiness under a thin topcoat.

The weight, which is usually the reason

An 18 mm sheet weighs 24.6 kg, which is 11.8 kg lighter than a birch board of the same size. That is a third off, and it is the difference between passing sheets up onto a roof comfortably and fighting them.

It shows up most on the jobs where you are handling a lot of sheets in a day. Boarding a shed roof, sheathing a wall on your own while you find the first screw, or getting a sheet up a ladder are all jobs that a birch board turns into a two person operation and this one does not. Over a whole roof that difference decides whether you need a second pair of hands for the day, which is why it gets specified on garden rooms and extensions as often as it does.

The 2440 mm length is still awkward on a windy day whatever the board weighs, so it is the length rather than the weight that catches people out on a first floor scaffold.

Class 3 bonding explained

The board is bonded to Class 3, which is the exterior category. That means the glue holds up to weather exposure, so the sheet can go on a roof, a wall or anywhere else it will get rained on during the build. Given the gap between boarding out and covering up on most jobs, that is not a luxury: an interior bonded board left open to two wet weeks is often ruined, and there is no drying it back out again.

Class 3 describes the glue rather than the timber, so the spruce itself wants covering outdoors. Under a roof covering, a membrane or a cladding system it lasts the life of the building, and that is exactly the job it is made for. Any face that stays exposed, such as a soffit or a gable edge, should be painted or given an exterior oil from our wood oils and stains range, with the cut edges sealed as well.

If the board is going to be genuinely wet rather than occasionally rained on, marine plywood is the one to choose.

What people use it for

WISA spruce plywood is the board for building work where a lot of sheets go up in a day. The regular jobs are:

• Roof decking: sheds, garden rooms, garages and extensions, and flat roofs under membranes and single ply systems, where a flat, consistent sheet keeps steps from telegraphing through the covering.
• Wall sheathing: timber frame walls and garden buildings, often from the same pack as the roof.
• Flooring: structural floors under a finish.
• Hoardings and formwork: light to move, and it takes a nail without splitting.

Working with it

It cuts easily and takes a nail or a screw without fuss, which is another reason it suits roof work where you are fixing a lot in a short time. Support the sheet across the cut and pilot near the edges as you would with any softwood board, since spruce splits along the grain more readily than a hardwood ply.

Land every sheet edge on a rafter or a stud rather than leaving it hanging, and stagger the joints across the run so you are not building a continuous line of weakness down the deck. On a roof, fix at closer centres around the perimeter than in the field, because the edges are where wind uplift does its work.

Keep it dry while it waits. Exterior bonding means the board survives a wet spell during construction, not that it is designed to sit out for months, and a pack left standing in the rain will cup and swell at the edges even if the glue lines are fine. Stack it flat, off the ground and covered, and get it closed in as soon as you reasonably can.

How much does WISA spruce plywood cost?

WISA spruce sits with the lighter structural boards on price, and what you pay for over a general building plywood is the consistency: sheets that are the thickness they say, lie flat and save time on every joint. It comes in one size, 18 mm at 2440×1220 mm, so comparing per sheet and per square metre gives the same answer. Enter your roof or wall area in the calculator on the product page to see how many sheets you need, and the cart adds the matching extras automatically.

WISA spruce vs birch and softwood plywood

WISA spruce is the lightweight structural choice for work that will be covered. Where the board will be seen rather than covered, birch plywood gives a clean pale face and a crisp edge, at a heavier sheet weight. Softwood plywood in European pine is the other Class 3 building board we stock, for sheds, hoardings and site work.

WISA spruce plywood in Dublin and across Ireland

We stock WISA spruce plywood in our Dublin warehouse, for collection or delivery across Ireland. Before you order, plan the cutting pattern around your rafter or stud centres so every edge lands on a support. The rest of the range, and how the grades compare, is on the main plywood page.