I built my workshop in an uninsulated Colorbond shed and spent one Brisbane summer regretting it. By 10am on a 34-degree day, the inside temperature hit 45 degrees. By noon, it was genuinely unsafe to work in there. Tools were too hot to pick up. Metal surfaces could burn skin.

The following winter, I insulated the whole thing. Cost me about $2,200 in materials and two weekends of work. Best money I’ve spent on the workshop. Summer inside temperature dropped by 15-20 degrees. Still warm, but workable — especially with a fan running.

Here’s how to do it properly.

Why Sheds Get So Hot (and Cold)

Steel sheds are basically metal boxes. Colorbond steel absorbs solar radiation, heats up rapidly, and radiates that heat inward. There’s no thermal mass to buffer temperature swings. On a 35-degree day, an uninsulated steel shed can reach 50+ degrees inside.

In winter, the same principle works in reverse. The steel loses heat rapidly overnight. A winter morning in an uninsulated shed feels significantly colder than the outside temperature because the cold steel radiates chill into the space.

Insulation does two things: it slows heat transfer through the walls and roof, and it reduces radiant heat from the steel surface reaching you inside.

Roof Insulation: The Priority

If you can only insulate one thing, insulate the roof. About 60-70% of heat gain in a steel shed comes through the roof — it has the largest surface area and receives the most direct sun.

Option 1: Reflective Foil Insulation (Best Value)

Reflective foil (like Sisalation or similar products) is the most common shed insulation in Queensland. It works by reflecting radiant heat before it enters the space.

Installation: Fix timber battens (35x35mm or similar) to the underside of the roof purlins. Staple the reflective foil to the battens, shiny side down (facing the interior), leaving a 25mm air gap between the foil and the steel roof. This air gap is essential — the foil reflects radiant heat, and the air gap prevents conductive heat transfer.

Performance: Reduces roof heat transfer by approximately 60-70%. In my shed, this alone dropped peak summer temperatures by about 10 degrees.

Cost: Foil roll (30m x 1.35m): $80-120. Timber battens: $50-100. Total for a 6x6m shed roof: approximately $300-500 in materials.

DIY difficulty: Moderate. Working on ladders inside the shed, stapling overhead. Not technically difficult but physically demanding. A second pair of hands makes it much easier.

Option 2: Bulk Insulation Batts

Glass wool or polyester batts (like Bradford Gold or Knauf Earthwool) provide better thermal performance than foil alone. They resist both radiant and conductive heat transfer.

Installation: Requires a ceiling or at minimum purlins and battens to hold the batts in place. Friction-fit between purlins and hold in place with battens, wire, or a plasterboard ceiling.

Performance: R-value of 2.0-3.5 depending on thickness (100mm to 175mm). Combined with an air gap and reflective foil, this gives excellent insulation. My shed has R2.5 batts under a reflective sarking, and summer peak temperature sits around 30-32 degrees when it’s 35+ outside.

Cost: Batts for a 6x6m roof: $400-700. Add battens and fixings: another $100-200. Total: $500-900.

DIY difficulty: Moderate. Handling batts overhead is itchy and awkward. Wear long sleeves, gloves, a dust mask, and safety glasses. Polyester batts (like Bradford Polymax) are non-irritating if fibreglass isn’t your thing — they cost more but are much more pleasant to install.

My Recommendation

Combine both. Reflective foil on the underside of the roofing (against the purlins), then batts between ceiling battens below. The foil reflects radiant heat, the batts insulate against conductive heat, and the air gap between them adds another insulation layer.

This combination provides the best performance for a reasonable cost. It’s what I have in my shed and it works well in Brisbane conditions.

Wall Insulation

Wall insulation makes less difference than roof insulation because walls receive less direct sun (except the western wall in afternoon). But it contributes to overall comfort, particularly for the west-facing wall.

Western wall priority: If you’re only doing one wall, insulate the western one. Afternoon sun hammers the west side and that’s when temperatures peak.

Installation: Similar to roof — batts between wall girts, held in place with a lining material. You can use plywood, OSB, or even Hardiflex as a wall lining over the insulation.

Cost: Batts for walls of a 6x6m shed: $300-500. Lining material: $200-400 depending on what you choose.

Note: Wall insulation usually requires lining because batts need to be enclosed. This adds cost but also gives you a nice interior surface for mounting shelves, pegboards, and tool storage.

Floor Insulation

Concrete slab sheds don’t need floor insulation in Queensland. The slab provides thermal mass that moderates temperature, and ground temperatures are relatively stable.

If your shed has a timber floor on stumps, insulating underneath with batts and a moisture barrier is worthwhile. Timber floors lose heat in winter and can feel cold underfoot. Anti-fatigue mats on top provide additional comfort for standing work.

Vapour Management

Brisbane’s humidity creates a risk of condensation inside insulated sheds. When hot, humid air contacts a cool insulated surface (or warm interior air contacts cold steel in winter), moisture condenses. Over time, this causes corrosion, mould, and degradation of insulation.

Prevention:

• Maintain ventilation even after insulating (see my previous post on ventilation)
• Use vapour barriers on the warm side of insulation
• Ensure air gaps in the roof assembly allow moisture to dissipate
• Don’t seal the shed completely — some air exchange is necessary

What About Spray Foam?

Closed-cell spray foam insulation is excellent in theory — high R-value, air-sealing, moisture resistant. But it’s expensive ($3,000-6,000 for a typical shed) and must be professionally applied.

It’s worth considering if budget allows, particularly for the roof. The air-sealing properties are superior to batt insulation and it eliminates condensation concerns.

For most home workshops, the cost doesn’t justify the performance improvement over well-installed batts and foil.

Adding a Ceiling Fan

Insulation slows heat transfer. A ceiling fan circulates air and provides wind chill, making the insulated space feel even cooler. The combination of insulation plus ceiling fan is significantly more effective than either alone.

Industrial ceiling fans (1200-1400mm diameter) move more air than residential fans and handle dusty workshop environments better. Cost: $150-300 installed. Have it wired by an electrician when they install your power.

Cost Summary

Basic insulation (reflective foil, roof only): $300-500 materials Good insulation (foil + batts, roof and west wall): $1,000-1,800 materials Comprehensive insulation (roof, all walls, lining): $2,000-3,500 materials

Add roughly 30-50% for professional installation if you’re not doing it yourself.

Is It Worth It?

Without question. An insulated workshop is usable for at least 4-6 more months per year than an uninsulated one in Brisbane. That’s the difference between a workshop you use occasionally when the weather’s mild and one you use year-round.

For anyone serious about their workshop — whether it’s woodworking, mechanical work, or any trade — insulation should be in your setup budget from day one. It’s much easier to insulate during construction than to retrofit later, though retrofitting (as I did) is entirely feasible.

For more information on building standards and insulation requirements, Queensland Building and Construction Commission has guidelines for habitable outbuildings, though most shed workshops fall below the threshold for mandatory compliance.

Get it insulated. Your future self working comfortably in January will thank you.