The Irish problem in one sentence. Ireland has one of the highest ambient humidity levels in Europe. Cold air holds less moisture than warm air, so every time warm air inside your insulated shed hits a cold surface (the wall, the roof underside), it drops its moisture as condensation. Get the insulation or vapour barrier wrong and you're trapping that moisture inside the structure. Within 2–3 years, you'll have mould, soft timber, and a ruined shed interior, even if the insulation itself is performing perfectly.
First: is your shed worth insulating?
Before spending €600–€1,500 on insulation materials and fitting, ask three questions:
- Is it structurally sound? Insulating a shed with a soft floor, rotting cladding, or a failing roof is throwing money away. Fix the structure first. See the maintenance guide for what to check.
- Is it airtight enough? A shed with significant gaps at the eaves, around the door frame, or at the base won't hold heat. Insulation requires a relatively airtight envelope: draughts bypass it entirely. Seal the obvious gaps before you start.
- What are you heating it for? A workshop where you're in and out matters differently than a garden office where you're sitting still for 4–6 hours. A workshop can be kept at 10–12°C with a small electric heater and no insulation at all. A garden office needs to hit 18–20°C comfortably. That requires proper insulation and a real heat source.
If you're converting a basic storage shed to a garden office, the full insulation spec below applies. If you just want to take the edge off a potting shed, a simpler (and cheaper) approach works fine. See the budget option at the end.
The insulation materials: what to use and what to avoid
PIR rigid foam board (Kingspan, Celotex, Quinn Therm)
Best choice for IrelandPIR (polyisocyanurate) rigid board is the right choice for Irish shed insulation. It has a low moisture absorption rate, high thermal resistance per mm (important when you're working inside a timber frame with limited depth), and it doesn't sag over time. Kingspan K5 or Quinn Therm QR (available at Chadwicks, Buildbase, Heitons) are the standard specification.
For a garden office standard in Ireland, you want a minimum of 50mm in walls and 75–100mm in the roof (heat rises, the roof does more work). Some builders go 75mm in walls and 100mm in the roof. This is better thermal performance but adds cost and reduces internal width by 50mm each side.
Important: PIR board must be finished on the interior with a fire-rated lining (12.5mm plasterboard or fire-rated OSB). It's a legal requirement if the space is occupied, and the foil facing emits toxic fumes if it catches fire unprotected.
Mineral wool / Rockwool / glass fibre batts
Use with extreme care in IrelandMineral wool is the insulation most Irish builders reach for by default, because it's cheap and familiar. In a house (where you have ventilated cavities, vapour-controlled membranes, and a drying mechanism), it's fine. In a shed, it's a risk.
Mineral wool absorbs moisture readily. Once saturated, it loses most of its insulating value and becomes a wet sponge pressed against your timber frame. In an Irish shed without a perfectly installed vapour barrier on both sides and a working ventilation path, mineral wool will be damp within two years. The timber behind it will start to rot before you notice: from inside the wall, invisible until the board comes off.
When it's acceptable: Mineral wool works in a shed insulation spec IF (a), you fit a continuous airtight vapour barrier on the warm side with all joints properly taped, AND (b), you create a ventilated airspace between the mineral wool and the outer cladding. This is achievable but it requires getting both details right. Most DIY installs don't. If in doubt, use PIR board instead.
Reflective foil multifoil insulation (Actis, YBS, SuperQuilt)
Useful as a supplement, not a standaloneMultifoil insulation, the bubblewrap-with-foil-faces product sold at hardware shops and on Amazon, is heavily marketed for sheds. The claims on some packaging are extraordinary. Treat them sceptically. Independent testing (including studies by the Irish National Standards Authority and BRE in the UK) consistently shows that multifoil performs significantly below claimed values when tested in standard conditions.
That said, multifoil does have a legitimate role as a vapour barrier and as a supplement to PIR board on the roof: stapled between the rafters and the internal ceiling board to add a reflective layer. It's also useful as an affordable partial solution for a low-budget job where full PIR is out of reach. Just don't expect a single layer of multifoil to turn a cold shed into a warm office.
