Richard looks into whether we should be installing modern floor finishes in heritage buildings.
THERE are very few aspects of our industry that aren’t connected in some way with sustainability and installing new floors in heritage buildings is no exception. I want to look at why we might want to meet the challenges of working with older buildings in the first place, then to go on to talk about the special considerations that might arise when we look at replacing or assessing floors in older buildings.
I’ve seen many discussions among designers about the benefits of reusing, extending, and adapting older buildings for continued or reuse, rather than demolishing them and building from new. In purely financial terms this may not result in a lower project cost because there’ll often need to be more investigative work such as structural and condition surveys and investigation of building services. Buildings that are being adapted for new uses will often need to be altered to suit current space planning and access requirements and to include modern heating, cooling, and communications technology.
However, refurbishment and adaptation of buildings provides significant environmental opportunities compared with newbuild because there’ll usually be less waste from demolition, and therefore a lower burden upon landfill, reprocessing, transport, and reduced use of raw materials, especially in relation to materials with high embodied carbon such as concrete, plastics, ceramics/clay products and steel.
There are social benefits too. There’s usually a strong desire to retain our architectural heritage, and often the most attractive and valued streetscapes are those that have a blend of building styles and ages. Many older buildings will have a connection with local history and losing the building altogether can weaken people’s unique sense of community, identity and belonging.
The people living and working in the building will often value the fact their workplace or home has a connection with the town or nation’s past. The fact it may have an unusual layout can be seen as ‘character’ and can provide as sense of uniqueness that may be missing from a new building. Sometimes of course if the building is listed or in a conservation area demolition may not be an option and so the owner and their designer will have no choice but to meet the challenges of adaptation.
Floor finishes
Anyone who’s beginning the process to renovate or adapt a building for a new purpose you’ll want to know if the existing floor finishes are going to be suitable. If replacement is required the decision-making process may be complex and will often not be as simple as ‘out with the old, in with the new’. In fact, this approach can sometimes result in new defects arising if the nature of the existing floor and building isn’t fully understood.
We need to have a thorough understanding of the way the existing building materials and structure behaves. We need to know about defects; which of them can be cured and if there are any that must be accommodated, and what limitations this may put on the choice of new floorcovering.
When talking about how this might happen in practice, I think we can cover a lot of ground by considering just a few commonly found types of floor construction.
Solid ground floors where there is no DPM
This category includes floors built directly on the earth, sometimes with an aggregate or concrete base, with or without a dampproof membrane (DPM). In the UK solid ground-bearing concrete floors became commonplace from the ‘60s onwards and a dampproof membrane was a normal part of the construction.
However, for flooring contractors today pre-installation moisture checks are very much recommended with older floors to ensure the DPM hasn’t been breached or has failed in any way. Solid floors older than this can include the centuries old method of building directly on the earth with no DPM.
Damp issues may be common in very old buildings largely because, up to a point this was considered normal with some older forms of construction. Floors that were built on compacted earth, sometimes with an aggregate bedding, would have no means of preventing damp from reaching the floor finish, so the choice of finish was somewhat limited to whatever would survive best. Flagstone finishes for example won’t be affected by damp, and moisture will slowly pass through them without harm. Textile finishes can also work well if they’re fully breathable.
This approach to floor construction is sometimes used today for heritage building restorations where flagstones or tiles may be laid on a ‘limecrete’ slab or screed with aggregate or a glass foam bedding layer beneath. This is often referred to as a ‘breathable’ floor construction and it normally contains no DPM. This is really the modern equivalent of early methods of floor construction, but whether we have an original or new breathable subfloor, we must select our new floor finish carefully. A safe choice will be a breathable non-moisture sensitive finish such as flagstones, breathable textile, or tiles.
However, this limits our options and we may want to use other materials for their appearance, durability, or historical authenticity. Using an impervious, water-resistant floor may mean moisture will be trapped below, and this can lead to subfloor or adhesive failure. One solution can be to adopt another traditional approach and suspend the new floor finish above the subfloor on joists and to ventilate the void below.
This can significantly increase the height of the whole construction and in some older buildings where the ceiling height may be quite low it may not always be an option. A thinner construction is sometimes possible by using a ventilated DPM, which is a more modern innovation. Some products originally designed for basement tanking, eg, ‘cavity drain’ membranes have been adapted for use with floors and they can be one way of maintaining the breathable nature of the subfloor while allowing the use of moisture sensitive or impervious floor finishes.
