Installation of SWIP IWI

Before installing the SWIP IWI System a comprehensive property survey should be carried out to establish the condition of the building, its suitability to receive the system and identify any remedial work needed prior to starting the upgrade process. At this point, a decision can be made as to whether an internal or external wall insulation system is most appropriate for the property under survey.

1. Where plaster is sound, fix directly through it, removing existing skirting boards if required before fixing the SWIP Studs (Figure 9). If not sound, remove the decayed plaster and, for greatest airtightness, seal with a parge coat. SWIP Studs are to be installed with the OSB facing into the room.

2. Screw fix SWIP Studs horizontally to the foot of the existing wall. A minimum fixing penetration of 40mm is required into the existing masonry wall (excluding thickness of plaster). Five fixings per SWIP Stud are required but the number can be increased as required, or as dictated by site conditions. Position the fixings at 600mm maximum centres and 75mm from the end of each SWIP Stud as shown below. These SWIP Studs should be positioned so that, if the wall is bowed or not vertical, the verticality of the SWIP IWI System is maintained. The horizontal SWIP Studs should also be located to that the OSB facing can provide a fixing point for the skirting board (Figure 10).

Three SWIP Stud thicknesses are available, 65, 80 and 95mm, which can be combined to give a variety of thickness solutions.

3. Screw fix SWIP Studs horizontally at the head of the wall following the same process as in step 2. Then, fix SWIP Studs vertically between the top and bottom horizontal SWIP Studs as indicated in step. 4, spacing them at 600mm horizontal centres to coincide with plasterboard dimensions. Ensure that the vertical SWIP Studs are cut and installed so as to be in close contact with the horizontal studs at floor and ceiling level (Figure 11). Where the ceiling line is irregular, cut SWIP Studs to extend from the horizontal SWIP Stud at the foot of the wall to the ceiling and fix as described in step 2. Once the SWIP Studs are fixed in position, mechanically fix SWIP Stud noggins between the studs at ceiling level to receive plasterboard fixings.

4. Fix all vertical SWIP Studs to the existing wall using screws and suitable universal wall plugs.

5. If there are irregularities in the wall surfaces, pack out the SWIP Studs using suitable materials which are unaffected by moisture such as marine ply, preservative treated timber or plastic packing pieces (Figure 12).

6. Friction fit SWIP Batts between the SWIP Studs ensuring the insulation zone is completely filled. There should be no gaps between the SWIP Batts and they should be installed so as to be in intimate contact with the SWIP Studs and the SWIP Vapour Control Layer (Figure13). Where SWIP Batts require cutting, they should be cut 5mm wider than the space that are intended to fill (Figure 14).

7. Once the insulation has been installed, staple SWIP Vapour Control Layer, to the SWIP Studs. SWIP Vapour Control Layer should be free from holes, any gaps should be made good, with tears repaired and overlaps sealed with aluminised tape. Screw 12.5mm stand-ard plasterboard to the SWIP Studs using 38mm drywall screws, or wood screws, at nominal 300mm horizontal and vertical centres, reducing to 200mm centres at corners. Ensure that there is a 3-5mm gap between the plasterboard and the existing floor to allow space for sealing, as in step 8. The plasterboard sheets should be installed full height vertically. (Figure 15)

8. Seal all joints at the perimeter of the plasterboard using SWIP Multi-Purpose Sealant to prevent air movement behind or through the SWIP IWI System.
(Figure 16)

9. Mechanically fix the skirting boards through the plasterboard to the horizontal SWIP Studs at the foot of the wall, or fix them with a high strength instant grab adhesive to the plasterboard. Seal the skirting to the floor with SWIP Multi-Purpose Sealant as a final precaution against air leakage. See page 18 for an alternative method for fixing skirting boards Footnote: The plasterboard selected should be suitable for the activities to be undertaken within the space being upgraded. For instance, where the walls may be subject to mechanical damage, consider using an impact-resistant plasterboard such as SWIP Denseshield.

Pullout strength Pullout strength tests have confirmed that SWIP Stud performs equally to that of metal or timber studs, 38mm Drywall screws or wood screws should be used when securing plaster-board to SWIP Studs.

SWIP Vapour Control Layer should be installed in accordance with the recommendations of BS 5250: 2011 ‘Code of practice for control of condensation in buildings’ and should be installed on the warm side of the insulation.

All laps in SWIP Vapour Control Layer and junctions at interfaces with other elements and materials in the building e.g. metal and timber studs and joists, cementitious boards and uPVC window frames should be sealed with an aluminised tape. The layer of the SWIP Vapour Control will be reduced unless it is effectively sealed to other elements of the building.

