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Structural and base materials · Timber & Wood

Hardwood Timber (Broadleaf Species)

Sets out what hardwood timber is, why the hardwood and softwood split is botanical rather than a hardness ranking, and which species, moisture and finishing questions to raise before committing to it.

Typical role:Internal surfaceStructureExternal surface
Commonly met in:Internal walls and ceilingsFloorsExternal works and landscapeStructural frame

Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.

Overview

What hardwood timber is

Hardwood timber is sawn from broadleaf, mostly deciduous trees such as oak, ash, beech, maple and walnut, as distinct from the coniferous trees that produce softwood. The division is botanical, based on how the trees reproduce and how their wood cells are arranged, and it is not a ranking of hardness. Balsa is a hardwood and yew is a softwood, which is why the label alone tells you little about a given board.

In practice hardwoods differ enormously from one another. Density, pore structure, colour, figure, working characteristics and natural resistance to decay all vary by species, and even between boards cut from the same tree. That is why a species is discussed by name rather than by the general term, and why a physical sample rather than a written description is usually the honest basis for a decision.

Like all timber, hardwood is anisotropic and moves with changes in humidity, more across the grain than along it, and differently again depending on how the board was cut from the log. Acclimatising boards in the room where they will live, and accepting that seasonal movement continues for as long as they are in service, are ordinary parts of working with the material.

Terminology

Common names and aliases

These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.

  • Hardwood lumber (US)
  • Broadleaf timber
  • Hardwood

Applications

Common applications

Where this material is typically encountered. A typical application is not a statement that it suits your project.

  • Internal joinery such as doors, stair parts, window boards and made-to-measure furniture.
  • Solid timber flooring, treads and nosings where a hard wearing surface is expected.
  • Skirtings, architraves and mouldings intended to be finished clear rather than painted.
  • Worktops and table tops built up from strips or staves glued edge to edge.
  • External joinery, decking and garden structures using species chosen for exposed positions.
  • Exposed beams and semi-structural elements in traditional building and restoration work.

Consideration

Where it is commonly considered

  • Where the timber will be seen and its figure, colour and grain are part of the design intent.
  • Where a surface will take wear and a solid section allows later sanding and refinishing.
  • Where matching or repairing existing hardwood joinery or flooring is the objective.
  • Where a species with natural durability is being discussed for an exposed external position.
  • Where a clear or oiled finish is wanted rather than paint, so the timber itself is the finish.

Professional review

Where additional professional review is especially important

These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.

  • Where humidity will swing widely, since wide solid boards move noticeably and joints can open up.
  • In wet areas and permanently damp positions without a discussion of species, detailing and finish.
  • Where a structural role is intended, because sizing and adequacy are engineering decisions.
  • Where sourcing matters and the species, origin and chain-of-custody paperwork cannot be confirmed.
  • Where a perfectly uniform appearance is expected, as natural variation is inherent to the material.

Properties

Key properties to discuss

Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.

Appearance
Colour, figure and pore structure differ by species and by how the log was cut, and many hardwoods darken or lighten with light exposure. Comparing samples under the actual lighting of the room is the usual way to avoid surprises later.
Moisture behaviour
Hardwood moves with humidity, most of all across the grain, and quarter-cut boards move differently from flat-cut ones. Acclimatisation before fixing, and details that let boards move, are standard conversations to have.
Surface wear
Density varies widely between species, and denser timbers generally mark less readily. How a surface will actually be used, and how much marking is acceptable to the household, matter more than the species name on its own.
Weathering and exposure
Some species contain extractives that make them more resistant to decay outdoors, but exposure, detailing and drainage still govern the outcome. Externally, untreated hardwood usually weathers towards a grey tone unless it is maintained.
Repairability
Solid hardwood can often be sanded, filled, patched or scarfed, which is one reason it is chosen for surfaces expected to take wear. How many times a floor or worktop can be refinished depends on how it is built.
Maintenance
The finish rather than the timber usually sets the upkeep routine, and oiled, waxed and lacquered surfaces are renewed in quite different ways. What the finish manufacturer states for the specific product is the practical guide.
Documentation
Species name, origin, drying method and any sourcing certification are worth obtaining in writing, along with the supplier's guidance on acclimatisation and on which finishes suit the timber.
Installation dependency
Fixing methods have to allow for movement, and adhesives and finishes need to suit the species, since some oily timbers interfere with curing. The supplier's advice on this is species-specific rather than general.

Exposure

Exposure and environmental conditions

  • Will the timber sit in a heated interior, an unheated space, or outdoors exposed to weather?
  • How much seasonal humidity change does the location see, and is underfloor heating involved?
  • Is the position subject to strong direct sunlight that could change the colour over time?
  • Could the timber be splashed or wetted regularly, and how quickly would it dry again?
  • For external use, is the species one the supplier describes as intended for exposed positions?