They work on the principle of providing ventilation space around the floor’s perimeter and this prevents the build-up of vapour pressure in the subfloor. In fact, this means most of the moisture remains beneath the membrane out of harm’s way and there’s no tendency for the moisture to accumulate over time. This approach provides opportunities to use solid hardwood floors for example – a classic feature of heritage building interiors.
Suspended ground floors – joisted floors
Suspended wooden floors, ie, floorboards on joists have been used since Victorian times. Their success relies on good subfloor ventilation and the use of damp proofing material between the timber joists and their supports. Joists will normally be supported by brick sleeper walls, with the other ends of the joists built into the external walls of the building above the level of the damp proof course.
Properly constructed these floors will last for the life of the building but failures can occur as a result of other work being carried out where the owner is perhaps unaware of the consequences. This can include blocking the air bricks by extending the property, creating planting beds, installing raised paving, or blocking air bricks deliberately to guard against increasing flood risks. Reducing the airflow can cause the joists to rot.
Raised soil and paving levels may also breach the damp-proof course which again leads to rot in the joist ends. Consequently, decayed joists and floorboards, and damp walls may require work that perhaps was not at first anticipated when initially deciding to change the floor finish.
This perhaps shows the importance of having a full understanding of how and why the floor construction ‘works’ and what can cause it to fail. When advising customers on choosing a floor finish and installation method I have been asked many times what damp protection should be used over an old timber floor because they suspect it may not be completely dry. The only way to ensure the success of the new floor is to make sure the original floor ‘system’ is working properly and is dry. Putting damp protection over a damp timber floor may indeed protect the new floor finish- at least for a time, but it’s likely to cause the old subfloor to rot even faster. Using a vapour check membrane on top of the joists before fixing the floorboards is in fact good practice, especially where insulation is fitted between the joists, as this will help to prevent interstitial condensation. This will only work though if the subfloor void is dry and properly ventilated.
Preserving antique floors
Where an original floor has historical value removing it will probably not be an option, but conservation officers may allow the floor to be overlaid with a new finish provided the fixing method does not damage the original floor, and so a modern floating floor system may be acceptable.
But as with other floors we have talked about, especially for ground floor areas, basements and the like, having an understanding of the way moisture moves through the floor is vital if the original floor is to remain undamaged. Old parquet and wood block floors are a good example. Installing any kind of impervious finish such as vinyl or linoleum on top of parquet isn’t an option.
Small amounts of moisture vapour will have been passing through the wooden floor from the day it was fitted but if that movement of moisture is prevented by a new moisture-proof finish the old wooden floor is likely to swell and buckle.
Some old wooden floors rely on bitumen or pitch-based adhesive to protect the wood from ground moisture, but this is often not fully effective and so impervious overlay finishes should still be avoided.
It’s sometimes possible to lift and relay old floors made from wood, tiles, or stone. The lifespan of a wood parquet floor for example can be many decades, even a century is possible, and if the parquet itself is still serviceable but the subfloor has failed in some way it may be possible to carefully remove the wood blocks, clean them up and re-lay them after the subfloor issues have been rectified. It wouldn’t be unusual for some blocks to be damaged or even missing; you’ve probably seen badly neglected parquet floors where a few missing blocks have been ‘temporarily’ infilled with screed. When trying to source replacement blocks, tiles, stone flags etc it can of course be difficult to find a perfect match and it isn’t unusual for building conservation experts to accept non-matching materials, the difference being regarded as an honest way of representing the repair as part of the building’s story.
Repurposing and reuse of building materials is of course a key part of the conversation about sustainability in construction and some floor types have much to offer in this respect.
A high level of sustainability can be achieved by using reclaimed flooring, and for heritage buildings there appears to be a particularly healthy demand for repurposing reclaimed timber floors. The exceptionally long lifespan of a solid timber floor makes it a good choice for projects where the client wishes to build sustainably or is ‘building for disassembly’.
I hope I’ve shown there are many types of floor finish that can be used in heritage buildings, but we have to approach this in a different way from modern buildings. We cannot assume the subfloor is dry – indeed a fully dry base may not have been the primary objective of the original builders. We need to ask if there will be any consequences of fitting thermal insulation in a certain way. We need to understand what other mechanisms help the floor function properly, such as DPCs and ventilation, and ensure we don’t compromise them.
It can be helpful to think of the whole floor construction as a ‘system’, rather than to focus on the finish alone. Likewise, we need to understand the properties of the new floor finish. Armed with a full understanding of site and materials we’ll be able to tell if the old and new are going to work successfully together.
www.junckers.co.uk
Richard Aylen is technical manager
at Junckers
