A cold loft, a creaking ladder, and a winter bill that bites harder each year. The question isn’t if your attic needs insulation, it’s what kind will actually make the space above your head work for you, not against you.
The joists were dusted with the odd, thin layer of ancient wool that looked more like tired cobwebs than anything resembling thermal protection. You could feel the night pulling heat out of the house like a slow tide.
A few months later, the same ladder, new rolls of soft mineral wool, and a quiet satisfaction every time the boiler rested. The upstairs felt calmer, less twitchy. *The loft is where your home’s weather story is written.*
And the right material changes the plot.
The attic insulation shortlist: what actually works
Let’s start with the obvious players: mineral wool (glass or rock), cellulose, rigid foam boards (PIR/PUR), and spray foam. Each has a personality. Mineral wool is affordable and forgiving. Cellulose packs tight and loves old timber frames. PIR is thin but mighty. Spray foam expands into every gap, then sparks debates at mortgage meetings.
Then there are quieter names. Sheep’s wool that breathes and handles moisture like a seasoned mountaineer. Wood fibre boards that add summer comfort and a softer, natural feel. Reflective multi-foil that shines in niche setups but rarely stands alone. **For a cold loft, mineral wool batts remain the best bang-for-buck in the UK.**
One thing holds true in most homes: around a quarter of your heat tries to escape through the roof. Stop that, and you feel it fast. I watched a neighbour in Leeds go from a drafty upstairs box to a steady, warm calm after cross-layering 270 mm of mineral wool. A quick thermal camera check the next evening showed the roof tiles glowing less like a toaster. He didn’t brag. He just slept better.
Choosing and fitting: material by material
Cold loft first. That means insulating the floor of the attic, not the underside of the roof. Aim for roughly 270–300 mm of mineral wool to hit current expectations. Lay between joists, then cross-lay over the top. If you store boxes, fit raised storage boards or a loft platform so the insulation stays fluffy. Thin PIR over joists can help where height is tight.
Warm loft (habitable roof) is a different puzzle. Insulate the roof line with PIR boards between and under rafters, then add a vapour control layer on the warm side. Open-cell spray foam can deliver a neat fit in tricky rafters, yet it can create headaches with surveyors and lenders. A ventilated air gap under the tiles is non-negotiable. Moisture always finds you if you don’t give it a way out.
Here’s how the materials stack up in real life. Mineral wool: lambda roughly 0.032–0.044 W/m·K, fire-resilient, cost-friendly, great for a cold loft. Cellulose: around 0.038–0.040, dense coverage, low embodied carbon, loves old roofs that need to breathe. PIR: ~0.022–0.026, so you get high insulation in less thickness, ideal for rafter work. Closed-cell spray foam: ~0.025, air-seals brilliantly, yet can trap moisture in timber if detailing is sloppy. **Cellulose shines in older timber roofs that need breathability.**
Doing it right so it actually works
Method matters. Start by checking joist depth and measuring the loft hatch. Clear a safe walkway. Fit downlight covers if you have recessed lights, then layer the insulation away from eaves so you don’t choke ventilation. Keep a gentle airflow path at the eaves and around any cold water tank. Insulate and lag pipes before you roll out the big stuff.
We’ve all had that moment when a Saturday job turns into a two-week saga. Don’t panic. Common slips: compressing wool under storage boards, blocking eaves vents with a perfect roll, forgetting the loft hatch (a fleece-lined coat for your ceiling), and leaving bathroom extractor ducts flapping loose. Let’s be honest: nobody actually does that every day. A focused afternoon makes a different house by evening.
“Think of insulation as a duvet that only works when it’s fluffy and dry,” a veteran roofer told me on a frosty site visit. “Squash it, soak it, or trap moisture, and you’ve paid for a thick jumper that doesn’t warm you.”
- Cold loft, no storage: mineral wool to 270–300 mm, cross-layered.
- Cold loft, storage: raised deck or loft legs, keep the wool uncompressed.
- Warm loft conversion: PIR between and under rafters, continuous vapour layer.
- Breathable heritage roof: cellulose or sheep’s wool, with careful ventilation.
- Hard-to-reach corners: consider blown cellulose or a pro install.
What this means for your attic, and your nights
Your attic doesn’t care about brochures. It cares about physics, moisture, and the shape of your house. That’s why the best insulation isn’t a brand; it’s a match. The quieter upstairs. The boiler that sighs less. The way summer heat stops pooling on the landing like a stalled car.
Pick the material that speaks your roof’s language, not your neighbour’s. If you can go thick and simple, mineral wool wins. If rafters are shallow and space is precious, PIR does heavy lifting. If the house is old, breathability keeps timbers happy. **The best attic insulation is the one your house accepts and your future self forgets about.**
Ask around. Borrow a thermal camera. Listen for the quiet that wasn’t there last winter. A good loft doesn’t shout. It rests with you, night after night.
| Point clé | Détail | Intérêt pour le lecteur |
|---|---|---|
| Thickness vs performance | 270–300 mm mineral wool meets modern targets; PIR achieves similar with less depth | Choose the right build-up for storage and headroom |
| Moisture and ventilation | Keep eaves clear, add vapour control on warm side for roofline insulation | Protect timbers, avoid condensation and mould |
| Surveyor-friendly choices | Mineral wool, cellulose, PIR low-risk; spray foam can affect valuations | Reduce future mortgage and resale friction |
FAQ :
- What’s the best insulation for a typical cold loft?Mineral wool batts, cross-layered to around 270–300 mm. It’s cost-effective, fire-resilient, and easy to fit without specialist tools.
- Is spray foam a bad idea?It can work thermally, yet it’s often viewed cautiously by surveyors and lenders. If you ever plan to sell or remortgage, pick safer, reversible build-ups unless a specialist specifies it with guarantees.
- How thick should attic insulation be in the UK?For loft floors, aim near 270–300 mm of mineral wool to reach roughly 0.16 W/m²K. With PIR you can go thinner, but detail the vapour layer well in a roofline setup.
- Will insulation make the upstairs hot in summer?Good insulation stabilises temperatures. Mineral wool and cellulose also slow heat flow in hot spells. Add shading and ventilation for peak heat days.
- Is sheep’s wool worth the extra cost?For breathable, moisture-tolerant retrofits, yes. It buffers humidity, handles minor condensation gracefully, and is pleasant to install. In tight budgets, mineral wool still wins on price.
Great breakdown. For a cold loft with lots of recessed downlights, what’s the best way to maintain ventillation at the eaves while getting to ~300 mm? I’ve got shallow joists (100 mm), storage boards in the center, and a water tank near the hatch. Plan: 100 mm between joists, 200 mm cross‑lay, downlight covers, loft legs for a raised deck, and baffle trays at the eaves. Anything I’m missing re: vapour control or pipe lagging to avoid condensaton?