Assembly

Substrate and system dependencies

What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.

  • What the timber is fixed to determines how movement is accommodated, so the substrate is part of the decision.
  • Solid boards fixed rigidly to a stable base can cup or split, which is why fixing patterns are specified.
  • Where hardwood meets masonry or concrete, a separating layer is usually discussed to limit moisture transfer.
  • Adjacent materials move differently, so junctions and shadow gaps often do the work of concealing movement.
  • In flooring, the subfloor's flatness and dryness govern the result at least as much as the timber does.

Appearance

Appearance and finish considerations

  • Species, cut and board width together produce the look, and changing any one of them changes the result.
  • Oiled, waxed and lacquered finishes give different sheen, feel and repair behaviour on the same species.
  • Stains take unevenly on some species because of variable pore structure, and a test piece is the honest check.
  • Boards from different batches can differ in colour, so mixing from several packs while laying is common practice.
  • End grain absorbs finish far more than face grain, which changes how exposed board ends look.

Durability

Durability questions

Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.

  • How hard wearing does this surface need to be, and what level of denting or marking is acceptable?
  • Does the species have natural resistance to decay, and what does the supplier actually claim about it?
  • Will the finish be renewable in place, or does refinishing mean removing and replacing components?
  • What happens at the vulnerable points, such as end grain, thresholds and any ground contact?
  • How would seasonal movement or shrinkage show itself in this particular assembly?

Upkeep

Maintenance and repair considerations

  • What routine cleaning does the chosen finish tolerate, and what would damage the surface?
  • Can worn areas be spot-repaired, or does the whole surface need re-treating to look consistent?
  • How often does the finish manufacturer expect recoating in this kind of use?
  • Are offcuts worth retaining so that later repairs can be matched for species and colour?
  • Who should be asked about a repair where the timber also has a structural role?

Installation

Installation dependencies

What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.

  • Boards usually need to sit in the finished conditions of the room before they are cut and fixed.
  • The building is normally dried out and the heating settled before hardwood flooring is installed.
  • Fixing, adhesive and finish products must suit the species, and manufacturers state their own compatibility.
  • Machining dense hardwood is slower and harder on tooling than softwood, which affects how joinery is planned.
  • Expansion allowances at perimeters and junctions are set out by the flooring or joinery manufacturer.

Documentation

Documentation to request

Ask for these in writing, for the specific product being proposed, and keep them with the project record.

  • The botanical species name as well as the common name used by the supplier, plus the region of origin.
  • Confirmation of how the timber was dried and the moisture condition it is being supplied in.
  • Any sourcing or chain-of-custody documentation the supplier holds for the timber.
  • Manufacturer guidance for the intended finish, including compatibility with oily species.
  • The supplier's acclimatisation and storage instructions for the specific product supplied.

Conversations

Questions for qualified professionals

Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.

  • Which species suit this use, and what are the practical differences between those on the shortlist?
  • How will seasonal movement be accommodated in this particular assembly?
  • What acclimatisation is needed on site, and how will that be confirmed before fixing begins?
  • Is the intended finish compatible with the species, and has a sample been prepared and seen?
  • For external use, what detailing keeps water off end grain and out of the joints?
  • Where the timber carries load, who is confirming the sizing and the connections?
  • What sourcing documentation is available, and does it satisfy the requirements of this project?
  • How should the finished surface be cleaned and maintained once the work is complete?

Blind spots

Commonly overlooked points

  • Hardwood and softwood are botanical categories; balsa is a hardwood and some softwoods are harder than many hardwoods.
  • Two boards of the same species can look quite different depending on how each was cut from the log.
  • Many hardwoods change colour after installation, so a fresh sample is not what the finished room will look like.
  • Oily species can prevent some adhesives and finishes from curing, which is a compatibility question, not a quality one.
  • Solid timber continues to move seasonally for as long as it is in service, not only during the first year.

What this page does not do

  • Species names in trade use can cover several botanical species, so the paperwork matters more than the common name.
  • Where hardwood forms part of a structure, its adequacy is an engineering decision for a qualified professional.
  • Natural resistance to decay varies by species and within a log, and does not replace detailing that sheds water.
  • Build Design Hub does not test, certify or endorse timber species, suppliers or finishing products.

Component forms

Building components commonly formed from this material

Elements this material is commonly used to make, named by the position they occupy in an assembly rather than by what they are bought as. This states common practice only — it is not a statement that this material suits any of these components in a particular building.

