What building materials are best for building a home

How many people consult their structural engineer for their opinion on preferred building materials before they build?

Not Many.

As structural engineers in Queensland, we inspect and design the structure of houses in this great state – so why don’t more people ask a structural engineer for an opinion on preferred building materials and methodologies before they build?

Building Materials

These are my opinions on the best generic construction materials for a new home or extension with the reasoning that only extends to their structural performance. When selecting your building materials, you’ll need to consider other issues such as:

• Building covenants in a subdivision.
• Energy efficiency rules.
• Ground conditions.
• Material availability.
• Availability of subcontractors.
• Wind loads; and
• Budget!

Steel Roof Cladding vs Tiles

Let’s start at the top of your typical house.

Roof cladding.

The major choices are clay or concrete tiles, steel roof sheeting and timber shingles.

My preference: Steel roof sheeting. I think Colorbond Steel is the best choice for a Queensland home.

In fact, I can’t understand why people use clay or concrete tiles.

My rationale:

• Steel roofing is through-fixed using screws to hold it to the supporting frame. That makes it very hard to dislodge steel roof sheeting in a storm or cyclone. In comparison, the fixing for tiles has traditionally been one nail in every second tile. That leaves a lot of unfixed tiles on a typical roof. (Note that the recommended use of tile clips and screws has changed for cyclonic areas subsequent to Cyclone Yasi.)
• Steel roofing comes in a variety of colours making it part of the aesthetic of your house.
• Steel roofing is easier to lift and replace if a section gets damaged.
• It is easier to make new penetrations in steel roofing than roof tiles if you need to install a roof ventilator, skylight or vent.
• Steel roofing can be used at shallow pitches to achieve architectural objectives. Short tiled roofs should be pitched at a minimum of 15 degrees and long runs should be the preferred pitch of 22.5 degrees.
• Just one cracked or dislodged roof tile can cause a lot of damage to ceiling plasterboard when it rains if sarking is not installed or has been damaged.

Colorbond roofing is more expensive than tiles and that’s why tiles are more popular, but I see the installation cost of roof tiles increasing as tilers start to install tiled roofs to the current standards.

Screwed Roof Sheeting vs Clipped Roof Sheeting

My preference is screwed roof sheeting over clipped roof sheeting because:

• clipped roof sheeting can’t easily be temporarily removed without damaging the sheet.
• screwed roof sheeting provides an opportunity to use cyclone washers in high wind areas to provide extra fastener strength

Steel Frame vs Timber Frame

I personally prefer softwood timber frames. Timber is a popular choice in Queensland. Timber framing is readily available and very well understood by Queensland builders, inspectors and engineers.

I prefer timber over steel frames because timber is easier to make adjustments on site. Screws installed on-site in steel frames can make it difficult to install plasterboard cladding.

Steel frame suppliers stress that steel frames are less susceptible to termite attack.

That’s true.

However, treated timber and termite barriers have come a long way. In my opinion, those advances outweigh the benefit of using a steel frame.

The other issue is that many steel frames in volume built houses are being inspected and signed off by the steel frame manufacturer.

I’ve always thought an independent inspector is a better choice for signing off a house frame.

Concrete Masonry Walls vs Brick Veneer Walls

In my opinion, the outside walls of a new house should be concrete masonry.  Concrete masonry walls have a huge structural advantage over brick veneer walls.

You just have to remember that brickwork in a brick veneer wall is only there for aesthetics. At worst, it’s a liability.

• Brickwork is just a wall cladding that needs to be properly supported by a timber frame by metal ties that could corrode and disintegrate in time.
• Brickwork is liable to crack if the foundations move.

Concrete masonry walls in comparison are reinforced with steel rods and filled with concrete. When complete, a concrete masonry perimeter wall becomes a very stiff, deep beam that can stabilise the outside of a house by becoming one with the footings.

Concrete Floor vs Timber Floor

I prefer timber floors on sloping sites and concrete floors on flat sites.

Timber floors make a lot of sense on sloping blocks. The height of steel or timber posts can be adjusted to suit the lie of the land, the building floats above stormwater runoff and timber floors are cooler in a hot environment.

Timber floors have the added advantage over concrete floors that they can be adjusted if the house is subject to slab heave (so long as there is access under the floor).

Concrete floors on flat sites make a lot of sense too. They are quicker to build, can be lower to the ground than a timber floor and are con-combustible in high fire risk areas.

Building Layout

Homebuilders can avoid unnecessary expenses by observing these hints:

• Avoid curved walls or roofs.
• Avoid odd wall angles. Keep all walls square.
• Select a wall height to suit plasterboard supplies (2400 or 2700 are both easily achievable).

Retaining Walls

I think concrete masonry retaining walls are far superior to timber and sleeper retaining walls because timber and sleeper retaining walls rely on cantilevered posts for their support.

When posts are cantilevered out of the ground a lot of assumptions are made about how these forces are transmitted into the ground – and in perfect conditions, these walls work. However, I don’t think that even well-treated timber should be designed to be in permanent contact with the ground.

Timber retaining walls compound all the bad things you can do to timber in one structure:

• the timber is unable to be inspected because the retained ground obscures it.
• the tensile surface of the timber is closest to the ground and this is where the timber is likely to fail first.
• poor drainage results in loss of fines through the wall, timber rot, failure of the soil on the low side and eventual rotation and failure of the wall.

Phew.

A concrete masonry retaining wall has a large, wide footing that relies on the weight of the retained soil (and its own weight) for its stability.

Concrete masonry walls are more expensive than timber retaining walls or sleeper walls, and maybe they don’t have the same aesthetics, but I think that a properly constructed concrete masonry retaining wall will outlast and outperform a timber or sleeper wall.

Reference Material

Some reading for further information on building materials:

MonierTiles – Construction Requirements

CSR Roofing Architectural Manual

Monier Roof Tiles – Tile Mythbusting