All joints in the SWIP Vapour Control should be lapped by a minimum of 75mm, and sealed with aluminised tape, which should be applied equidistantly over the lap.

Whenever possible, laps in the SWIP Vapour Control Layer should be coincident with an SWIP Stud in order to aid the sealing process. The number of laps can be kept to a minimum by installing full roll widths of SWIP Vapour Control Layer.

Where the heads of fixings penetrate the SWIP Vapour Control Layer they should be sealed with an aluminised tape, as should any tears, holes or cuts. The tape should overlap the damaged area by a minimum of 75mm. Where larger areas of damage occur they should be repaired with a patch of SWIP Vapour Control Layer and aluminised tape applied as detailed above.

10. Around openings (windows, doors etc), screw fix SWIP Studs to the wall at the edge of jambs, sills and heads as determined by on-site requirements
(Figure 17).

11. Line the openings with a SWIP reveal board, preferably, with a minimum thermal resistance of 0.34m2K/W. If there are thickness constraints due to the size of the window or door frame, install as thick a thermal laminate board as is practicable. The edge of the thermal laminate board should finish flush with the face of the SWIP Studs
(Figure 18).

12. The thermal laminate reveal board should be fully bedded into position (a multi purpose plaster adhesive is suitable) in order to prevent air move-ment behind the board. Once the adhesive has set, secure the thermal laminate with localised mechanical fixings, typically at 600mm vertical centres, or as determined by on site requirements Complete continuity of insulation should be achieved around the opening at the junctions of heads, jambs & sills by cutting back the plasterboard at the edge of the thermal laminate board (Figure 19).

13. When setting out SWIP Studs adjacent to openings in relation to plasterboard dimensions, make allow-ance for the fact that the plasterboard needs to extend beyond the centre line of the jamb SWIP Stud to cover the thermal laminate board. For example, the dimension between the centre lines of the jamb SWIP Stud & the next SWIP Stud needs to be 600mm, less the thermal laminate thickness (inc adhesive dabs), less 25mm (half the SWIP Stud width) (Fig 20).

Whenever possible skirting boards should be removed prior to installation in order to maintain insulation thickness and continuity.However, where this is not possible the following method may be used. Screw fix horizontal SWIP Studs (between vertical SWIP Studs) at the appropriate height in order to provide a fixing point for new skirting board and facilitate securement and sealing of the SWIP Vapour Control Layer.The depth of the horizontal SWIP Studs should be reduced accordingly to ensure that they are installed in line with the face of the vertical SWIP Studs. Where necessary reduce the thickness of the SWIP Batts to suit the reduction in depth of the SWIP Studs. Fixings should be located 75mm in from each end and one in the centre of the horizontal SWIP Stud. A minimum fixing penetration of 40mm is required into the existing masonry wall (excluding thickness of skirting board and plaster).

14. Install a new window frame towards the outside of the wall and build out head and jamb reveals with a suitably sized timber infill piece to accommodate the recommended thickness of thermal laminate board, ensuring a strip of damp proof membrane is fixed to the back of the timber using galvanised nails or stainless steel staples, i.e. between the timber and the external wall (Figure 21).

15. Fix SWIP Studs to the face of the jambs and flush with the timber infill piece and form a continuous insulated lining around the opening with the plasterboard cut back accordingly (Figure 22). Internal cornerInternal corners should be installed in accordance with Figure 23 and the corner void fully filled with SWIP Batt. The centre of the SWIP Stud adjacent to the corner SWIP Stud should be adjusted to accommodate the corner detail (Figure 23).

External corners should be installed in accordance with figure 24. In order to provide additional rigidity at the junction of the plasterboard linings a timber batten (minimum 25mm x 25mm) should be screwed fixed in position as indicated and the corner void fully filled with SWIP Batt. The centre of the SWIP Stud adjacent to the corner SWIP Stud should be adjusted to accommodate the corner detail (Figure 24).

In order to accommodate a taped and jointed finish, taper edged plasterboards should be installed. After applying a primer coat over the plasterboard and joints, a reinforced tape and jointing compound should be used to achieve a seamless finish. SWIP Drywall provides a comprehensive range of jointing compounds and tapes. In all instances follow the plasterboard manufacturers instructions.

Skim Coat

A 2mm to 5mm thick coat of SWIP Multicover or SWIP Universal Board Finish can be applied to the face of the plasterboards. The board joints should be reinforced with paper or fibre tape.


Follow manufacturer’s instructions regarding priming requirements prior to the installation of wallpaper or specialist coverings.


Face SWIP Studs with SWIP Moistureshield or Aquapanel when the SWIP IWI System is installed in humid or wet areas such as kitchens and bathrooms. The weight of tiling (including adhesive) fixed direct to plasterboard (without plaster skim) should not exceed 32kg/m2.