Infill →Turned or square timber balusters are the traditional form of infill in domestic flights.Column →Encountered in traditional and exposed structural work.Bearer →Durable hardwood is used where longevity in exposure governs.Deck Joist →Durable hardwoods are met where longevity in exposure governs.Door Frame →Used for external frames and where durability or appearance governs.Leaf →Hardwood is met in solid leaves, in edge lippings and where an external leaf has to take weather and wear.Threshold →Timber thresholds are met in traditional joinery, with durability depending on species and exposure.Fascia →Met where durability without frequent redecoration is wanted.Fence Post →Durable hardwood posts are met where a long life in contact with ground is wanted.Packer →Timber packers are met in traditional joinery, with durability depending on the position's moisture conditions.Bead →Used where the bead is exposed externally or where a clear finish is wanted.Handrail →Shaped hardwood rails are the form most commonly met where the rail is intended to be seen and touched as timber.King Post →Encountered in traditional and exposed structural carpentry, where the jointing tradition differs from softwood practice.Queen Post →Encountered in traditional carpentry, where the joints at head and foot follow a different tradition from softwood practice.Tread →Met where the tread is intended to be the visible surface rather than a base for a covering.Winder →Met where the winder is the visible surface and the taper is intended to be seen.Window Frame →Used where durability without frequent maintenance is wanted.Sash →Used where exposure is severe or where durability without frequent redecoration is wanted.Sill →Timber sills are met in traditional joinery, forming part of the window itself.

Related entries

Alternatives to consider

Entries that may be considered instead of this one for a similar job. Not a statement that they are interchangeable, or equal in any respect.

Cellular PVC trim board →Both are used for exposed trim and roof-edge boards, and they behave differently in movement, finishing and repair.Preservative-treated timber →Timber into which preservatives have been introduced, commonly under vacuum and pressure, to reduce the risk of decay and insect attack in the situation it is going into.Thermally modified timber →Timber altered by controlled heating with oxygen largely excluded, which changes how the wood takes up moisture and typically leaves it more brittle than before.

Related entries

Common comparisons

Entries met at the same decision but which behave differently, so the comparison is about the difference rather than a swap.

Bamboo flooring →Flooring made from a fast-growing grass, processed either into laminated strip boards or into dense strand-woven blocks that behave quite differently from one another.Butcher Block →Hardwood staves or end-grain blocks glued into a thick slab made specifically as a work surface, finished with a penetrating oil or hardwax rather than a film.Engineered bamboo →Boards and panels made by breaking bamboo culms down into strips or strands and bonding them back together, a grass-derived material that does not behave like hardwood.Reclaimed Timber Flooring →Flooring made from timber recovered out of earlier buildings, sorted and remachined, so species, dimensions, past damage and moisture condition all vary within a single delivery.Structural softwood →Sawn coniferous timber sorted for strength and used for framing, joists and roof members, where moisture movement and correct sizing govern how it behaves.Wood veneer →A thin slice of real timber bonded to a panel, where the veneer decides how the surface looks and the substrate beneath decides how the panel actually behaves.

Related entries

Often used alongside

Entries commonly encountered together with this one. Co-occurrence only — never a claim that any combination is compatible or suitable.

Alkyd Paint →Alkyd paint cures by oxidation of a resin carried in solvent, flowing out to a harder, more level film than water borne emulsion and used mainly on joinery, trim and metal.Blockboard →Panel with a core of edge-glued solid timber strips sandwiched between veneers, stiffer along the core direction and lighter than a comparable plywood.Cane Webbing →A woven open mesh of rattan cane skin used as a decorative cabinet front, tensioned in a groove or captured in a frame, with no core and no structural capacity.Exterior Wood Oil →A penetrating finish for exterior timber such as decking and cladding that soaks into the wood rather than forming a film, so it fades and is recoated rather than flaking.Linseed Oil Paint →Linseed oil paint uses drying oil alone as its binder, with no alkyd resin, so it penetrates timber, forms a thin film and is maintained by recoating rather than stripping.Wood Stain →A colouring product that soaks into timber to change its tone without building a protective film, normally requiring a separate sealing or finishing coat over the top.

Related entries

Used in

Entries this is commonly incorporated into as a constituent or layer.

Engineered wood flooring →A genuine hardwood wear layer bonded over a cross-bonded core, giving a real timber surface on a base that is dimensionally more settled than solid boards.

Inspiration

Related Ideas Library pages

Design directions where this material commonly appears.

Preparation

Related planning checklists

Owner-side preparation before the conversation where this material comes up.

Go deeper

Related Build Design Hub guides

Planning guidance and neutral comparisons behind the decisions on this page.

Timber & Wood-Based Materials

Reference entries for solid timber and wood-based panels and engineered products — from structural softwood and plywood to cross-laminated timber, OSB, MDF and veneers.

Browse all timber & wood entries →