Basement Conversions
Homeowners looking to improve their property, but faced with restrictions on a tight site, might find themselves looking to extend ‘down’ rather than ‘out’ with the construction of a basement conversion.
U-value Calculator
Start your U-value calculationWith the aid of glass mineral wool insulation or rigid PIR insulation, converting an existing basement represents a potential solution to providing extra living space when a garage conversion or loft conversion is not possible.
Creating basement living space
Converting an existing basement or constructing a new below-ground structure imposes various design challenges, all of which are dictated by the constraints imposed by the site and the existing property. Professional design advice should therefore be sought as well as engaging consultants like structural engineers from an early stage.
A basement must be capable of resisting the effects of the ground, both structurally and in terms of hydraulic pressure (water ingress). When providing a habitable room or rooms, it must also meet other relevant requirements in national building regulations, like contributing to the overall energy efficiency of the property and being properly ventilated.
Thermal insulation can be installed to the outside or inside of the basement structure. Only certain thermal insulation types with high levels of moisture resistance are suitable for applying to the outside of a basement structure. For a project where an existing below-ground space is undergoing conversion it is likely to be impractical to dig out around the basement and install external insulation.
Insulating a basement conversion
To create a below-ground habitable space, the floor and walls must meet thermal performance targets just like any other element of the property. Other things to consider include:
- Acoustic performance.
- Fire performance.
- Vertical space restrictions.
- Ease of handling, cutting and installing.
Insulating a basement conversion
Our range of insulation products can be used throughout a basement conversion project and installed internally. Rigid, lightweight Celotex PIR insulation provides a thermally efficient solution, while our XPS insulation range offer both thermal and acoustic insulation.
To create a below-ground habitable space the floor and walls must meet thermal performance targets just like any other element of the property. Thermally insulating a floor with PIR insulation boards is relatively straightforward, using Celotex GA4000 or XR4000 on the floor slab and tanking and with a floating screed or chipboard covering.
The same two products can be used for the walls, installed either between timber battens or behind a non-load-bearing leaf of lightweight blockwork (depending on the specific requirements of the project). Celotex PL4000 can also be used, either on its own or to supplement one of the other products, providing thermal performance and internal finish in one operation.
Alternatively, the walls may be thermally insulated using a glass mineral wool product, however, there is no requirement to achieve a certain level of acoustic performance from the external walls in a basement project. Depending on the size of the space, internal partitions separating different rooms may need to minimise sound transmission.
It may also be a requirement to install insulation within the floor structure between the ground floor and the basement to provide the required level of sound insulation.
The building detail is for illustrative purposes only. It does not constitute advice and should not be relied upon.
Insulation products
| Product Name | Thickness Range | Sizes | Lambda |
|---|---|---|---|
| Celotex GA4000 | 50-100mm | Width 1200mm, Length 2400mm | 0.022 |
| Celotex XR4000 | 110-200mm | Width 1200mm, Length 2400mm | 0.022 |
| Celotex PL4000 | 25-65mm (+12.5mm Plasterboard) | Width 1200mm, Length 2400mm | 0.022 |