Follow guidance and recommendations from tiling manufacturers and BS 5385 accordingly.

Heating Radiators

Installing the SWIP IWI System on the external wall of a room may provide an opportunity to install a smaller radiator and also allow it to be re-sited on an internal wall. Alternatively, it may be possible to replace wall hung radiators with skirting radiators. Further information should be obtained from, for instance, a heating engineer or radiator manufacturer.

Fixing Radiators

Do not fix radiators to plasterboard alone. Sufficient support is provided only when radiator brackets are fixed:

  • Through the plasterboard into the SWIP Studs
  • To horizontal timber battens (fixed over the plasterboard)
  • To horizontal timber battens, fixed between the SWIP Studs and to the masonry wall
  • To SWIP Drywall Fixing Channels, screw fixed to the SWIP Studs behind the plasterboard to the masonry wall using suitable stand-off fixings. Timber battens are suitable for loads up to 75kg per metre run acting parallel to the plasterboard and should be used for heavier radiators.

SWIP Drywall Fixing Channels are suitable for loads up to 50kg per metre run acting parallel to the plasterboard and can be used for small radiators.

Picture Rails and Dado Rails

Picture rails and dado rails should be removed before installing the SWIP IWI System as they will prevent the SWIP Studs being fixed tightly against the wall. However, picture rails and dado rails can be fixed to the new plasterboard lining using an instant grab adhesive after installation of the SWIP IWI System, or the rails can be fixed to the SWIP Studs using suitable screws.

Fixing to Plasterboard

Light to medium weight items such as mirrors, pictures, shelving and curtain poles can be fixed in position using standard self-drilling, winged or toggled plasterboard fixings and fixings such as SWIP Drywall anchors which are suitable for loads up to 20kg acting parallel to the plasterboard.

For heavier items, such as kitchen cupboards, specialist heavy duty cavity anchor fixings should be used or they can be fixed to timber battens which have been secured to the existing external walls at pre-determined positions. Heavier items can also be secured by fixing back to the masonry wall using proprietary stand-off fixings or a suitably sized standard screw. Alternatively, screw fixing an 18mm plywood sheet to the face of the SWIP Studs over the entire wall area (after installing the SWIP Vapour Control Layer) to provide a solution to a wide range of fixing problems.

Socket and Switch Boxes

Socket and switch boxes should be fixed into the plasterboard lining in accordance with the manufacturer’s instructions. Plasterboard and drywall socket and switch boxes simply clip into place when inserted into a pre-prepared opening. When the faceplate is tightened onto the socket box, the box grips against the plasterboard, before the face plate is finally fixed, the boxes should be sealed against the plaster-board using SWIP Multi-Purpose Sealant to prevent air leakage. Cables penetrating the socket box should be sealed with SWIP Multi-Purpose Sealant. (Figure 25).As with an existing installation, back-boxes fitted into the front plaster-board face of the insulated wall should be of the type intended for plasterboard or dry walls. The SWIP Batt insulation behind the back box should be cut away to the depth of the back-box rather than forcing the back-box in and compressing the SWIP Batt.

Surface Mounting of New Cables

Where new surface mounted electric cables are installed (horizontally) on the room side of the SWIP IWI System they should be run in metal conduit to where the fixings/outlets are required prior to the installation of the vapour control layer. The SWIP Studs should be notched to suit the dimensions and shape of the metal conduit.

Installation of New Circuits

The requirements of Part P of the Building Regulations and BS 7671 must be adhered to when installing new ring circuits. Where a completely new electrical installation, or a single new circuit, is to be fitted in a house having internal wall insulation installed the electric cabling should be run behind the plasterboard but in front of the SWIP Batt insulation slabs. The cable ratings for this situation should be taken as those given for Reference Method A in BS 7671. The rating for a 2.50mm flat twin and earth cable installed in this position is 21 amps (Table 4, D5, Col 4, BS 7671) of 20 amps if in conduit in this position. Thus with this installation method, a 2.50mm cable is suitable for a 32 amp ring circuit. Also, 1.00mm or 1.50mm cables are suitable for lighting circuits protected by 6 amp or 10 amp fuses or circuit breakers. For a circuit supplying a cooker or electric shower which is protected by a 45 amp device, a 10.00mm cable would be required.

BS 7671 includes specific requirements for cables that are concealed in a wall or partition at a depth of less than 500mm from the surface. Cables installed in an internal wall insulation system fall into this category. The specific requirements include the use of metal conduit or trunking or other mechanical protection against penetration by nails and the like, the use of armoured cables or cables to BS 8436 and running the cables in specific zones. If the option of running the cables in specific zones is selected then additional protection by means or a residual current breaker (RCD) is also required. The recommended option is that of running the cables in the zones specified in Regulation 522.6.6 with the installation of an RCD. Note: As with all electrical work, if at all in doubt consult a suitably competent person such as a qualified electrician.

