Insulation in House Construction

Insulation in House Construction

Integral to modern house construction in the UK is insulation. It is used to achieve thermal resistance around the building creating comfort and economy.

Insulation properly installed will reduce heating costs by reducing heat loss.

Starting at floor level, it is now a requirement of the Building Regulations to insulate ground floors. The standard method is to lay sheets of polystyrene or similar above the ground floor and then lay a screed or a timber floor over.

But some systems incorporate insulation within the floor itself, underfloor insulation boards must be fully supported over their entire area with no voids and no projections. The silver foil covering acts as a vapour barrier or vapour control layer and also stops moisture from the freshly poured concrete slab penetrating the insulation.

The actual heat loss through the floor is considerably less than that of the walls or roof, but given the ease with which it can be utilised during building, it represents good value.

Polystyrene solid panels, or even on-site spray are another modern alternative.

As the walls begin construction sheets of slab insulation are fitted as the walls go up: a typical build process would be inner leaf first to one course over wall tie height; insulation; outer leaf to the top of the insulation; then continuation of the inner leaf. In both cases, the slabs are sized to fit between standard-spaced wall ties (usually 450mm or two block courses in height) in order to aid installation.

Partial-fill is the standard choice for most new developments. It involves leaving a 25mm or 50mm gap between the outer face of the insulation and the external leaf. This has the advantage of reducing the chance of any moisture that does penetrate the outer leaf bridging through to the internal structure. For that reason, the system is required in many building regulations.

Semi-rigid batts of glass mineral wool or rock wool are the traditional choice. Their flexibility allows them to fit snugly against the masonry as well as knit together at abutments.

A typical brick and block wall has a 150mm cavity and most rigid or semi-rigid panels inserted will give good returns.

The other major cavity wall insulation method allows for quicker overall construction time, but this blown-in method is does not perform quite as well.

The roof insulation is of great importance, as most roofs are “cold” roofs, which means that the lower surface of the loft space, that is, the horizontal joists to which the ceiling is attached underneath, will carry the insulation that prevents the rising heat from the rest of the house escaping. This is usually rolls of rock wool or polystyrene slabs or pellets.

Warm roofs are those roof spaces which are in used as a living space and the insulation therefore has to be installed directly under the roof in the plane of the roof’s pitch (slope). Insulation will reduce heat loss and your loft space won’t become excessively hot in summer or cold in winter.

One important point to remember with a warm loft solution is the need for ventilation immediately below the roof tiles. This prevents condensation build up or water getting in through or around the tiles, which could cause the roof structure to rot.

81 thoughts on “Insulation in House Construction

  1. sage advice uk

    New houses are built based on cost, not on optimum specification. If they were all built with the latest energy harvesting and saving tech we would make a massive impact on energy consumption.

  2. BCN

    Insulation of loft space is much harder with living spaces in the eves due to the limitations of depth of insulation materials available.

      1. RB

        Big builders flit between profit and loss so rapidly, the government just needs to get it’s timing right, introducing new requirements so they are affordable. It would also drive tech costs down faster.

  3. Wisdom Tips

    New properties could be much better built than they are. They could have rainwater recycling, roofs made of integrated solar panels and ground source heat pumps

    1. Trip Tip

      Too many people assume that buying a new home protects them from weather damage, but quite often it’s new builds that suffer more than older properties.


      Watch this space, in 5 years, once millions of new homes have been built & all the EU workers have gone home, leaving them empty, we will no doubt want to re-spec all these properties and it’ll cost twice as much as it would have done!


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