Spray foam
Avoid in most shed applicationsClosed-cell spray foam has excellent insulation properties and is genuinely moisture-resistant. The problem in a shed context is twofold: it's expensive (€40–€80/m² installed vs €15–€22/m² for PIR board), and it permanently bonds to whatever it touches. If you ever need to access the framing for repairs, which you will in a timber shed, you cannot get to it without tearing out the spray foam. It also raises questions for mortgage lenders if you spray a building that's connected to or attached to the house.
For a standalone garden shed in Ireland, PIR board is better value and more practical in every dimension.
The correct layer order: walls
This is where most DIY insulation jobs in Ireland go wrong. The order of layers matters as much as the materials.
Correct wall build-up (inside → outside)
- Internal lining: 12.5mm plasterboard or fire-rated OSB board: the finish surface, also acts as fire protection for PIR
- Vapour control layer: 500-gauge polythene or proprietary VCL membrane, all joints lapped and taped: on the warm side of the insulation
- PIR board (50mm min): Cut to fit between studs, all gaps filled with low-expansion foam
- Timber stud frame (existing shed framing)
- Breather membrane: Vapour-permeable felt or Tyvek: allows moisture to escape outward but not enter inward (check it's already fitted; most modern sheds have it behind the cladding)
- Exterior cladding (existing timber boards or steel panels)
The vapour barrier rule: In Ireland, the vapour control layer must go on the warm side of the insulation: between the insulation and the interior of the shed. If it goes on the cold side (between insulation and cladding), it traps moisture inside the insulation. This is the single most common DIY error and it causes the most damage.
The correct layer order: roof
The roof is where heat loss is highest (heat rises) and where condensation risk is greatest. It gets the most insulation and the most careful attention to vapour control.
Correct roof build-up (inside → outside)
- Internal ceiling board: Plasterboard or plywood, the interior finish
- Vapour control layer: Continuous, all joints lapped and taped, no gaps at wall junctions
- PIR board (75–100mm): Between or below rafters, all gaps sealed
- Air gap of minimum 25mm: Between PIR board and roof felt. This is non-negotiable in Irish conditions; it allows moisture to ventilate out rather than pool on the cold roof underside
- Roof felt / membrane: The existing weatherproofing layer
- Roofing boards / battens
- Roof covering: Felt, bitumen, metal sheet
The 25mm air gap is critical and often omitted. Without it, any moisture that gets past the VCL has nowhere to go and condenses on the underside of the cold roof. In an Irish climate this happens fast. You'll see black mould on the ceiling board within 18 months.
Ventilation: the counter-intuitive part
Most people installing shed insulation think the goal is to seal everything airtight. In a house with a mechanical ventilation system (MVHR), yes: you do seal it airtight and mechanically manage the air exchange. In a shed, you almost certainly don't have that. Which means you need deliberate passive ventilation to prevent moisture build-up.
This sounds contradictory: you're insulating to keep heat in, but you need to let air out. The resolution is to ventilate the roof void (above the VCL, below the roof covering) rather than the occupied space directly. You do this with:
- Soffit vents at eaves level: small louvred gaps that let cool outside air enter the roof void
- Ridge or high-level vent: lets warm moist air exit at the apex of the roof
This creates a passive stack effect: cool dry air enters at the bottom, warm moist air exits at the top, moisture can't accumulate. The vapour control layer protects the insulation from interior moisture, and the roof ventilation removes the moisture that gets past into the roof void.
If your shed has a flat or near-flat roof (most budget metal and timber sheds do), ventilation is harder to achieve. This is one of the main reasons converting a flat-roofed shed to a garden office is a more complicated job than a pitched-roof building.
The floor: often forgotten
Up to 20% of heat loss in a shed can be through the floor, and it's the element most often left uninsulated. For a garden office, floor insulation is essential for comfort: a cold floor makes a room feel cold regardless of wall and roof spec.