Electric Cables in Existing Walls
In a large number of instances the SWIP IWI System will be installed onto existing walls where the electric cables will be buried within the internal finishes. The current carrying capacities for electric cables buried in plaster are contained in Appendix 4 of BS 7671, Requirements for electrical installations – IET Wiring Regulations – Seventeenth edition.

The most commonly used cable sizes in domestic properties are 2.50mm for 32 amp ring circuits serving socket outlets and 1.00mm or 1.50mm for lighting circuits.

The current-carrying capacity for the 2.50 mm cables sunk into plaster is given in BS 7671 as 27 amps for twin and earth cable and 24 amps for wiring in conduit.

The effect of installing a layer of insulation over the inner surface of the wall would reduce the current-carrying capacity of the 2.50mm cables to 25 amps and 22 amps for the twin and earth and conduit wiring respectively, and apply when insulation has been installed only on one side of the wall. Where the SWIP IWI System is installed and there is also existing cavity wall insulation, the cables should not require any additional de-rating due to the high thermal mass of the wall which will in Note: The SWIPIWI system can only be installed by SWIP Insulation approved SWIPIWI installers effect negate the risk of the cables reaching elevated temperatures. Regulation 433.1.5 of BS7671 requires cables used for 32 amp ring circuits to have a minimum current-carrying capacity of 20 amps. Because the ratings derived above are greater than 20 amps existing 2.50mm, 32 amp ring circuit cables will continue to meet the requirements of BS 7671 for current carrying capacity after the internal wall insulation system has been installed.

Lighting Circuits

Lighting circuits are generally protected by either 6 amp of 10 amp fuses or circuit breakers. The current-carrying capacity of 1.00mm or 1.50mm cables sunk into plaster will remain suitable for lighting circuits when an internal wall insulation system is fitted. Larger cable sizes, such as 6.00mm twin and earth, are likely to be used with 45 amp fuses or circuit breakers for heavier loads such as electric cookers or electric showers. The current-carrying capacity of a 6.00mm cable sunk into plaster will be such that it will still be suitably protected by a 45 amp device after the installation of an internal wall insulation system. From the above, it is concluded that the current carrying capacity of existing ring circuits, lighting circuits and 6.00mm cable circuits for cookers or electric showers will remain adequate after the installation of an internal wall insulation system. Note: As with all electrical work, if at all in doubt consult a suitably competent person such as a qualified electrician.

Extending cables for socket outlets & accessories

When socket outlets on the existing external wall need to be repositioned on the new SWIP Stud lining, it is likely that the existing cables will need to be extended. If there is the sufficient spare length in the existing cables then they should be pulled through so that they can be re-connected to the accessory fitted to the SWIP IWI System.

However, if the existing cable has to be extended BS 7671 requires joints and terminations to be made in suitable enclosures, one solution is for the additional length of cable to be connected into the back-box of the existing accessory which is then fitted with a blank cover plate.

The additional cable could then be taken through a knock-out panel in the existing back box (with a grommet fitted) and fed through to the new fitting.

The section of cable running from the old socket outlet position to the new position needs to be considered in accordance with BS 7671 and de-rating factors may need to be applied as detailed in Table 52.2 of BS 7671. The application of a de-rating factor to the cable used in this situation is unlikely to result in the cable rating falling below 20 amps (as detailed in BS 7671) although each case should be judged upon its own merits. Further requirements for joints and terminations are detailed in BS 7671. BS 7671 also requires (with some exceptions) that ‘every connection shall be accessible for inspection testing and maintenance’. BS 7671 published on 1st July 2011 has added another ‘exception’ to the list which applies in this instance. Insulation displacement or insulation piercing connections complying to BS 5733 and marked MF (maintenance free) do not need to be accessible.Electric cables that have been extended can then be run forward in conduit and sealed to the vapour barrier. Extending cables in this manner are not classified as “notified work” (according to Approved Document P, 2006 Design and installation of electrical installations) and can be carried out by a suitably competent person. All electrical work should be carried out in accordance with Approved Document P, the relevant part of the current IEE Regulations and associated Guidance. Note: As with all electrical work, if at all in doubt consult a suitably competent person such as a qualified electrician.

Electric cables & extruded polystyrene

PVC insulated cables should be located in suitable conduit to avoid being in direct contact with extruded polystyrene insulation in order to prevent plasticiser migration which can cause loss of protection to the conductors.