Chemical Delignification

What is chemical delignification?

Chemical delignification is the breakdown of lignin caused by salts and other chemicals being leached from the clay tiles by the timber battens and spreading through to other structural timbers throughout the roof frame. To understand delignification first we must understand lignin.

Chemical delignification for roofs in Perth

Chemical delignification is a quite common problem that largely goes undetected.
It will commonly only be detected on a building inspection or during a timber pest inspection.

Picked up on a pre purchase building inspection it can make or break the deal.
That is where Powerdrive Roofing comes to the rescue.

Powerdrive Roofing been working closely together with other building inspectors and chemical delignification treatment specialists in Perth for many years now.

A treatment was perfected and patented by Powerdrive Roofing using a timber hardening chemical to re strengthen the timber and regain the structural integrity in your roof.

Weather it is for the settlement to go ahead or just for your peace of mind chemical delignification treatment should be put at the top of the to do list when it comes to addressing structural defects.

What is lignin?

Lignin is a class of complex organic polymers that form key structural materials in the support tissues of vascular plants and some algae.

Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are cross-linked phenolic polymers.

A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and acts as a filtering mechanism.

Cell walls are present in most prokaryotes (except mollicute bacteria), in algae, fungi and eukaryotes including plants but are absent in animals.

A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters.

What causes chemical delignification?

Chemical Delignification is believed to be caused by a number of factors including high traffic areas and being close to industrial areas but as the attached report obtained by Powerdrive Roofing and Inspect My Home shows the proven cause of Delignification is the timber batten acting as a wick and leaching water salts and other chemicals from the porous clay tiles, this causes the breakdown of the lignin which will appear as a fluffy or hairy substance on the external face of the batten, hence why it was once known as hairy timber.

Is Chemical Delignification a Structural Defect?

Chemical delignification is generally a problem associated with timber roof battens when identified within the roof void space whilst conducting a Pre-Purchase Building Inspection.

Although Chemical Delignification can affect all timbers in the roof frame the first in the firing line are the Structural timber battens, this is due to the clay tiles being mechanically fixed to the Structural timber battens and the leaching affect described earlier.

If for instance a timber-framed roof had Structural timber battens and a tiled roof covering, it would be fair to assume that a roof collapse would occur prior to any significant delignification occurring to any structural framing members.

Although chemical delignification has been associated to timbers with poor durability properties such as Douglas fir (Oregon), here in Perth we have witnessed first-hand that Chemical Delignification can occur to reasonably durable timbers such as Jarrah. Jarrah has an above ground durability rating of 15-40 years, therefore making many homes around Perth susceptible to this risk.

Now with the introduction of pine and other softwoods Chemical Delignification is taking hold a lot quicker and therefore needs to be addressed a lot quicker, don’t be fooled by the hand full of inspectors with unknown intentions trying to downplay the severity of the issue.

Although chemical delignification can take several years before collapse occurs, it will be classified as a MAJOR STRUCTURAL DEFECT whilst conducting a pre-purchase building inspection.

Furthermore, it is not recommended to walk on any roof cover when chemical delignification is identified, due to the threat of the roof cover collapsing.

It would also be prudent to consider the cause of the chemical delignification, as the cause may have bearing on the future health of occupants.

Examples of causes include:

  • In areas close to the sea, airborne salts attack the timber. This process may be accelerated for homes with terracotta roof tiles, as any tile fretting or spelling will allow further amounts of contaminated moisture through to the structural roof framing timbers.
  • Areas of high pollution, such as homes near industrial areas or main roads, airborne pollutants are believed to cause or accelerate chemical delignification.
    Another believed (unconfirmed) cause of chemical delignification is the release of gases into the roof loft space. This may include the escape of gases from appliances such as slow combustion stoves or perforations to ducting from flued gas appliances.
  • Hot water systems located within the roof loft space may also accelerate chemical delignification.

Is chemical delignification a timber pest?

In short, YES, it is.

Chemical delignification much like termites and other timber pests, Chemical Delignification attacks the timber and weakens it from the inside out, this will leave the fluffy appearance on the external face of the Structural batten and once sanded can give the misconception that it is all fine and back to normal, but internally the structure is extremely compromised.
Chemical delignification is classed both as a timber pest and as a major structural defect and should be treated as a matter of urgency.

Proof of battens being structural.

As a roof tiler we also install the roof tile battens so some building inspectors will falsely have you believe that the roof tile battens are part of the roof cover and not the roof frame or roof structure because they are not put in by a licenced carpenter. Well truth of the matter is as a roof tiler we are also bound by Australian standards.
As2049 and as2050 for roof tilers clearly states we are to refer to part 3.4.3 please see below national construction code image

Which is part of the 1684.2 and 1684.4 timber framing and span tables. And it guides you then as you can see from the next image to p2.1.1 performance requirement

It then explains structural stability and resistance to actions as shown in the final image.

So, do not be conned by these inspectors trying to have it written off as a major non-structural defect, here is all the proof you need, is a batten part of the roof structure?

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