Can SIP walls increase the usable space in a house?

This relationship has a practical dimension with a fixed building outline. A thinner complete external envelope can leave more space on the inner side of the walls. The designer can use it for a wider passage, space at the table or a more convenient position for a wardrobe. The benefit depends on the layout of the floor plan, so there is no single percentage gain for all houses.

Let us take, purely for comparison, a single-storey outline of 10 by 10 metres. When each external wall is 30 centimetres thick, the internal dimensions are 9.4 by 9.4 metres. This gives 88.36 square metres before internal partitions are separated off. With walls of 25 centimetres, 9.5 by 9.5 metres remain, that is 90.25 square metres.

The difference is 1.89 square metres. This is a geometric example, not a declaration of the parameters of a specific SIP system. It does not take into account partition walls, columns, stairs or the rules for calculating usable floor area. It does, however, show why comparing the total thickness of envelopes can make sense already when choosing a technology, before the final house design is produced.

An internal finishing lining may be needed for aesthetics, fire protection and acoustics. Space for services is also often provided. On the external side there is a water protection layer and the façade. In a solution with a ventilated cladding, the supporting frame and a suitable cavity must be taken into account. All these elements take up space.

That is why two panels of identical thickness can lead to two different finished wall dimensions. For the client, a cross-section from the inner paint surface to the outer plane of the façade will be useful. Such a drawing allows offers to be compared without omitting layers. It also makes it easier to assess the depth of reveals and the way the windows are set.

The thermal advantage of the core is described by the thermal conductivity coefficient. At the same thickness, a lower lambda means better insulation of the layer. A chosen SIP panel with a PUR or PIR core can therefore achieve the intended result with a thinner core than a comparable EPS variant. Specific declarations must be compared, because polystyrene also comes in various grades.

The thickness of the element must not, however, be reduced solely on the basis of thermal calculations. The panel dimension may result from the wall height, loads or the spacing of supports. A reserve of insulation does not replace the required stiffness. The final choice should simultaneously meet structural and thermal requirements and suit the planned finish.

In the kitchen, it is worth checking not only the length of the wall but also the position of the service zone. In the bathroom, risers, built-in units and cable routing matter. In a built-in wardrobe, a few extra centimetres can make it easier to arrange the fittings. These elements should appear on the plan before SIP panels with pre-formed openings are ordered.

The gain in space should not always be used to increase the number of rooms. Sometimes it is more sensible to leave a more comfortable passage or to arrange furniture better. This is a functional decision that is easier to make on two comparable drawings. One can show the base variant, the other the wall layout with the chosen polyurethane insulation.

Saving space should not lead to the removal of necessary acoustic layers. A lightweight wall requires an assessment of sound insulation together with the linings and joints. Fire protection is similar. What counts is the classification of the relevant assembly, not merely an assurance about the properties of the foam. The design cross-section must take both issues into account.

The routing of services is equally important. If cables later require additional casings, part of the planned space saving may disappear. Agreeing the needs of the electrician, plumber and ventilation contractor in advance helps to maintain the intended internal dimensions. Prefabrication rewards such preparation, because many decisions are made before the elements are delivered.

SIP panels are worth considering where the external outline is strongly constrained. This may be a compact house, a narrow building or a design with small rooms. It is important to check whether the full cross-section of the chosen system will actually be thinner than the comparison solution. The name of the technology alone does not yet determine the result.

The best basis for a decision is a shared table of requirements and two drawings made at the same scale. They should cover a similar level of insulation, fire protection and acoustic comfort. Such a comparison shows the real benefit of the polyurethane core. It is then possible to decide whether the additional internal space is worth choosing a particular panel assembly for a given house.