Floor Insulation

With the latest changes in regulations, the requirement is to achieve a U value of 0.20. This translates to a rigid board insulation of 80mm plus. The boards used for this work are the Celotex GA400 range or the Kingspan TF70 range.

Insulating the floor is usually achieved in one of two ways. Either you screed over the top of your insulation boards or you can lay insulation over the final screed and under your finished floor. When installed correctly and with a hard surface on top of them, the insulation boards can support a large amount of weight.

Installation

Screeding Over Boards

Ensure the boards are laid above the damp proof membrane. The boards must be laid on a flat surface free from projections and continually supported. The boards should be laid with butted, staggered joints. A polythene sheet should be laid over the entire surface to prevent screed getting into the joints or use the tape that we sell. A 20 mm insulation should be inserted vertically around the perimeter of the floor. This should be screeded over with a sand screed cement of 65mm.

Your board choice here is a little complicated by whether you are intending to integrate under floor heating. Celotex for example do a proprietary board especially aimed at under floor heating known as their FF4000 range. Many people will use regular GA4000 boards for this application. For best value you are best to stick to regular PIR foam type boards.

The phenolic range as offered by Kingspan, Kingspan K3 is in the region of about 7-10% more efficient than the PIR boards however the benefits probably don't warrant the much higher cost. All the rigid boards have good compressive strength qualities so you may choose to lay insulation over the floor slab and lay a tongue and grooved floor directly over the top of that. Typically the same thickness of insulation is required whether you go under the slab or over it.

Insulating A Suspended Timber Floor?

The void below an insulated suspended timber floor must be well ventilated. The insulation must be cut to fit tightly between the joists to prevent heat loss.