Dormer Loft Insulation

Dormer lofts are very difficult to insulate as access is the biggest problem here,you may have to first decide whether you want to dismantle the plasterboard and loft/roof conversion to do a proper job of insulating correctly then reinstating it all afterwards?

1. Is your loft a heated space? If it is you need to have it straight insulated on line with building regulations requirements. In case of lost conversion you would have your roof insulated between and under rafters. Vapour barrier might be required as well. If your loft is not heated is recommended to install 270mm thick insulation between loft and the level below. This will do escaping from heated spaces below. 2. For loft floor insulation of you follow requirements you would need 270mm of will insulation of equivalent of that in PIR. 3. If your loft is heated you would insulate the walls with your neighbors. Party walls are usually a solid brick construction, you will need to install appropriate insulation. 5. The materials used in your loft conversion, such as the flooring, doors, walls and loft stairs all need to offer at least 30 minutes of fire resistance. So if you create internal walls at your loft you either use fire rated plasterboard or two layers of standard plasterboard.

1) Floor – Do I need insulation or just lay floorboards? ✅ Yes, you need insulation. Don’t just lay floorboards directly. Recommended: 100mm Mineral Wool (Rockwool or Knauf) between floor joists — helps with both heat and sound. On top of that: T&G chipboard (18–22mm) or OSB — for a solid floor surface. ❌ Don’t use PIR under the floor — it has poor sound insulation properties. 2) Joists – Is 100mm PIR okay in the roof rafters? ✅ Yes, 100mm PIR is good, but keep this in mind: You must leave a 50mm ventilation gap between the back of the PIR and the roof tiles (unless you have a breathable membrane). Seal joints with foil tape to improve airtightness. Install a vapour control layer (VCL) over the insulation before plasterboarding. 3) Neighbour's wall (terraced house) – insulation needed? 🟡 Not required by Building Regulations, but highly recommended for soundproofing. Use: 100mm acoustic mineral wool (like Rockwool RWA45) in a stud wall. Over that: Standard plasterboard, or Acoustic plasterboard for better results. 4) Internal walls – is quilt insulation enough? How to board? ✅ Yes, quilt insulation (50mm) is fine for internal partition walls. Steps: Fit insulation between timber studs. Board over with either: Standard plasterboard, or Plywood + plasterboard if you want to hang heavy items. 5) Can I use normal plasterboard or do I need fire-rated board? Depends on the location: Use fire-rated plasterboard (pink) around: Stairs/escape routes Ceilings under habitable rooms Shared party walls (in flats or multi-occupancy) Everywhere else: standard plasterboard is fine.