Under floor heating preparation guidelines

Cathedral Flooring has been proved to work with underfloor heating. Unfortunately a guarantee can not be offered for its use in this situation due to reasons which are beyond the control of the supplier and fitter. If a dispute arises there is no reliable way of recording or monitoring the under floor heating system settings or room conditions over a period of time. Because of this it is impossible to prove or disprove how the system had been used or abused by the customer.

Development tests over time have proved that Cathedral Flooring out performs traditional solid hardwood floors and block board core products when used with under floor heating. This is due to the structural characteristics of ply wood. Ply wood is probably the most stable wood product available on the market todate. Due to the construction of Cathedral Flooring it conducts heat whilst keeping its stability much better in comparison to traditional solid or other engineered flooring.

If Cathedral Flooring is fitted in accordance with the guidelines of the under floor heating companies instructions then the floor will eventually reach an equilibrium within the room. This is where the temperature and relative humidity levels are maintained within a fairly consistent range.

It is best if the screed is dried naturally - the under floor heating should not be turned on before the correct moisture level is achieved. If you turn the heating on to dry the screed out you may find that it will crack. The sub floor must be heated before the wooden flooring is laid. This heating up has the sole purpose of allowing any residual moisture which may be present within the screed or have formed to escape from the cement floor. Heating up the of new cement floors should be commence at the earliest 21 days after they have been laid, the procedure being that the flow temperature of the heating is increased by a maximum of 5C per day until the maximum temperature is reached. This is to be maintained for 6-7 days and not reduced at night.

To test that the floor is dry enough to lay a wooden floor you must do a trapped hygrometer test. Place a hygrometer on the floor directly on top of the screed, cover with polystyrene blocks, cover again with plastic and tape to the floor. After 12 hours check the meter. If the reading is over 75% the floor is too wet to lay. Do this test on at least 2 areas of the floor. Doing this you are measuring the escaping moisture. A good rule of thumb to work to is four weeks for the first inch, four weeks for the second inch and 6 weeks for the third inch.

These steps must be followed even when laying the floor in the summer.

The laying of the flooring can only start when all the heating procedures have been completed. All plastering and any decorating should also be completed prior to installation.

Following the fitting of your floor you can then turn on the heating, this must be increased by a maximum of 5C per day until the flow temperature is reached.

At the beginning and end of the heating period regulate your floor heating so that flow temperature is increased or reduced in stages of a maximum of 5C.

As a result of the insulating properties of wood, it may take longer than if compared to stone or ceramic tile to heat the room to a comfortable temperature of 20 - 22C. In this event do not raise the set flow temperature of your heating. This would have an adverse effect on your floor.

The temperature of the surface of the wood should never exceed 27C. Any higher will cause the floor to fail.

For Screed floors

The screed should be dry. Test to make sure moisture is correct.

The screed must be level to +/-3mm over 3m.

If the floor is stuck down a suitable adhesive should be used, which will act as both adhesive and moisture barrier.

If the floor is stuck down direct to the screed this can sometimes fail and as such we do not recommend it. This is due to problems with the screed itself and not the flooring.

The floor may be fixed down in the following methods:-

1. Battens within the screed - underlay, dpm, 6mm ply adhesive and then wood floor.

2. Screed, underlay, dpm, chipboard/ply, adhesive and then wood floor.

3. Insulation with heating pipes contained within, 18mm ply/chipboard, adhesive and then wood floor.

We recommend the use of an intermediate layer of a minimum 6mm ply onto which the flooring can be stuck with a good quality D3 moisture resistant PVA adhesive. We also recommend that you should use a 1.5mm foam underlay sheet covered by a DPM between the ply and the screed.

With whatever method of fixing you use always leave a 15mm gap on all four edges to allow for expansion and contraction of the floor.

Under floor heating guidelines

The maximum operating water temperature should be 50C and the maximum temperature at the underside of the wood should be 40C.

Relative atmospheric humidity should be maintained between 40 - 55%.

The room temperature should be maintained between 18C - 26C.

The heating should be run in strict accordance with the manufacturers instructions.

Whilst fitting the heating should be off and the floor cold.

If fitted as a stuck down floor a minimum of 2 days should be allowed for the glue to cure before the heating is turned back on.

Underfloor heating

Due to the Ply base of Cathedral Flooring it is extremely stable and therefore more suitable with underfloor heating than most other types of wood flooring. Even though ! it can not be guaranteed that there will be no movement at all. Small gaps and movement may occur and possibly some shakes. These can be filled at a later date.

If underfloor heating is present Cathedral Flooring needs to be glued down onto a timber type substraight that has been laid with staggered joints. Ply would be most suitable.

This helps to distribute the heat evenly and gives added insurance of minimal movement.

The substraight may be floated or fixed over screed, joists or battens.

On first floor level joists it is advisable to fix the substraight to give structural lateral stability to the joists which may be acting as ties to the outside walls.