Cement Building Board

If you are looking to give a building kerb appeal, upgrade the insulation in the walls or keep out the wind and rain then weatherboard is a quick and easy way of achieving these things. Thankfully these days that doesn’t have to mean lots of maintenance because there is a product called fibre cement board siding that has the appearance of timber without the expensive upkeep.

Historically weatherboard siding was made of timber, but most timber requires maintenance and can twist, warp and rot...

What is Cement Board Siding?

Siding is an American term for cladding such as shiplap and clapboard but confusingly you will also find it used to describe much larger sheets of the same material, often with a smooth face rather than a wood grain. These are mainly used on blocks of flats and commercial buildings. What we are looking at here is the weatherboard or plank style of siding manufactured by companies such as Marley Eternit and James Hardie.

Why Cement Board?

Historically weatherboard siding was made of timber, and still is, but most timber (apart perhaps from cedar) requires maintenance and can twist, warp and rot over time. Fibre cement board overcomes these problems and is available in factory finished colours so it doesn’t need painting, though to be honest some of the coastal properties shown here will, after 20 years or so taking the full brunt of salt laden gale force winds and hot sun, begin to look a bit shabby. At this point the easiest thing to do is to spray the siding with an alkaline resisting masonry paint to give it a new lease of life but the base material, which has a service life of well over 50 years, will still be sound. Unlike timber it won’t need sanding, filling or scraping to get it back to new condition, but all that is many years down the line.

How is it fixed?

The board can be fixed in a number of ways. In both of the installations shown it was nailed to timber battens that were screwed to the wall. At the same time the insulation on the single skinned garage was upgraded by adding PU insulation board to the exterior and then covering this with a breathable membrane. You can take a view on whether the membrane was strictly necessary. If you have brick wall and pressure treated battens the tiny amount of moisture that manages to get through in a severe storm is not going to do any harm and will be taken away by the air flow. The board is easily cut by scoring and snapping. At the external corners and around windows you will need a cover strip, however some manufacturers also provide colour matched aluminum trims for these details. There is no need to pilot drill before nailing the boards provided you don’t fire the nails in too close to the edges. If you are nailing cover strip then pilot through the strip and the host board.

The bottom board is where you start and this needs to be a ripped down kicker strip or starter profile to pick up the edge because each board is designed to overlap the one below. Cut two identical spacers to check that each board is correctly positioned and work with a partner at the other end. If you fix the first one dead level then they should all follow but a periodic check is a good idea especially if you don’t trust the person helping you. You can use plated nails for the fixing but all plating has a limited life, and if it’s a coastal property like some of these shown here, it may not be long before the rust stains spoil all your lovely work, so do yourself a favour and spend a little extra on stainless steel nails. You can also buy colour matched poly topped nails for exposed fixings at the top of the run but many people now prefer to use an adhesive such as Sika Flex for the top row and corner trims.

Installing Cedral Weatherboard
  • Fixing vertical timber battens

    1 of 5 | Fix vertical timber battens to the building. These should be at least 50mm wide and spaced at a maximum of 600mm. Once this has been done, install a 30x10mm tilting allowing at least 150mm between the bottom edge and ground level for the installation of the first board.

  • Cedral Weatherboard is available in 3600mm lengths

    2 of 5 | Cedral Weatherboard is available in 3600mm lengths, 190mm wide and 10mm thick and can easily be cut with a saw on site or with a guillotine.

  • Nail or screw the weatherboard horizontally to the vertical timber battens

    3 of 5 | Nail or screw the weatherboard horizontally to the vertical timber battens. Ensure that the spacing between boards is equal and that they are parallel. Pre-drilling is only required if screws or nails are placed within 50mm of the end of the board.

  • A minimum of 20mm from the edge must be allowed for screws and nail placings

    4 of 5 | A minimum of 20mm from the edge must be allowed for screws and nail placings. The bottom edge of the first course should overlap the bottom edge of the tilting fillet by at least 3mm. Overlap successive courses by 30mm. Try to fix each weatherboard to at least three battens, if fixing to two battens reduce the width between each batten to 400mm.

  • Job done

    5 of 5 | Job done. When used as an external cladding, Cedral Weatherboard from Marley Eternit, looks as good as timber but requires very little maintenance as well as offering excellent impact resistance. It has Class 0 fire performance and is immune to attack by pests and insects.

New Build

Cement board sidings are now being used extensively in new build to produce some quite stunning looking buildings that hark back to traditional timber frame, timber clad buildings often found by the sea. The nautical theme is picked up in details such as the curved roof and portholes. As an alternative to PVCu cladding it is admittedly a bit more expensive but in appearance and durability it is in a completely different class and will surely add value to your home. The fact that it is cement and not plastic also means that it has negligible expansion and contraction so you don’t have a dawn chorus of creaks and groans as the sun hits the front of the house.

In new build you can fix battens to concrete blocks or counter batten timber framed buildings over the breather membrane and fix to these. The air gap should be maintained behind the weatherboard to allow migrating moisture from within to dissipate rather than condense on the back of the boards. Fixing to battens rather than directly to the OSB or sarking board also gives a straighter line.

Where to buy

In the UK and mainland Europe you are likely to find a wide number of merchants to supply Marley Cedral Weatherboard and their global distribution is growing. Their Eternit brand is already long established in roofing materials, rain screens and cladding so these stockists are likely to have Cedral samples for you to see. The company currently has 23 colours and four wood stains to choose from in the Cedral range or alternatively you can choose the natural board which can be painted on site with water based paint.

James Hardie is an International manufacturer that started in Australia and is the established brand leader in America and Canada. They have a UK based distribution centre for Europe but in the UK we found their dealer network seemed patchy. Their colour range is similar to Marley.

Environmental choice

Fibre cement Weatherboard can achieve an A+ rating as defined in the Building Research Establishment’s (BRE) Green Guide to Specification based on generic rating for autoclaved fibre cement (calcium silicate) cladding - (Element Ref: 806220701, 806220675, 806220676). That means if you are building to a reduced carbon footprint. Achieving an A+ rating also means it can be used as part of a zero-carbon self-build project, where its lightweight yet strong nature provides additional benefits.


Cement weatherboard’s ability to protect your home from the elements can reduce dampness too, particularly if your walls don’t have a cavity. A dry wall has far greater insulation than a wet one and getting rid of the damp mouldy smell brings a breath of fresh air into your home. The fact that the cladding allows an air gap to be maintained behind the rain screen is a great advantage in drying out old buildings with no damp course.