Richard Aylen takes a closer look at different installation methods for hardwood floors.
IN my role as Junckers UK technical manager I’m often contacted by designers who ask for help with their specifications for timber flooring and at some point, the conversation usually turns to the matter of how the floor will be fixed.
This time around I would like to talk about the main installation methods available from manufacturers, and why you may choose one over the other.
In order to arrive at a decision, you need to know what the floor is going to be used for, the type of subfloor it will be laid on and the height available from subfloor to finished floor level.
When I refer to ‘installation method’ I’m mainly talking about a packaged system of floorboards and undercarriage as provided by a single manufacturer, as this is what most specifiers are looking for.
This provides certainty about the way the floor will perform and with the better quality systems the client will usually be able to obtain a manufacturer’s warranty for the whole package.
For timber floors there are three main installation options:
- Nailing to battens or joists
- Direct bonding to the subfloor
- Floating overlay installation
Let’s look now at these three installation methods in a little more detail.
Nailing to battens or joists
Suspended joists are mainly found in older buildings and fixing load bearing hardwood floorboards direct to these should not present too many problems provided the building is dry, the joists are sound, spaced correctly and there is sufficient ventilation of the subfloor void.
The floorboards will be ‘secret nailed’ to the joists so the nail heads are concealed, and you can run services in the void and fit thermal insulation if you wish.
In modern buildings it’s more common to find floorboards nailed to timber battens which are laid on a screed or concrete slab. Batten systems are very versatile as you can use levelling systems to achieve a specific height, or if the subfloor is uneven.
You can also introduce foam or rubber elements to provide a ‘sprung’ floor. The Junckers New Era levelling system for example has a height range starting at 74mm and extending upwards to over 400mm.
Many acoustic floor systems will use battens fitted with dense rubber or composite pads between the battens and subfloor to reduce impact sound transmission to the accommodation below.
As with joisted floors you can run services between the battens and include thermal insulation. If you are choosing an installation method for acoustic floors the acoustician may have to take into account, the whole floor construction including the ceiling below as the sound reduction offered by these elements may have a bearing upon the amount of acoustic insulation the floor finish needs to provide.
Direct bonding to the subfloor
The origins of gluing hardwood floors to the subfloor goes back at least to Victorian times when wood blocks were laid in bitumen. In times before buildings had damp-proof membranes the bitumen acted as a moisture barrier to protect the timber floor from rising moisture. Today we routinely use separate damp proof membranes and wood floor adhesives are designed to be flexible, fast drying and easy to use.
If you have a flat, sound and dry subfloor such as timber or screed, and you don’t require a sprung floor then bonding the hardwood floor to the base may be a good choice. This method will also keep the finished floor height to a minimum, which can be a benefit for refurbishments and where levels are set by stairs or door thresholds.
A glued down floor will provide a hard surface with no ‘give’ and this solidity is often perceived by clients as a mark of high quality and may fit their perception of how a hardwood floor should feel.
A floating floor will usually have a slightly cushioned feel underfoot but in fact in technical terms there is no better or worse option, it is simply a matter of what the client thinks about how a wooden floor should feel. Glued down and floating floor systems both require much the same type of subfloor in terms of flatness, dryness and load bearing ability.
Fully bonded floors are sometimes chosen in preference to floating floors where noise level need to be kept to a minimum, such as in museums and libraries. Here, a fully bonded floor will produce very little sound when a visitor’s shoe strikes the floor whereas a floating floor can in a small way behave like a drum and produce slightly more noise.
The difference is not great, but this can sometimes be the deciding factor for some types of projects.
Gluing a floor down of course means that if it should ever need to be lifted or repaired the boards or wood blocks usually cannot be re-used. This sets glued floors apart from nailed and many floating floor systems. Some manufacturers will offer exactly the same product for many years so there will be a fair chance that replacement material will be available in the future.
However, there are many wood floor products on the market, particularly where offered under own label brands where there is really no prospect at all of obtaining spare boards, and this is often overlooked by designers and clients when choosing floors.
Floating floor, overlay installation method
A floating floor is usually laid on an existing floor rather than joists or battens. The base must be flat, sound, dry and load bearing. The new floorboards will usually be laid on a foam or felt underlay. If the subfloor is screed or similar, then a moisture barrier is required.
These floors usually have a very low construction height which makes this method useful for refurbishments where floor height may be limited. Floating floor installation can also be a good choice for heritage buildings because the original subfloor can be left undisturbed beneath the new finish.
Given a dry, flat and sound subfloor overlay floor systems are among the easiest to install, compared with nailed or glued down floors.
As far as ease of repair, lifting and re-laying is concerned, overlay floors are something of a mixed bag. Boards that are fully edge-glued will be difficult to salvage and if the clients’ priorities include the need for lifting and relaying the floor and having ease of repair, then a ‘dry jointed’ system will suit them better.
Systems fitting this description include the Junckers Clip system, which has been around since the ‘70s, or the ‘click’ system engineered board with special interlocking tongue and groove profiles.
Increasingly, clients and specifiers are choosing products that have low embodied carbon and the lowest possible effect on global warming. Solid hardwood is one of the best options in this respect, but we are now seeing more focus on the environmental impacts of different fixing method in terms of recycling and the circular economy. Solid hardwood floors have an unusually long lifespan, often well beyond the normal 60 year design life of the building. This means that some of the hardwood floors being laid today may become redundant before being worn out, perhaps as a result of building adaptations or a change of use.
By choosing a fixing method that is reversible and leaves the reclaimed floorboards in good condition the floor can more easily be reused with less damage and waste. In ‘design for disassembly’ projects the ability to reuse the materials the building is made from is crucial to the success of the design.
Lifting a floor that has been glued to the subfloor is likely to result in a high proportion of waste and damage and will probably result in the whole floor being disposed of, so on environmental grounds direct bonding is not the most sustainable choice.
Most nail-fixed floors can be lifted, and a reasonable amount of re-useable flooring can be salvaged. Unlike glued down floors nailed floors once de-nailed, are relatively uncontaminated and easy to prepare for re use.
Overlay floors can vary widely in their suitability for re-use. If the boards are edge-glued together, as found with some engineered wood floors the damage to the tongue and groove joints is such that re- use is not usually viable.
However, overlay systems where the boards are ‘dry-jointed’ using glue less joints or where the boards are joined with removeable metal clips are likely to produce the greatest amount of re-useable boards.
Hardwood floor manufacturers have developed these systems over many years and most wood floor companies will offer most or all of these installation options in their ranges.
While manufacturers try to offer the simplest solution to every flooring need there are still occasions when the installation method needs to be adapted to suit unusual site conditions such as restricted height combined with uneven subfloors.
Sometimes a fast-track solution is needed when the floor must be laid before the subfloor has fully dried, there are damp issues of some other kind or acoustic insulation needs to be incorporated into the floor construction. It’s when these situations arise that choice of floor manufacturer can be important as a company that offers qualified technical support can offer project-specific solutions so expensive mistakes can be avoided.
Richard Aylen is technical manager at Junckers UK