The simplest approach for a shed with a concrete slab base: lay 50mm PIR board directly on the slab, cover with 18mm tongue-and-groove chipboard flooring, glue and screw. Damp-proof membrane between the slab and PIR if there's any sign of rising moisture. Cost for an 8×6 floor: approximately €180–€250 in materials, DIY fit.
For a timber floor (most shed suppliers fit a timber bearer floor), check the floor is sound first. PIR board can be fitted between the floor joists from below if accessible, or a floating floor overlay (PIR + chipboard) can go on top if you have headroom to spare.
Costs for a full garden-office spec
| Element | 8×6 (4.5 m²) | 10×8 (7.4 m²) |
|---|---|---|
| PIR 50mm walls (materials) | €120–€160 | €200–€265 |
| PIR 75mm roof (materials) | €110–€150 | €180–€240 |
| PIR 50mm floor (materials) | €80–€110 | €135–€175 |
| Vapour control layer + tape | €40–€60 | €65–€95 |
| Plasterboard lining (walls + ceiling) | €130–€180 | €220–€290 |
| T&G chipboard floor overlay | €70–€100 | €120–€160 |
| Fixings, foam, tape, breather membrane top-up | €50–€80 | €80–€120 |
| Total materials | €600–€840 | €1,000–€1,345 |
| Labour (if hiring a local handyman) | €400–€700 | €600–€1,000 |
| Total installed | €1,000–€1,540 | €1,600–€2,345 |
These are materials-only prices for sourcing at a builders' merchant (Chadwicks, Heitons, Buildbase), not B&Q retail pricing, which runs 15–25% higher. A local handyman will charge less than a registered insulation contractor. Get quotes from both if you're not going DIY.
The budget option: take the edge off without full conversion
If you just want to use the shed as a workshop in winter without it being miserable, not a full 18°C office spec, there's a simpler and much cheaper approach:
- Seal obvious draught points: door frame gap, base gap, eaves openings that aren't intentional vents
- Fix a single layer of multifoil insulation (e.g. YBS SuperQuilt) to the inside of the roof, stapled to the rafters with the foil facing inward
- Add a 2kW electric fan heater: a shed at 4°C will reach working temperature (12–14°C) within 20–30 minutes with a decent fan heater, even with no wall insulation
- Put a cheap foam-backed carpet remnant on the floor if it's concrete
Total cost: €150–€300 including the heater. This won't make the shed a comfortable office in December, but it makes a winter workshop viable and doesn't require any structural work or vapour barrier installation. Running costs for a 2kW heater at Irish electricity rates (approx €0.40/kWh): about €0.80/hour, cheaper than heating your house for the same space.
Planning permission for an insulated shed
Insulating the inside of an existing shed does not trigger a planning permission requirement. You're not changing the external footprint or appearance. However, if your insulation project is part of a broader conversion to a home office and you're adding electrics, a separate toilet, or a kitchen, the picture changes. A shed with a WC becomes a "separate dwelling" under planning law and almost certainly requires permission regardless of size. See the planning guide and garden office conversion guide for the full picture.
For most people (adding insulation, a plug socket and a desk lamp to a garden shed), no planning permission is needed.
Quick reference: what to specify when buying a new shed
If you're buying a new shed with the intention of insulating it, a few decisions at purchase time will save significant cost and effort later:
- Minimum 44mm stud frame depth: this lets you fit 40mm PIR board between the studs with room for a vapour barrier. Many entry-tier timber sheds have 28mm frames that make this impossible without furring out.
- Roof pitch of at least 15°: gives you room to create the ventilation gap above the insulation. Flat-roof sheds (common in cheaper steel ranges) are much harder to insulate properly.
- Breather membrane behind cladding: ask the supplier if it's included. Most quality suppliers fit it as standard; budget suppliers don't. Without it, any moisture that gets into the wall cavity has no exit.
- Pressure-treated (not dip-treated) framing: the inside of the frame will get damp at some point; pressure-treated timber resists rot far better when it does.
For a full list of things to check before signing for any shed, read the buyer's guide. To compare quotes from suppliers offering these specs, use the free multi-quote form.