Roof Insulation in Jersey

Warm roof or cold roof

In a cold roof the insulation sits at ceiling level and the roof void above stays ventilated and cold. It is the simplest option for an unused loft, and mineral wool laid between and over the joists does the job well provided eaves ventilation is kept clear.

In a warm roof the insulation sits at rafter or deck level, keeping the structure itself within the heated envelope. This is what rooms in the roof, vaulted ceilings and most flat roofs need, and it relies on rigid PIR board, multifoil rolls and a correctly placed vapour control layer to stop warm moist air condensing inside the construction.

On reroofs we often combine the two, mineral wool at joist level over unused areas and PIR or multifoil at rafter level over habitable rooms, so each part of the roof is treated the way it is used.

What the job involves

For a standard loft, the work involves laying insulation between and over the ceiling joists to the recommended depth while keeping eaves ventilation gaps clear. We also check for existing damp or timber issues before insulating over them, since insulation can mask problems if they are not dealt with first.

Where a roof is being re-covered or converted, we fit rigid PIR between and below the rafters, or multifoil where depth is tight, combined with a vapour control layer and, where the design calls for it, a ventilated cavity above the insulation. Flat roofs are usually insulated above the deck as a warm roof so the deck stays warm and dry.

Common problems we fix

• Old, thin or disturbed loft insulation no longer meeting current recommended depths
• Condensation and mould forming where warm moist air meets cold roof timbers
• Blocked eaves ventilation from insulation pushed too far into the eaves
• Cold spots and draughts in converted loft rooms with inadequate rafter insulation
• Insulation compressed or displaced by storage boarding laid directly on top
• Missing or badly lapped vapour control layers in warm roof build-ups
• Damp timber discovered under old insulation that had been trapping moisture
• Heat loss through poorly insulated hatch covers and loft access points

Materials and standards we use

We fit mineral wool at joist level in cold lofts, rigid PIR board at rafter and deck level where higher performance per millimetre matters, and multifoil rolls where the available depth is limited and a thinner build-up is needed.

All insulation work is carried out with proper attention to ventilation and vapour control, since trapping moisture in an unventilated roof causes more problems than it solves. Where insulation forms part of a reroofing project, the covering itself is completed to a high standard.

How much does it cost in Jersey

Cost depends largely on the size and shape of the roof, whether it is a simple open loft or broken up by tanks, hip ends and awkward access. A top-up in an accessible loft is far quicker than a full warm roof build-up in a converted roof space.

Material choice between mineral wool, PIR and multifoil affects price, as does freight to the island for specific products, and whether the work is carried out as a standalone job or alongside a reroof while scaffolding is already up.

We give every customer a free, written estimate so the scope and the reasoning behind the specification are clear from the outset.