Insulating a flat roof over, between and underneath its joists allows heat conservation while meeting Building Regulations requirements, while eliminating roof void ventilation costs and cutting into existing structures.
Warm roofs offer superior thermal performance at an economical cost and installation is quick and simple, using SuperQuilt as part of its design to reduce profile height and internal head height impact.
Benefits
Warm flat roofs contain an insulating layer laid atop timber rafters to maintain an ambient temperature in the loft area, helping reduce energy bills and improving an EPC rating of the property.
However, this type of roof construction can increase the risk of condensation if moisture penetrates insulation and timber below it. A condensation risk analysis should be completed prior to choosing this option.
An effective alternative is using a continuous quilt like SuperQuilt over, between and under the joists for fast installation and superior thermal performance. It offers quick build times as it doesn’t require vapour barrier membrane installation – saving both money and time during construction. Furthermore, SuperQuilt can even be recessed into its position in the joists to reduce any impact to roof profile height or internal head height.
Installation
Warm flat roof insulation between joists is often the first choice for refurbishment projects, providing quick and easy insulation that meets building regulations with high thermal values. To do it safely and properly, professional installers should be employed and scaffolding may be needed for some parts of the process.
Cold roof build-ups, in which insulation is laid directly between joists, can be more challenging to install as ventilation gaps need to be left between each panel. However, they can often be cheaper than warm roofs while providing adequate U-value ratings.
If you opt for insulation boards, be sure they fit comfortably between the flat roof joists and are secured in place by the rafters. Foil insulation may be even easier to install; simply staple and tape together its sections on each roof joist before covering any joins with tape.
Materials
Under Part L of the Building Regulations, roof insulation must meet an acceptable U-value to comply with Part L of the regulations. Unfortunately, calculating this number can be complex due to different insulation materials having differing thermal properties; thankfully there are various online tools that can assist you with this calculation process.
Warm flat roof builds typically feature a vapour control layer above the deck and insulation below, attached either mechanically or adhesively. They’re frequently seen over extensions to existing dwellings with timber joists and plywood decks – this method reduces risk from interstitial condensation by insulating against its structure itself.
Kingspan Thermaroof TR31 insulation can be easily integrated into any build-up process, featuring water absorption resistance and microbial attack protection in its core and facings. It can be mechanically attached or adhered down for installation on many different roof membranes.
Cost
Insulating your flat roof as part of a conversion or extension project or new build requires choosing insulation with the appropriate U-value (a measure of its thermal properties that’s detailed in Part L of Building Regulations). To get this right it’s crucial that the material used meets requirements set by building regulations – this means selecting an insulation that achieves this benchmark U-value value.
Cold roof construction can also be considered, though this requires isolating each deck and joist separately to minimize expense of installation and ensure moisture cannot move up into the insulation material. Vapour control layers must also be added for added moisture control purposes.
Warm flat roofs are the more economical and thermally protective choice, though it must take into account any roof windows or fire escapes that could be blocked by raising the height of insulation. Furthermore, ventilation must be created so hot air and moisture can escape; otherwise your insulation could suffer dampness and decay.