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Frequently Asked Questions - Pitched Roofing
What is a Warm Roof?
A warm roof is where the insulation is located above or above and between timber rafters.
What is a Cold Roof?
A cold pitched roof is where the insulation is placed either between the rafters only or at ceiling joist level. A cold roof may be ventilated or non-ventilated.
What is nilvent and when do you use it?
Kingspan nilvent is a breathable membrane which is generally used for a pitched roof construction. The breathable membrane allows the construction to breathe allowing any moisture vapour to escape as well as providing a waterproof barrier.
When using sarking felt do I need to ventilate the roof?
Yes, when sarking felt is used as the waterproofing layer on a pitched roof, you would need to ventilate the roof. You would need a 50mm ventilated air space between the insulation (installed between the rafters) and the top of the timber rafters.
Does Kingspan Kooltherm K18 Insulated Plasterboard have an integral vapour layer?
Yes, Kingspan Kooltherm K18 Insulated Plasterboard has an integral vapour control barrier as part of the product.
How do I fit insulation between rafters?
Kingspan would recommend fitting the insulation flush between the timber rafters to form a tight fit. Any gaps should then be filled with an expanding urethane sealant or flexible mastic. Please see step by step guide.
  1. Measure the space between the rafters before cutting the boards as spacings vary
  2. Cut an insulation board such as Kingspan Kooltherm K7 Pitched Roof Board to size using a sharp knife or fine toothed saw.
  3. Install the correct thickness of insulation in such a manner that it is flush with the bottom of the rafters but does not fill the rafter depth.
  4. In all cases ensure that insulation boards between rafters are fitted tightly.
  5. Fill any gaps with expanding urethane sealant.
  6. Measure up before cutting the boards
  7. Cut the insulated plasterboard such as Kingspan Kooltherm K18 Insulated Plasterboard Board to size using a sharp knife or fine toothed saw.
  8. Where board dimensions allow, fix the boards at right angles to the underside of the rafters.
  9. Boards should be fixed with dry-wall timber screws, long enough to allow 25 mm penetration of the timber. These should be placed at 150 mm centres and not less than 10 mm from the edges of the board along all supporting edges.