# Wi-Fi Site Surveys: Why You Cannot Design Coverage From a Floor Plan

Source: https://elementdigital.com.au/blog/wifi-site-surveys/
Published: 2025-11-25

> Wi-Fi planned on paper works on paper. What a site survey measures, why industrial sites break the predictions, and when you actually need one.

Wi-Fi designed on a floor plan works on the floor plan. Then somebody builds it, and the far corner of the warehouse drops out every time the roller door opens.

A site survey is how you avoid that. It is also the step most often cut when a budget gets tight, which is why we keep getting called back to sites that were designed on paper.

## What the plan cannot tell you

Planning software will predict coverage from a drawing. The prediction is genuinely useful and it is built on assumptions about what the building is made of.

Buildings do not read the assumptions. Concrete tilt panels absorb far more signal than plasterboard. Metal racking reflects it in ways no model handles well. Cool rooms are effectively sealed boxes. Water absorbs the 5 GHz band, which matters more in food processing and aquaculture than anyone expects.

Then there is what is already in the air. The neighbouring tenancy's access points, the microwave in the lunch room, the wireless bridge somebody installed in 2019 and forgot. None of that is on your drawing and all of it affects what you get.

## What a survey actually measures

A passive survey walks the site and records what the air looks like, with real equipment at the heights and in the places people actually work.

Signal strength is the obvious one. More useful is signal to noise ratio, because a strong signal in a noisy environment still performs badly. Channel utilisation tells you how busy each channel already is. Interference sources get identified rather than guessed at.

An active survey goes further and measures throughput and roaming behaviour while connected, which is what you need if devices move.

Roaming is the one people forget. A forklift crossing a site, or a handheld scanner walking a picking aisle, hands off between access points constantly. Coverage can be fine everywhere and the experience still be terrible, because the handoffs are slow or the device clings to a distant access point rather than switching.

## Where predictions break worst

Industrial and warehouse sites, consistently.

High ceilings change everything. Mounting access points at 12 metres is not the same as mounting them at three, and the pattern on the floor is not what the model drew.

Stock levels change the building. A racking bay full of product in January and empty in July is two different radio environments, and coverage designed against one of them fails against the other.

Outdoor and semi-outdoor areas are the other trap. Loading docks, yards and covered walkways are usually drawn as an afterthought and used constantly.

## When you need one

If you are designing a new site, deploying to an industrial or warehouse environment, supporting devices that move, or building anything that will carry voice, get a survey.

If you are adding two access points to a small office, you probably do not.

The middle case is the interesting one. A site where Wi-Fi mostly works but has two or three dead spots nobody has ever fixed is worth surveying, because the usual cause is not lack of coverage. It is co-channel interference between access points that are all working correctly and all shouting over each other. Adding more hardware makes that worse.

## Survey twice

The other thing worth budgeting for is a validation survey after installation.

You design against the predictive model, adjusted by the pre-installation survey. Then you install it, and the building does something you did not expect. A short validation pass tells you whether you got what you designed, while the installer is still on site and the ladder is still up.

That second visit costs a fraction of the first and it is the difference between believing the network is right and knowing it.

Element Digital does [infrastructure work](/infrastructure/) in Hobart and across Tasmania. If you have a site where the Wi-Fi has never quite worked, [get in touch](/contact/).