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Roofing Materials

4 Types of Structural Roof Deck

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Timber Roof Deck Image Copyright: krakatuk / 123RF Stock Photo

Just as the overall foundations of a building are crucial to its performance, so the design and choice of material for a structural roof deck has a huge influence on the overall strength and performance of your entire roof.

In many ways, the roof deck is the backbone of any roof and requires professional design and top grade material. Although the roof deck is obviously important in terms of load bearing capabilities, it also influences everything from the roof’s thermal properties, waterproofing and performance when subjected to high winds.

4 Common Structural Roof Deck Materials

Roof deck can be constructed from many different types of material but the four most common are metal, concrete, wood and PIR (together with combinations of the above such as cementitious wood and reinforced concrete).

Metal
Metal roof deck is made from either steel (galvanised or coated) or aluminium. The metal is profiled, usually in a trapezoidal pattern, with its thickness, spacing, acoustic perforation and finish chosen to fit the span and load capabilities of the roof it is supporting.

Aluminium deck has a minimum thickness of 0.9mm while steel can afford to be slightly thinner at 0.7mm. Neither metal generally exceeds 1.2mm in thickness.

The exact type of metal deck required will depend upon many factors such as the amount and distribution of load (which will effect midspan deflection and hence drainage performance), aesthetics and how the deck is to be integrated with the roof’s insulation and waterproofing systems. This will also affect the type of fasteners you need.

Concrete

Concrete roof deck can either be pre-cast offsite and lifted into place with cranes (the quickest option) or poured while on site. Reinforced concrete (cast in situ) combines the properties of concrete and steel by setting steel bars within the concrete matrix, supplementing the compression strength of the concrete with the tensile strength of the steel. Pre-stressing the steel before the concrete is poured helps to increase the composite’s strength after curing (which takes around a month).

Made from a mixture of cement, fine aggregates and an expansion agent, autoclaved aerated concrete (AAC) provides a lightweight, flexible and workable material with the strength and fire resistance of concrete but at around a quarter of the weight. It is also water, insect and mould-resistant and provides excellent soundproofing but though tough is not quite as durable as concrete. In addition, building codes can make some uses of AAC impractical. AAC panels are joined to one another with a thinset mortar.

Wood

The vast bulk of wooden roof deck is supplied as pre-formed sheets although timber boarding is used during re-roofing work.

New timber roof deck is normally at least 25mm thick and connected using tongue-and-groove joints to protect from shrinkage. Alternatives to real wood include OSB – a material formed of bonded cross-directional timber strands – and plywood; these materials are normally no less than 18mm thick.

When using these options for a roofing project it is important to be aware of the relevant BS standards that are required (e.g. EN300 for OSB and EN636 for plywood).

Cementitious wood fibre deck combines the properties of timber and cement including workability, ease of installation and acoustic control.

Polyisocyanurate (composite)

PIR is a modern plastic foam which has superb insulating properties. In roof deck, it is often bonded with a steel liner to create a waterproof and thermally efficient layer.

This is just a brief introduction to the four most common types of roof deck you are likely to come across. Your roofing supply merchant will have more specific details about the best type of deck for your specific project.

Roof Damage

Has your Roof Suffered Hail Damage?

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When we think about the battering our roofs get over the winter months we usually focus on the risk of damage from torrential rain, howling gales and even the odd lightning strike. Hail damage is usually beneath the radar, partly because most of the hail we get down in the south west is petits pois-sized. But with man-made climate change supposedly increasing the likelihood of freak weather conditions perhaps it’s time we thought about what conditions lead to hail damage and how we can check if our roofs have suffered any hail damage.

Copyright: indyedge / 123RF Stock Photo

Can Hail Really Damage your Roof?

The good news is that hail under an inch in diameter (say 10p size) is unlikely to cause any problems unless the roof is really degraded. Even the softest asphalt shingles can usually withstand hailstones below this size. But what about the rare occasion when the sky starts raining golf balls?

There are many factors that will affect the type and extent of hail damage. These can broadly be split into weather conditions and roof conditions.

Weather conditions include:

  • Size of the hailstones
  • Their speed
  • Their density
  • Their direction of travel
  • Their shape (hailstones are rarely smooth but some are more jagged than others)

Roof conditions include:

  • Roof materials
  • Age of roof
  • State of repair
  • Pitch
  • Number of shingle/tile layers (shingles on shingles are more susceptible than shingles on wood)

In terms of roof materials, shingles are the most likely to suffer hail damage but while harder materials such as wood and clay can withstand all but the big tennis ball size hailstones, they tend to crack or shatter completely when they are damaged.

Inspecting a Roof for Hail Damage

One of the main problems with hail damage is becoming aware of it in the first place. Since we can’t see our roofs – or at least the entire roof – from ground level it can sustain a lot of damage without us noticing. Sometimes it is damage to rainwater goods that first alert us to a problem or evidence from a shed roof or external fixture.

We would always recommend that if you want a proper roof inspection for any reason, including hail damage, then it is best to get an experienced roofing firm in.

If you do decide to take a peek yourself, make sure you follow all the usual safety guidelines including wearing soft rubber-soled shoes and a good quality ladder that is high enough to extend above the eaves (never stand on any rungs above the eaves).

Metal most readily show the signs of hail damage so start by looking at your flashing and any metal vents for dents and discolouration. As mentioned above, wood and clay tiles are likely to crack or shatter and you should see dent marks at the point of impact along with some staining – often a brown/orange colour.

Shingles can be trickier to inspect with some signs of hail damage very subtle. Be on the lookout for bald patches where the granules have been displaced on impact. You may then start to notice dents, fractures and tears.

What are the Implications of Hail Damage?

The integrity of your roof is dependant on all of the structure and  materials keeping their integrity. While a cracked clay tile looks more serious and should prompt a replacement, displaced granules on shingle tiles can be as bad if not worse. Exposing the shingle beneath to direct sunlight will accelerate its degradation and over time it will begin to crack and  blister, losing its ability to keep out water. Algae will also establish a foothold until, before long, the entire roof is compromised leading to water ingress and disinterested insurers who will tell you you should have checked and maintained your roof properly!

To avoid this unwanted scenario, get a roofing firm to give your roof the once over if you suspect hail damage.