Frequently asked questions on thermal insulation
The new changes to Part L are being implemented on 6th April 2006. These much awaited changes will have a significant effect on current design and construction practices.
The new Part L sets out to make buildings more energy efficient, saving one million tonnes of carbon per year. To satisfy the requirements of the EPBD, new improved energy performance standards of 20% – 27% have been set for all new buildings, based on the ‘whole building’ Target CO2 Emission Rate (TER) see new Interim Part L guide. Following questions will soon be updated accordingly.
1. What is the thermal conductivity of Rockwool Products?2. What is the U value required to achieve the part L thermal regulations 1/4/02 for insulation laid between joists?4. We are building a timber framed house can you tell me the thickness of insulation?3. What is the U Value required to achieve part L of the thermal regulations as of 1/4/02 for insulation between rafters?5. What insulation do you do for insulating cavity walls, and what guarantees do they have?6. Can I install Rockwool Cavity below DPC?
1. What is the thermal conductivity of Rockwool Products?
The thermal conductivity ( λ value) of Rockwool products at a mean temperature of 10°C is in the range of 0.034 to 0.044 W/mK. The thermal resistance (R value) of a specific product can be found by dividing its thickness in meter by the λ value.
2. What is the U value required to achieve the part L thermal regulations 1/4/02 for insulation laid between joists?
You will require a U value of 0.16 W/m2K is can be achieve by putting 100mm Rockwool rollbatts between joists and 170mm over the top of the joists.
4. We are building a timber framed house can you tell me the thickness of insulation?
To comply with the building regulations you require a U value of 0.35 W/m2K for walls and 0.25 W/m2K. For the walls, this can be achieved by using 120mm of Rockwool Flexi between the timber studs and for a timber suspended ground floors, this can be achieved by using 170mm Rockwool Roll.
3. What is the U Value required to achieve part L of the thermal regulations as of 1/4/02 for insulation between rafters?
The thermal regulations require a U value of 0.20 W/m2K on all new build, and 0.30 W/m2K if it is a conversion of an original roof. To achieve a U value of 0.20 W/m2K you require 210mm Rockwool Flexi between rafters @ 600 c/c. To achieve a U value of 0.30 W/m2K you require 150mm Flexi between rafters @ 400c/c.
5. What insulation do you do for insulating cavity walls, and what guarantees do they have?
Rockwool manufacture a number of cavity wall insulations, we have two full fill options and one partial fill option. Rockwool Cavity is a slab for fully filling the cavity and is installed during construction and Rockwool EnergySaver is granulate that is blown in to the cavity by Rockwool approved installers.
HP Partial Fill is a slab for partially filling the cavity with a residual cavity of a minimum 25 mm. If NHBC is involved, please check with their requirements.
A British board of agreement certificates covers all the materials. Rockwool EnergySaver is also covered by CIGA, the Cavity Insulation Guarantee Agency.
6. Can I install Rockwool Cavity below DPC?
Yes, Rockwool Cavity may be fitted below DPC level, but must be cut to bring into course with the first row of wall ties. Otherwise, the first row of slabs must be supported by two wall ties per slab, and cut to course with the next row of wall ties.
