Do the pedestals have to be metal?

Regulation 7(3) of the Building Regulations 2010 (SI 2010/2214) lists specific exceptions to the general requirement that building work use materials which adequately resist the spread of fire. Two of those exceptions, paragraphs 7(3)(h) and 7(3)(k), turn up repeatedly in arguments for why a plastic pedestal does not need to meet the reaction to fire classification that would otherwise apply to it. Read them against what a pedestal deck actually is, and neither closes the question.

What 7(3)(h) excepts

Regulation 7(3)(h) of SI 2010/2214 excepts seals, gaskets, fixings, sealants and backer rods from the general materials requirement. The paragraph is written for small, discrete items that join or seal one surface to another. A pedestal is not any of the five named items, whatever it is made from.

What 7(3)(k) excepts

Regulation 7(3)(k) of SI 2010/2214 excepts a top horizontal floor layer of a balcony that reaches class A1fl or A2fl-s1 reaction to fire classification, where the whole of that layer sits on an imperforate substrate. The exception describes a continuous floor finish laid directly onto a solid base. It does not describe a system of separate units raised on point supports.

Why an open-jointed deck does not fit either description

A pedestal deck is built from individual paving or decking units, set apart from each other, standing clear of the slab on point supports, with a ventilated void underneath. That arrangement is not a seal, gasket, fixing, sealant or backer rod under 7(3)(h). It is not a single floor layer sitting on an imperforate substrate under 7(3)(k) either, because the imperforate surface in that arrangement is the slab under the void, not the paving above it. Citing either paragraph to settle what the pedestal itself must be made from answers a question that paragraph was not drafted to answer.

Route (b) is the second way a balcony build-up can satisfy Approved Document B Volume 1 paragraph 10.10 where the pedestals, or any combustible layer in the deck, would not meet the reaction to fire classification required under route (a). Route (b) asks what sits beneath the balcony: if the soffit is imperforate (meaning it has no gaps, joints or openings that fire or smoke could pass through) and that soffit achieves REI 30, the guidance treats the balcony as adequately protected.

What the imperforate soffit has to do

An imperforate soffit is a solid, continuous underside to the balcony, with no perforations for drainage, servicing or anything else. The guidance is not making a statement about the pedestal at all here; it is making a statement about the construction below the deck, and that construction has to hold back fire and smoke on its own, independently of what is standing on top of it.

REI 30: what the rating actually tests

REI 30 is a fire resistance classification. R is load-bearing capacity, E is integrity (no flame or hot gas passing through), and I is insulation (the unexposed face does not get hot enough to ignite anything on the other side). The number is the duration in minutes the construction has to hold all three under test conditions. A soffit achieving REI 30 is certified to do this for thirty minutes; a soffit that has not been tested, or that has gaps, cannot be assumed to meet it regardless of what it is made from.

The 300 millimetre band at a compartment boundary

Where the soffit or any adjoining construction is built from a material classified B-s1, d0 or worse and that material crosses a compartment boundary, a band 300 millimetres wide, centred on the boundary, has to be built from material classified A2-s1, d0 or better. This is a separate requirement from the REI 30 rating on the soffit itself: REI 30 is about how long the construction resists fire, and the 300 millimetre band is about stopping a lower-classified material carrying fire sideways across a line that is meant to separate one compartment from another. Both requirements can apply to the same soffit, and a specifier checking route (b) needs to confirm each one against the actual materials and the actual compartment lines on the drawing.

Where a soffit detail is being proposed as the route (b) justification for a combustible pedestal above it, the question to put to the designer or supplier in writing is whether the soffit construction has a test certificate or assessment confirming REI 30, and whether the 300 millimetre band has been checked against every compartment boundary the soffit crosses.

A balcony reaches the fire-class question because it meets the definition of a specified attachment in regulation 2(6)(c) of SI 2010/2214. A roof terrace does not meet that definition. That difference decides which part of Approved Document B you read, and the two compliance routes set out under paragraph 10.10 do not apply to a roof terrace at all.

Where Approved Document B sends a roof

Paragraph 10.21(c) of Approved Document B Volume 1 states that any part of a roof is dealt with under Section 12, not under the balcony provisions in Section 10. A pedestal deck laid on a roof terrace is assessed as part of the roof under that section, with its own provisions for reaction to fire and separation from a compartment wall.

The route (a) materials test and the route (b) imperforate soffit test were written for a balcony as a specified attachment. Carrying either one across to a roof terrace answers a question the regulations are not asking at that point. Before you specify pedestals for a roof terrace, check which part of Section 12 governs your build-up and ask your building control body or warranty surveyor to confirm it in writing. You can see the two balcony routes set out in full on the compliance routes overview, and work through how to check a provision like this one against its source on the citation checking page.

Regulation 7(3) of the Building Regulations 2010 (SI 2010/2214) lists a set of exceptions to the general materials requirement in regulation 7(2). Two of those exceptions, lettered (h) and (k), are the ones most often quoted at specifiers trying to work out whether an open-jointed pedestal deck needs a metal pedestal underneath it. The two sides of the pedestal market read those letters differently, and the reading you are given tends to match what the person giving it to you sells.

The reading sold alongside plastic pedestal systems

One reading treats the exceptions as covering the pedestal itself, on the basis that an open-jointed paving system sits clear of the structure below and is not the kind of element the materials requirement was written to catch. On this reading, a plastic pedestal needs no fire-classified material at all, because the exception removes it from the requirement before the question of reaction-to-fire classification arises. This is the position you will meet from manufacturers whose pedestals are not A1 or A2-s1,d0 rated.

The reading sold alongside metal pedestal systems

The other reading holds that exceptions (h) and (k) were written for different elements of a building and do not extend to a pedestal supporting an external balcony or terrace deck at all, regardless of how the paving is jointed. On this reading, the pedestal still has to meet the reaction-to-fire classification set by whichever route under paragraph 10.10 applies to the building, and only a metal pedestal meets it. This is the position you will meet from manufacturers selling classified metal systems.

Neither reading comes with a determination behind it. Regulation 7(3) does not mention pedestals, decking or terraces by name, so both sides are applying general wording to a specific product, and a specifier reading the sub-paragraphs cold could reasonably land on either answer. What would close the question is a written interpretation from the body that will actually sign off your building. Put the exact wording of exception (h) or (k) to your building control body or approved inspector and ask them to confirm, in writing, whether it applies to the pedestal in your build-up before you commit to either product.

You can check the sub-paragraph wording yourself against the published regulation, and you can see which organisations sell each reading set out plainly.