Home » Lahendused » Ühiskondlikud hooned » Pitched Roof - Ceiling Level

Pitched Roof - Ceiling Level

Insulation placed at flat ceiling level creates a cold roof space and overall is the lowest cost option for insulating a roof. Very high levels of thermal insulation can be achieved because there is virtually no restriction on the thickness of insulation that can be installed.

Knauf Insulation Products

Good – Classic 040 provides low conductivity for a good level of energy efficiency especially when installed to a thickness above 300mm.

Basic – Classic 044 provides a basic level of thermal resistance yet can still dramatically reduce a homes heating bill.

Design Considerations

Ceiling Level Insulation

This is the most common and economic way to insulate a pitched roof and creates a ‘cold roof’. It has the advantage of minimising both the heated volume and the quantity of insulation material needed.

Cold ‘Breathing’ Roof

The features of a cold breathing roof are:

A vapour control layer at ceiling level to limit the amount of water vapour entering the roof void
A vapour permeable underlay as the roof underlay, to allow dissipation of water vapour from the roof void and, just as importantly, to act as a windproof layer
25mm deep counter battens to provide an airspace above the vapour permeable underlay for dissipation of moisture vapour
Ceiling level insulation that is pushed up tight against the vapour permeable underlay to prevent air leakage into the roof void at eaves level Insulation is laid at ceiling level in two layers, the first layer between the joists and the second layer across the joists.

Cold Ventilated Roof

With the ventilated design, the insulation is also placed at ceiling level, but cross ventilation of the roof void is used to disperse moisture vapour.

It is important to allow a clear, unobstructed ventilation path between the insulation and the tiling underlay to allow outside air to enter the roof void and prevent the build-up of moisture.

The ventilation requirements for roofs with a double pitch are shown above. Lean-to and mono-pitch roofs should have a continuous gap equivalent to 10mm at the eaves and high level or ridge ventilation equivalent to a continuous gap of 5mm.

Ventilation openings should prevent the entry of insects. A 3mm or 4mm mesh across the ventilation holes should be incorporated. A separate vapour control layer is not necessary, but all gaps and holes in the ceiling should be sealed to restrict the amount of water vapour that enters the roof void.

Cold Roof – Other Precautions

All tanks and pipes in the roof void should also be insulated to prevent freezing. Tank insulation jackets should be used

The roof access hatch should also be insulated to a minimum depth of 50mm and draught stripped. Provide catches or bolts to compress the draft seal and prevent air leakage from wind uplift.

Typical Specification Clauses

Ventilated Cold Roof

The whole area of the ceiling to be insulated with two layers of Classic 040 of total thickness ......mm. Width of first layer of insulation to be appropriate to the joist spacings and of a thickness equal to joist depth. The insulation to be laid between the joists and to finish over wall plate on external walls. The second layer to be laid at right angles to the first layer. All joints between the rolls of insulation to be close butted.

Maintain an airspace between insulation and sarking felt/sarking board at the eaves.

Do not insulate under cold water tanks. Cold water tanks and pipes to be insulated separately.

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

Cold Breathing Roof

The whole area of the ceiling to be insulated with two layers of Classic 040 of total thickness ......mm. Width of first layer of insulation to be appropriate to the joist spacings and of a thickness equal to joist depth. The insulation to be laid between the joists and to finish over wall plate on external walls and pushed up tight to breather membrane. The second layer of Classic 040 to be laid at right angles to the first layer.

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

Do not insulate under cold water tanks. Cold water tanks and pipes to be insulated separately.

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

Upgrading Existing Insulation

The two alternative specifications:

a) Between joists (where applicable)

The whole area of the existing ceiling to be insulated with Classic 040, thickness ......mm. Insulation of width appropriate to the joist spacings to laid over the existing loft insulation and dressed over wall plate.

b) Across the joists

The whole area of the existing ceiling to be insulated with Classic 040, thickness ......mm. To be laid over the joists, with all lateral joints close butted.

For both methods all joints to be close butted. Maintain airspace between insulation and sarking felt/sarking board at eaves.

Do not insulate under cold water tanks. Cold water tanks and pipes to be insulated separately.

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