What lurks beneath can be most important!
David Hayward, ATFA Technical Manager, stresses the importance of assessing what lies beneath the timber floor.
“MY JOB was to lay the floor, surely I couldn’t have been expected to”.. are words sometimes heard when a floor fails and this is irrespective of whether the flooring is solid or engineered, on joists or direct stuck to a slab. Nobody wants a problem floor and failures that relate to inappropriate sub-floor conditions often result in highly expensive repairs.
In such instances there will always be conjecture, as so often the building element or conditions that affected the floor was not directly related to the installation of the floor. However, the stance that it was only ‘my job to lay the floor..’ is a dangerous one to take, as invariably, irrespective of the merit of the argument, the installer is likely to get drawn into a lengthy and at times costly debate. There are a number of common problems that are initiated from beneath floors and it is important that we understand these and can take the steps to avoid these situations.
To an extent we covered those relating to slabs in a previous issue where we considered slab moisture, the height of slab above ground level and the integrity of the surface in terms of cleanliness and soundness. However, particularly with floors on joists there are a number of specific areas that cause us grief which we will focus on.
Wet conditions beneath a floor are a common source of problem. There are situations where some give little regard to runoff into the sub-floor area after the floor has been laid, even though there had been clear signs of this during the earlier part of the building process. There are those that gain a false a sense of security from particleboard or plywood flooring that they are fixing to and which hides what is beneath. Long term moisture will pass through these sheet floors. These aspects must be considered and just as important is the ventilation that is provided to the sub-floor space.Ventilation provides conditions beneath the floor that are similar to external conditions and this is important. While there are many floors that perform with less than the desired amount of ventilation anything that causes higher than normal levels of humidity in the subfloor space, which is then trapped due to insufficient ventilation, will be manifested in expansion related problems and cupping in the timber floor.
Special attention required
Special attention is required when house foundations are cut into the surrounding land causing part of the subfloor area to be below the ground level, around part of the dwelling.While all may seem fine at the time of floor installation the possibility of seepage must be considered. There are many instances of this causing problems with floors.
The sub-floor space must be dry, remain dry and be well ventilated and if this rule is not followed then at some stage you will experience a problem floor to deal with, there is no doubt about this. Again the stance can be that these aspects are the builder’s responsibility and they are, but it is the installer that has accepted what has been provided when laying the timber floor and for this reason the installer becomes part of the problem.
The second area we need to cover is the fixing of particleboard and plywood floors onto joists. Timber flooring is often adhesive bonded and secretly fixed to sheet sub-floors. When this is done, a composite panel is produced similar in some ways to engineered flooring. With a natural increase in moisture content, the flooring will expand more than the sheet floor it is bonded to and due to the composite nature, the panel will try to arch over the width of the sheets. Hence, if the fixing of the sheet floor to the joists is not sufficient, it can result in buckling with separation of the sheet floor from the joists. Most floors and particularly those of lower density timbers do not experience any problems as they generally do not have sufficient strength. However, if the sheet flooring is not fixed strongly to the joists and the flooring is of higher density species, then under conditions where the floor expands it can result in the buckling of the sheet flooring off the joists. Incorrectly sized nails, poor adhesive bonding of the sheet floor to the joist, an insufficient number of fixings and the incorrect screw type in steel joists are all reasons why the fixing strength between the sheet floor and joists can be inadequate. Also realise that nail fixing to pine joists will have significantly less holding power than to hardwood joists. Sheet flooring generally has more fixings around the perimeter than in the main body of the sheet. Due to the arching of the sheet floor that can potentially occur, what is of greater importance to resist buckling of the sheet is the fixing in the main body of it.
Considering all aspects
Again, a floor installer would say they did not lay the sheet floor and that you cannot see what size fixing was used, however it is considered that the prudent floor installer will have considered these aspects along with the flooring species being laid and climate in the area and had the opportunity to raise possible concerns with the builder prior to laying the floor. In the situations outlined above, whether it is perhaps seepage into a subfloor space or the incorrect screw type into a steel joist, floor failures do occur. When problems occur everybody is quick to try to hide from the issues. However, it would be better for the installer, their clients and the industry if a more thorough assessment was made of what may ‘lurk beneath the floor’ before commencing installation.
ATFA can be contacted via our website www.atfa.com.au by phone 1300 36 1693 or email email@example.com