Decking boards compared: treated wood, thermowood or composite

Treated wood: the cheapest start, the most work later

Pressure-treated pine is the usual budget choice and the cheapest board per metre by a clear margin. It is easy to cut, easy to fix with standard screws, and any timber merchant in Harju county stocks it in common widths. For a first terrace on a tight budget, it does the job.

The trade-off arrives from the second year onward. Treated wood needs oiling or staining roughly every one to two years to keep its colour and to stop the surface greying and splitting at the grain. Skip that maintenance and the boards silver off within a couple of summers, then start to check and splinter as damp gets into open grain.

Wet treated wood, especially green-tinted algae-prone boards in shaded gardens, gets slippery by the second autumn if it is not cleaned. A build-up of moss on the north side of a house is common and needs a stiff brush and occasionally a plastic-safe algae cleaner, not just a hose.

Thermowood: a higher purchase price, less upkeep

Thermowood is ordinary softwood heat-treated at high temperature, which changes the wood's structure so it takes up less moisture and moves less with the seasons. It costs noticeably more per metre than treated pine, but the boards stay straighter and are less prone to cupping through a Tallinn winter.

It still needs an oil or UV-protective treatment every couple of years if you want to keep the honey-brown colour; left untreated it fades to a silvery grey, which some owners are happy with and others are not. Either way it does not rot the way untreated softwood would, and the heat treatment reaches all the way through the board, not just the surface.

Underfoot it behaves much like treated wood when wet: fine once cleaned regularly, slick if algae or pine needles are left to sit on it over winter. The main gain over treated pine is fewer splinters and less warping, not less cleaning.

Composite: the highest initial cost but the least to do

Composite decking, a mix of wood fibre and recycled plastic, is the most expensive option to buy, often by a significant margin over both wood options. In return it does not need oiling, staining or annual treatment of any kind for the life of the board.

After several Tallinn winters composite keeps its colour far better than either wood option, though cheaper composite boards can look plasticky in a way that some owners mind and others do not notice once the terrace is furnished. It does not splinter, crack or cup, which matters on a terrace used by children or bare feet.

Grip when wet varies a lot by brand and surface texture. Smooth composite boards can be genuinely slippery in wet weather or with a light frost; boards with a grooved or brushed surface grip far better. This is worth checking with an actual sample underfoot before ordering, not just from a photograph.

What we would choose for a typical Tallinn house or flat terrace

For a first terrace on a modest budget, or a rental property where the owner is not going to keep up annual oiling, treated wood is a reasonable honest choice as long as you accept the maintenance or accept that it will grey. For a terrace attached to a house where appearance matters and someone is willing to oil it every couple of years, thermowood is generally worth the extra cost over treated pine.

For anyone who wants to build once and not think about the terrace again beyond a hose-down, composite is the material that delivers that, provided you choose a textured rather than smooth board and budget for the higher purchase price.

There is no wrong answer among the three; the decision is really about how much annual upkeep you want to take on in exchange for a lower purchase price.

• Treated wood: cheapest to buy, needs oiling every one to two years, greys and can splinter if neglected
• Thermowood: higher purchase price, needs treatment every couple of years, straighter and more stable than treated pine
• Composite: highest purchase price, no annual treatment, choose a textured surface for grip when wet
• All three can get slippery with moss or algae if not cleaned; a stiff brush and occasional wash matters more than the material

The frame and fitting matter as much as the board you choose

Whichever board you pick, how well it lasts depends heavily on the substructure underneath it: joist spacing, ventilation gap under the deck, and whether the frame itself is treated or protected from ground moisture. A good board on a poorly built frame will still cup, sag between joists, or trap water and rot from below.

Fixings matter too. Stainless or coated screws set slightly below the surface, correct gaps between boards for drainage and seasonal movement, and a frame that lets air circulate underneath all add years to a terrace regardless of which decking material sits on top.

This is where a lot of self-built terraces go wrong even when the board choice was sound. We build and fit decking and terraces from 90 € per job, and for smaller fixes to an existing frame or board replacement, hourly odd-job work is available from 39 € per hour.