Insulating a flat roof properly
Re-covering a flat roof without upgrading the insulation is a missed opportunity, but adding insulation carelessly creates a damp roof instead of a warm one.
Rigid PIR above the deck
The standard warm-roof approach: a vapour control layer, insulation boards, then the waterproofing. Good thermal performance for the thickness, which matters when height is limited.
Tapered insulation
Where the existing structure has no fall, tapered boards create one so water actually reaches the outlet. It's the fix for chronic ponding without rebuilding the structure.
The vapour control layer
Below the insulation, always. Without it, moisture from inside condenses within the build-up and the insulation gets wet from below.
Height constraints
Doors, windows and abutment flashings limit how much you can build up. Higher-performance boards buy thermal value in less thickness where that's tight.
Outlets and upstands
Raising the roof level means the outlets, upstands and trims all move too. This is routine but it must be designed, not improvised at the edge.
FAQs
A significant re-cover may engage building regulations for thermal upgrade. We'll tell you where that applies to your job.
That's a cold roof, and it needs ventilation to work. Above-deck is the more reliable build-up.
Combined with a correctly installed vapour control layer, yes — that's exactly what it's for.
Related reading
More on materials & systems and the jobs that usually come with it.
- Soffit vents, over-fascia vents and airflow at the eavesMaterials & systems
- Warm roof vs cold roof constructionComparisons
- Access, neighbours and awkward propertiesProcess & paperwork
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
Get a fast quote
Family-run and Hampton-based. Tell us what you're seeing on the roof and we'll come and look properly before quoting.