Irish Minimum Roof Pitch: What TGD Part C Doesn't Set

The requirement

TGD Part C sets no minimum roof pitch at all. Not for tile, not for slate, not for sheet. The current 2023 edition never states one. The word “pitch” does not appear in it. The real minimum comes from the product standard and the maker of your tile or slate.

TGD Part C is short for Technical Guidance Document C. Its full title is “Site Preparation and Resistance to Moisture”. It is the current guidance to Part C of the Building Regulations 1997, as amended. The 2023 edition is the one in force.

The document sets out Requirement C4. Floors, walls and the roof “shall be so constructed as to prevent penetration of moisture”. That is a performance rule, not a design number. It asks for an outcome and stops there.

Search the full 2023 text and you get zero hits for “pitch”. No roof slope number appears anywhere in it. There is no minimum-pitch table for tile, slate or sheet roofing.

What TGD Part C covers	What it doesn’t cover
Ground moisture resistance below a solid floor	A minimum pitch for tile, slate or sheet roofing
Moisture resistance of external walls	Product-specific pitch/exposure limits
Roof weathertightness, as Requirement C4’s general outcome	Fixing specifications for any roofing material

So you may have heard “the regs say” a set pitch for slate or interlocking tile in Ireland. That number is not from TGD Part C. It comes from somewhere else. This page can name that route. It cannot reprint the figures.

Where the actual numbers live

In practice, minimum roof pitch in Ireland runs on two things. First, the IS EN product standards for the tile or slate you are laying. These are the Irish versions of the European product standards, issued through NSAI. Second, the maker’s own fixing instructions. Each maker declares a minimum pitch for their own product.

The UK works the same way. Approved Document C is silent on pitch too. It points to a product standard, BS 5534, plus maker data. Ireland’s route runs through IS EN standards and NSAI, not BS 5534 directly. But the gap between “the code” and “the actual number” is the same shape.

TGD C treats the right standard, fitted right, as a way to meet Requirement C4. Like the UK document, it never restates the pitch figures itself.

What this means on site

There is no TGD C clause to build to. So the job is to follow the standard and the product, not a page number.

Check the IS EN product standard for the exact tile or slate you are laying. Go through NSAI or your trade supplier. Do not work from memory or from a different job.
Get the maker’s fixing spec for the exact product. Their declared minimum pitch is what a building control authority or an assigned certifier checks against. It can be tighter than the general figure in the product standard.
Match the exposure. Maker specs often lift the minimum pitch for wind, and add fixings. A coastal or upland site can need a steeper roof than a sheltered one. Same product, different site.
Keep the paperwork. With no code clause to cite, your proof is the standard you followed and the maker’s data sheet. Add a record that you fitted the roof as specified.

Irish Building Regulations hub: how the one national rule book and its TGDs work.
UK minimum roof pitch: what Approved Document C doesn’t set: the same gap on the other side of the Irish Sea.

Sources

Technical Guidance Document C — Site Preparation and Resistance to Moisture (2023 amendment), Requirement C4 — confirmed by full-text search of the current document to contain zero occurrences of “pitch” or a numeric roof slope. Read it at gov.ie.

Read this first. These figures reflect the 2023 edition of TGD Part C. IS EN product standards and manufacturer fixing data are the actual source of any roof-pitch number — always confirm the current standard and the specific product’s data sheet before you rely on a pitch figure for a real roof. (Verified against TGD Part C, 2023 amendment, as at 2026-07-31.)

Frequently asked questions

What is the minimum roof pitch in Ireland, under TGD Part C?

There is no number. Technical Guidance Document C, the current guidance to Part C of the Building Regulations 1997 (as amended), has no minimum-pitch table for any roofing. A search of the 2023 edition finds zero hits for 'pitch' or a roof slope figure. The real minimum lives in product standards and maker data.

Does TGD Part C set any roof-pitch figure at all?

No. Requirement C4 says floors, walls and roofs must resist the passage of moisture. That is an outcome, not a design number. The current 2023 text of TGD C never states a minimum pitch for tile, slate or sheet roofing.

What actually sets minimum roof pitch in Ireland?

IS EN product standards for tiles and slates, plus each maker's own fixing instructions and declared minimum pitch for their product. TGD C accepts these as a way to meet the performance rule. It does not state the number itself. The UK's Approved Document C works the same way.

Is this the same situation as the UK's Approved Document C?

Yes, the shape is the same. Both codes set roof moisture resistance as an outcome, not a pitch table. Both leave the number to product standards and maker data. The standards differ, though. Ireland's route runs through IS EN standards and NSAI, not BS 5534 directly.

What should I check before I lay a roof, if the code gives me no number?

Check the IS EN standard for the tile or slate you are laying. Then get the maker's fixing spec and declared minimum pitch for that exact product. That is what a building control authority or an assigned certifier checks against on site, since there is no TGD C clause to point to.