Retrofit design

Internal wall insulation guidance on specification and design

Internal wall insulation needs to be carefully considered and specified before installation. The following is an analysis and a suggestion for design.

INTERNAL INSULATION FOR SOLID WALLS
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Specification
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DESCRIPTION
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The flat will need to be insulated from the inside. There is a suggested sequence and specification below but this will need to be agreed with the installer and the client. The preparatory works in the living room mean it should be relatively simple.
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LOCATION
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The initial wall to be insulated is the balcony wall of the living room.
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EXISTING FORM / CONDITION
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The wall has been stripped back to the brickwork
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ESTIMATED U-VALUE
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Currently 2.06 W/m²K aiming for 0.41 W/m²K
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Thermal bridges present
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Location
Type of bridge
Mitigation
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Join with neighbouring house
Linear
Extend insulation to a suitable internal point
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Join with neighbouring house
Linear
Extend insulation to a suitable internal point
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Join with roof
Linear
Extend insulation to a suitable internal point
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Round right angle
small area
Extend insulation to a suitable internal point
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Ground level
Linear
monitoring
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Around windows
small area
slim insulation in reveal
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Around doors
small area
slim insulation in reveal
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Sequence and products
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Sequence
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1. Pre-installation work to external walls
2. Preparation of wall surface and all elements that penetrate and are fixed to the wall (joists, services, window reveals etc) and elements that lie within the thickness of the insulation installation (e.g. radiators).
3. Installation of insulation, accessories and plaster finish to manufacturer’s guidance and specification below. Lime plaster finish must be breathable and compatible with insulation
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SUGGESTED PRODUCTS
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· Parge coat lime-based: Baumit Klima RK 38 or similar approved
· Timber fibre insulation tongue and grooved boards 80mm thick with conductivity value of 0.038-0.04 W/mK: STEICO internal or Pavadentro or similar and approved with fixings and accessories
· Airtightness tape to seal junctions with window/ masonry wall / ceiling - ProClima SOLSL80 Contega Solido SL 80mm wide or equivalent performance and approved
· Lime plaster finish must be breathable and compatible with insulation: Baumit Klima RK 38 or Breathaplasta lime plaster or similar approved
· Paint finish - permeable - finish to be confirmed by client
· Plastic corner and edge beading
· New softwood skirtings type and finish to be confirmed by client
· Picture rail to living room details to be confirmed
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Installation sequence and notes
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SPECIFICATION
SUPPORTING NOTES
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PRE-INSTALLATION WORK
Review survey information and identify on site any requirements for remedial work to external render finish, bricks, brick pointing and other elements such as guttering that may cause water ingress or otherwise affect the performance of the building.
1. Render repairs: Check for loose and ‘hollow’ render. To be removed with care to minimise the amount of render removed. Areas of removed render and visible cracks in the render to be cleaned of dirt and dust. Apply new render to the areas of removed render and cracks. Prepare render surface for paint finish to be confirmed.
PREPARATION in advance of installation
2. Remove all elements that will impede the installation of the insulation (e.g. radiators on external walls to be insulated, electrical sockets etc.)
Remove sufficient timber floorboards adjacent to all external walls and returns to be insulated to allow access to area between joists and install insulation below finished floor level.
3. Intermediate floor
Where timber joists are embedded in the external wall they should be treated as follows:
· Prior to the placement on insulation, fill cracks and mortar joints around the joints ends with lime mortar. Allow to go off.
· Add a layer of lime parge coat on wall and continue onto the first 100mm of timber joist.
· Any new structural timber element mounted against the brick wall to have a rubber shim placed on the wall surface before mounting.
4. Install first fix services as shown on architect’s drawings
5. Prepare wall surface:
· Remove existing plaster unless it is a breathable finish
· Remove dust, surface contaminants and loose or friable existing plaster.
· Consolidate and level wall with lime base plaster coat where necessary, allow to dry (1 day per 1mm)
INSTALLATION
· Windows and insulated window reveals and surrounds: the windows including the rigid insulation board surrounds should be in place before starting the wall insulation installation. (Refer to section 5)
6. Insulation installation
· Apply absorbent lime plaster or manufacturer’s approved adhesive as adhesive bond
· Securely fix to wall 80mm wood fibre boards according to manufacturer specification. Ensure full adherence of the insulation to the wall avoiding any voids and removing excess adhesive/ lime plaster from between boards. Boards to be laid horizontally with staggered joints.
· Ensure continuous insulation around windows as per drawings below
· Insulate minimum 600mm of internal partitions abutting the external wall as shown on plans
· Once adhesive/ lime plaster is dry, install mechanical fixings to manufacturer’s recommendations.
7. Associated elements
· Carry out electrical and plumbing second fix.
· Install and finish window cills
· Decorate with vapour permeable paint
The external wall must be fully intact and able to prevent water ingress. Joints should be fully filled, and any crack should be repaired to avoid water ingress. Water can otherwise penetrate to the interior side of the wall and the insulation could become damp and ineffective.
CONTINUOUS INSULATION AND REDUCING RISK OF MOULD
The exterior wall should be insulated as comprehensively as possible without leaving un-insulated areas, junctions with other elements and penetrations.
Any uninsulated areas would result in areas of the wall being colder than the surrounding and liable to mould growth as humidity condenses on the colder parts of the walls.
AIRTIGHT CONSTRUCTION
Timber joists set in external walls can be associated with gaps in the building fabric that can allow warm air to escape, thus increasing heating requirements. By sealing around the joists and applying a parge layer the ventilation gaps should be sealed.
REDUCING RISK OF MOULD
To avoid vapour condensing within the structure all materials used in the wall construction should be vapour permeable. Vapour permeable materials are less likely to trap moisture in the construction, which may condense at low temperatures.
EFFECTIVE AND CONTINUOUS INSULATION
Ensuring full adherence of the insulation to the wall will avoid air gaps between the two materials. Air gaps between building materials can transfer hot and cold air in and out of the building and reduce the effectiveness of the insulation.
CONTINUOUS INSULATION
The wall within the floor void needs to be insulated to achieve a continuous insulation layer around the whole building.
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