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PRODUCT
INFO |
Underfloor heating - pipe and
screed installation.
Fact Sheet 2 Screed & Concrete Floors
The following diagrams indicate two standard methods of securing
the Wirsbo system within a screed or concrete floor.
Steel Grid Fixing
Recommended for standard sand/cement screed
The above floor section incorporates the following:
1 Structural concrete slab or oversite
2 Sub-floor insulation in accordance with Building Regulations
3 Polyethylene sheet
4 Steel grid (usually A 142 reinforcing mesh)
5 Wirsho PEX pipe secured with wire or plastic ties
6 Finishing screed or concrete. Recommended thickness 7Smm from top of insulation
7 Final floor finish laid in direct contact with the screed/concrete.
Plastic Cliprail Fixing
Recommended for sand/cement or liquid flow screeds.
The above floor section incorporates the following:
1 Structural concrete slab or oversite
2 Sub-floor insulation in accordance with Building Regulations
3 Polyethylene sheet taped on every joint.
4 Flat plastic ciprail with clip positions every 50mm.
5 Wirsbo PEX pipe snapped into cliprail or secured with individual U-clips.
6 Finishing screed or concrete. Recommended thickness 75mm from too of insulation.
7 Final floor finish laid in direct contact with the screed.
The plastic rail illustrated is in 600mm sections with hinged joints for easy
handling. Fixed into EHD/N polystyrene insulation board with 'u' holding pins.
Individual fixing clips can also be supplied for the location of single pipes
in any position.
General
The different fixing systems can he used individually or in any combination
required to suit the building design.
For example if there is a difficult shaped area where steel grid would be inappropriate then a small quantity of cliprail can be used. Equally ciprail can be more appropriate where access is difficult for large sheets of steel grid such as apartments on upper floor levels.
All of the methods of clipping are acceptable for Wirsbo pipe systems and provided the pipe is adequately secured the more convenient method should he selected for the individual project.
Floor Construction
There are many different types of floor construction which use screed or concrete
and these can be of the insitu poured types or alternatively in the form of
precast units.
These types of construction will normally require a layer of insulation below the heating loops to prevent downward heat transmission and to help reduce the inertia of the system where a quicker response is required. The insulation used should be sufficient to meet the requirements of the current Building Regulations.
Various types of insulation are available on the market and the following will normally all be found to he acceptable.
It is not possible to give precise details here of the many types of construction possible and how a Wirsbo system can be incorporated. We can always advise on any special construction methods.
| Type |
Typical Brand name |
Thermal Conductivity W/m K |
| Expanded Polystyrene |
Jablite |
0.033 - 0.037 |
| Extruded Polystyrene |
Styrofoam |
0.026 - 0.028 |
| Vacuum extruded Polystyrene |
Polyfoam |
0.026 - 0.027 |
| Polyisocyanurate |
Celotex |
0.020 |
| Rockwool |
Rockfloor |
0.035 |
General Notes
1. Moisture Control.
When using sub-floor insulation care must be exercised to ensure that screed
or concrete cannot bridge between the insulation panels. This is important
to inhibit both sound and heat bridging and to reduce the risk of some types
of insulation becoming excessively wetted by the screed or concrete.
In order to eliminate this risk it is advisable to either tape the individual
joints between sheets of insulation or cover the insulation with a protection
layer of polythene sheet.
This must not be regarded as the damp-proof membrane which would normally
be installed above or below the structural slab.
The polythene sheet can also act as a vapour control membrane where timber
floor finishes are being used, some of which can be susceptible to moisture
migrating up from the oversite concrete.
2. Edge Isolation/Insulation
To comply with Building Regulations and relevant Codes of
Practice it is important to ensure that the screed or concrete does not form
a bridge to either external or internal walls.
To avoid this, edge insulation is laid against all walls. Wirsbo edge insulation
has a flap of polyethylene designed to be lifted and laid on the floor insulation
to stop screed bridging the gap between the edge of the wall and the floor
insulation. Any surplus is easily trimmed once the screed has cured. The following
illustration shows how the edge isolation can he incorporated with the other
building elements on a standard floor.
Heat loss from the external walls of the building alternative
construction methods to increase the should be controlled by cavity wall construction
and cavity fill material which should be designed to inhibit lateral edge
loss. The following illustration show an example of the correct and incorrect
methods of external wall construction to reduce such lateral losses.
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There are many different types of floor and wall construction that may require special consideration and Wirsbo systems can be integrated with all forms of solid floor. These are usually the simplest form of construction in which underfloor heating can be used.
In all cases professional advice should be sought where unusual constructions are being used or where special consideration is required for floor and edge insulation such as raised ventilated floors which can have a higher than normal downward loss.
Where floors are being constructed on very large buildings where it is not always necessary to install floor insulation then it may be necessary to consider and thermal resistance of the external walls and edge cavity fill material which should be designed to construction particularly below the ground level.
Screed and Concrete Mixtures
Wirsbo underfloor heating systems can be covered by all types of solid material
including
Wirsbo PEX pipe does not impart any excess stress to the screed or the concrete and in no way possesses the strength to crack a screed or concrete floor at the temperatures used. For this reason it is not necessary to reinforce the normal floor because of the underfloor heating system.
General Guide on Floor Laying
The floor should be constructed in the normal way and in accordance with the
relevant British Standards together with the following advice
1 Floor laying should take place as soon as possible after an underfloor heating zone is laid and pressure tested.
2 Pressure gauges should be fitted to the manifold(s) and checked periodically
3 Ensure that the insulation, mesh and pipework are laying flat and that adequate cover of material over the pipes is possible across the entire floor.
4 Boards should he laid to allow for wheelbarrows to be walked over the system without causing damage
5 The screed or concrete should be well compacted around the pipes to ensure there are no voids or hollows.
6 Take care when using shovels and trowels so as not to damage the system.
Floor Joints
Day joints can be made in the screed as required without reference to the
location of pipes, however where purpose made construction joints are being
inserted within the floor then the following recommendations should be followed:
The following illustration shows a typical
arrangement of crossing a construction joint.
After Floor Laying
The floor should be covered with a membrane to retard the drying out process
particularly in warm weather. The floor should be allowed to cure and dry
naturally until full strength is reached in accordance with relevant British
Standards and manufacturers instructions. The time that this will take will
depend upon the floor material used together with the thickness laid but for
an ordinary sand/cement screed laid 70mm thick a period of 28 days would he
normal.
The Wirsbo underfloor heating system must not be used to dry standard sand/cement or concrete floors since the rapid migration of moisture can lead to excessive cracking and a weak floor.
When the underfloor heating is switched on, the water temperature should he increased slowly over a period of days during the initial phase and should operate 24 hours per day with adequate ventilation of the building to enable moisture to escape.
All types of floor finishes can be laid over a Wirsho underfloor heating system including carpet, vinyl, ceramics, stone, timber etc.
It may be necessary with certain types of floor finish such as vinyl or timber to ensure that the moisture content of the floor meets the manufacturer's recommendations. Please inform Wirsbo what covering is to be used and ensure that Wirsho are given any special instructions from the floor manufacturer, including any temperature limitations.
Provided the screed or concrete is fully cured and dry then it is acceptable to run the underfloor heating system to assist in laying floor coverings.
