Frequently Asked Questions

A building specification is a clear description of the materials, products, performance levels, and installation standards required for a project. It matters because it helps avoid mistakes, keeps pricing aligned with the design intent, and reduces the risk of using products that are not suitable for the application. A good specification also makes it easier for contractors, suppliers, and building control teams to work from the same page.

The required insulation thickness depends on the target thermal performance, the type of construction, and the product being used. Different insulation materials have different thermal conductivities, so the thickness needed to hit the same result can vary a lot. In most cases, the goal is not simply “fit as much as possible” but to achieve the required U-value while keeping the build-up practical. Current guidance continues to focus heavily on thermal performance, and floor insulation requirements remain a major part of compliance decisions. 

A U-value tells you how quickly heat passes through a building element such as a floor, wall, or roof. The lower the U-value, the better that element is at reducing heat loss. It is one of the key figures used when specifying insulation because it helps show whether a proposed construction is likely to meet the required thermal standard. Energy Saving Trust and current Building Regulations guidance both continue to use U-values as a core measure of thermal performance. 

That depends on the system type, insulation layer, pipe or cable layout, screed or overlay board, and final floor finish. This is one of the biggest traps in renovation and extension work because people often focus on the heating system first and only later realise the floor height no longer works with thresholds, doors, and adjoining rooms. Current industry guidance keeps hammering this point because build-up depth and compatibility with low-temperature heating are make-or-break issues. 

Not always. Underfloor heating can work brilliantly, but it needs the right floor build-up, insulation strategy, heat source, and room-by-room design. Some projects are ideal for it, while others are better suited to low-profile systems or alternative heating approaches. It works best when considered early rather than shoehorned in at the last minute like an over-optimistic project manager with no tape measure. Current guidance around low-temperature heating and future standards makes this an increasingly important design question. 

The right screed depends on the substrate, thickness available, drying time needed, final floor finish, and whether underfloor heating is included. Some projects need a traditional sand and cement screed, while others may suit a flowing screed, rapid-drying screed, or thin-section renovation build-up. The best choice is the one that matches the job constraints, not the one somebody had left over from another site. Thickness, programme, and compatibility with the rest of the floor system all matter.

For many domestic and mixed-use projects in England, the main ones are Approved Document L for energy efficiency and Approved Document E for acoustic performance where separating floors or walls are involved. Depending on the project, other documents may also matter, but these two are regular heavy hitters for floors, insulation, and internal build-ups. Part L remains central to thermal compliance, while Part E is key where sound insulation performance matters. 

If the floor is part of a separating construction, a conversion, or a build-up where sound transfer matters, acoustic insulation may be essential. Even where minimum compliance is possible, many projects benefit from going beyond the bare minimum to improve real-world performance. This is especially relevant in flats, mixed-use buildings, and renovations where impact sound and airborne sound can become major headaches after completion. Approved Document E continues to set the baseline, but many specifiers aim higher where performance expectations are greater. 

Sometimes, but not always. Some systems are designed to combine functions, but many projects still need separate layers to achieve the required result. The right answer depends on what the floor or wall needs to do: reduce heat loss, resist impact sound, support load, house heating pipes, control moisture, or all of the above. This is exactly why proper specification matters. A product that is brilliant thermally may be useless acoustically, and vice versa. One-board-fixes-all is usually sales patter until the details get involved.

As early as possible. Technical advice is most valuable before products are ordered and before site levels, thresholds, and build-ups are locked in. If you wait until materials arrive, you are no longer specifying; you are managing fallout. Early advice is especially useful for insulation thickness, floor build-up, underfloor heating compatibility, U-value targets, acoustic requirements, and tricky renovation details. With current standards tightening around fabric and heating performance, early coordination is only getting more important.