Pc01-Between & Above Joists in One Layer

PC01 - Between and above joists one layer

Advantages

Insulation installed in a single layer
Lowest cost solution
Familiar construction method
Excellent thermal performance
Enhances acoustic performance

Products

Crown Loft Roll One is made from glass mineral wool and formed into unfaced rolls which are lightweight, flexible, resilient and noncombustible. Its manufacture has a very low impact on the environment and is classified as Zero ODP and Zero GWP*

Optional

Knauf Breatheline is a breathable membrane and Type LR Roof Tile Underlay with a polypropylene non-woven coating on both sides

* Ecohomes and Code for Sustainable Homes classification

Typical construction

A pitched roof of timber trussed rafters with tiles or slates on battens and Roof Tile Underlay optionally on sarking board. Plasterboard ceiling below. Crown Loft Roll One is installed in one layer between and overlapping the joists to minimise thermal bridging through the ceiling joists

Ventilation requirements

If using Breatheline or similar third party accredited type LR roof tile underlay with a well sealed ceiling – no ventilation required In all other circumstances ventilation at eaves and ridge required.

Installation

Crown Loft Roll One is laid between the joists. The insulation should be taken over the wall plate to link up with the wall insulation. All joints between the insulation to be close butted. The insulation should be pushed up tight against the Roof Tile Underlay if no ventilation is required or tight to the eaves ventilator, taking care not to block the ventilation air path if ventilation is required.

Performance

Thermal performance

Crown Loft Roll One has a thermal conductivity of 0.044 W/mK. Table 1 gives U-values for typical constructions insulated with Crown Loft Roll One.

Fire performance

Crown Loft Roll One is classified as Euroclass A1 to BS EN ISO 13501-1.

Typical specification
The whole area of the ceiling to be insulated with one layer of Crown Loft Roll One of total thickness 270mm. Width of insulation to be appropriate to the joist centres. The insulation to be laid between the joists and to finish over wall plate on external walls. All joints between the rolls of insulation to be close butted. Maintain a minimum 25mm airspace between insulation and HR roof tile underlay at the eaves. Do not insulate under cold water tanks unless they are elevated. Cold water tanks and pipes to be separately insulated. Loft hatch to be insulated with a minimum 100mm depth of insulation. Alternatively, refer to NBS clauses: P10/120 and 130.

Typical specification

NBS Plus Logo The whole area of the ceiling to be insulated with one layer of Crown Loft Roll One of total thickness 270mm.

Width of insulation to be appropriate to the joist centres. The insulation to be laid between the joists and to finish over wall plate on external walls.

All joints between the rolls of insulation to be close butted.

Maintain a minimum 25mm airspace between insulation and HR roof tile underlay at the eaves.

Do not insulate under cold water tanks unless they are elevated. Cold water tanks and pipes to be separately insulated.

Loft hatch to be insulated with a minimum 100mm depth of insulation.

Alternatively, refer to NBS clauses: P10/120 and 130.

Typical section

PC01 - Typical Section

Table 1: Typical U-values of ventilated cold roof with ceiling level insulation

Product	Thickness (mm) Between & Over Joists	U-values (W/m²K)
Crown Loft Roll One	270	0.16

Product

Thickness (mm)

Between & Over Joists

U-values

(W/m²K)

Crown Loft Roll One

270

0.16

N.B. Joist sizes assumed to be 100 x 48mm at 600mm centres (8% bridging plus 1% for cross noggings). The U-value has been calculated in accordance with BS EN ISO 6946:1997.