Profile: Alpine Buildings

A look at the key reasons why wind damage happens and what types of construction are best suited to these high-wind zones

If you think back in time for a moment, there’s a high chance you can recall a story from a friend about a shed severely damaged in a big storm or strong wind. This is not uncommon; in fact, it’s quite a regular occurrence in many regions around New Zealand.

While almost any shed provider can technically design for the wind zone in your area, there’s a practical element to building a suitable shed that doesn’t seem to be written in the rule book. A commonly asked question is if the sheds are designed for the wind zone, then why do these stories keep surfacing?

In this article, we look at the key reasons why wind damage can happen, what types of construction are best suited to these high-wind zones, and what construction methods are more susceptible to damage.

What is a wind zone?

Let’s go back to the basics and clarify what wind zones are. In New Zealand, a wind zone is a way of calculating the design load of building materials needed for construction in a given location. It also helps engineers and designers understand how to use those materials. There are three main categories: high, very high, and extra high.

What are the best materials to use?

Typically, when building sheds in high wind locations, you want to look at what materials the shed is constructed from and consider the durability of these materials. An understanding of the structural strength and durability of these materials will give you a good idea of what will work best from a practical standpoint.

Timber, poles, and structural steel are all great options to work with, as they are robust and you get good solid bolted connections that will easily stand up to the pressure of extreme wind zones.

Timber

Timber is an age-old building material and has been used for decades. You just need to look at some older buildings in Europe, which are still standing strong after well over 100 years. However, in today’s world, there are some precautions you may want to consider.

Many shed manufacturers use timber products, but there’s one thing to note: you want to make sure the supplier has used pre-dried and graded timber. It’s quite common for sheds to be supplied with wet or damp timber straight from the treatment plant.

When a shed is constructed from wet timber, it will shrink and move after the shed is built, which can reduce overall strength and put pressure on the fixings.To ensure you get the best results, it’s well worth installing your shed using pre-dried timber. A shed installed using pre-dried timber will stay straight and strong and the joints will remain firm. It’s a simple process that makes a significant difference and will give you peace of mind that your shed will hold its strength and value long-term.

Poles

It’s hard to beat a timber pole for strength when it comes to wind loadings. They are very solid and let’s not forget they grew up in the elements so it’s safe to say they’re no strangers to the wind.

Sheds constructed with poles are generally a safe option given the poles are typically between 175SED and 275SED (Small End Diameter). They’re concreted into the ground, typically anywhere between 1.2 and 2 metres
deep depending on the size of the shed so they’re not going to easily budge in
the wind.

Structural steel

Structural steel is a stand-out product for these high-wind areas. It relies on its thickness for strength rather than its shape or profile. Structural steel is widely considered a lot more durable than lighter-weight roll-form steel designs and is an ideal component for buildings in windy regions.

What materials should you be wary of?

As mentioned, most types of construction can be designed in a way that will comply with the rule book.

Roll-form steel

Roll-form steel designs are essentially made of flat sheets of 2–3mm thick tin that are rolled into specific shapes to gain structural strength. Sheds made with this construction method generally rely on many components, such as brackets, screws, as well as knee and apex braces.

To meet these high wind requirements, these components need to be added to or bolstered to bring the structural strength up to a level that’s satisfactory to engineers. Due to the multiple components and connections that are generally fixed with tek screws, over time, these connections can rattle loose, screw holes can slog out from movement, and weak points are created. This could make the structure much more liable to give way under the pressure of high winds.

The balance between well-engineered and over-engineered

There are several ways shed companies take into account the wind loading design requirements. Chain store or merchant pole shed suppliers typically use off-the-shelf generic designs that have set specifications depending on what wind zone and region the shed is destined for. Companies that specialise in sheds 100% of the time will usually do a site-specific engineered design. The difference between these two methods is that the site-specific design is typically more cost-efficient, given the extra strengthening for wind loading is done where required, rather than over-engineering the whole shed.

For example, Alpine recently had a client who purchased a 12-metre clear-span shed in a high wind area, with the site-specific engineered foundations being 1.5 metres deep and extra wall bracing where required to meet design requirements. The client had also not long before purchased a smaller eight-metre deep centre pole shed with narrow bays. These plans were generic from a chain store shed provider and stipulated foundations two metres deep, an example of significant over-engineering that cost the client a lot of unnecessary concrete. The answer here is that it’s essential to work with a shed supplier who has a track record of sheds that have stood the test of time and gets site-specific engineering to ensure you’re getting a quality shed along with value for money.

In summary, it’s worth thinking outside the world of compliance to take the time to analyse the integrity of the actual materials that sit behind the tidy external look of the shed. There’s a lot more to a shed than its outward appearance. So, whether you’re about to embark on your project or you’re nearing the final stages and about to lock it all in, why not pause for a moment and consider the above findings. As the saying goes, “you only get one chance to get it right” and your shed is no exception.

To discuss your specific location with a specialist, or if you are ready to start your next project, contact the Alpine Buildings team.  

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