“New I.S. 465:2026 Standard Explained: What Homeowners, Buyers and Sellers Need to Know About Defective Concrete Block Reports”

2nd June 2026

By Franklins Admin

The National Standards Authority of Ireland has published a new version of I.S. 465, the Irish Standard used for assessing buildings affected by defective concrete blocks.

The updated standard is known as **I.S. 465:2026** and replaces the earlier **I.S. 465:2018+A1:2020** version.

For many homeowners, buyers and sellers, block reports can be difficult to understand. They often contain technical terms such as mica, pyrite, pyrrhotite, sulphides, petrography, SEM analysis and internal sulfate attack. The purpose of this article is to explain the main changes in simple terms.

 

What is I.S. 465?

I.S. 465 is the standard used by engineers and geologists when assessing buildings where defective concrete blocks may be an issue.

It sets out a process for:

• Inspecting buildings
• Categorising visible damage
• Taking samples
• Testing concrete blocks and, where required, foundations
• Interpreting the results
• Recommending possible remedial works

It is important to note that I.S. 465 is mainly concerned with buildings showing damage consistent with defective concrete blocks. It is not a general pre-purchase survey, and it does not replace advice from a suitably qualified engineer, surveyor or solicitor.

 

Why has the standard changed?

The earlier versions of I.S. 465 were often associated in public discussion with “mica” or “pyrite”.

However, more recent research has shown that some of the most serious defective block cases in Donegal are linked to **iron sulfides**, particularly **pyrrhotite** and reactive forms of pyrite. These materials can oxidise over time and contribute to a process known as **internal sulfate attack**, often shortened to **ISA**.

The new I.S. 465:2026 reflects this updated understanding.

In simple terms, the standard has moved away from looking only at whether mica or pyrite is present and now places more emphasis on whether the concrete is actually at risk of ongoing deterioration.

The biggest practical change: reports should be more structured

Under the new standard, the process is more clearly set out.

A building assessment generally involves:

1. A desk study and building inspection
2. A building grouping based on visible damage
3. Sampling, where appropriate
4. Laboratory testing
5. Classification of risk
6. An engineer’s final report and remedial recommendations

This should help make reports more consistent, although the results will still need to be interpreted carefully.

 

Building Groups still matter

The building condition assessment remains a key part of the process.

Buildings are categorised based on the level and type of visible damage. In simple terms:

• Group 1 – means no significant damage consistent with defective concrete blocks
• Group 2 – means some damage is present
• Group 3 – means more significant damage is present
• Group 4 – means severe damage or possible structural concerns

For property sales, this is very important. A property with no visible defective-block damage is very different from a property where serious cracking, distortion or deterioration is already present.

 

New focus on iron sulfides and ISA

One of the most important changes in I.S. 465:2026 is the increased focus on iron sulfides, including pyrrhotite.

The key question is not simply:

“Is pyrite or pyrrhotite present?”

The better question is:

“Is there evidence that these materials are reacting and causing deterioration?”

That is where **internal sulfate attack**, or ISA, becomes important.

ISA is a chemical deterioration process within the concrete. If active and advanced, it can lead to expansion, cracking and weakening of the concrete blocks.

 

New risk classifications

The new standard introduces clearer risk classifications which help explain the test results.

Two important classifications are:

1. Aggregate Risk Factor

This looks at the material inside the concrete, especially whether the aggregate contains potentially problematic rock types or reactive iron sulfides.

In simple terms, this asks:

“Does the concrete contain materials that could potentially cause deterioration?”

2. Active ISA Risk Factor

This looks at whether there is evidence that internal sulfate attack is actually happening.

In simple terms, this asks:

“Is the damaging reaction already active?”

This distinction is very important for buyers and sellers. A report may identify some potentially concerning materials, but if there is no evidence of active deterioration, the overall interpretation may be very different.

 

Foundation testing is now addressed more clearly

Another major change is that I.S. 465:2026 now includes more detail on foundation concrete.

This has been a major concern for homeowners, particularly where demolition and rebuild works are being considered.

The new standard includes guidance on when foundation concrete may be retained or removed, depending on the test results and risk classifications.

Importantly, the standard notes that, at the time of publication, there is no known occurrence of deterioration of dense strip footing foundation concrete in Ireland attributable to internal sulfate attack. It also recognises that buried foundation concrete is generally exposed to different environmental conditions than external wall blocks.

That does not mean foundations will never require investigation, but it does mean the new standard provides a more evidence-based framework for considering them.

 

What does this mean for sellers?

For sellers, the main point is that block test results need to be explained carefully and accurately.

A good marketing summary should not simply say “mica found” or “pyrite found”. Those phrases can be misleading on their own.

A more useful summary should refer to the report’s actual conclusions, such as:

• Building group
• Mica-related risk classification
• Iron sulfide risk classification
• Whether there is evidence of internal sulfate attack
• Whether the engineer recommends remedial works

Where a report is positive, it may be appropriate to say that testing has been completed and that the report classified the tested samples as low or negligible risk, depending on the exact wording of the report.

Where a report is less clear, the safest approach is to provide the full report to interested parties and allow their engineer, surveyor, solicitor or lender to review it.

 

What does this mean for buyers?

For buyers, the main advice is not to focus on one number in isolation.

For example, a percentage of mica or sulfur on its own may not tell the full story.

Instead, buyers should look at the overall conclusion of the report:

• Is the property visibly damaged?
• What building group has been assigned?
• What are the risk classifications?
• Is there evidence of active internal sulfate attack?
• What does the engineer recommend?
• Are foundations discussed?
• Does the report relate to the full property or only limited samples?

A buyer should always take independent professional advice before making a decision.

 

What does this mean for estate agents?

For estate agents, the new standard should help improve consistency, but it also means that reports may become more technical.

When describing a property, agents should avoid giving their own engineering opinion. Instead, they should accurately summarise the wording of the report.

For example:

“Concrete block testing has been completed. The report classified the tested samples as [classification] for mica-related deterioration and [classification] for iron sulfide degradation. Full report available on request.”

This type of wording is usually safer than making broad claims such as “mica-free”, “pyrite-free”, “defective”, or “not defective”.

 

Our advice

If you are selling a property with a block report, make sure the report is read in full and summarised accurately.

If you are buying a property, do not rely on a headline or a single test result. Ask for the full report and have it reviewed by your own professional adviser.

At Franklins, we regularly deal with properties where concrete block testing has been carried out. We understand how confusing these reports can be and we aim to present the information clearly, fairly and responsibly for both sellers and buyers.

 

Final note

This article is intended as a general guide only. It is not engineering, legal or valuation advice. Anyone buying, selling or remediating a property should seek advice from a suitably qualified engineer, solicitor, surveyor or other relevant professional.